EP0511366A1 - Chemiluminescent compounds - Google Patents

Abstract

New chemiluminescent compounds are suitable for use in labeling biological molecules for assays such as immunoassays. These chemiluminescent labels are characterized by the incorporation of stable leaving groups. One class of such chemiluminescent labels includes salts in which the leaving group contains a carboxyl carbon atom or its isoelectronic equivalent and a five-membered ring, including at least one heteroatom. The heteroatom is preferably oxygen or sulfur. This leaving group is bound to a positively charged moiety that can produce light by chemiluminescence, and possibly an acridinium, phenanthridinium, quinolinium, or benzacridinium moiety. Both the leaving group and the positively charged moiety may be substituted, for example with reactive substituents to covalently associate the tag or label with a biological molecule. Substituents on the five-membered ring of the leaving group can form an additional ring. An additional class of such chemiluminescent labels comprises a chemical group which can produce light by chemiluminescence and covalently linked to a leaving group comprising a moiety containing a sulfur, phosphorus or carbon atom linked by a double bond to one or more electronegative atoms.

Description

CHEMILUMINESCENT COMPOUNDS

FIELD OF THE INVENTION

The present invention is directed to chemiluminescent compounds for use as labels in analytic reactions such as immunochemical reactions.

BACKGROUND OF THE INVENTION

In many assays for biological molecules, particularly immunoassays, enzyme assays, and nucleic acid hybridization assays, it is necessary to detect small quantities of specifically labeled molecules. In most cases, when particularly high sensitivity is required, three types of labels have been used:

radioactive labels, fluorescent labels, and enzyme labels. While all of these labels are used extensively, each type of label has unique disadvantages.

Radioactive labels, particularly high-energy radioactive labels such as ¹²⁵I (the most commonly employed radioisotope in immunochemistry), have several disadvantages. For example, the radioisotopes have a short half-life, i.e., ¹²⁵I decays with a half-life of approximately sixty days. Moreover, when a radioactive atom incorporated in a molecule decays, it destroys the molecule in which it is incorporated and can cause damage to other molecules in the preparation. As such,

radioactively labeled preparations have extremely short shelf-lives. Moreover, because of the radiation they emit, radioactive labels require special safety

precautions, such as the use of lead shielding. Their disposal is also subject to special restrictions imposed by the Nuclear Regulatory Commission, state licensing bodies, and even local agencies. Radiation emitted also poses a potential health hazard to workers using

radioactive labels.

Fluorescent labels avoid the disadvantages of radioactive labels but have other disadvantages of their own. Notably, they are less sensitive than radioactive labels, and the use thereof requires activation by an extrinsic light source. This requirement of activation by an extrinsic light source makes their detection more difficult, as two wavelengths of light are involved, an emission wavelength and an excitation wavelength.

Accordingly, more complex apparatuses are required to be utilized in conjunction with these labels.

Enzyme labels can be extremely sensitive, but these too have disadvantages. Their detection requires at least one additional step, a development step, to allow the enzyme to carry out its reaction so that a detectable product can be produced. This step requires the use of additional reagents to the reaction, including buffers, substrates and/or coenzymes. Moreover, it is not possible to use enzyme labels in all assays. If the assay requires a step that inactivates or denatures the enzyme or results in ionic, pH, or other conditions incompatible with the activity of the particular enzyme used as the label, enzyme labels cannot be used. Because of the above deficiencies, increased attenti.on has focused on chemilumi.nescent labels as alternative labels for these types of assays.

Chemiluminescence is a direct generation of light from a chemical reaction. The mechanism of most

chemiluminescent reactions is not known in detail, but a generalized mechanism can be outlined:

A→ B^* → B + hv.

Compound A undergoes a chemical reaction, usually oxidation, to yield a product in an electronically excited state ("B^*"). As this product returns to its ground state ("B"), it gives off energy in the form of light ( "hv" ). Typically, the light is in the visible range.

Generally speaking, chemiluminescence occurs when the vibronically excited product of an exogenic chemical reaction reverts to its ground state with the emission of protons, with the reactions invariably being both oxidative and biphasic. Because the excitation energy is obtained from the chemical energy of reaction, the process is chemiluminescence. The characteristics and behavior of several different chemiluminescent compounds can be found in Gundermann & McCapra,

Chemiluminescence in Organic Chemistry (Springer-Verlag 1987).

Chemiluminescent labels are preferred over the previously noted labels for several reasons.

Chemiluminescent labels have high sensitivity ╌ in many cases, sensitivity down to the femtomole (10^-15 mole) to attomole (10^-18 mole) range has been recorded. In

immunoassays, chemiluminescent labels can thus match or exceed the sensitivity of radioactive labels or enzyme labels.

Luminol and isoluminol derivatives are the most widely used chemiluminescent reagents for immunoassays. The light-yielding reaction is initiated by oxidation with alkaline hydrogen peroxide in the presence of catalysts such as horseradish peroxidase,

microperoxidase, or transition metal ions. Light

emission occurs at about 465 nm, which corresponds to the fluorescence emission of the product, aminophthalic acid. Aminobutylethyl isoluminol ("AEEI") can be used as a label in immunoassays and is commercially available.

A second group of chemiluminescent reagents is aryl oxalates. These reagents have been used as

commercial cold light sources and in high-performance liquid chromatography ("HPLC") detectors. It is thought that aryl oxalates react with hydrogen peroxide in buffered or unbuffered solvents to give a dioxetane-dione that decomposes quickly to give CO₂ in an excited state. Energy is then transferred by electron transfer to a fluorescent molecule that emits light. In some

applications, bis-N-alkyl-N-trifluoromethyl sulfonyl oxalamides have been substituted for the aryl oxalate esters. A third group of reagents,

10-methyl-acridinium-9-carboxylic acid aryl esters, are chemiluminescent in the presence of alkaline hydrogen peroxide and in the absence of a catalyst. The mechanism is believed to involve initial attack by a hydroperoxide anion, followed by intramolecular displacement of the phenolate (the "leaving group") to give a strained dioxetane-one. The strained dioxetane-one decomposes to CO₂ and excited N-methyl-acridone, which emits light at 430 nm. Carboxy-substituted acridinium salts have been used as labels in immunoassays. Also, 5-methyl-phenanthridinium-6-carboxylic acid aryl esters, which are isomeric with the acridinium aryl esters, have been used as labels in immunoassays.

These previously used types of chemiluminescent labels have several disadvantages, including relatively low quantum yield and undue sensitivity to hydrolysis, especially under conditions necessary to preserve the stability of the labile biological molecules such as antibodies to which they are attached. For example, it has been reported that antibody-conjugated phenyl

10-methyl-9-acridinium carboxylates lose More than 10% of their activity within three days at about pH 4.0. These labels are only stable below pH 4.0, a degree of acidity to which many antibodies and other proteins are

sensitive.

Because of the ongoing need for

chemiluminescent labels due to the disadvantages of radioactive, fluorescent, and enzyme labels, acridinium, phenanthridinium, or other chemiluminescent compounds useable under conditions compatible with labeling of biological molecules would be useful and highly

desirable. SUMMARY OF THE INVENTION

In order to meet these needs, we disclose novel chemiluminescent compounds. The labels are represented generically by the structure

where U represents a chemical group that can produce light by chemiluminescence, F represents a leaving group, and n has a value of at least one.

One class of these chemiluminescent compounds comprises salts in which the leaving group contains a carboxyl carbon atom or its isoelectronic equivalent and a five-membered unsaturated ring, including at least one heteroatom. For this class, the moiety represented by "U" contains a polycyclic aromatic moiety containing a quaternary nitrogen atom, covalently linked to a moiety C=Z'.

This class of molecules comprises a cation and an anion wherein:

(1) the cation is represented by the following schematic:

where:

(a) n is at least one;

(b) A⁺ is a positively charged moiety capable of producing light by chemiluminescence, such as an acridinium, substituted acridinium, phenanthridinium, substituted phenanthridinium, quinolinium, substituted quinolinium, benzacridinium, or substituted

benzacridinium moiety; and

(c) Z' is selected from the group

consisting of O, S, NH, NOH, NR' and NOR' where R' is C₁-C₅ alkyl;

(d) F is selected from the group

consisting of moieties of the structure O-CH=CH-W, and moieties represented by the following schematic:

where:

(i) W is selected from the group consisting of hydrogen and C₁-C₅ alkyl; and

(ii) X is selected from the group consisting of O, S, Se, Te and NR" where R" is C₁-C₅ alkyl or arylsulfonyl;

(iii) Q is selected from the group consisting of the following structures: an d

where:

(A) Y is selected from the group consisting of O, S, S=O, Se, SO₂, Se=O, SeO₂, Te, Te=O, TeO₂ and N-R'", where R'" is selected from the group consisting of hydrogen and C₁-C₅ alkyl;

(B) A₂, A₃ and A₄ are each independently selected from the group consisting of a valence bond, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₂ cycloalkyl, C₅-C₁₂ cycloalkenyl and aryl; and

(C) Z₂, Z₃ and Z₄ are each independently selected from the group consisting of hydrogen, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime, isocyanate, sulfo, N-succinimidylcarboxyl and N-maleimido, except that where all of A₂, A₃, and A₄ are valence bonds, all of Z₂, Z₃, and Z₄ are not hydrogen unless X is NR" where R" is arylsulfonyl; and

(2) the anion is selected from the group consisting of sulfate, methosulfate, perhalomethosulfate, haloborate, haloacetate, halophosphate, phosphate, halide, phosphite, nitrate, nitrite, carbonate, and bicarbonate. In this chemiluminescent salt, A⁺ can be an acridinium moiety represented by the following schematic:

where:

(a) A₁ is selected from the group consisting of a valence bond, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₂ cycloalkyl, C₅-C₁₂ cycloalkenyl, and aryl;

(b) Z₁ is selected from the group consisting of hydrogen, methyl, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime, isocyanato, sulfo, N-succinimidylcarboxyl, and N-maleimido groups, with the condition that where A₁ is a valence bond, Z₁ is not hydrogen;

(c) R₁, R₃, R₅, R₇ and R₉ are each independently selected from the group consisting of a valence bond, hydrogen, and a moiety A-Z where A is defined as A₁ above and Z is defined as Z₁ above, with the conditions that only one of R₁, R₃, R₅, R₇ and R₉ is a valence bond; and

(d) R₂, R₄, R₆ and R₈ are each independently selected from the group consisting of hydrogen and a moiety A-Z where A is defined as A₁ above and Z is defined as Z₁ above. In such an acridinium moiety, at least one of the carbon atoms of A₁ other than the carbon atom located furthest from the acridinium moiety can be substituted with a substituent selected from the group consisting of hydroxy, halo, alkoxy, amino, alkylamino, arylamino, carboxyl, carboxyester, carboxythioester,

thiocarboxyester, sulfonyl, nitro, sulfonic acid,

sulfoester, sulfinyl, cyano, isothiocyano, ureido, oxo, imino, mercapto, carboxamide, alkylthio, mercaptoester, phosphoryl, and phosphorylester.

When A₁ is selected from the group consisting of substituted and unsubstituted straight chain aliphatic groups, at least one of the carbon atoms of A₁ other than the carbon atom located furthest from the acridinium moiety can be replaced with a replacement moiety selected from the group consisting of -O-, -NH-, and -NL-, wherein L is selected from the group consisting of alkyl groups, cycloalkyl groups, oxo groups, hydroxy groups, sulfo groups, sulfoester groups, carboxyester groups,

phosphoryl groups, and phosphorylester groups.

Alternatively, A₁ can selected from the group consisting of benzyl and aryl groups, in which case at least one of the aromatic carbon atoms of A₁ can be replaced with a replacement moiety selected from the group consisting of -N= and , wherein L' is selected from the group consisting of C₁-C₅ alkyl, C₃-C₁₂

cycloalkyl, oxo, and hydroxyalkyl.

In the acridinium moiety, A₁ can be a valence bond, in which case Z₁ can be selected from the group consisting of carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime, isocyanato, sulfo, N-succinimidylcarboxyl, and N-maleimido. These reactive groups can be used to couple the chemiluminescent compound to a biomolecule. Preferably, R₅ is a valence bond and the leaving group moiety is linked to R₅; R₁, R₂, R₃, R₄, R₆, R₇, R₈, and R₉ are each hydrogen.

Preferably, in these chemiluminescent salts, Z' is O and X is S. Q is

Preferably, Y is S. In one preferred embodiment, A₁ is a valence bond and Z₁ is CH₃; A₂, A₃ and A₄ are each valence bonds; and the anion is CF₃SO₃.

The moiety A⁺ can also be a phenanthridinium moiety represented by the structure

in which:

(1) A₁ is selected from the group consisting of a valence bond, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₂ cycloalkyl, C₅-C₁₂ cycloalkenyl, and aryl;

(2) Z₁ is selected from the group consisting of hydrogen, methyl, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime, isocyanato, sulfo, N- succinimidylcarboxyl, and N-maleimido groups, except that where A₁ is a valence bond, Z₁ is not hydrogen;

(3) each of R₁₄, R₁₇, and R₁₈ is selected from the group consisting of a valence bond, hydrogen, and a moiety A-Z in which A is one of the groups defined as A₁ above and in which Z is one of the groups defined as Z₁ above, in which the A and Z can be selected independently for each of R₁₄, R₁₇, and R₁₈ with the condition that only one of R₁₄, R₁₇, and R₁₈ is a valence bond; and

(4) each of R₁₀, R₁₁, R₁₂, R₁₃, R₁₅, and R₁₆ is selected from the group consisting of hydrogen and the moiety A-Z, in which the A and Z can be selected

independently for each of R₁₀, R₁₁, R₁₂, R₁₃, R₁₅, and R₁₆.

The phenanthridinium moiety can be substituted in a manner analogous to that for the acridinium moiety previously described.

In another class of chemiluminescent compounds according to the present invention, a second ring of at least five atoms can be formed in the moiety Q by

eliminating two of the terminal groups Z₂, Z₃, and Z₄, and linking the corresponding groups of A₂, A₃, and A₄ on which the terminal groups have been eliminated. In this class of compounds, Q is selected from the group

consisting of the following structures:

a second ring containing at least five atoms in addition to the five-membered unsaturated heterocyclic ring being formed by covalent linkage of two of A₂, A₃, and A₄, where:

(1) Y is selected from the grpup consisting of O, S, S=O, SO₂, Se, Se=O, SeO₂, Te, Te=O, TeO₂, and N-R'", wherein R'" is selected from the group consisting of hydrogen and C₁-C₅ alkyl;

(2) the moiety A₂, A₃, or A₄ not involved in formation of the second ring is selected from the group consisting of a valence bond, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₂ cycloalkyl, C₅-C₁₂

cycloalkenyl, and aryl;

(3) the moiety Z₂, Z₃, or Z₄ not involved in the formation of the second ring is selected from the group consisting of hydrogen, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate. carboxamido, cyano, carboxime, isocyanato, sulfo, N- succinimidylcarboxyl, and N-maleimido;

(4) of the two of A₂, A₃, and A₄ involved in formation of the second ring, one is a valence bond and the other is selected from the possible groups A₁ as defined above, the valence bond being linked to the terminal carbon of the other group to form the second ring. The carbon atoms of Q, except for those carbon atoms involved in formation of the second ring, can be substituted as described above.

Another class of chemiluminescent compounds according to the present invention comprises arylsulfonyl esters. This class of compounds comprises a cation and an anion wherein:

(1) the cation is represented by the following schematic:

where

(a) A⁺ is a positively charged moiety capable of producing light by chemiluminescence, and

(b) Y is selected from the group

consisting of O, S, S=O, Se, SO₂, Se=O, SeO₂, Te, Te=O, TeO₂ and N-R'", where R'" is selected from the group consisting of hydrogen and C₁-C₅ alkyl; and

(2) the anion is selected from the group

consisting of sulfate, methosulfate, perhalomethosulfate, haloborate, haloacetate, halophosphate, phosphate,

halide, phosphite, nitrate, nitrite, carbonate, and

bicarbonate.

In this class of compounds, the positively

charged moiety capable of producing light by

chemiluminescence can be selected from the group

consisting of acridinium, substituted acridinium,

phenanthridinium, substituted phenanthridinium,

quinolinium, benzacridinium, and substituted benzacridinium.

Another class of chemiluminescent compounds according to the present invention is chemiluminescent

salts comprising an anion and a cation, the cation

comprising at least one chemical group capable of

producing light covalently linked to a leaving group

selected from the group consisting of the following

chemical structures:

where:

(1) the chemical group that can produce light by chemiluminescence is a heterocyclic ring or ring system selected from the group consisting of acridinium, phenanthridinium, quinolinium, and benzacridinium;

(2) R₁ is selected from the group consisting of alkoxy groups, aryloxy groups, thioderivatives of alkoxy groups, thioderivatives of aryloxy groups, pyrrole and substituted derivatives thereof, imidazole and

substituted derivatives thereof, pyrazole and substituted derivatives thereof, triazole and substituted derivatives thereof, oxazole and substituted derivatives thereof, thiazole and substituted derivatives thereof, tetrazole and substituted derivatives thereof, indole and

substituted derivatives thereof, primary amino groups, secondary amino groups, tertiary amino groups, quaternary amino groups, anilino derivatives, and morpholine

derivatives;

(3) R₂ is selected from the group consisting of hydrogen, alkyl groups and thioderivatives thereof, aryl groups and thioderivatives thereof, alkoxy groups and thioderivatives thereof, aryloxy groups and

thioderivatives thereof, and derivatives of alkyl, aryl, alkoxy, aryl, and aryloxy groups substituted with at least one of nitro, cyano, halo, and sulfonyl; (4) R₃ is selected from the group consisting of O, S, NH, NR₁, NR₂, CH₂, C (R₁) ₂, C(R₂)₂, and CR₁R₂ where R₁ and R₂ are as defined above; and

(5) the anion is selected from the group consisting of sulfate, methosulfate, perhalomethosulfate, haloborate, haloacetate, halophosphate, phosphate, halide, phosphite, nitrate, nitrite, carbonate, and bicarbonate. In this class of compounds, the chemical group producing light is preferably N-methylacridinium, and the leaving group is preferably

in which R₁ is selected from the group consisting of pyrrole, pyrazole, 2-methylindole, and isatin and R₃ is O.

Another aspect of the present invention is a method for determining the quantity of a biomolecule in solution by using any of the chemiluminescent compounds of^; the present invention. The method comprises:

(1) reacting a covalent conjugate comprising the cation of a chemiluminescent salt of the present invention covalently linked to the biomolecule with an oxidizer selected from the group consisting of hydrogen peroxide, molecular oxygen, and organic peroxide to generate light by chemiluminescence; and

(2) determining the quantity of light generated to determine the quantity of the biomolecule present. DESCRIPTION

We have developed novel chemiluminescent compounds suitable for attachment to biological molecules for use as labels. In general, these chemiluminescent compounds comprise a conjugated heterocyclic ring or ring system covalently linked to a stable leaving group. The present invention encompasses both a number of possible conjugated heterocyclic rings or ring systems and a number of different leaving groups. In general, the leaving groups all include a polar moiety containing phosphorus, sulfur, or carbon bonded to a different atom, which can be carbon, nitrogen, oxygen, or sulfur. This bond can be a double bond. For example, the leaving group can include a carbonyl, thiocarbonyl, sulfone, sulfoxide, or imide moiety.

As used herein, "leaving group" is defined as that portion of the chemiluminescent compound susceptible to attack by molecular oxygen, hydrogen peroxide, or organic peroxides to form an intermediate that decays to produce chemiluminescence. Typically, the compound includes an ester, thioester, amide, or comparable functional group derived from condensation of an acid function, although other compounds are intended to be within the scope of the present invention. When the chemiluminescent compound includes a functional group derived from condensation of an acid function, the bond that is broken is the single bond between the carbon and the substituted oxygen (in an ester) or nitrogen (in an amide); i.e., the C-O bond in a -COOH group. The

carbonyl group remains with the conjugated aromatic ring; it is electronic transitions within the portion of the molecule bearing the conjugated aromatic ring that eventually produce light. The remainder of the ester, amide, or comparable function constitutes the leaving group. The stability of the leaving group is important in obtaining efficient chemiluminescence, i.e., a

relatively high quantum yield, because a stable leaving group means that the C-O bond or its equivalent is more readily broken. The present invention encompasses a number of leaving groups not previously known to be used in chemiluminescent molecules.

I. CHEMILUMINESCENT COMPOUNDS

A. Chemiluminescent Compounds in Which the Leaving Group Contains a Carboxyl Carbon Atom or Its Isoelectronic Equivalent and a Five-membered Ring, Including at Least One Heteroatom

It has been found that chemiluminescent compounds in which the leaving group contains a carboxyl carbon atom or its isoelectronic equivalent and a

five-membered ring, including at least one heteroatom, exhibit chemiluminescent quantum yields than which are equivalent to or higher than previously described

chemiluminescent compounds. This class of molecules is represented generically by the structure:

wherein the bracketed portion of the molecule includes A⁺, a positively charged moiety capable of producing light by chemiluminescence attached by a valence bond to a leaving group F. Preferably, A⁺ is a polycyclic aromatic moiety containing a quaternary nitrogen atom. The anion associated with the quaternary

nitrogen atom is typically sulfate; methosulfate; perhalomethosulfate; haloborate; halophosphate;

halosulfonate; haloacetate; phosphate; halide; phosphite; nitrate; carbonate; or bicarbonate. Preferably, the anion is CF₃SO₃- or FSO₃-.

1. The Leaving Group

The leaving group F can be: (a) a vinyl ester; (b) a vinyl ester in which the terminal vinylic carbon is substituted with C₁-C₅ alkyl; or, preferably (c) a moiety having the following structure (Structure II):

where X is attached to the group A⁺ by a moiety C=Z', where Z' can be O, S, NH, NOH, or NOR', where R' is C₁-C₅ alkyl. Preferably, Z' is O. For the preferred F

represented by Structure II:

(1) X is O, S, Se, Te, or NR", where R" is

C₁-C₈ alkyl or arylsulfonyl; preferably, X is O; and

(2) Q is a five-membered unsaturated ring containing a heteroatom, the five-membered unsaturated ring being of Structure III or IV:

In Structure III or IV:

(a) Y is O, S, S=O, SO₂, Se, Se=O, SeO₂, Te, Te=O, TeO₂, or N-R'". R'" is hydrogen or C₁-C₅ alkyl.

Preferably, Y is S. (b) Each of A₂, A₃, and A₄ can be independently chosen from the following: a valence bond, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₂ cycloalkyl, C₅-C₁₂ cycloalkenyl, and aryl. As used herein in the

specification and claims, the term "aryl" refers to unsubstituted or substituted aromatic moieties containing a single unfused benzene ring, and the terms "alkyl," alkenyl," alkynyl," "cycloalkyl," and "cycloalkenyl" refer to unsubstituted or substituted groups. The terms "alkyl, ""alkenyl," alkynyl," "cycloalkyl,"

"cycloalkenyl," and "aryl" as used herein further

encompass groups in which one or more carbon atoms are optionally replaced by a replacement moiety as described in the specification.

The carbon-containing groups can themselves be substituted. Thus, at least one of the carbon atoms of any of A₂, A₃, or A₄ (other than the carbon atom directly attached to Z₂, Z₃, or Z₄ and most distant from the five-membered ring) can be substituted with a

substituent. The carbon atom most distant from the five-membered ring is the carbon atom separated from the ring by the greatest possible number of carbon atoms of A₂, A₃, or A₄. Thus, if A₂ is a propyl (C₃) group, the carbon atom most distant from the five-membered ring is

separated from the ring by the other two carbon atoms of the propyl group. The substituents can be any of the following: hydroxy, halo, alkoxy, amino, alkylamino, arylamino, carboxyl, carboxyester, carboxythioester, thiocarboxyester, sulfonyl, nitro, sulfonic acid,

sulfoester, sulfinyl, cyano, isothiocyano, ureido, oxo, imino, mercapto, carboxamide, alkylthio, mercaptoester, phosphoryl, or phosphorylester. When A₂, A₃, or A₄ is a substituted or

unsubstituted straight-chain aliphatic group, such as, for example, an alkyl, alkenyl or alkynyl group, at least one of the saturated carbon atoms of A₂, A₃, or A₄ (other than the carbon atom directly attached to Z₂, Z₃, or Z₄ and most distant from the five-membered ring as defined above) can be replaced with a replacement moiety. The replacement moiety can be -O-, -NH-, or -NL-. L can be alkyl, cycloalkyl, oxo, hydroxy, sulfo, sulfoester, carboxyester, phosphoryl, or phosphorylester.

Alternatively, when A₂, A₃, or A₄ is a benzyl or aryl group, at least one of the aromatic carbon atoms of A₂, A₃, or A₄ can be replaced with a replacement moiety. The replacement moiety can be -N= or . L' can be C,C₅ alkyl, C₃-C₁₂ cycloalkyl, oxo, or hydroxyalkyl.

(c) Each of Z₂, Z₃, or Z₄ can independently be chosen from any of the following: hydrogen, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime, isocyanato, sulfo, N-succinimidylcarboxyl, or N-maleimido. With the exception of hydrogen, these groups are reactive and can be utilized to couple the chemiluminescent label to the molecule to be labeled, such as, for example, an antigen or antibody. See, for example: (a) EPO No. 0 273 115A, which describes the conjugation of N-sulfonyl acridinium carboxamide to antigens, haptens, and antibodies; (b) EPO No. 0 322 926A, describing the coupling of (2,6-dimethyl-4-substituted) phenyl-N-methyl-acridinium-9-carboxylate to haptens and proteins; (c) Weeks, et al. "Acridinium Esters As High-Specific-Activity Labels in Immunoassay," Clin. Chem. 29. 1424-1479 (1983), describing the reaction of 4-(2-succinimidyloxy carboxylethyl) phenyl-10- methylacridinium-9-carboxylate with proteins. Other conjugation reactions and methods are considered to be well known to those in the art. When all of A₂, A₃, and A₄ are valence bonds

(i.e., when Z₂, Z₃, and Z₄ are all attached directly to the five-membered ring), all of Z₂, Z₃, or Z₄ cannot be hydrogen unless Z' is O and X is NR", where R" is

arylsulfonyl. In other words, when all of A₂, A₃, and A₄ are valence bonds, all of Z₂, Z₃, and Z₄ are hydrogen, Z' is oxygen, and n is 1, the cation is of Structure V:

where A⁺ and Y are as described above. The sulfonamide group is relatively resistant to hydrolysis and does not require the protection of additional bulky groups such as A₂, A₃, and A₄. Chemiluminescent sulfonamides are

described further below in Section 1(B) of the

disclosure.

Alternatively, a second ring structure in addition to the unsaturated heterocyclic five-membered ring can be formed and two of the terminal groups Z₂, Z₃, and Z₄ can be eliminated, forming one of the structures depicted below as Structures VI-XI. This second ring structure contains at least five atoms. The additional ring structure can be formed where one of A₂, A₃, or A₄ is a valence bond and the other of A₂, A₃, or A₄ involved in the formation of the second ring is one of the following groups:

(1) an alkyl group;

(2) an alkenyl group;

(3) an alkynyl group;

(4) an alkyl, alkenyl or alkynyl group in which at least one of the carbon atoms other than the carbon atom located furthest from the original

unsaturated heterocyclic five-membered ring is

substituted with any one of the following substituents:

(a ) hydroxy;

(b ) halo;

(c) alkoxy;

(d) amino;

(e) alkylamino;

(f) arylamino;

(g) carboxyl;

(h) carboxylester;

(i) carboxylthioester;

(j) thiocarboxylester;

(k) sulfonyl;

(l) nitro;

(m ) sulfonic acid;

(n) sulfoester;

(o) sulfinyl;

(p) cyano;

(q) isothiocyano;

(r) ureido;

(s) oxo;

(t) imino;

(u) mercapto;

(v) alkylthio;

(w) mercaptoester; (x) phosphoryl;

(y) phosphorylester; or

(5) an alkyl, alkenyl or alkynyl group in which at least one of the saturated carbon atoms other than the carbon atom located furthest from the original unsaturated heterocyclic five-membered ring is replaced with any of -O-, -NH-, or -NL-, in which L is C₁-C₅ alkyl; C₃- C₈ cycloalkyl; oxo; hydroxy; sulfo; sulfoester;

carboxylester; phosphoryl; or phosphorylester.

In defining the possible structures formed by substitution, the carbon atom located furthest from the original unsaturated heterocyclic five-membered ring is the carbon atom separated from the ring by the greatest pos-sible number of carbon atoms, as explained above for the moiety Q.

The additional ring is formed in this alternative when the terminal carbon of the group A₂, A₃ or A₄ is linked by the valence bond to the five-membered unsaturated ring of Q.

2. The Polycyclic Aromatic Moiety The polycyclic aromatic moiety, A⁺, is

preferably either an acridinium moiety or substituted acridinium moiety of the structure (Structure XII)

or a phenanthridinium moiety or substituted

phenanthridinium moiety of the structure (Structure XIII)

As used herein, the terms "substituted acridinium moiety" and "substituted phenanthridinium moiety" encompass the full range of possible

substitutions and replacements described herein unless otherwise limited. Alternatively, the polycyclic

aromatic moiety can be a quinolinium or benzacridinium moiety. The quinolinium or benzacridinium moiety can be substituted analogously to the acridinium or

phenanthridinium moieties.

Preferably, A⁺ is an acridinium moiety of

Structure XII. a. The Acridinium Moiety

In the acridinium moiety, A₁ can be:

(1) a valence bond;

(2) C₁-C₁₀ alkyl;

(3) C₂-C₁₀ alkenyl;

(4) C₂-C₁₀ alkynyl;

(5) C₃-C₁₂ cycloalkyl;

(6) C₅-C₁₂ cycloalkenyl; or

(7) aryl.

When A₁ is other than a valence bond, at least one of the carbon atoms (other than the carbon atom furthest from the fused ring structure, as defined above) can be substituted with a substituent. The substituent can be hydroxy, halo, alkoxy, amino, alkylamino, arylamino, carboxyl, carboxylester, carboxylthioester,

thiocarboxylester, sulfonyl, nitro, sulfonic acid, sulfoester, sulfinyl, cyano, isothiocyano, ureido, oxo, imino, mercapto, carboxamide, alkylthio, mercaptoester, phosphoryl, or phosphorylester.

Alternatively, when A₁ is a substituted or unsubstituted straight-chain aliphatic group, at least one of the saturated carbon atoms of A₁ (other than the carbon atom furthest from the ring nitrogen atom) can be replaced with a replacement moiety. The replacement moiety can be -O-; -NH-; or -NL-, where L is alkyl, cycloalkyl, oxo, hydroxy, sulfo, sulfoester,

carboxyester, phosphoryl, or phosphorylester. When A₁ is a benzyl or aryl group, at least one of the aromatic carbon atoms of A., can be replaced with a replacement moiety. The replacement moiety can be -N= or wherein L' is C₁-C₅ alkyl, C₃-C₁₂ cycloalkyl, oxo, or hydroxyalkyl.

With further reference to acridinium structure XII, Z₁ can be a hydrogen, methyl, or chemically reactive group. Typically, this chemically reactive group is carboxyl, carboxylhalide, sulfonylhalide, carboalkoxy, carboxy acylate, carboxamido, cyano, carboxime,

isocyanato, sulfo, N-succinimidylcarboxy, or N-maleimido. When A₁ is a valence bond, Z₁ is not hydrogen. In one preferred embodiment, A₁ is a valence bond and Z₁ is methyl.

Further referencing the above acridinium structure, one of R₁, R₃, R₅, R₇, and R₉ is a valence bond for attachment to the remainder of the compound. The remainder of R₁, R₃, R₅, R₇, and R₉ can be independently either hydrogen or a moiety A-Z where both A and Z in the A-Z moiety are defined as A₁ and Z, as above,

respectively. Furthermore, each A and Z in the A-Z moiety can be selected independently for each of R₁, R₃, R₅, R₇, and R₉. Preferably, R₅ is a valence bond, with R₁, R₃, R₇, and R₉ being hydrogen.

Each of R₂, R₄, R₆, and R₈ can be either hydrogen or a moiety A-Z as defined in the preceding paragraph. The moiety A-Z can be selected independently for each of R₂, R₄, R₆, and R₈. Preferably, all of R₂, R₄, R₆, and R₈ are hydrogen. b. The Phenanthridinium Moiety In phenanthridinium Structure XIII depicted above, one of R₁₄, R₁₇, and R₁₈ is a valence bond for attachment to the remainder of the compound. The

remainder of R₁₄, R₁₇, and R₁₈ can be independently hydrogen or a moiety A-Z, defined as above. The A and Z can be selected independently for each of R₁₄, R₁₇, and R₁₈.

Preferably the two of R₁₄, R₁₇, and R₁₈ that are not valence bonds are hydrogen. Each of R₁₀, R₁₁, R₁₂, R₁₃, R₁₅, and R₁₆ is either a hydrogen or a moiety A-Z as defined above. Preferably, each of R₁₀, R_{1 1}, R₁₂, R₁₃, R₁₅, and R₁₆ is hydrogen.

3. Preferred Embodiments of Acridinium Salts With reference to the general structure

A⁺ is an acridinium moiety represented by Structure XII where A₁ is a valence bond; Z₁ is methyl; R₅ is a valence bond; each of R_1; R₂, R₃, R₄, R₅, R₆, R₇, R₈, and R₉ is hydrogen; Z' is O; F is represented by Structure II (X-Q) where X is O; and Q is represented by the five-membered ring of Structure III

where Y is -S-, each of A₂, A₃, and A₄ are valence bonds, and Z₂, Z₃, and Z₄ can be one of the following set of alternatives:

(1) each of Z₂, Z₃, and Z₄ is hydrogen;

(2) Z₂ is COOC₂H₅ and each of Z₃ and Z₄ is hydrogen;

(3) Z₂ is COOCH₃, Z₃ is COOC₂H₅, and Z₄ is hydrogen;

(4) each of Z₂ and Z₃ is COOCH₃ and Z₄ is hydrogen;

(5) each of Z₂ and Z₃ is COOCH₃ and Z₄ is CH₃;

(6) Z₂ is COOC₂H₅, Z₃ is carboxyl, and Z₄ is methyl;

(7) one of Z₂, Z₃ , and Z₄ is methyl, the others being hydrogen;

(8) Z₂ and Z₄ are each hydrogen and Z₃ is phenyl; and

(9) Z₂ and Z₃ are each COOCH₃ and Z₄ is Br.

Most preferably, each of Z₂, Z₃, and Z₄ is hydrogen.

Preferred chemiluminescent acridinium salts according to the present invention accordingly have the following structure (Structure XIV):

B. Chemiluminescent Sulfonamide Derivatives

The present invention also encompasses chemiluminescent sulfonamide derivatives comprising a cation and an anion. The cation has the general

structure shown as Structure XV

In this structure, the increased resistance of the sulfonamide to hydrolysis means that bulky protecting groups in the five-membered unsaturated heterocyclic ring are not required.

In compounds of Structure XV, A⁺ is a positively charged moiety capable of producing light by

chemiluminescence, which can be acridinium, substituted acridinium, phenanthridinium, substituted

phenanthridinium, quinolinium, or benzacridinium.

Preferably, A⁺ is N-methylacridinium. Y is O, S, S=O, SO₂, Se, Se=O, SeO₂, Te, Te=O, TeO₂, or N-R'", where R'" is hydrogen or C₁-C₅ alkyl. Preferably, Y is S. The anion is as described above. Preferably, the anion is CF₃SO₃- or FSO₃-

A preferred chemiluminescent sulfonamide derivative according to the present invention has the structure shown below as Structure XVI.

C. Other Chemiluminescent Compounds Capable of

Covalent Attachment to a Biologically Active

Molecule

Other chemiluminescent compounds capable of covalent attachment to a biologically active molecule are also within the scope of the invention. These comprise a chemical group that can produce light by chemiluminescence coupled to a leaving group containing phosphorus, sulfur, or carbon double-bonded to C, N or O. If phosphorus or sulfur is part of the leaving group, it is in a relatively polar moiety in which the phosphorus or sulfur is bonded to more electronegative atoms. The leaving groups include the following structures

(Structures XVII-XXV):

In the leaving groups depicted above, R₁ can be any of:

(1) an alkoxy group, an aryloxy group, or a thioderivative of an alkoxy or an aryloxy group;

(2) pyrrole, imidazole, pyrazole, triazole, oxazole, thiazole, tetrazole, or a substituted derivative of any of these heterocycles;

(3) a primary, a secondary, a tertiary, or a quaternary amino group; or

(4) an aniline derivative or a morpholine derivative. The term "derivative" as used herein

encompasses all derivatives that do not affect the reactivity of the leaving group.

R₂ can be any of:

(1) hydrogen;

(2) an alkyl group, an aryl group, an alkoxy group, an aryloxy group, or a thioderivative of any of these groups; or

(3) a derivative of an alkyl, an aryl, an alkoxy, or an aryloxy group substituted with at least one of nitro, cyano, halo, or sulfonyl.

R₃ can be O, S, NH, NR₁, NR₂, CH₂, C(R₁)₂, C(R₂)₂, or CR₁R₂, where R₁ and R₂ are defined as in the preceding two paragraphs. With respect to chemiluminescent labels having Structures XVII-XXV, inclusive, the chemical group that can produce light by chemiluminescence is a heterocyclic ring or ring system. The ring or ring system can be acridinium, phenanthridinium, quinolinium, or

benzacridinium.

With chemiluminescent labels of the type disclosed in this section, the preferred chemical group that can produce light by chemiluminescence is an

acridinium group. The leaving group is preferably either , in which R₁ is pyrrole and R₃ is pyrazole, or

in which R₁ is pyrrole or pyrazole. II.. PREPARATION OF CHEMILUMINESCENT COMPOUNDS

The chemiluminescent compounds as disclosed in Section I, above, can be prepared by reacting an acyl chloride derivative, or other comparably reactive

derivative of the acridinium, phenanthridinium, or other light-producing cyclic nitrogen-containing moiety

directly with the leaving group. The reaction is a condensation between the activated carboxyl function and a hydroxyl, mercapto, or similar function of the leaving group. The reaction is preferably performed in a

chlorinated methane, such as dichloromethane or

chloroform, as solvent, in the presence of triethylamine at room temperature. The resulting acridine derivative is then quaternized by reacting the derivative with a methylating agent such as, for example, methyl

fluorosulfonate. See Examples 1-6, infra., for

preparation of several chemiluminescent compounds

according to the present invention. III. REACTION OF CHEMILUMINESCENT COMPOUNDS WITH

BIOLOGICAL MOLECULES

In order for the chemiluminescent compounds to be used as labels in immunoassays, as well as other analytical assays, it is necessary to attach the compound covalently to the biological molecule to be measured or to a biological molecule reacting specifically with the biological molecule to be measured. Typical biological molecules or biomolecules to which the chemiluminescent compounds of the present invention can be attached include, for example, peptides, haptens, antigens, antibodies, enzymes, receptor proteins, hormones,

carbohydrates, phospholipids, glycolipids,

oligonucleotides, nucleic acids, therapeutic drugs, and drugs of abuse.

A number of methods considered to be well known in the art can be used to react the chemiluminescent compound with the biological molecule. Where the

compound contains a reactive group such as, for example, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxamido, carboxime, or N-succinimidylcarboxy, such groups can be coupled covalently to hydroxyl functions or amino functions using conjugation reagents such as, for example, carbodiimides or 1,1-carbonyldiimidazole.

N-maleimido groups react directly with sulfhydryl

residues in proteins. If the compound contains aromatic amino groups, these can be converted to diazonium salts and reacted with phenol groups such as those found in tyrosine groups of proteins. Either a reactive group present in the polycyclic aromatic moiety or other lightproducing group, or one present in the leaving group, can be used to attach the compounds of the present invention to the biological molecule. IV. USE OF LABELS TO PRODUCE CHEMILUMINESCENCE

In general, labels according to the present invention produce chemiluminescence by reaction with hydrogen peroxide, molecular oxygen or an organic peroxide in an alkaline solution. The pH of the solution has a range from about 7 to about 14; preferably, the pH is at least 10; most preferably, the pH is about 13.

These reactions preferably take place at room

temperature. When hydrogen peroxide or an organic peroxide is used to trigger the reaction, it is

preferably present in a stoichiometric excess. In place of hydrogen peroxide, organic peroxide can be used, including, for example, perbenzoic acid, benzyl peroxide, or t-butyl hydroperoxide.

Chemiluminescence is typically measured at 425-430 nm in a commercially available luminometer, such as a Berthold Chemiluminometer produced by Berthold

Laboratorium, Wildbat, Germany.

EXAMPLES

The following Examples are presented for illustration purposes only and are not intended to limit the scope of the invention, this disclosure, or the claims that follow.

Example 1

Preparation of N-Methyl-Acridinium 9-Carboxylic Acid 2- Methyl-3-Furanthiol Thioester

A quantity of acridine-9-acyl chloride (1940 mg) was placed in a 100 ml round-bottom flask with a stirring bar. Dry CHCl₃ (15 ml) was added to dissolve the solid acid chloride. Triethylamine (1300 μl) and

2-methyl-3-furanthiol (800 μl) were added and the flask was rinsed with 3× 1.5 ml CHCl₃, capped and stirred overnight at room temperature. Thin-layer chromatography of the reaction product on silica gel in CHCl₃-EtOAC (9:1) showed the thioester at an R_F of 0.68 and four additional bands at 0.61 , 0.50 , 0.37 , and 0.00.

The solvent was then removed by distillation at a pot temperature of 90-100°C. The flask was then cooled and the residue was triturated with approximately 25 ml cyclohexane . The residue, initially a dark brown oil, became a yellow solid; the solid was filtered and washed with cyclohexane. The yellow solid was dissolved in heated methane and dried onto 8 g of silica gel. The silica gel was placed in a 2.5 × 60 cm column packed with 110 g silica gel slurried with chloroform. The column was eluted sequentially with chloroform, 98%

chloroform-2% ethyl acetate, 97% chloroform, 3% ethyl acetate, 95% chloroform-5% ethyl acetate, and 90%

chloroform-10% ethyl acetate. A yellow band began eluting in the 97%-chloroform-3% ethyl acetate, and continued through the 95% chloroform-5% ethyl acetate, ending at the 90% chloroform-10% ethyl acetate. Fractions containing the yellow band were collected and subjected to thin layer chromatography (on silica gel). A band of R_F 0.73 was seen. The thioester was crystallized from ethyl acetate, yielding 400 mg of solid with a melting point of 170-171°C, which was designated R170TD.

A mass spectral analysis of a comparable recrystallized fraction from another preparation yielded a molecular ion with an M/Z of 320 consistent with a molecular formula of C₁₉H₁₃NO₂S or a structural formula of:

An elemental analysis of the preparation subjected to mass spectroscopy provided results of:

71.35% C, 4.10% H, 4.33% N, 10.51% 0, and 9.71% S, in essential agreement with the calculated values of 71.45% C, 4.10% H, 4.39% N, 10.02% O, and 10.04% S. Spectroscopy in the visible and ultraviolet regions revealed a major peak at 258.5 nm, with minor absorption peaks at 219.5 nm and 363 nm. For quaternization of the acridinium thioester, approximately 110 mg of R170TD was placed in a 25-ml round bottom flask and dissolved in 6 ml of dry CH₂Cl₂. Approximately 250 μl of methyl fluorosulfonate was added to the flask. The reaction vessel was flushed with nitrogen gas, capped, and then placed in the dark for 2-3 days, after which period of time crystals were observed on the bottom of the flask. The solution was filtered, and 70 mg of a solid was obtained. This solid was designated R171TD.

A mass spectral analysis of R171TD yielded a molecular ion with an M/Z of 334 consistent with the formula C₂₀H₁₆NO₂S having a structure:

An elemental analysis of this preparation gave results of: 55.34% C, 3.71% H, 3.21% N, 14.92% S, and 2.59% F. Calculated values were as follows: 55.41% C, 3.72% H, 3.23% N, 14.79% S, and 4.38% F. Spectroscopy in the visible and ultraviolet regions revealed a major peak at 261.5 nm, with minor peaks at 221.5 nm and 368.5 nm.

Both the acridinium thioester and the quaternized acridinium thioester exhibited

chemiluminescence with the quaternized compound yielding approximately 40-fold greater chemiluminescence at 10^-15 moles than did the thioester at 10^-12 moles.

Example 2

Preparation of N-Methyl-Acridinium 9-(5-Ethoxycarbonyl-2- Methoxycarbonyl-3-Thienyl Ester Fluorosulfonate

Acridine-9-acyl chloride (483 mg) was placed in a 25-ml round-bottomed flask and dissolved in 7 ml of dry chloroform. To the solution was added 500 mg of ethyl methyl 3-hydroxythiophene-2,5-dicarboxylic acid ester. Triethylamine (242 mg, or 0.34 ml) was added dropwise while stirring at room temperature. The mixture was stirred for one hour, during which time a white

precipitate was formed. The precipitate was collected by filtration and washed with chloroform to give a pure product (250 mg). The filtrate was then evaporated to dryness, 10 ml of water was added to the residue

remaining from the evaporation, and the residue was digested. The solid separated was collected by

filtration, washed with water, dried, and recrystallized from ethyl acetate to yield another 450 mg of product. The total yield of product was 700 mg or 80%.

The product was quaternized by placing 50 mg in a 10-ml round-bottom flask, dissolving in 3 ml of dry methylene chloride, and adding 200 μl of methyl

fluorosulfonate. The flask was left in the dark

overnight. A few drops of hexane was added to the solution. The crystalline material that separated out after standing for two hours was collected by filtration, washed with hexane, and dried to give the product (45 mg, 71% yield).

The product had a melting point of >250°C.

Nuclear magnetic resonance in DMSO-d₆ gave the following chemical shifts δ (ppm): 8.96 (d, 2H, J = 9.3 Hz, C₁H and C₈H); 8.82 (d, 2H, J = 8.6 Hz, C₄H and C₅H); 8.57 (t, 2H, C₃H and C₆H); 8.54 (s, 1H, thiophene-C₄H); 8.17 (t, 2H, C₂H and C₇H); 4.97 (s, 3H, N⁺-CH₃); 4.42 (q, 2H, ethyl-CH₂); 3.83 (s, 3H, ester-CH₃); and 1.38 (t, ethyl-CH₃). Mass spectroscopy gave a quasi-molecular ion corresponding to the anticipated M⁺ at M/Z 450. Because the compound is a quaternary nitrogen salt it has a pre-existing positive charge and does not acquire an extra proton from the matrix ionization. Also, the negatively charged

fluorosulfonate ion did not show as part of the molecular ion. Elemental analysis gave C 52.36%, H 3.82%, N 2.29%, and F 3.62%, in essential agreement with the calculated values for C₂₄H₂₀NO₉FS₂ of C 52.45%, H 3.67%, N 2.54%, and F 3.48%.

Example 3 Preparation of 9-(N-pyrryl)carbonyl-N-methylacridinium

Fluorosulfonate

A quantity of acridine-9-carboxylic acid (22.3 g; 0.1 mol) was placed in a 250-ml round-bottom flask. Freshly distilled thionyl chloride (70 g; 42 ml) was added, and the resulting reaction mixture was heated under reflux for 3 hours, yielding acridine-9-carboxylic acid chloride hydrochloride. The excess of thionyl chloride was removed by distillation and the traces left were removed by washing with dry benzene. The solid acid chloride was kept under dry benzene. It was collected by filtration to give the acid chloride as a yellow solid. The yield was 24.7 g, or 90%.

The acridine acid chloride (0.277 g; 1 mmol) was dissolved in 20 ml of dry chloroform in a round-bottom flask. Pyrrole (67 mg; 1 mmol) was added, followed by addition of triethylamine (0.30 g; 0.32 ml; 3 mmol). The reaction mixture was left overnight with stirring. The solvent was removed under reduced pressure and the residue was dissolved in water and extracted with ethylacetate. Thin-layer chromatography on silica gel in hexane-ethyl acetate (70:30) showed a major fluorescent spot, the product. Purification of the product, 9-(N-pyrryl)carbonyl acridine, was achieved using silica gel column chromatography using hexane-ethyl acetate as eluant to yield 165 mg (61%). The 9-(N-pyrryl)carbonyl acridine was converted to 9-(N-pyrryl)carbonyl-N-methylacridinium fluorosulfonate by treatment with methyl fluorosulfonate. A quantity of the acridine compound (1.36 mg; 0.5 mmol) was dissolved in 20 ml of dry

methylene chloride in a 50-ml round-bottom flask.

Methylfluorosulfonate (0.5 ml) was added and the flask was kept in the dark overnight. The yellow solid which formed was collected by filtration and washed with CH₂Cl₂ and hexane, and dried to give a yield of 150 mg or 83%. Example 4

Preparation of 9-(2-pyrazolyl)carbonyl-N-methylacridinium

Fluorosulfonate

Acridine 9-carboxylic acid chloride (0.83 g; 3 mmol) was dissolved in 50 ml of dry chloroform. Pyrazole (0.3 g; 4.4 mmol) was added, followed by triethylamine (0.91 g; 9 mmol). The reaction mixture was left

overnight with stirring. The solvent was removed under reduced pressure and the residue was dissolved in water and extracted with ethyl acetate. Evaporation of the ethyl acetate afforded a crude product. Thin-layer chromatography on silica gel in ethyl acetate-hexane (40:60) showed a fluorescent major spot along with some impurities. Purification of the product, 9-(2-pyrazolyl)carbonyl acridine was achieved by using silica gel column chromatography with ethyl acetate-hexane

(60:40) as eluant. Evaporation of the fractions

containing the product gave the substituted acridine in a yield of 617 mg (75% yield).

The substituted acridine was converted to 9-(2-pyrazolyl)carbonyl-N-methylacridinium fluorosulfonate by treatment with methyl fluorosulfonate as in Example 3. The reaction used 0.273 g (1 mmol) of the substituted acridine along with 20 ml of CH₂Cl₂ and 1 ml of methylfluorosulfonate. The yield was 310 mg (80%). Example 5

Preparation of 9-(N-2-methylindolyl)carbonyl-N- methylacridinium Fluorosulfonate

The compound 9-(N-2-methylindolyl)carbonyl-N-methylacridinium fluorosulfonate was prepared essentially as in Examples 3 and 4, starting with acridine acid chloride and 2-methylindole. The reaction mixture comprised 1.385 g of acridine acid chloride (5 mmol), 0.655 g of 2-methylindole (5 mmol), and 1.515 g of triethylamine (15 mmol), in 50 ml of dry chloroform.

The substituted acridine product was purified by silica gel chromatography, using hexane-ethylacetate (50:50). The yield was 0.62 g of a pale yellow semi-solid (37%). This compound, 9-(N-2-methylindolyl)carbonyl acridine, was converted to the N-methyl fluorosulfonate by reaction with methyl

fluorosulfonate as in Examples 3 and 4. The end

methylfluorosulfonate was purified by dissolving in distilled water, filtration, and evaporation until dryness to yield a dark yellow semi-solid product. Example 6

Preparation of 9-(N-isatinyl)carbonyl-N-methylacridinium

Fluorosulfonate 9-(N-isatinyl)carbonyl-N-methylacridinium fluorosulfonate was prepared essentially as in Examples 3-5 starting with acridine acid chloride, isatin and triethylamine. The reaction mixture comprised 1.4 g of acridine acid chloride (5 mmol), 0.4 g of isatin (5 mmol), and 1.51 g of triethylamine (15 mmol) in 50 ml of dry chloroform. The yield after column chromatography on silica gel using ethylacetate-hexane (80:20) was 0.64 g (36%) as a pale yellow semi-solid product.

This product, 9-(N-isatinyl)carbonyl acridine, was converted to the N-methylfluorosulfonate by reaction with methylfluorosulfonate as in Examples 3-5. The reaction product was a dark brown gum. It was purified by dissolving in distilled water and filtration from the brown impurities. The water was evaporated under reduced pressure. The product was dried, washed with n-hexane, and dried to give a yellow solid.

ADVANTAGES OF THE INVENTION

The present invention provides chemiluminescent compounds with quantum yield and stability equal to or exceeding the quantum yield and stability of presently available compounds that are suitable for use in labeling biological molecules. The compounds are particularly suitable for conjugation to biomolecules such as

antibodies and haptens for immunoassays and other

specific binding assays.

While the invention has been described with respect to specific embodiments and compounds, it is to be understood that modifications and equivalents may be apparent to those skilled in the art and are intended to be within the scope of the invention.

Claims

We claim:

1. A chemiluminescent salt comprising a cation and an anion wherein:

(a) the cation is represented by the following schematic:

where

(i) n is at least one;

(ii) A⁺ is a positively charged moiety capable of producing light by chemiluminescence attached by a valence bond to a leaving group F;

(iii) Z' is selected from the group

consisting of O, S, NH, NOH, NR' and NOR' where R' is C₁-C₅ alkyl;

(iv) F is selected from the group

consisting of moieties of the structure O-CH=CH-W, and moieties represented by the following schematic:

where:

(A) W is selected from the group consisting of hydrogen and C₁-C₈ alkyl; and

(B) X is selected from the group consisting of O, S, Se, Te and NR" where R" is C₁-C₅ alkyl or arylsulfonyl;

(C) Q is selected from the group consisting of the following structures: and

where:

(i) Y is selected from the group

consisting of O, S, S=O, Se, SO₂, Se=O, SeO₂, Te, Te=O, TeO₂ and N-R'", where R'" is selected from the group consisting of hydrogen and C₁-C₅ alkyl;

(ii) A₂, A₃ and A₄ are each independently selected from the group consisting of a valence bond, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₂ cycloalkyl, C₅-C₁₂ cycloalkenyl and aryl; and

(iii) Z₂, Z₃ and Z₄ are each independently selected from the group consisting of hydrogen, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime, isocyanate, sulfo, N-succinimidylcarboxyl and N-maleimido, except that where all of A₂, A₃, and A₄ are valence bonds, all of Z₂, Z₃, and Z₄ are not hydrogen unless X is NR" where R" is arylsulfonyl; and

(b) the anion is selected from the group consisting of sulfate, methosulfate, perhalomethosulfate, haloborate, haloacetate, halophosphate, phosphate, halide, phosphite, nitrate, nitrite, carbonate, and bicarbonate.

2. The chemiluminescent salt of claim 1 wherein A⁺ is selected from the group consisting of acridinium, substituted acridinium, phenanthridinium, substituted phenanthridinium, quinolinium, substituted quinolinium, benzacridinium, and substituted

benzacridinium.

3. The chemiluminescent salt of claim 1 wherein F is a moiety of the structure O-CH=CH-W, wherein

W is selected from the group consisting of hydrogen and C₁-C₅ alkyl.

4. The chemiluminescent salt of claim 3 wherein W is H.

5. The chemiluminescent salt of claim1 herein A⁺ is an acridinium moiety represented by the following structure:

where:

(a) A₁ is selected from the group consisting of a valence bond, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₂ cycloalkyl, C₅-C₁₂ cycloalkenyl, and aryl;

(b) Z₁ is selected from the group consisting of hydrogen, methyl, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime, isocyanato, sulfo, N-succinimidylcarboxyl, and N-maleimido groups, with the condition that where A₁ is a valence bond, Z₁ is not hydrogen;

(c) R₁ , R₃, R₅, R₇ and R₉ are each independently selected from the group consisting of a valence bond, hydrogen, and a moiety A-Z where A is defined as A₁ above and Z is defined as Z₁ above, with the condition that only one of R,, R₃, R₅, R₇ and R₉, is a valence bond; and

(d) R₂, R₄, R₆ and R₈ are each independently selected from the group consisting of hydrogen and a moiety A-Z where A is defined as A₁ above and Z is defined as Z₁ above.

6. The chemiluminescent salt of claim 5 wherein at least one of the carbon atoms of A₁ other than the carbon atom located furthest from the acridinium moiety is substituted with a substituent selected from the group consisting of hydroxy, halo, alkoxy, amino, alkylamino, arylamino, carboxyl, carboxyester,

carboxythioester, thiocarboxyester, sulfonyl, nitro, sulfonic acid, sulfoester, sulfinyl, cyano, isothiocyano, ureido, oxo, imino, mercapto, carboxamide, alkylthio, mercaptoester, phosphoryl, and phosphorylester.

7. The chemiluminescent salt of claim 5 wherein A₁ is selected from the group consisting of substituted and unsubstituted straight chain aliphatic groups.

8. The chemiluminescent salt of claim 7 wherein at least one of the carbon atoms of A₁ other than the carbon atom located furthest from the acridinium moiety is replaced with a replacement moiety selected from the group consisting of -O-, -NH-, and -NL-, wherein L is selected from the group consisting of alkyl groups, cycloalkyl groups, oxo groups, hydroxy groups, sulfo groups, sulfoester groups, carboxyester groups,

phosphoryl groups, and phosphorylester groups.

9. The chemiluminescent salt of claim 6 wherein A₁ is selected from the group consisting of benzyl and aryl groups.

10. The chemiluminescent salt of claim 7 wherein at least one of the aromatic carbon atoms of A₁ is replaced with a replacement moiety selected from the group consisting of -N= and , wherein L' is selected from the group consisting of C₁-C₅ alkyl, C₃-C₁₂

cycloalkyl, oxo, and hydroxyalkyl.

11. The chemiluminescent salt of claim 5 wherein A₁ is a valence bond.

12. The chemiluminescent salt of claim 11 wherein Z₁ is selected from the group consisting of carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime,

ispcyanato, sulfo, N-succinimidylcarboxyl, and N-maleimido.

13. The chemiluminescent salt of claim 5 wherein R₅ is a valence bond and the leaving group moiety is linked to R₅.

14. The chemiluminescent salt of claim 13 wherein R₁, R₂, R₃, R₄, R₆, R₇, R₈ and R₉ are each hydrogen.

15. The chemiluminescent salt of claim 14 wherein Z' is O and X is S.

16. The chemiluminescent salt of claim 15 wherein Q is

17. The chemiluminescent salt of claim 16 wherein Y is O.

18. The chemiluminescent salt of claim 16 wherein Y is S.

19. The chemiluminescent salt of claim 18 wherein A₁ is a valence bond and Z₁ is CH₃.

20. The chemiluminescent salt of claim 19 wherein A₂, A₃ and A₄ are each valence bonds.

21. The chemiluminescent salt of claim 20 where the anion is CF₃SO₃-.

22. The chemiluminescent salt of claim 21 wherein Z₂, Z₃ and Z₄ are each H.

23. The chemiluminescent salt of claim 21 wherein Z₂ is COOC₂H₅, and Z₃ and Z₄ are H.

24. The chemiluminescent salt of claim 21 wherein Z₂ is COOCH₃, Z₃ is COOC₂H₅, and Z₄ is H.

25. The chemiluminescent salt of claim 21 wherein Z₂ and Z₃ are COOCH₃, and Z₄ is H.

26. The chemiluminescent salt of claim 21 wherein. Z₂ is COOCH₃, Z₃ is COOH, and Z₄ is CF₃.

27. The chemiluminescent salt of claim 21 wherein Z₂ is CH₃, and Z₃ and Z₄ are H.

28. The chemiluminescent salt of claim 21 wherein Z₂ and Z₄ are each H, and Z₃ is CH₃.

29. The chemiluminescent salt of claim 21 wherein Z₂ and Z₄ are each H, and Z₃ is C₆H₅.

30. The chemiluminescent salt of claim 21 wherein Z₂ and Z₃ are each COOCH₃, and Z₄ is Br.

31. The chemiluminescent salt of claim 1 wherein A⁺ is a phenanthridinium moiety represented by the structure:

where:

(a) A₁ is selected from the group consisting of a valence bond, C₅-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₂ cycloalkyl, C₅-C₁₂ cycloalkenyl, and aryl; (b) Z₁ is selected from the group consisting of hydrogen, methyl, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime, isocyanato, sulfo, N-succmimidylcarboxyl, and N-maleimido groups, except that where A₁ is a valence bond, Z₁ is not hydrogen;

(c) each of R₁₄, R₁₇, and R₁₈ is selected from the group consisting of a valence bond, hydrogen, and a moiety A-Z in which A is one of the groups defined as A₁ above and in which Z is one of the groups defined as Z₁ above, in which the A and Z can be selected independently for each of R₁₄, R₁₇, and R₁₈ with the condition that only one of R₁₄, R₁₇, and R₁₈ is a valence bond; and

(d) each of R₁₀, R₁₁, R₁₂, R₁₃, R₁₅, and R₁₆ is selected from the group consisting of hydrogen and the moiety A-Z, in which the A and Z can be selected

independently for each of R₁₀, R₁₁, R₁₂, R₁₃, R₁₅, and R₁₆.

32. The chemiluminescent salt of claim 31 wherein at least one of the carbon atoms of A₁ other than the carbon atom located furthest from the

phenanthridinium moiety is substituted with a substituent selected from the group consisting of hydroxy, halo, alkoxy, amino, alkylamino, arylamino, carboxyl,

carboxyester, carboxythioester, thiocarboxyester,

sulfonyl, nitro, sulfonic acid, sulfoester, sulfinyl, cyano, isothiocyano, ureido, oxo, imino, mercapto, carboxamide, alkylthio, mercaptoester, phosphoryl, and phosphorylester.

33. The chemiluminescent salt of claim 31 wherein A₁ is selected from the group consisting of substituted and unsubstituted straight chain aliphatic groups.

34. The chemiluminescent salt of claim 33 wherein at least one of the carbon atoms of A₁ other than the carbon atom located furthest from the acridinium moiety is replaced with a replacement moiety selected from the group consisting of -O-, -NH-, and -NL-, wherein L is selected from the group consisting of alkyl groups, cycloalkyl groups, oxo groups, hydroxy groups, sulfo groups, sulfoester groups, carboxyester groups,

phosphoryl groups, and phosphorylester groups.

35. The chemiluminescent salt of claim 31 wherein A₁ is selected from the group consisting of benzyl and aryl groups.

36. The chemiluminescent salt of claim 35 wherein at least one of the aromatic carbon atoms of A₁ is replaced with a replacement moiety selected from the group consisting of -N= and wherein L' is selected from the group consisting of C₁-C₅ alkyl, C₃-C₁₂

cycloalkyl, oxo, and hydroxyalkyl.

37. The chemiluminescent salt of claim 31 wherein Z' is O and X is S.

38. The chemiluminescent salt of claim 37 wherein Q is

39. The chemiluminescent salt of claim 38 wherein Y is O.

40. The chemiluminescent salt of claim 38 wherein Y is S.

41. The chemiluminescent salt of claim 40 wherein A₁ is a valence bond and Z₁ is CH₃.

42. The chemiluminescent salt of claim 41 wherein A₂, A₃ and A₄ are each valence bonds.

43. The chemiluminescent salt of claim 42 wherein the anion is CF₃SO₃-.

44. A chemiluminescent salt comprising a cation and an anion wherein:

(a) the cation is represented by the following schematic:

where

(i) n is at least one;

(ii) A⁺ is a positively charged moiety capable of producing light by chemiluminescence attached by a valence bond to a leaving group F;

(iii) Z' is selected from the group

consisting of O, S, NH, NOH, NR' and NOR' where R' is C₁-C₅ alkyl;

(iv) F is selected from the group

consisting of moieties represented by the following schematic:

where:

(A) X is selected from the group consisting of O, S, Se, Te and NR" where R" is selected from the group consisting of C₁-C₅ alkyl and arylsulfonyl; and

(B) Q is selected from the group consisting of the following structures:

a second ring containing at least five atoms in addition to the five-membered unsaturated heterocyclic ring being formed by covalent linkage of two of A₂, A₃, and A₄, where:

(1) Y is selected from the group consisting of O, S, S=O, SO₂, Se, Se=O, SeO₂, Te, Te=O, TeO₂, and N-R'", wherein R'" is selected from the group consisting of hydrogen and C₁-C₈ alkyl;

(2) the moiety A₂, A₃, or A₄ not involved in formation of the second ring is selected from the group consisting of a valence bond, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₂ cycloalkyl, C₅-C₁₂

cycloalkenyl, and aryl;

(3) the moiety Z₂, Z₃, or Z₄ not involved in the formation of the second ring is selected from the group consisting of hydrogen, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime, isocyanato, sulfo, N-succinimidylcarboxyl, and N-maleimido; and

(4) of the two of A₂, A₃, and A₄ involved in formation of the second ring, one is a

valence bond and the other is selected from the possible groups A₁ as defined above, the valence bond being linked to the terminal carbon of the other group to form the second ring; and

(b) the anion is selected from the group consisting of sulfate, methosulfate, perhalomethosulfate, haloborate, haloacetate, halophosphate, phosphate, halide, phosphite, nitrate, nitrite, carbonate, or

bicarbonate.

45. The chemiluminescent salt of claim 44 wherein A⁺ is selected from the group consisting of acridinium, substituted acridinium, phenanthridinium, substituted phenanthridinium, quinolinium, substituted quinolinium, benzacridinium, and substituted

benzacridinium.

46. The chemiluminescent salt of claim 45 wherein at least one of the carbon atoms of A₂, A₃ or A₄ that is not involved in formation of the second ring, other than the carbon atom located furthest from the unsaturated heterocyclic 5-membered ring, is substituted with a substituent selected from the group consisting of hydroxy, halo, alkoxy, amino, alkylamino, arylamino, carboxyl, carboxyester, carboxythioester,

thiocarboxyester, sulfonyl, nitro, sulfonic acid, sulfoester, sulfinyl, cyano, isothiocyano, ureido, oxo, imino, mercapto, carboxamide, alkylthio, mercaptoester, phosphoryl, and phosphorylester.

47. The chemiluminescent salt of claim 45 wherein the one of A₂, A₃ and A₄ that is not involved in formation of the second ring is selected from the group consisting of substituted and unsubstituted straight-chain aliphatic groups and at least one of the carbon atoms of the one of A₂, A₃ and A₄ not involved in

formation of the second ring, other than the carbon atom located furthest from the unsaturated heterocyclic 5-membered ring, is replaced with a replacement moiety selected from the group consisting of -O-, -NH-, and -NL-, wherein L is selected from the group consisting of alkyl groups, cycloalkyl groups, oxo groups, hydroxy groups, sulfo groups, sulfoester groups, carboxyester groups, phosphoryl groups, and phosphorylester groups.

48. The chemiluminescent salt of claim 45 wherein Z' is O and X is S.

49. The chemiluminescent salt of claim 48 wherein Y is O.

50. The chemiluminescent salt of claim 48 wherein Y is S.

51. The chemiluminescent salt of claim 50 wherein the anion is CF₃SO₃-

52. The chemiluminescent salt of claim 44 wherein A⁺ is an acridinium moiety represented by the following structure:

where:

(a) A₁ is selected from the group consisting of a valence bond, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₂ cycloalkyl, C₅-C₁₂ cycloalkenyl, and aryl;

(b) Z₁ is selected from the group consisting of hydrogen, methyl, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime, isocyanato, sulfo, N-succinimidylcarboxyl, and N-maleimido groups, with the condition that where A₁ is a valence bond, Z₁ is not hydrogen;

(c) R₁, R₃, R₅, R₇ and R₉ are each independently selected from the group consisting of a valence bond, hydrogen, and a moiety A-Z where A is defined as A₁ above and Z is defined as Z₁ above, with the condition that only one of R₁, R₃, R₅, R₇ and R₉ is a valence bond; and

(d) R₂, R₄, R₆ and R₈ are each independently selected from the group consisting of hydrogen and a mdiety A-Z where A is defined as A₁ above and Z is defined as Z₁ above.

53. The chemiluminescent salt of claim 52 wherein at least one of the carbon atoms of A₁ other than the carbon atom located furthest from the acridinium moiety is substituted with a substituent selected from the group consisting of hydroxy, halo, alkoxy, amino, alkylamino, arylamino, carboxyl, carboxyester,

carboxythioester, thiocarboxyester, sulfonyl, nitro, sulfonic acid, sulfoester, sulfinyl, cyano, isothiocyano, ureido, oxo, imino, mercapto, carboxamide, alkylthio, mercaptoester, phosphoryl, and phosphorylester.

54. The chemiluminescent salt of claim 52 wherein A₁ is selected from the group consisting of substituted and unsubstituted straight chain aliphatic groups.

55. The chemiluminescent salt of claim 54 wherein at least one of the carbon atoms of A₁ other than the carbon atom located furthest from the acridinium moiety is replaced with a replacement moiety selected from the group consisting of -O-, -NH-, and -NL-, wherein L is selected from the group consisting of alkyl groups, cycloalkyl groups, oxo groups, hydroxy groups, sulfo groups, sulfoester groups, carboxyester groups,

phosphoryl groups, and phosphorylester groups.

56. The chemiluminescent salt of claim 52 wherein A₁ is selected from the group consisting of benzyl and aryl groups.

57. The chemiluminescent salt of claim 56 wherein at least one of the aromatic carbon atoms of A₁ is replaced with a replacement moiety selected from the group consisting of -N= and wherein L' is selected from the group consisting of C₁-C₅ alkyl, C₃-C₁₂

cycloalkyl, oxo, and hydroxyalkyl.

58. The chemiluminescent salt of claim 52 wherein A₁ is a valence bond.

59. The chemiluminescent salt of claim 58 wherein Z₁ is selected from the group consisting of carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime,

isocyanato, sulfo, N-succinimidylcarboxyl, and N-maleimido.

60. The chemiluminescent salt of claim 52 wherein R₅ is a valence bond and the leaving group moiety is linked to R₅.

61. The chemiluminescent salt of claim 60 wherein R₁, R₂, R₃, R₄, R₆, R₇, R₈ and R₉ are each hydrogen.

62. The chemiluminescent salt of claim 61 wherein A₁ is a valence bond and Z1 is CH₃.

63. The chemiluminescent salt of claim 44 wherein A⁺ is a phenanthridinium moiety represented by the structure:

where:

(a) A₁ is selected from the group consisting of a valence bond, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₂ cycloalkyl, C₅-C₁₂ cycloalkenyl, and aryl;

(b) Z₁ is selected from the group consisting of hydrogen, methyl, carboxyl, carboxyl halide, sulfonyl halide, carboalkoxy, carboxyl acylate, carboxamido, cyano, carboxime, isocyanato, sulfo, N-succinimidylcarboxyl, and N-maleimido groups, except that where A₁ is a valence bond, Z₁ is not hydrogen;

(c) each of R ₁₄, R ₁₇, and R ₁₈ is selected from the group consisting of a valence bond, hydrogen, and a moiety A-Z in which A is one of the groups defined as A₁ above and in which Z is one of the groups defined as Z₁ above, in which the A and Z can be selected independently for each of R. ₁₄, R₁₇, and R₁₈ with the condition that only one of R₁₄, R₁₇, and R₁₈ is a valence bond; and

(d) each of R₁₀, R₁₁, R ₁₂, R ₁₃, R₁₅, and R₁₆ is selected from the group consisting of hydrogen and the moiety A-Z, in which the A and Z can be selected

independently for each of R₁₀, R₁₁, R₁₂, R₁₃, R₁₅, and R₁₆.

64. The chemiluminescent salt of claim 63 wherein at least one of the carbon atoms of A₁ other than the carbon atom located furthest from the phenanthridinium moiety is substituted with a substituent selected from the group consisting of hydroxy, halo, alkoxy, amino, alkylamino, arylamino, carboxyl,

carboxyester, carboxythioester, thioσarboxyester,

sulfonyl, nitro, sulfonic acid, sulfoester, sulfinyl, cyano, isothiocyano, ureido, oxo, imino, mercapto, carboxamide, alkylthio, mercaptoester, phosphoryl, and phosphorylester.

65. The chemiluminescent salt of claim 63 wherein A₁ is selected from the group consisting of substituted and unsubstituted straight chain aliphatic groups.

66. The chemiluminescent salt of claim 65 wherein at least one of the carbon atoms of A₁ other than the carbon atom located furthest from the acridinium moiety is replaced with a replacement moiety selected from the group consisting of -O-, -NH-, and -NL-, wherein L is selected from the group consisting of alkyl groups, cycloalkyl groups, oxo groups, hydroxy groups, sulfo groups, sulfoester groups, carboxyester groups,

phosphoryl groups, and phosphorylester groups.

67. The chemiluminescent salt of claim 63 wherein A₁ is selected from the group consisting of benzyl and aryl groups.

68. The chemiluminescent salt of claim 66 wherein at least one of the aromatic carbon atoms of A₁ is replaced with a replacement moiety selected from the group consisting of -N= and wherein L' is selected

from the group consisting of C₁-C₅ alkyl, C₃-C₁₂

cycloalkyl, oxo, and hydroxyalkyl.

69. The chemiluminescent salt of claim 63 wherein A₁ is a valence bond and Z₁ is CH₃.

70. A chemiluminescent salt comprising a cation and an anion wherein':

(a) the cation is represented by the following schematic:

where

(i) A⁺ is a positively charged moiety capable of producing light by chemiluminescence, and

(ii) Y is selected from the group

consisting of O, S, S=O, Se, SO₂, Se=O, SeO₂, Te, Te=O, TeO₂ and N-R'", where R'" is selected from the group consisting of hydrogen and C₁-C₅ alkyl; and

(b) the anion is selected from the group consisting of sulfate, methosulfate, perhalomethosulfate, haloborate, haloacetate, halophosphate, phosphate, halide, phosphite, nitrate, nitrite, carbonate, and bicarbonate.

71. The chemiluminescent salt of claim 70 wherein Y is S.

72. The chemiluminescent salt of claim 70 wherein A⁺ is selected from the group consisting of acridinium, substituted acridinium, phenanthridinium, substituted phenanthridinium, quinolinium, substituted quinolinium, benzacridinium, and substituted

benzacridinium.

73. The chemiluminescent salt of claim 71 wherein A⁺ is an acridinium moiety represented by the following chemical structure:

74. The chemiluminescent salt of claim 73 wherein the anion is SO₃CF₃ ^⊝,

75. A chemiluminescent salt represented by the following chemical structure:

76. A chemiluminescent salt comprising an anion and a cation, the cation comprising at least one chemical group capable of producing light by

chemiluminescence covalently linked to a leaving group selected from the group consisting of the following chemical structures:

where :

(a) the chemical group that can produce light by chemiluminescence is a heterocyclic ring or ring system selected from the group consisting of acridinium, phenanthridinium, quinolinium, and benzacridinium;

(b) R₁ is selected from the group consisting of alkoxy groups, aryloxy groups, thioderivatives of alkoxy groups, thioderivatives of aryloxy groups, pyrrole and substituted derivatives thereof, imidazole and

substituted derivatives thereof, pyrazole and substituted derivatives thereof, triazole and substituted derivatives thereof, oxazole- and substituted derivatives thereof, thiazole and substituted derivatives thereof, tetrazole and substituted derivatives thereof, indole and

substituted derivatives thereof, primary amino groups, secondary amino groups, tertiary amino groups, and quaternary amino groups, anilino derivatives, and

morpholine derivatives;

(c) R₂ is selected from the group consisting of hydrogen, alkyl groups and thioderivatives thereof, aryl groups and thioderivatives thereof, alkoxy groups and thioderivatives thereof, aryloxy groups and

thioderivatives thereof, and derivatives of alkyl, aryl, alkoxy, aryloxy groups substituted with at least one of nitro, cyano, halo and sulfonyl; (d) R₃ is selected from the group consisting of O, S, NH, NR₁, NR₂, CH₂, C(R₁)₂, C(R₂)₂, and CR₁R₂ where R₁ and R₂ are as defined above; and

(e) the anion is selected from the group consisting of sulfate, methosulfate, perhalomethosulfate, haloborate, haloacetate, halophosphate, phosphate, halide, phosphite, nitrate, nitrite, carbonate, and bicarbonate.

77. The chemiluminescent salt of claim 76 wherein the chemical group producing light is N-methylacridinium.

78. The chemiluminescent salt of claim 77 wherein the leaving group is

in which R₁ is selected from the group consisting of pyrrole, pyrazole, 2-methylindole, and isatin and R₃ is O.

79. A method of determining the quantity of a biomolecule present in a solution comprising:

(a) reacting a covalent conjugate comprising the cation of the chemiluminescent salt of claim 1

covalently linked to the biomolecule with an oxidizer selected from the group consisting of hydrogen peroxide, molecular oxygen, and organic peroxide to generate light by chemiluminescence; and

(b) determining the quantity of light generated to determine the quantity of the biomolecule present.

80. A method of determining the quantity of a biomolecule present in a solution comprising:

(a) reacting a covalent conjugate comprising the cation of the chemiluminescent salt of claim 44 covalently linked to the biomolecule with an oxidizer selected from the group consisting of hydrogen peroxide, molecular oxygen, and organic peroxide to generate light by chemiluminescence; and

(b) determining the quantity of light

generated to determine the quantity of the biomolecule present.

81. A method of determining the quantity of a biomolecule present in a solution comprising:

(a) reacting a covalent conjugate comprising the cation of the chemiluminescent salt of claim 70 covalently linked to the biomolecule with an oxidizer selected from the group consisting of hydrogen peroxide, molecular oxygen, and organic peroxide to generate light by chemiluminescence; and

(b) determining the quantity of light

generated to determine the quantity of the biomolecule present.

82. A method of determining the quantity of a biomolecule present in a solution comprising:

(a) reacting a covalent conjugate comprising the cation of the chemiluminescent salt of claim 75 covalently linked to the biomolecule with an oxidizer selected from the group consisting of hydrogen peroxide, molecular oxygen, and organic peroxide to generate light by chemiluminescence; and (b) determining the quantity of light generated to determine the quantity of the biomolecule present.

83. A method of determining the quantity of a biomolecule present in a solution comprising:

(a) reacting a covalent conjugate comprising the cation of the chemiluminescent salt of claim 76 covalently linked to the biomolecule with an oxidizer selected from the group consisting of hydrogen peroxide, molecular oxygen, and organic peroxide to generate light by chemiluminescence; and

(b) determining the quantity of light

generated to determine the quantity of the biomolecule present.