NO179247B - Non-ionic contrast compound and radiological preparation comprising it - Google Patents

Abstract

Triiodo-5-aminoisophthalamides in which the amino and one of the amide nitrogen groups are substituted are indicated. The compounds have at least two hydroxyl groups and low viscosity and osmolality. Processes for the preparation of the compounds are indicated.

Description

Technical area

The field of the invention is non-ionic contrast compounds and radiological preparations comprising them.

Background

Radiographic contrast media for visualization of the cardiovascular system and body cavities must have a low viscosity, be easily water-soluble, non-toxic and have a high iodine content. Low viscosity is absolutely necessary for rapid delivery, to instantly replace fast-flowing blood,

such as in cardioangiography or high-dose urography, or contrast enhancement in computed tomography. To be non-toxic, the compound must be highly hydrophilic, non-ionic and with an osmolality close to that of the body environment. Although, according to the state of the art, the non-ionic, monomeric media have a reasonable biological tolerance and usable viscosity, they are hyperosmolal in the body environment. At the diagnostically applicable concentration of 300 mg I/ml, they thus significantly exceed the physiological value of 310 mOsm. The hyperosmolality of these solutions necessarily drives water out of cells, which breaks up cell membranes, disrupts the overall electrolytic balance and damages the surface of blood vessels or organ cavities. Hyperosmolality has also been shown to be one cause of vascular pain that is invariably triggered by hyperosmolal contrast media.

Most nonionic contrast agents, regardless of whether they

are monomeric or oligomeric, are aromatic amides with one or more polyhydroxy, lower aliphatic alkyl and acyl subgroups attached to nitrogen, with ring-shaped carboxamides and amino groups. The triiodinated benzene ring contains a number of groups in close spatial relationships. The state of the art describes several hydroxyalkylamines attached as amides. Examples of

these amines include: serinol, 1-amino-2,3-propanediol, N-methyl-1-amino-2,3-propanediol, aminotetritols, ethanolamine, diethanolamine and tromethamine.

Replacement of the carboxyl groups in the 1- and 3-positions with the same hydroxyalkylamine severely limits the design, as the substituents available in practice are either too small to solubilize the molecule or too large to result in a low-viscosity solution (US patent documents no. 4,021,481, 3,701,771 and 4,001,323 ). For this reason, improved compounds were developed in which the two hydroxyalkylamines were different (US Patent No. 4,364,921). However, such compounds have a complex synthesis and are expensive to synthesize.

Relevant literature

US Patent Nos. 3,701,771, 4,001,323, 4,021,481, 4,364,921, 4,547,357 and US Patent Application No. 214,663, filed July 1, 1988, are illustrative of various compounds reported as useful for nonionic contrast media.

Summary of the invention

Nonionic contrast compounds based on an asymmetric triiododisophthalic acid diamide have been provided where the remaining ring position is occupied by a substituted nitrogen atom, one of the carboxyl groups being unsubstituted amide and the other of the carboxyl groups being at least one mono-(hydroxyalkyl)-substituted amide. The molecule has at least two hydroxyl groups. Radiological preparations are also provided.

Detailed description of the invention and description of specific embodiments

Non-ionic contrast compounds have thus been provided based on an acylamido-substituted triiododisophthalic acid diamide in which only one of the amide nitrogen atoms is at least mono-substituted. The compounds can be synthesized cheaply in good yield and obtained with high purity. The compounds according to the invention have been found to provide low osmolality while maintaining medium to low viscosity.

The compounds according to the present invention have the following formula (I):

with at least two hydroxyl groups, and where

Rx is hydrogen, lower alkyl or hydroxy-substituted lower alkyl, where the alkyl group contains from 1 to 6 carbon atoms,

R2 is hydroxyalkyl with from 2 to 6 carbon atoms, with from 1 to n-1 hydroxyl groups, where n is the number of carbon atoms,

R3 is lower alkyl, hydroxy-substituted lower alkyl or lower alkoxy-substituted lower alkyl and having from 1 to 6 carbon atoms, or a residue of formula (II):

and

R4 is hydrogen or alkyl with from 1 to 6 carbon atoms with from 0 to n-1 hydroxyl groups, where n is the number of carbon atoms,

with the exception of 3-[N-(1,3-dihydroxyprop-2-yl)carbamoyl]-5-(2-hydroxy-1-oxopropyl)amino-2,4,6-triiodobenzamide.

Furthermore, a radiological preparation is provided which is characterized in that it comprises a non-ionic contrast compound according to claim 1 in a physiologically acceptable carrier.

The alkyl groups can be straight chain or branched, usually straight chain where carbon atoms will not normally be quaternary.

The alkyl residue in the mono- or polyhydroxyalkyl groups Rx and R2 will usually have 2-4 carbon atoms. Preferably, the residues will have 1-3 hydroxy groups. These hydroxy groups can be primary, secondary or tertiary. Examples include trishydroxymethylmethyl, hydroxyethyl, dihydroxypropyl and tri-hydroxybutyl. Ureas can be prepared using 3-amino-1,2-propanediol, serinol or aminotetritols, i.e. threitol and erythritol, either in D,L mixture or optically pure forms, ethanolamine or diethanolamine, or tromethamine, or derivatives thereof, where the hydroxyl groups are reversibly protected. Rx is usually hydrogen or lower alkyl, preferably hydrogen or methyl. R 3 is a lower alkyl or oxyalkyl group with 1-6, usually 1-4, carbon atoms, preferably methyl, hydroxymethyl or hydroxyethyl. Also exemplified are alkoxyalkyl groups containing alkoxyl groups with 1-3 carbon atoms, preferably 1-2 carbon atoms, and alkyl groups with from 1 to 3 carbon atoms, especially methoxy-methyl. Alternatively, two R3 groups together are a bond, methylene or ethylene, especially methylene. R4 is hydrogen, alkyl or mono- or polyhydroxyalkyl of 1-6, usually 1-4, carbon atoms, including methyl, ethyl, propyl, hydroxyethyl and dihydroxypropyl.

Monomeric compounds of interest include: 5-[N-(2-hydroxyethyl)methoxyacetamido]-2,4,6-triiodo-3-[N-(1,3,4-trihydroxybut-2-yl)]carbamoylbenzamide,

5- [N-(2-hydroxyethyl)hydroxyacetamido]-2,4,6-triiodo-3-[N-(2,3-dihydroxypropyl)]carbamoyl-benzamide,

5- [N-(2,3-dihydroxypropyl)acetamido]-2,4,6-triiodo-3-[N-(2,3-dihydroxypropyl)]carbamoyl-benzamide,

5- [N-(2,3-dihydroxypropyl)glycolamido]-2,4,6-triiodo-3-[N-(2-hydroxyethyl)]carbamoyl-benzamide,

5-[N-(1,3,4-trihydroxy-but-2-yl)acetamido]-2,4,6-triiodo-3-[N-(2-hydroxyethyl)] carbamoyl-benzamide,

5-[N-(methyl)glycolamido]-2,4,6-1rijod-3-[N-(1,3,4-trihydroxy-erythro-but-2-yl)]carbamoyl-benzamide and

5-[N-(2-hydroxyethyl)acetamido]-2,4,6-triiodo-3-[N-(1,3,4-trihydroxythreo-but-2-yl)]carbamoyl-benzamide.

Dimeric compounds of interest include: malonic acid-bis-[{3-N-(2,3-dihydroxypropyl-carbamoyl)-5-carbamoyl}-2,4,6-triiodo-N-(2,3-dihydroxypropyl)],

malonic acid-bis-[{3-N-(2,3-dihydroxypropyl-carbamoyl)-5-carbamoyl}-2,4,6-triiodo-N-(2-hydroxyethyl)anilide] and

malonic acid bis-[{3-N-(1,3,4-trihydroxy-but-2-yl-carbamoyl)-5-carbamoyl}-2,4,6-triiodo-N-methylanilide].

The preparations according to the present invention will contain from approx. 50 to 52% iodine, usually approx. 51%, have a viscosity in a solution of 300 mg I/ml at 37°C (eps) in the range of approx. 4-5, and an osmolality of a solution of 300 mg I/ml at 37°C in Mosm for an aqueous solution in the range of approx. 275-400, more common approx. 285-375, while in a pharmaceutical preparation it will vary from approx. 300 to 400, more commonly approx. 325 to approx. 390.

The present preparations are designed in accordance with normal conditions. Usually, the preparations will comprise an aqueous medium which includes a physiologically acceptable, gelated calcium salt, e.g. EDTA, a buffer to give a pH in the range of approx. 6.5-7.5, especially approx. 7, where the buffer may comprise tris, carbonate, citrate or combinations thereof. Other additives that may be included are bicarbonate, phosphate etc. The gelated calcium will generally be present at from approx. 5 to 15, usually approx. 10 mg/100 ml, while the buffer will generally be present in an amount from approx. 2 to 10 mM.

A method for the preparation of compounds of the general formula I is characterized in that

a) compounds of the general formula V

where hydroxy groups found in R: and R2 are optionally protected, are transferred by reaction with R3CO-X, where X is halogen or an ester residue, in catalyzing solvents such as e.g. pyridine, DMA or DMF, and optionally with subsequent removal of protective groups in the end product with the general formula I where R4 is hydrogen, or in intermediate products with the general formula I' where R4 is R3CO, and converts these, optionally with protected hydroxy groups, then about desired by alkylation under basic conditions with R4-containing reagents, optionally after subsequent removal of the protective groups, to end products with the general formula I where R4 is not hydrogen, or b) reacts compounds with the general formula VI

where R5 is Rx or hydrogen, R6 is R2 or hydrogen, and X is

halogen or an ester residue, with ammonia or with hydroxyalkyl amines containing the residues Rx and R2, the hydroxy groups may be protected, and then possibly splitting off the protective groups.

Common reactions can be combined in a defined reaction order to produce the present compounds. By one method, the products according to this invention can thus be produced, e.g. from the compound of formula (II):

where R 1 and R 2 are as previously defined, and X is either a lower alkyl ester or a halogen atom.

Compounds of the general formula (II) are prepared by reacting a hydroxy alkyl amine (NHRi, R2) in which OH groups are protected or unprotected, with a commercially available monoester of 5-nitroisophthalic acid, followed by activation of the remaining carboxyl group. Such activation is suitably achieved when X is a halogen atom, such as Cl, Br or I, or alkoxy, chlorine and methoxy being preferred.

The ester group in the monoester of 5-nitroisophthalic acid is aminolyzed with the hydroxyalkylamine of the general formula HNR1R2 as defined above, or the aminolysis can be achieved with ammonia first. The remaining carboxyl group is then activated as described above. If the hydroxyl groups in the residue NRXR2 are unprotected and can be affected by the activation, they can be appropriately protected using common means, such as O-acetylation or by isopropylidination.

The compound with the general formula (II) can be crystallized in the usual way from water or lower alcohols.

After reaction with anhydrous ammonia or ammonium hydroxide, where the asymmetric isophthaldiamide is obtained, the compound is hydrogenated, triiodinated and acylated in the usual way, whereby compounds of the general formula (III) are obtained:

where Rlf R2 and R3 are as defined above.

Reduction and iodination are usually carried out using standard methods where palladium-on-carbon or Raney nickel in water or lower alcohols, and hydrogen under low or high pressure are used as catalysts. The resulting 5-aminoisophthalic acid bisamide is then iodinated using known methods. The compound is then recovered in the usual way as it crystallizes from the reaction mixture, washed, dried and subjected to acylation, also by following known methods. An activated acyl group, R3CO-X, where X is halogen, or the same acyl group is then converted into an anhydride, and such catalytic solvents as pyridine, DMA or DMF can be used.

If compounds according to formula (I), where R 4 is different from hydrogen, are prepared, the alkylation is carried out using standard methods. Apart from lower alkyl groups which are usually introduced at an earlier step in the synthesis, the reaction with hydroxyalkyl residues is usually carried out as the last step. Such alkylation can be carried out in a glycol solvent with a high boiling point, such as ethylene or propylene glycol, and very basic pH is achieved with sodium methoxide, sodium hydroxide or other inorganic or organic bases.

Alternatively, it is sometimes advantageous for purification purposes, when by-products are formed which would otherwise be difficult to remove by conventional purification methods, to maintain the presence of a carboxyl group until the last steps of the reaction sequence, so that the compound can readily dissolve in water as a salt and then precipitated or re-precipitated with an inorganic acid. Preferred salts include ammonium, sodium, potassium, calcium, barium or lithium.

Such an alternative method is based on the reduction, iodination and acylation of compounds of formula (II) (where X = OH) in the manner described above to arrive at compounds of formula (IV):

where Rlf R2 and R3 are as defined above.

The hydroxyl groups are protected before the activation of the carboxyl group. It is also necessary to diacylate the anilide with R3CO, as this nitrogen atom would likewise be adversely affected during carboxyl activation. The carboxyl group will be activated as described above, the acid chloride being preferred, although mixed anhydrides may be used, e.g. t-butyloxycarbonyl. Compounds of formula (IV) can be readily crystallized from an aprotic solvent and reacted with ammonium hydroxide or ammonia, followed by alkylation as the final step.

Efficient amidation usually requires the use of either an excess of amidation base as acid acceptors or alternatively such tertiary amines as triethylamine, tributylamine or pyridine, or such inorganic bases as bicarbonate or carbonate.

Yet another variation of the synthesis procedure can be used when unwanted by-products occur. Alkylation of the anilide can thus be carried out before the amidation. Alkylation of the compounds of the general formula (IV), where R 1 R 2 and R 3 are as defined above, can be carried out using known methods as described above.

During alkylation to introduce R4, the protecting groups R3CO are lost, and the hydroxyl groups in R1 and R2 (also R4 if present) must therefore be reprotected before carboxyl activation and subsequent amidation with ammonia. Acetyl groups are most often used for this purpose.

If hydroxyl groups are still protected, as would be the case when alkylation is carried out as the final step, the protecting groups may conveniently be removed after the final step by such standard means as exposure to ion exchange resins, or the use of acids or bases in catalytic amounts in alcoholic or aqueous solutions -funds.

Desalination can be carried out using known methods. Salts will typically be removed using ion exchange resins, either in a mixed layer or in separate columns that each contain an anionic or cationic exchange resin. Alternatively, the compounds of the general formula (I) can be absorbed on a polystyrene absorbing neutral resin and then eluted.

After removal of the salts, the product can now be crystallized from several different solvents, preferably lower alcohols. Decolorization is achieved by boiling with reflux cooling in an aqueous solution with activated charcoal.

The dimer is conveniently prepared from the benzamide, with the amino nitrogen atom alkylated and the remaining carbonyl group activated, e.g. chlorocarbonyl. The dibasic acid is used in activated form, particularly as the diacyl dichloride in an organic, aprotic, polar solvent. The ring carbonate-bound chlorocarbonyl is then hydroxyalkylamidated, whereby the final product is obtained.

The compounds according to the invention and with the general formula (I) are stable in aqueous solutions; they readily form supersaturated solutions that also remain stable. The solutions can be autoclaved using standard means. At diagnostically applicable iodine concentrations, the compounds have osmolalities that are typically very close to the physiological values. At the same time, the viscosity of the solution is low. The object of the invention, to overcome the previously recognized mutual exclusion of the two factors, i.e. low osmolality and low viscosity, has thus been achieved. As a result, the new compounds have excellent local and systemic tolerance. The compounds have good biological tolerance and high iodine content, especially compared to currently available, non-ionic radiography contrast media.

As examples of the properties of the compounds in the benzamide class, data were produced for the compounds (11)

(claim 5) and (19) (claim 6). For comparison, data relating to previously known compounds are also shown in Table I.

The observed low osmolality and accompanying low toxicity were previously only achieved in non-ionic dimers which, however, cannot be exploited in general uroangiography due to the high viscosity which, for a comparable solution concentration, is at least two times higher.

The new compounds exhibit excellent general biological tolerance, as high osmolality is a causative factor for vascular pain and a major side effect of imaging the peripheral limb vasculature (Sovak, M., Current Contrast Media and Ioxilan, Comparative Evaluation of Vascular Pain by Aversion Conditioning, Investigative Radiology, September 1988, supp.). This is one of the most important diagnostic procedures in vascular radiology. The new compounds according to the invention are expected to cause practically no pain in such procedures. Because of their physiochemical and pharmacological properties, the new compounds are suitable as water-soluble contrast media for the visualization of the urinary and urinary cardiovascular systems, and body cavities and for general contrast enhancement in computed tomography. The injectable solutions of the new compounds can be prepared by dissolving in water and adding standard, physiologically compatible buffers, and stabilizing agents, such as gelating agents. The compounds are also suitable for enteral application when formulated with carriers commonly used in pharmacopoeias. The dimers find particular application for myelograms.

For intravascular use, the compounds according to the invention contain 20-80% by weight/volume, with iodine concentrations of 150-400 mg/ml being preferred.

The following examples are given as an illustration.

Experimental

Example 1

Amidation of monomethyl ester of 5-nitroisophthalic acid (1) with (threo)-2-amino-1,3,4-butanetriol to

5-nitro-3-fN-(1.3.4-trihydroxys-threo-but-2-yl)Icarbamoyl-benzos<y>re ( 2)

22.5 g (0.1 mol) of the starting material (1) was mixed with 30.25 g (0.25 mol) of (threo)-2-amino-1,3,4-butanetriol, and

the suspension was heated to 110-120°C for 30 min. Complete conversion of the product was confirmed by TLC and the solution was poured into 200 ml of 1 N hydrochloric acid to precipitate the product. After cooling overnight, the product was filtered off and washed with 2 x 20 ml ice-cold water. Drying under vacuum afforded 21.0 g (67% yield) of a white solid (2).

Example 2

Esterification of 5-nitro-3-{"N-(1.3,4-trihydroxy-threo-but-2-yl))-carbamoyl-benzoic acid (2) with dimethyl sulfate to

methyl- 5- nitro- 3- fN-( 1. 3. 4- trihydroxy- threo- but- 2- yl) Tcarbamo-yl- benzoate ( 3)

15.7 g (0.05 mol) of the title compound (2) was dissolved in 55 ml of 1 N sodium hydroxide solution, and the solution was cooled to <20°C. 9.45 g (0.075 mol) of dimethyl sulfate was added over 5 min, and the pH was maintained between 8 and 10 by occasional addition of 5 N sodium hydroxide solution. The solution was stirred for approx. 12 hours at room temperature, after which the insoluble solid was filtered off. The pasty solid was washed with 2 x 50 ml cold water and dried under vacuum to give 11.8 g (72% yield) of a powder (3).

Example 3

Amidation of methyl-5-nitro-3-fN-(1.3.4-trihydroxy-threo-but-2-yl)Tcarbamoyl-benzoate (3) with ammonia to

5- nitro- 3- fN-( 1. 3. 4- trihdroxy- threo- but- 2- yl) Icarbamoyl- benzamide ( 4)

10.0 g (0.0305 mol) of the ester (3) was dissolved in

50 ml of methanol, and 20 ml (about 0.3 mol) of concentrated ammonium hydroxide were added. The suspension was heated in a closed container at 50-60°C for 30 min until TLC indicated completion of the reaction. The methanol and ammonium hydroxide were removed by distillation and replaced with 50 ml of H 2 O. The mixture was cooled overnight, after which the insoluble product was filtered off and washed with 2 x 5 ml of cold water. Vacuum drying gave 7.15 g (75% yield) of the white mixed amide (4).

Example 4

Chlorination of the monomethyl ester of 5-nitroisophthalic acid with thionyl chloride to

the monomethyl ester, the monoacid chloride of 5-nitroisophthalic acid ( 5 )

225 g (1 mol) of the title compound (1) was dissolved in 0.5 ml of ethyl acetate, and 0.1 ml of N,N-dimethylformamide was added as a catalyst. The solution was heated to 70°C, and 219 mL (3 mol) of thionyl chloride was added over 1.25 hours. The temperature was then maintained at 70°C for 2 hours.

The thionyl chloride was distilled together with 3 x 200 ml of ethyl acetate and the product dissolved in 250 ml of ethyl acetate and precipitated with 1 1 of cyclohexane, filtered and washed with 2 x 200 ml of cyclohexane. Drying at 50°C under vacuum afforded 216 g (89% yield) of a white solid (5_).

Example 5

Amidation of the monomethyl ester monoacid chloride of 5-nitroisophthalic acid ( 5) with aminodioxepane to

methyl- 5- nitro- 3- fN-( trans- 2, 2- dimethyl- 6- hydroxy- 1, 3- dioxepan- 5- yl) Tcarbamoyl- benzoate ( 6)

100 g (0.411 mol) of the monoester monochloride was dissolved in dry tetrahydrofuran, and 132.8 g (0.825 mol) of the solid aminodioxepane was added in portions over 15 min while maintaining the temperature below 25°C using of an ice bath. The heterogeneous mixture was then allowed to stir for 30 min at room temperature, after which TLC showed complete reaction.

The insoluble amine hydrochloride was filtered off and the tetrahydrofuran removed from the filtrate by distillation. The residue was dissolved in 400 ml of ethyl acetate near the boiling point, and the solution was allowed to stand for several days until crystallization of the product was complete. The solid was filtered off, washed with 2 x 50 ml of cold ethyl acetate and dried in a vacuum oven, whereby 82.4 g (55% yield) of an off-white product (6) was obtained.

Example 6

Amidation of methyl- 5- nitro- 3- fN-( trans- 2, 2- dimethyl- 6- hydroxy-1, 3- dioxepan- 5- yl) Icarbamoyl- benzoate ( 6) with ammonium hydroxide to

5- nitro- 3- fN-( trans- 2. 2- dimethyl- 6- hydroxy- 1, 3- dioxepan- 5-yl)} carbamoyl- benzamide ( 7)

An 800 ml Parr pressure reactor was charged with 80 g (0.22 mol) of the title compound (6.), 110 ml methanol and 225 ml (3.38 mol) 15 N ammonium hydroxide. The reaction vessel was closed and immersed in a water bath at 50°C for 2 hours when TLC indicated complete reaction. The heterogeneous reaction mixture was mixed with 100 mL of H 2 O and then stripped to a foam. The foam was slurried in 100 mL H 2 O, filtered and washed twice with 50 mL H 2 O to give 60.4 g (79% yield) of a white solid (7).

Example 7

Reduction and deprotection of 5-nitro-3-{N-(trans-2,2-dimethyl-6-hydroxyl-1,3-dioxepan-5-yl)Icarbamoyl-benzamide (7) with hydrogen and palladium-on-carbon and hydrochloric acid to 5-amino-(hydrochloride)-3-fN-(1,3,4-trihydroxy-threo-but-2-yl) 1-carbamoyl-benzamide ( 8)

A 2.0 L Parr pressure reactor was charged with 58 g (0.16 mol) of the title compound (7), 410 mL 1 N hydrochloric acid and 5.8 g palladium-on-carbon (10% Pd/C, 1 wt % Pd). The reaction vessel was connected to a hydrogenator and shaken under 50 psi hydrogen gas for 2 hours when HPLC indicated 90% conversion to product (8_). The palladium catalyst was filtered off, and the acetone formed during the deprotection was removed under vacuum at 50°C. The resulting clear solution (8)

(450 ml, 90% yield) was taken directly for iodination.

Example 8

Iodination of 5-amino-(hydrochloride)-3-fN-(1,3,4-trihydroxy-threo-but-2-yl)Icarbamoyl-benzamide (8) with iodine monochloride to 5-amino-2,4,6- triiodo-3-fN-(1,3,4-trihydroxy-threo-but-2-yl)>-carbamoyl-benzamide (9)

0.14 mol of the title compound (8_) in 450 ml of 1 N hydrochloric acid was heated to 85°C, and 135 ml (0.49 mol) of iodine mono-

chloride was added. The reaction mixture was heated at 85°C for 2 hours when HPLC indicated that the reaction was complete. The reaction mixture was cooled to 25°C and extracted with 2 x 200 ml cyclohexene, 3 x 300 ml dichloromethane and 5 x 200 ml chloroform until all violet color was removed from the aqueous layer. The resulting pale yellow solution was recycled onto a column containing 800 g of "Duolite-A340" and 266 g of "Dowex 50W-X8" resins. The resins were rinsed with 6 L of H 2 O and the solution concentrated to 300 mL when a white crystalline solid began to crystallize. The product was filtered off, giving 40 g (0.06 mol, 43% yield) of a white solid (9).

Example 9

Acetvlerinq of 5- amino- 2, 4, 6- triiodo- 3- fN-( 1. 3, 4- trihydroxy-threo- but- 2- yl) Icarbamovl- benzamide ( 9) with acetic anhydride to 5- diacetylamino- 2, 4,6-triiodo-3-fN-(1,3,4-triacetoxy-threo-but-2-yl)Icarbamoyl-benzamide (10) 90 g (0.14 mol) of the title compound was mixed with 500 ml (4 .95 mol) of acetic anhydride at 70°C with vigorous stirring. 0.36 mL (0.004 mol) of perchloric acid catalyst was added, causing the temperature to rise to 85°C. The reaction mixture was stirred at 85°C for 1 hour when it became homogeneous and TLC indicated reaction completion. 0.33 g (0.004 mol) of sodium acetate was added to neutralize the perchloric acid and the solvent was removed to give a thick brown oil. The oil was diluted with 200 ml of butyl acetate at 70°C, followed by solvent removal. The stripping procedure was repeated twice to give 113 g (0.13 mol, 93% yield) of a brown foam (10).

Example 10

Deacetylation and alkylation of 5-diacetylamino-2,4,6-triiodo-3-{N-(1,3,4-triacetoxy-threo-but-2-yl)Icarbamoyl-benzamide (10) with sodium methoxide and 2-chloroethanol to

5- fN-( 2- hydroxyvetvlacetamido) >- 2, 4, 6- triiodo- 3- fN-( 1. 3. 4- trihydroxy- threo- but- 2- yl) 1carbamoyl- benzamide ( 11)

113 g (0.13 mol) of the title compound (10) was dissolved in 500 ml of methanol to which 55 g (0.25 mol) of 25% sodium methoxide was added at 50°C. After 5 hours, HPLC indicated that the deacetylation was complete, and the solution was neutralized with 10 g of "Dowex 50W-X4" resin. The resin was filtered off and the filtrate concentrated to 400 ml. The neutral methanol solution was heated to 45°C and charged with 129 g (0.34 mol) of trisodium phosphate dodecahydrate and 18.2 ml (0.272 mol) of 2-chloroethanol. The reaction mixture was stirred at 45°C for 48 hours, after which 4.7 ml (0.07 mol) of chloroethanol and 14.7 g (0.07 mol) of sodium methoxide were added. After 71 hours, HPLC indicated that the reaction had gone to completion. The insoluble salts (89 g) were removed by filtration and the solution neutralized with 7 ml of 6 N hydrochloric acid. The solution was concentrated to give 94 g (0.12 mol, 92% yield) of a brown foam (1JL).

Example 11

Amidation of the monomethyl ester of 5-nitroisophthalic acid (1) with 3-amino-1,2-propanediol to

5- nitro- 3- fN-(2, 3- dihydroxypropyl) Icarbamoyl- benzoic acid ( 12)

225 g (1 mol) of the starting material (1) was mixed with 227.8 g (2.5 mol) of 3-amino-1,3,4-propanediol, and the heterogeneous mixture was heated to 110-120°C in 1 hour. At this point the reaction was complete and the homogeneous mixture was mixed with 1 L of water and 170 ml of concentrated HCl. The mixture was cooled for several days to completely precipitate the product, and the solid was filtered off and washed with 2 x 50 mL of cold water. Vacuum drying gave 193 g (68% yield) of a white solid (12).

Example 12

Reduction of 5-nitro-3-fN-(2,3-dihydroxypropyl)Icarbamovl-benzoic acid (12) with hydrogen and palladium-on-carbon to 5-amino-(hydrochloride)-3-fN-(2,3-dihydroxypropyl) ) Icarbamovl-benzoic acid ( 13

180 g (0.634 mol) of the nitro acid (12) was mixed with 1 L of water and 60 ml of concentrated HCl, and 18 g of 10% palladium-on-carbon was added. The suspension was hydrogenated at 2-4 atmospheres until the pressure remained constant, after which HPLC and TLC indicated complete reaction. The palladium-on-carbon was

removed by filtration and the homogeneous solution used without product isolation for the following reaction (13, approximate yield 98%).

Example 13

Iodination of 5-amino-(hydrochloride)-3-fN-(2,3-dihydroxypropyl)Tcarbamoyl-benzoic acid (13) with iodine monochloride to 5-amino-2,4,6-triiodo-3-fN-(2,3 - dihydroxypropyl) Icarbamoyl-benzoic acid ( 14)

About 0.62 mol of the title compound (13) in 1.5 L of water was further diluted with water to a total volume of 4 L and heated to 85°C. During 20 min, 499 ml (2.05 mol) of 4.1 molar iodine monochloride were added and the temperature was maintained at 90°C for 6-8 hours. HPLC indicated complete turnover. The homogeneous mixture was cooled, extracted with 500 ml of 1,2-dichloroethane/cyclohexane (9:1), followed by 2 x 250 ml of 1,2-dichloroethane. The aqueous layer was then concentrated by distillation to 0.9 L and cooled for several days to complete precipitation of the solid. Filtration, washing with 2 x 100 ml cold water and vacuum drying gave 286 g (73% yield) of golden brown product (14).

Example 14

Acetylation of 5-amino-2,4,6-triiodo-3-fN-(2,3-dihydroxypropyl)Icarbamoyl-benzoic acid (14) with acetic anhydride to 5-diacetylamino-2,4,6-triiodo-3-{" N-(2, 3- diacetoxypropyl) >-carbamoyl- benzoic acid ( 15)

100 g (0.158 mol) of the starting material (14) was

mixed with 300 ml (3.16 mol) of acetic anhydride and 0.2 ml of 80% perchloric acid and heated to 80-90°C for 8 hours. The mixture was neutralized with 0.25 g of anhydrous sodium acetate, and the acetic anhydride and acetic acid were removed by distillation at 70-80°C. The oily residue was azeotroped with 2 x 100 ml butyl acetate, then dissolved in 250 ml ethyl acetate and taken directly for chlorination (15, approximate yield 90%).

Example 15

Chlorination of 5-diacetylamino-2,4,6-triiodo-3-{"N-(2,3-diacetoxypropyl)Icarbamoyl-benzoic acid (15) with thionyl chloride to 5-diacetylamino-2,4,6-triiodo-3- fN-(2,3-diacetoxypropyl)1-carbamoyl-benzoyl chloride ( 16)

To approx. To 0.142 mol of the starting material (15) in 225 ml of ethyl acetate, 57 ml (0.78 mol) of thionyl chloride were added at 65-70°C, and the temperature increased little by little to 75-80°C over the course of 1 hour. Thionyl chloride and ethyl acetate were vacuum distilled. The residue was azeotropically distilled with 2 x 100 ml of butyl acetate and vacuum dried. The brown foam (16, ca. 130 g, calculated yield 95%) was taken directly to the subsequent amidation step.

Example 16

Amidation of 5-diacetylamino-2,4,6-triiodo-3-{N-(2,3-diacetoxypropyl)Tcarbamoyl-benzoyl chloride (16) with ammonia to 5-acetylamino-2,4,6-triiodo-3-fN -( 2, 3- diacetoxypropyl) 1-carbamoyl- benzamide ( 17)

About 0.135 mol of the acid chloride (16) was dissolved in 150 ml of dry N,N-dimethylacetamide. This solution was cooled to 0-5°C, approx. 20 mL of anhydrous ammonia was condensed into the mixture using a dry ice/acetone condenser, and the reaction mixture was kept sealed at room temperature for 24 hours. The ammonia and DMA were removed by vacuum distillation. 500 ml of 1-pentanol precipitated as a solid which was filtered off and washed with 2 x 150 ml of 1-pentanol. Vacuum drying gave 82 g (80.2% yield) of a golden brown solid (17).

Example 17

Deacetylation of 5-acetylamino-2,4,6-triiodo-3-{"N-(2.3-diacetoxypropyl)-carbamoyl-benzamide (17) to

5- acetylamino- 2, 4, 6- triiodo- 3- fN-( 2, 3- dihydroxypropyl) 1-carbamoyl- benzamide ( 18)

81.2 g (0.107 mol) of the title compound (17) was slurried in 203 ml of water and then treated with the dropwise addition of 16.9 ml (0.322 mol) of 50% by weight sodium hydroxide in water. Under stirring, the overall solution was obtained. Up-

the solution was degassed under vacuum for 30 min, after which 15 mL (0.18 mol) of 12 M HCl was added. After storage at 4°C, the resulting precipitated solid was filtered off, washed with 3 x 50 ml ice water, 80 ml ethanol and vacuum dried to give 54.1 g (75% yield) of the product (18.).

Example 18

Alkylation of 5-acetylamino-2,4,6-triiodo-3-!"N-(2,3-dihydroxys-propyl)1carbamoyl-benzamide (18) to

5-{N-(2,3-dihydroxypropyl)acetamido)-2,4,6-1ri iod-3-f N-(2,3-dihydroxypropyl)Icarbamoylbenzamide (19)

39.7 g (0.059 mol) of the title compound (18) was dissolved in 16.7 ml propylene glycol, 120 ml ethanol and 17.6 ml (0.077 mol) 25% by weight sodium methoxide. 9.78 g (0.0885 mol) of chloropropanediol was added and the mixture stirred at 25°C for 1 hour. The reaction mixture was warmed to 33°C and stirred for a further 19 hours during which time 3.4 ml (0.015 mol) of 25% by weight sodium methoxide was added. The reaction was quenched with 12 M HCl, the reaction mixture was distilled under vacuum, reconditioned with 200 mL H 2 O and redistilled to give an aqueous solution which was deionized with 62 g "Dowex 50 H<+>" resin and 140 g " Duolite A-340 OH"" resin. Elution of the resins with H 2 O and concentration gave a 150 g solution which was treated with 1.00 g "Norit Ultra S-X" activated carbon at

60°C for 14 hours. The activated carbon was filtered off, whereby an aqueous solution was obtained which was stirred for 2 hours with 1.0 g "Dowex 50 H<+>" and 4 g "Duolite A-340 OH-". The resin was filtered off and the aqueous solution distilled, yielding 50.3 g of an oil containing 32.8 g (74% yield) of the product (19)

in a glycerol/propylene glycol base. This oil was purified as described in the following step.

Example 19

Peracetylation, silica column purification and subsequent deacetylation of 5-{N-(2,3-dihydroxypropyl)acetamido>-2,4,6-triiodo-3-fN-(2,3-dihydroxypropyl)Icarbamoylbenzamide (19)

16.4 g (0.022 mol) of the title compound (19) dissolved in glycerol/propylene glycol oil (total mass 25.15 g) was diluted with 1.74 g (0.022 mol) pyridine and 115 g (1.12 mol)

acetic anhydride, and then heated to 60°C for 18 hours. The reaction mixture was distilled under reduced pressure to an oil which was dissolved in 100 ml CHCl 3 , and it was extracted with 2 x 50 ml 0.1 N HCl and 2 x 50 ml 15% w/v saline. The CHCl 3 layer was dried over MgSO 4 , filtered and distilled to an oil. This oil was purified on a 900 g silica column using a solvent gradient from 5% acetic acid, 95% chloroform to 5% acetic acid, 4% methanol, 91% chloroform. Purified fractions were pooled, distilled to a foam, and then treated with 30 mL of methanol and 0.98 g (0.0054 mol) of 25 wt% sodium methoxide in methanol. After 30 min, the solution was distilled, reconditioned with 20 ml of methanol and then stirred with 1.3 g of "Dowex 50 H<+>" resin. After the pH had decreased from 12 to 5, the resin was filtered to give a solution which was distilled to a foam, reconditioned with 25 mL H 2 O and evaporated to give 8.12 g (49% yield) of the solid title compound (19) .

Example 20

Deacetvlerinq of 5- diacetylamino- 2, 4, 6- triiodo- 3- fN-( 2, 3- diacetoxypropyl) Icarbamovl- benzoic acid ( 15) to

5- Acetylamino- 2, 4, 6- triiodo- 3- fN-(2, 3- dihydroxypropyl) 1-carbamoyl- benzoic acid ( 20)

720 g (0.9 mol) of the title compound (15) was dissolved in 500 ml of methanol, and 345 ml (1.5 mol) of 25% by weight sodium methoxide in methanol was added. After 4 hours at 45-50°C, the reaction mixture was distilled under reduced pressure, acidified with 124 ml (1.5 mol) 12 M HCl and the salts filtered off. The filtrate was distilled under reduced pressure, whereby an oil was obtained which was diluted with 680 ml of n-propanol. After crystallization at 4°C, the resulting solid product (20) was filtered off, washed with 2 x 300 ml of n-propanol and dried under vacuum. The yield was 391 g (64%).

Example 21

Alkylation of 5-acetylamino-2,4,6-triiodo-3-{"N-(2,3-dihydroxypropyl)Icarbamoyl-benzoic acid (20) to the sodium salt of 5-fN-(2,3-dihydroxypropyl) acetamido 1- 2, 4. 6- triiodo- 3- fN-( 2. 3-dihydroxypropyl) Icarbamoyl- benzoic acid ( 21)

100 g (0.148 mol) of the title compound (20) was dissolved in 400 ml of methanol. 140.6 g (0.37 mol) of solid Na 3 PO 4 -12 H 2 O was added, followed by 32.7 g (0.296 mol) of chloropropanediol and 24.1 g (0.111 mol) of 25 wt% sodium methoxide in methanol added dropwise. The reaction mixture was heated to 40°C for 10 hours during which time an additional 8.0 g (0.0368 mol) of 25% sodium methoxide was added in portions. Salts were filtered off and the methanol filtrate acidified with 3.5 mL of 12 M HCl, rotary evaporated to a thick, oily product (21) and taken directly to the next reaction.

Example 22

Acetylation of the sodium salt of 5-fN-(2,3-dihydroxypropyl)-acetamido>-2,4.6-triiodo-3-(N-(2,3-dihydroxypropyl)Icarbamoyl-benzoic acid (21) to

5 - { N - ( 2. 3 - diacetoxypropyl) acetamido >- 2, 4, 6- tri in od- 3- f N-( 2, 3-diacetoxypropyl) Icarbamoyl- benzoic acid ( 22 )

114 g (0.148 mol) of the title compound (21) in oil form was diluted with 11.7 g (0.148 mol) pyridine and 605 g (5.92 mol) acetic anhydride, and it was stirred at 65-70°C for 2 hours. The reaction mixture was distilled to an oil, azeotropically distilled with 2 x 100 ml of butyl acetate and distributed between 300 ml of water and 200 ml of toluene/ethyl acetate in the ratio 3:1. The aqueous layer was extracted with 3 x 100 ml toluene/ethyl acetate in the ratio 3:1 and acidified with 22.5 ml HCl in the presence of 300 ml

ethyl acetate. The acidified H 2 O layer was separated and extracted twice with 100 ml of ethyl acetate. The latter three ethyl acetate extracts were combined, dried over MgSO 4 , filtered and evaporated to give 118 g (87% yield) of a solid product (22).

Example 23

Chlorination of 5- 1N-(2, 3- diacetoxypropyl) acetamido>- 2, 4, 6- triiodo- 3-{ N-( 2, 3- diacetoxypropyl) Icarbamoyl- benzoic acid ( 22) to 5- f N-( 2 .3- diacetoxypropyl) acetamido >- 2. 4. 6- tri i od- 3- f N-( 2. 3-diacetoxypropyl) Icarbamovl- benzoyl chloride ( 23)

113.6 g (0.124 mol) of the title compound (22) was dissolved in 100 ml of ethyl acetate at 55°C, 44 g (0.37 mol) of thionyl chloride was added dropwise and the mixture boiled under reflux for 2 hours, rotary evaporated to a oil and then azeotropically distilled with 2 x 50 ml butyl acetate, whereby a foam was obtained which was dissolved in 200 ml chloroform and extracted with 100 ml 0.2 M pH 6.7 phosphate buffer. The organic layer was dried over MgSO 4 , filtered and evaporated to give 115 g (98% yield) of a solid product (23).

Example 24

Amidation of 5-{"N-(2.3-diacetoxypropyl)acetamidol-2.4,6-triiodo-3-fN-(2,3-diacetoxypropyl)Icarbamoyl-benzoyl chloride (23) to 5-fN-(2 , 3- diacetoxypropyl) acetamidoT- 2, 4, 6- triiodo- 3-- TN-( 2, 3- diacetoxypropyl) 1 carbamoyl- benzamide ( 24)

105 g (0.111 mol) of the title compound (23) was dissolved in 400 ml of acetonitrile to which anhydrous ammonia was added using a dry ice condenser at 25°C. After 3 hours of NH3 reflux, the turnover was complete. Salts were filtered off and evaporation gave 98.8 g (96% yield) of a solid product (24).

Example 25

Deacetylation of 5-fN-(2,3-diacetoxypropyl)acetamido'y-2,4,6-triiodo-3-fN-(2,3-diacetoxypropyl)Icarbamoylbenzamide (24) to 5-fN-(2. 3- dihydroxvpropyl) acetamidol- 2. 4. 6- triiodo- 3- fN-( 2. 3-dihydroxypropyl)"} carbamoyl- benzamide ( 19)

98.7 g (0.106 mol) of the title compound (24) was dissolved in 250 ml of methanol to which 2.30 g (0.0106 mol) of 25% by weight sodium methoxide in methanol was added at 25°C. After 15 min.

the solution was vacuum distilled to an oil, reconditioned with 200 ml of methanol and then stirred with 6.0 g of "Dowex 50 H<*>" resin until the pH decreased from 12 to 6. The resin was filtered off to give a solution which was distilled to a foam,

reconstituted with 320 mL water and 3.0 g "Norit S-X" activated carbon, boiled under reflux for 7 hours, filtered, deionized by stirring with 3 g "Dowex 50 H<+>" resin and 12 g "Dowex XUS-40123 OH-" resin, filtered and evaporated to 79.2 g (96% yield) of the solid product (19).

Example 26

Methoxyacetylation of 5-amino-2,4,6-triiodo-3-fN-(1,3,4-trihydroxy-threo-but-2-yl)Icarbamoyl-benzamide (9) with methoxyacetyl chloride to

5- methoxyacetylamino- 2, 4, 6- triiodo- 3- fN-( 1, 3. 4- trihydroxy- threo- but- 2- yl) Icarbamoyl- benzamide ( 25)

100 g (0.15 mol) of the title compound (9) was slurried in 250 ml of N,N-dimethylacetamide at 25°C, to which 68 ml (0.75 mol) of methoxyacetyl chloride was added over 30 min. The reaction mixture was stirred at 35°C for 5 hours when HPLC indicated that the reaction was complete. The reaction mixture was quenched with 97 g (0.45 mol) of sodium methoxide and the mixture stirred at 40°C for 2 hours. The solution was neutralized with "Dowex 50W-X4 " resin, filtered and diluted with 700 mL of n-butanol. A white precipitate formed immediately and was filtered off to give 80.6 g (0.11 mol, 73%) of an off-white solid (25).

Example 27

Alkylation of ioxythalamic acid ( 26) to

5-fN-(2.3-dihydroxypropyl)acetamido>-2,4,6-triiodo-3-| N-(2-Hydroxyethyl) T-carbamoyl- sodium benzoate ( 27 )

966 g (1.5 mol) of ioxythalamic acid (26) was dissolved in 1.5 1 1 N sodium hydroxide at room temperature, it was heated to 75°C, and 223.8 g (2.03 mol) of 3-chloro-l, 2-Propanediol and approximately 0.4 1 5 N sodium hydroxide were simultaneously added over 1.25 hours. The reaction mixture was heated to 80-90°C for a further 2.5 hours, after which HPLC showed completion of the reaction (approx. 90% conversion to product).

The reaction mixture was neutralized with approx. 3 ml of concentrated hydrochloric acid and evaporated. About half of the foam residue was taken up in 0.4 1 of water. After cooling, a white, crystalline solid precipitated which was filtered off and washed with ice-cold water. Drying gave 249 g of the crystalline product (27).

Example 28

Acetylation of 5-n-(2,3-dihydroxypropyl)acetamido>-2,4,6-triiodo-3-{N-(2-hydroxyethyl)Tcarbamoyl-sodium benzoate (27) to 5-n-(2,3- diacetoxypropyl)acetamidol-2,4,6-triiodo-3-fN-(2-acetoxyethyl)Icarbamovl-benzoic acid (28) 50 g (0.067 mol) of the title compound (27) was added to 102 ml (1.080 mol, 16.0 eq .) stirred acetic anhydride at 25°C. 5.4 mL (0.067 mol, 1.0 equiv) of pyridine was added and the temperature raised to 85°C for 1 hour, after which TLC indicated that the reaction was complete. The homogeneous reaction mixture was evaporated under vacuum to a thick oil, dissolved in 50 ml of butyl acetate and evaporated repeatedly. The oil was dissolved in 260 ml H 2 O and extracted with 4 x 100 ml toluene/ethyl acetate (2:1). The aqueous layer was acidified with 11 ml of 12 N hydrochloric acid and extracted with 3 x 50 ml of ethyl acetate. The organic layer was dried over magnesium sulfate, evaporated to a foam (28) and taken directly to the next step (55 g, 0.065 mol, 97% yield).

Example 29

Chlorination of 5-n-(2,3-diacetoxypropyl)acetamido>-2,4,6-triiodo-3-n-(2-acetoxyethyl)Icarbamoyl-benzoic acid (28) to 5-n-(2,3-diacetoxypropyl) ) acetamido>-2,4,6-triiodo-3-fN-(2-acetoxbutyl)Icarbamovl-benzoyl chloride (29) 55 g (0.065 mol) of the title compound (28) was dissolved in 170 ml of 1,2-dichloroethane and heated to 85°C. 9.8 mL (0.134 mol, 2.0 equiv) of thionyl chloride was added and TLC indicated that the reaction had reached completion after 3 hours. The reaction mixture was evaporated under vacuum to an oil, redissolved in 50 ml of butyl acetate and evaporated repeatedly. The product was isolated as a yellow foam { 29 , 51.9 g, 0.060 mol, 92% yield).

Example 30

Amidation of 5-fN-(2,3-diacetoxypropyl)acetamidol-2,4,6-triiodo-3-fN-(2-acetoxyethyl)Icarbamoyl-benzoyl chloride (29) to 5-fN-(2,3-diacetoxypropyl) acetamido1- 2, 4, 6-tri iod- 3-f N-(2-acetoxyethyl) 1carbamoyl-benzamide ( 30)

51.9 g (0.060 mol) of the title compound (29) was dissolved in 200 ml of acetonitrile, and excess anhydrous ammonia was added at 10°C. After 4 hours, TLC indicated complete turnover. The reaction mixture was filtered to remove ammonium chloride salts and the solvent was removed to give 47 g (0.056 mol, 93% yield) of a yellow oil (30).

Example 31

Deacetylation of 5-fN-(2,3-diacetoxypropyl)acetamidol-2,4,6-triiodo-3-fN-(2-acetoxyethyl)lcarbamoylbenzamide (30) to 5-fN-(2,3-dihydroxypropylacetamido) 1-2,4,6-triiodo-3-fN-(2-hydroxybutyl)Icarbamoylbenzamide (31) 47 g (0.056 mol) of the title compound (30) was dissolved in 240 ml of methanol, and 3.9 g (0.3 eq.) 25% sodium methoxide was added to raise the pH to ca. 12. The solution was stirred at 25°C for 1 hour when HPLC indicated that the deacetylation was complete. The reaction mixture was neutralized with 10 mL of 1 N HCl and solvent removal gave 39 g (0.054 mol, 97% yield, 98% purity) of an off-white foam (31) which was recrystallized from hot methanol (5 g in 15 mL with the addition of crystal grains).

Example 32

Amidation of 5-amino-2,4,6-triiodo-isophthaloyl chloride (32) to 5-amino-2,4,6-triiodo-3-chlorocarbonylbenzamide (33)

300 g (0.503 mol) of the starting material (32) was dissolved in 900 ml tetrahydrofuran and the homogeneous mixture cooled in ice to 5-10°C. 92.3 mL (1.38 mol) of concentrated ammonium hydroxide was added over 10 min and the temperature increased to 30°C.

The reaction mixture was stirred at room temperature for a total of 90 hours with additional additions of ammonium hydroxide (total 25.2 mL, 0.38 mol), then cooled and the insoluble salts removed by filtration. The filtrate was washed with 2 x 200 ml saturated NaCl.

The tetrahydrofuran was evaporated to give a viscous oil. 800 ml of ethyl acetate precipitated as a golden brown solid which was filtered, washed with 2 x 100 ml of ethyl acetate and dried, whereby 193 g (66.5% yield) of (33) was obtained. ■

Example 33

Dimeriserine of 5- amino- 2. 4, 6- triiodo- 3- chlorocarbonyl- benzamide ( 33) to malonic acid- bis- {( 3- chlorocarbonyl- 5- carbamovl)- 2. 4, 6- triiododanilidl ( 34)

20.0 g (34.7 mM) of the title compound (33) was dissolved in 100 ml of dry tetrahydrofuran, it was heated to 45°C, and 2.53 ml (26 mM) of malonyl dichloride was added over 3 min. , whereby a heterogeneous mixture was obtained. 100 ml of dry THF was added and the suspension stirred for 1 hour when TLC showed that the reaction was complete. The mixture was diluted with 150 ml of butyl acetate and the solid filtered off, washed with 2 x 50 ml of butyl acetate and dried under vacuum, whereby 13.18 g (62% yield) of the product (34) was obtained.

Example 34

Amidation of malonic acid-bis-{(3-chlorocarbonvl-5-carbamoyl)-2.4.6-triiodanilidl (34) to

malonic acid- bis- T f 3- N-( 1. 3. 4- trihydroxy- threo- but- 2- yl- carbamoyl- 5- carbamoyl>- 2, 4. 6- triiodanilidl ( 35)

8.0 g (6.56 mM) of the title compound (34) was dissolved in 10 ml of dry N,N-dimethylacetamide, 1.83 ml (13.12 mM) of triethylamine was added and the solution cooled to 20°C. 2.64 g (16.4 mM) of trans-5-amino-2,2-dimethyl-6-hydroxy-1,3-dioxepane was added over 3 min, and the homogeneous mixture was stirred at room temperature for 6 hours when TLC indicated complete turnover. The solvent was evaporated, 50 ml of water was added and the mixture heated at 75°C for 15 min to cleave the acetonides. The product was obtained by evaporation and precipitation with 100 ml of isopropanol. The solid was filtered off, washed with 2 x 20 ml of isopropanol and dried, thereby obtaining 8.6 g (94% yield) of (35).

Example 35

Amidation of 5-N-methylamino-2,4,6-triiodisophthaloyl chloride (36) to 5-N-methylamino-2,4,6-triiodo-3-chlorocarbonylbenzamide (37)

305 g (0.5 mol) of the starting material (36) was dissolved in tetrahydrofuran, and it was cooled to 10°C. 100 ml (1.5 mol) of concentrated ammonium hydroxide was added over 5 min, the temperature increased to approx. 25°C.

The reaction mixture was stirred at room temperature for 65 hours, with further portions of concentrated NH 4 OH added after 20 hours (3.5 ml) and 44 hours (3.5 ml).

After cooling, the insoluble salts and the bis-amide were filtered off and the THF filtrate was washed with 2 x 100 ml saturated sodium chloride solution.

The THF was evaporated and the product precipitated from the thick oil using 500 ml of ethyl acetate. Filtration, washing with ethyl acetate and drying gave 132.1 g (45% yield) of (37).

Example 36

Dimerization of 5-N-methylamino-2,4,6-triiodo-3-chlorocarbonvl-benzamide (37) to

malonsvre-bis-1" (3-chlorocarbonyl-5-carbamoyl)-2,4.6-triiodo-N-methvlanilidl (38) 25 g (42.3 mM) of the title compound (37) was dissolved in 100 ml of dry tetrahydrofuran , and the homogeneous solution was heated to 50° C. 3.05 mL (31.3 mM) malonyl dichloride was added over 2 min, followed by an additional 50 mL of tetrahydrofuran, and the suspension was heated for 1 h when TLC showed that turnover was complete.

After dilution with 50 ml of butyl acetate, the product was filtered off, washed with 2 x 25 ml of butyl acetate and dried, thereby obtaining 15.24 g (58% yield) of an off-white solid (38).

Example 37

Conversion of malonic acid-bis-{(3-chlorocarbonyl-5-carbamoyl)-2. 4. 6-triiodo-N- metvlanilide) ( 38) to

malonic acid- bis- f f 3-N- ( 1. 3. 4- trihydroxy- threo- but- 2- y3.- carbamovl )- 5- carbamoyl"}- 2. 4. 6- triiodo- N- methylanilide ( 39 ) 10 g (8 mM) of the starting material (38) was dissolved in 15 mL dry N,N-dimethylacetamide and 2.23 mL (16 mM) triethylamine.3.22 g (20 mM) trans-5-amino-2,2 -dimethyl-6-hydroxy-1,3-dioxepane (aminodioxepane) was added over 5 min and the homogeneous mixture was stirred for 8 h when TLC showed that the reaction was complete.

DMA was removed by vacuum distillation and the isopropylidenes cleaved with aqueous hydrochloric acid at 50°C. The water was removed on the rotary evaporator and isopropanol added to precipitate the product. Filtration, washing with 3 x 10 mL of isopropanol and drying gave 9.86 g (87% yield) of the dimer (39).

Example 38

5- N-( methyl) amino- 2, 4, 6- triiodo- 3- chlorocarbonyl- benzamide ( 36) to 5- fN-( methyl)- 2- acetoxyacetamidol- 2, 4, 6- triiodo- 3- chlorocarbonyl- benzamide (40) 25 g (42.3 mM) of the starting material (36) was dissolved in 50 ml of dry N,N-dimethylacetamide at room temperature.

6.83 mL (63.5 mM) of 2-acetoxyacetyl chloride was added and after stirring overnight, TLC indicated that the reaction was complete.

The product was precipitated by adding 200 ml of ice-cold water and filtered. After washing with water, the solid was dissolved in 200 mL tetrahydrofuran and the solution extracted with 250 mL saturated NaCl/saturated NaHCO 3 (3:1), followed by 100 mL saturated NaCl. The organic layer was dried (MgSO 4 ) and the solvent removed to give 22.1 g (77.2% yield) of a foam (40).

Example 39

Amidation and deprotection of 5-fN-(methyl)-2-acetoxyacetamidol-2,4,6-triiodo-3-chlorocarbonylbenzamide (40) to 5-fN-(methyl)-2-hydroxyacetamido>-2.4, 6-triiodo-3-fN-(1,3,4-trihydroxys-threo-but-2-yl) 1-carbamoyl-benzamide ( 41)

7.0 g (10.35 mM) of the title compound (40) was dissolved in a mixture of 40 ml of tetrahydrofuran and 1.44 ml (10.35 mM) of triethylamine, and it was cooled to 10°C. 2.0 g (12.41 mM) of solid aminodioxepane was added, the cooling was removed, and the reaction mixture was stirred at 25°C. After 18 hours, TLC indicated complete turnover.

The reaction mixture was diluted with 40 mL of tetrahydrofuran and 50 mL of saturated NaCl/saturated NaHCO 3 (3:1) and the layers were separated. The organic layer was washed with 2 x 40 ml saturated NaCl, dried (MgSO 4 ) and the solvent evaporated to give 6.9 g (82% yield) of a foam.

The foam was dissolved in 50 ml of methanol and 0.5 ml of 4.6 formal NaOMe solution added. The solution was stripped at 50°C to give an oil which was then mixed with 50 ml of water and 10 g of "Dowex 50 H<+>" resin. Heating at 60°C for 30 min finally gave a homogeneous solution, and HPLC indicated that ester and isopropylidene cleavage was complete.

The resin was filtered and the solution circulated through alternating "Duolite A 340 0H""/"Dowex 50 H<+>" columns until deionization was complete. The compound was eluted from the columns with water and then treated with "Norit Ultra S-X" carbon (0.4 g). After 1 hour at 70°C, the carbon was filtered off and the water evaporated to give 3.8 g (50% yield from (40)) of a white foam (41).

Example 40

Acetoksvacetvlerinq of 5- amino- 2, 4, 6- triiodo- 3- chlorocarbonyl-benzamide ( 33) to

5- acetoxvacetvlamino- 2, 4, 6- triiodo- 3- chlorocarbonyl- benzamide ( 42)

200 g (0.347 mol) of the starting material (33) in 1200 ml of dioxane was heated to 60°C. 142 g (1.041 mol) of acetoxyacetyl chloride were added dropwise over 15 min, after which the reaction mixture was heated to 90°C and held there for 6.5 hours. After cooling to 15°C, the solid product (42) was filtered, washed with 4 x 100 ml dioxane and vacuum dried to a weight of 200.5 g (yield 85%).

Example 41

Amidation of 5-acetoxyacetylamino-2,4,6-triiodo-3-chlorocarbonyl-benzamide (42) to

5- acetoxvacetvlamino- 2, 4, 6- triiodo- 3- fN-( 2, 3- dihydroxpropyl) 1- carbamoyl- benzamide ( 43)

118 g (0.174 mol) of the starting material (42) was added to a flask containing 180 ml of N,N-dimethylacetamide, 24.2 g

(0.266 mol) of 3-amino-1,2-propanediol and 18.0 g (0.177 mol) of triethylamine. The reaction mixture was kept at 25°C for 4 hours and was then diluted by dropwise addition of 1080 ml of n-pentanol under vigorous mechanical stirring. The resulting precipitate (43) was filtered, washed with 4 x 100 ml of n-pentanol and vacuum-dried to a weight of 124.9 g (crude yield 98%).

Example 42

Deacetylation of 5-acetoxyacetylamino-2,4,6-triiodo-3-fN-(2,3-dihydroxypropyl)Icarbamoylbenzamide (43) to

5- hydroxyacetylamino- 2, 4, 6- triiodo- 3- fN-( 2, 3- dihydroxypropyl) 1- carbamoyl- benzamide ( 44)

124.8 g (0.170 mol) of the starting material (43) was dissolved in 1.5 1 methanol and 0.5 1 water, and then it was treated with "Dowex 50 H<+>"- and "Biorex 5 OH"" -ion exchange resins. The resins were removed with a sieve after 20 hours of stirring and the resulting mixture distilled under reduced pressure to a solid residue. 400 mL of methanol and 36.9 g (0.17 mol) of 25 wt% sodium methoxide in methanol were added to the residue , yielding a solution which was filtered, distilled under pressure to remove methyl acetate, diluted with methanol, neutralized with concentrated HCl and then distilled under reduced pressure to a solid consisting of 9.9 g of NaCl and 94.0 g of the product (44) The yield was 80%.

Example 43

Protection of 5- hydroxyacetylamino- 2, 4, e- triiodo- S- fN- f2. 3-dihydroxypropyl)- carbamoyl- benzamide ( 44) with 3, 4- dihydro- 2H-pyran to

5-( 2- tetrahydropyranyloxy) acetylamino- 2. 4. 6 - 1 r i i od- 3 - f N - ( 2, 3 - tetrahydropyranyloxy) propyllcarbamovl- benzamide ( 45)

3.44 g (5 mmol) of the starting material (44) was mixed with 15 ml of dioxane and 29.6 mg (0.31 mmol) of methanesulfonic acid. 3.36 g (40 mmol) of 3,4-dihydro-2H-pyran was added and the mixture stirred at 25°C for 4 days. The reaction mixture was filtered, basified with 62 mg (0.62 mmol) of triethylamine, distilled under reduced pressure to an oil, reconditioned with methanol and distilled under reduced pressure to a product residue (45) which was taken directly to alkylation.

Example 44

Alkylation and deprotection of 5-(2-tetrahydropyranyloxy)-acetylamino-2,4.6-triiodo-3-fN-(2,3-tetrahydropyranyloxy)-propylIcarbamoylbenzamide (45) to

5- fN-(2- hydroxyethyl) hydroxyacetamido>- 2, 4, 6- triiodo- 3- fN-( 2, 3- dihydroxypropyl) Icarbamoyl- benzamide ( 46)

5.0 mmol of the starting material (45), a semi-solid residue from the previous step, was mixed with 18 ml of methanol and 4.75 g (12.5 mmol) of trisodium phosphate dodecahydrate and 805 mg (10 mmol) of chloroethanol. The resulting suspension was stirred at 40-45°C for 31 hours, filtered and diluted with 0.5 mL of concentrated HCl. The acidified filtrate was distilled under reduced pressure to an oil and reconstituted with 20 mL of 0.01 N HCl and 20 mL of methanol. After this was repeated two more times, the acidic solution was finally distilled under reduced pressure to a solid product (46) weighing 3.50 g, yield 95%.

Example 45

Alkylation of 3, 5- diacetylamino- 2, 4 . 6-triiodobenzoic acid (diatrizosvre, 47) to

sodium- 3,5-fN,N'-(2,3-dihydroxypropyl)diacetamidol-2,4,6-tri iodbenzoate ( 48)

To a suspension of 50 g (0.079 mol) of the starting material (47) in 300 ml of methanol was added 149 g (0.393 mol) of trisodium phosphate dodecahydrate and 35 g (0.314 mol) of 3-chloro-1,2-propanediol, and the reaction mixture was heated at 40°C for 24 hours. Insoluble salts were removed by vacuum filtration, the filtrate was neutralized with HCl and evaporated to approx. 59 g (yield 94% including 10% ester byproduct) of a white foam (48). The foam was taken directly to acetylation.

Example 46

Acetylation of sodium-3,5-fN,N'-(2,3-dihydroxypropyl)-diacetamidol-2,4,6- triiodobenzoate (48) to

3. 5-fN,N'-(2,3-diacetoxypropyl)diacetamido'}-2,4,6-triiodo-benzoic acid (49) 59 g (0.075 mol) of the starting material (48) was mixed with 150 ml (1 .58 mol) of acetic anhydride and 6 ml (0.075 mol) of pyridine, and it was heated to 85°C for 1 hour. The acetic anhydride, the acetic acid and the pyridine were removed by distillation at 70-80°C, and the yellow foam was azeotropically distilled with 2 x 50 ml of butyl acetate.

The product (sodium salt of 49) was dissolved in 300 mL of water and extracted with 3 x 150 mL of a 2:1 mixture of toluene and ethyl acetate to remove the ester byproduct from the preceding alkylation step. The aqueous solution was acidified with concentrated HCl to pH 2.5, and the white precipitate was extracted with 2 x 75 mL of ethyl acetate. The combined organic extracts were dried over magnesium sulfate and the solvent removed to give 58 g (83% overall yield from 47) of a yellow oil (49). The product was taken directly to chlorination.

Example 47

Chlorination of 3.5-fN,N'-(2,3-diacetoxypropyl)diacetamidol-2,4,6-triiodobenzoic acid (49) to

3, 5- fN. N'-(2.3-diacetoxypropyl)diacetamido>-2,4.6-triiodo-benzo<y>l chloride (50)

To approx. To 0.062 mol of the starting material (49) in 125 ml of ethyl acetate was added 23 ml (0.32 mol) of thionyl chloride at 65-70°C, and the temperature was increased to 75-80°C for 1 hour. TLC indicated that the reaction was complete, and thionyl chloride and ethyl acetate were removed under vacuum. The residue was azeotroped with 2 x 150 ml of butyl acetate and the resulting solid dried. About 56 g (yield 95%) of the golden-brown foam was taken directly to the subsequent amidation step.

Example 48

Amidation of 3.5-fN,N'-(2,3-diacetoxypropyl)diacetamido>-2,4,6-triiodobenzoyl chloride (50) to

3, 5- fN. N'-(2.3-diacetoxypropyl)diacetamido)-2,4,6-triiodo-benzamide (51)

To approx. 0.059 mol of the starting material (50) in 200 ml of acetonitrile was added in excess of anhydrous ammonia at 10°C, and the temperature was raised to 25°C for 5 hours. The reaction was shown to be complete by TLC, and the ammonium chloride was removed by filtration. The filtrate was evaporated to 53 g (calculated yield 97%) of a yellow foam (51). The foam was taken directly to deacetylation.

Example 49

Deacetylation of 3,5-fN,N'-(2,3-diacetoxypropyl)diacetamidol-2. 4, 6- triiodobenzamide ( 51) to

3. 5- f N, N' -( 2 . 3- dihydroxypropyl ) diacetamido>- 2, 4, 6- tri iodo-benzamide ( 52)

A resolution of approx. 0.057 mol of the starting material (51) in 250 ml of methanol was mixed with 5.0 g (0.023 mol) of 4.6 mol sodium methoxide, and it was stirred at room temperature for 30 min. HPLC showed that the deacetylation was complete, and the reaction mixture was neutralized with concentrated HCl. The insoluble sodium chloride was removed by filtration and the filtrate evaporated to 43 g (yield 97%, purity 98% by HPLC) of a yellow foam (52).

Example 50

Injection solutions containing 5-fN-(2,3-dihydroxypropyl)acetamidol-2.4. 6-triiodo-3-fN-(2,3-dihydroxypropyl))-carbamoyl-benzamide (19)

Approach:

The sodium/calcium salt of ethylenediaminetetraacetic acid, tris-(hydroxymethyl)aminomethane and the contrast medium were dissolved in water for injection and adjusted to pH 7.0 by the addition of 1 N hydrochloric acid. Solutions were made up to 100 ml with water for injection, filtered through a 0.22 µm membrane and into glass ampoules, capped and autoclaved for 20 min at 121°C.

Example 51

Injection solutions containing 5-fN-(2-hydroxymethyl)-acetamidol-2,4.6-triiodo-3-fN-(1.3.4-trihydroxy-threo-but-2-vl)) carbamoyl-benzamide (11)

Approach:

The calcium/disodium salt of ethylenediaminetetraacetic acid

acid, trisodium citrate and the contrast medium were dissolved in water for injection and adjusted to pH 5.0-6.0 with sodium carbonate and carbon dioxide. Solutions were made up to 100 ml with water for injection, filtered through a 0.22 µm membrane into glass vials which were capped and autoclaved for 20 min at 121°C.

From the above results, it is quite clear that new non-ionic contrast agents have been provided with significantly improved properties compared to compounds currently available. Due to the improvement in the physical characteristics, especially with regard to osmolality and viscosity, a wide range of body areas can be diagnosed, while achieving ease of administration and less pain. Despite the large number of compounds that have been synthesized and tested, the present compounds have been found to be better than previously described compounds. By ensuring that different nitrogen atoms are present in the molecule,

of which only two are substituted, the new properties are obtained. In addition, synthetic routes have been provided that are efficient and give high yields, while enabling the use of readily available materials.

Claims (8)

1. Non-ionic contrast compound, characterized in that it has formula (I): with at least two hydroxyl groups, and where Rx is hydrogen, lower alkyl or hydroxy-substituted lower alkyl, where the alkyl group contains from 1 to 6 carbon atoms, R2 is hydroxyalkyl with from 2 to 6 carbon atoms, with from 1 to n-1 hydroxyl groups, where n is the number of carbon atoms, R3 is lower alkyl, hydroxy-substituted lower alkyl or lower alkoxy-substituted lower alkyl and having from 1 to 6 carbon atoms, or a residue of formula (II): and R4 is hydrogen or alkyl with from 1 to 6 carbon atoms with from 0 to n-1 hydroxyl groups, where n is the number of carbon atoms, with the exception of 3-[N-(1,3-dihydroxyprop-2-yl)carbamoyl]-5-(2-hydroxy-1-oxopropyl)amino-2,4,6-triiodobenzamide. 2. Non-ionic contrast compound according to claim 1, characterized in that R2 contains 4 carbon atoms and 3 hydroxyl groups, R3 is not a residue of formula II and R4 contains from 2 to 3 carbon atoms and has at least one hydroxyl group. 3. Non-ionic contrast compound according to claim 1, characterized in that R2 contains 3 carbon atoms and 2 hydroxyl groups, R3 is not a residue with formula II and R4 contains 3 carbon atoms and 2 hydroxyl groups. 4. Non-ionic contrast compound according to claim 3, characterized in that R2 and R4 are the same. 5. Nonionic contrast compound according to claim 1, characterized in that it is a) 5-{N-(2-hydroxyethyl)acetamido}-2,4,6-triiodo-3-{N-(1,3,4- trihydroxy-threo-but-2-yl)}carbamoyl-benzamide, b) 5-{N-(2,3-dihydroxypropyl)acetamido}-2,4,6-triiodo-3-{N-(2,3- dihydroxy-propyl)}carbamoyl-benzamide, c) 5-{N-(2,3-dihydroxypropyl)acetamido}-2,4,6-triiodo-3-{N-(2-hydroxyethyl)}carbamoyl-benzamide, d ) 5-{N-(methyl)-2-hydroxyacetamido}-2,4,6-triiodo-3-{N-(1,3,4-trihydroxy-threo-but-2-yl)}carbamoyl-benzamide, e) 5-{N-(2-hydroxyethyl)hydroxyacetamido}-2,4,6-triiodo-3-{N-(2,3-dihydroxypropyl)}carbamoyl-benzamide, f) 3,5-{N,N '-(2,3-dihydroxypropyl)diacetamido}-2,4,6-triiodobenzamide, g) bis-[3-{N-(1,3,4-trihydroxy)-threo-but-2-yl}carbamoyl- 5-carbamoyl]-2,4,6-triiodo-N-(methyl)anilide-malonic acid, h) bis-[{3-N-(2,3-dihydroxypropyl-carbamoyl)-5-carbamoyl}-2,4 ,6-triiodo-N-(2,3-dihydroxypropyl)anilide-malonic acid, or i) bis-[{3-N-(2,3-dihydroxypropyl-carbamoyl)-5-carbamoyl}-2,4,6- triiodo-N-(2-hydroxyethyl)anilide-malo n acid. 6. Radiological preparation, characterized in that it comprises a non-ionic contrast compound according to claim 1 in a physiologically acceptable carrier. 7. Radiological preparation according to claim 6, characterized in that it comprises a non-ionic contrast compound according to claim 5a) in a physiologically acceptable carrier. 8. Radiological preparation according to claim 6, characterized in that it comprises a non-ionic contrast compound according to claim 5b) in a physiologically acceptable carrier.