CN106866621B - Radiofluorination reagent, preparation and application - Google Patents

Abstract

The invention discloses a radiofluorination reagent, its preparation and its application in the synthesis of fluorinated oxazolidinone compounds. The method provides a method for directly preparing radiofluorinated oxazolidinone compounds under mild conditions. The new imaging diagnosis and treatment reagents can be used for non-invasive examination of organisms and disease treatment research, including non-invasive research on the metabolic process of organisms and chemical and radiotherapy for diseases. We chose a representative radioactive oxazolidinone to inject into mice for PET imaging experiments, and no bone resorption signal due to defluorination of the tracer was observed.

Description

A kind of radiofluorination reagent, preparation and application

technical field

The invention relates to the technical field of positron emission tomography, in particular to a radiofluorinated reagent, its preparation and its application in the synthesis of radiofluorinated oxazolidinone compounds.

Background technique

The chemical, biological and physical properties of organic molecules can be significantly changed by introducing fluorine atoms, so organic fluorine compounds are widely used in chemical industries such as medicine, agriculture and materials. In addition, 18F-labeled organic compounds are widely used as positron emission tomography (PET) reagents in diagnostic medical and clinical pharmaceutical research. Therefore, there is an urgent need to develop novel synthetic strategies that can facilitate the preparation of complex fluorine-containing compounds. From a radiological point of view, a late fluorination strategy would greatly simplify the synthesis of complex radiotracers due to the short half-life of 18F.

The intramolecular fluorination cyclization reaction of compounds containing alkenes can construct ring structures with multiple new bonds including C-F bonds in one step, which can be used as general structural units for the construction of aliphatic fluorine-containing bioactive compounds. Among the reported synthetic methods, fluorocyclization using electrophilic fluorinating reagents is one of the most important methods. However, electrophilic fluorinating reagents are usually prepared from fluorine gas, and the preparation cost is high, which limits their application in industry and laboratory, especially in 18F radiolabeling. In addition, electrophilic fluorination reactions usually have low specific activity, which limits their application in radiofluorination reactions. Recently, hypervalent iodine reagents have attracted extensive attention as fluorine sources in the study of fluorinated cyclization reactions, because they exhibit unique reactivity and can be easily obtained from inexpensive fluorides. Although the reaction mechanism for this type of reaction is not well understood, most reports propose an ionic reaction pathway. Alkyl-substituted alkenes and styrene derivatives are used as effective nucleophiles in these reactions, whereas the fluorocyclization of substrates with electron-poor double bonds has not been reported in the literature.

Contents of the invention

The purpose of the present invention is to develop a radiofluorination reagent and apply the reagent to silver-promoted cyclization/1,2-(hetero)aryl migration/fluorination cascade reaction for the preparation of radiofluorooxazole alkanone compounds.

In order to achieve the above object, the technical scheme provided by the invention is:

The invention provides a radiofluorination reagent based on a hypervalent iodine compound, which reacts a hypervalent iodine chlorine compound with radioactive [ ¹⁸ F]-TBAF, introduces radioactive fluorine atoms into the hypervalent iodine fluoride compound, and prepares a novel radiofluorination reagent. Its structural formula is as follows:

The present invention also provides a preparation method of the above-mentioned radiofluorination reagent: mix the acetonitrile solution of hypervalent chloroiodide compound and [ ¹⁸ F]-TBAF in acetonitrile, and react the reaction mixture at 60°C for 10 minutes to prepare a novel radiofluorine chemical reagents;

Its reaction formula is as follows:

In the present invention, the above-mentioned radiofluorination reagent is used as an intermediate to carry out fluorination reaction to obtain a radiofluorooxazolidinone compound. The structural formula of the compound is as follows:

Specifically the following eight compounds:

The present invention adopts a one-pot method to realize radiofluorine cyclization reaction to obtain radiofluorooxazolidinone compounds, which specifically includes the following steps:

Step 1: Preparation of Radioiodine Fluorine Compound Intermediate 2

Hypervalent chloroiodo compound 1 (6 μmol) was mixed in 25 μL of anhydrous MeCN, then the resulting solution was combined with [ ¹⁸ F]-TBAF in MeCN, and the reaction mixture was reacted at 60 °C for 10 min to obtain the radioiodofluoroiodine intermediate Body ¹⁸ F-2 is the radiofluorination reagent, and the next reaction is directly performed without further purification;

Step 2: Synthesis of Radioactive Fluorooxazolidinones by Fluorine Cyclization

Add the acetonitrile solution of olefin precursor styrene or acrylamide compound 2 (6 μmol) and AgOTf salt (6 μmol) to the above reaction mixture, react at 80°C for 10 minutes, and add 1 mL 1:1 (v/v) water : Quenched by MeCN, filtered through a Sep-Pak light alumina N column, and then separated by HPLC to obtain the corresponding radioactive fluorooxazolidinones;

Its reaction formula is as follows:

Synthetic products include:

Further, the HPLC conditions are: Phenomenex, 5μm EVO C18 250×4.6mm liquid phase column; solvent A: 0.1% TFA/water; solvent B: 0.1% TFA/acetonitrile; 0 to 2 minutes: at 50% solvent B, 2 to 12 minutes, 50% to 95% solvent B Isocratic elution; flow rate: 1 mL/min, column temperature: 19 to 21 °C.

In order to verify the stability of the synthesized ¹⁸ F-oxazolidin-2-one [ ¹⁸ F]-3a in the present invention, we conducted in vivo and in vitro experiments on it. [ ¹⁸ F]-3a was added to a phosphate buffer solution with a pH value of 7.5, and analyzed after 3 hours, it was found that [ ¹⁸ F]-3a was hardly decomposed. Subsequently, we injected [ ¹⁸ F]-3a into mice, and obtained PET/CT images of nude mice 1 hour later, no bone resorption signal due to tracer defluorination was observed (see Figure 1, Figure 1 is PET/CT images of nude mice (PET image acquisition, injection of 0.1 mCi of [18F]-3a in 1X PBS pH 7.5 (300 μL) into nude mice via tail vein. At post-injection time points, isoflurane (2% Oxygen) to anesthetize the mouse, then place it on an imaging stand, and maintain body temperature. Then achieve and reconstruct a static PET/CT acquisition for analysis.). These conclusions can illustrate that this class of ¹⁸ F-labeled radioactive fluorooxazolidine Ketones can find application in the field of in vivo biomedical research.

Although fluorination reactions have been extensively reported in the literature, the successful translation of these methods to practical radiofluorination synthesis remains a challenge. Efficient radiofluorination synthesis has the following difficulties: 1) There are only a few available ¹⁸ F-containing fluorides; 2) Since the half-life of ¹⁸ F-radioisotope is 110 minutes, the reaction must be completed quickly; 3) People are sensitive to nuclear radiation. attention is increasing. Encouraged by the above experimental results, we attempted to radiofluorinate the alkene precursors (2a–c) via a one-pot synthesis that would enable the reaction to be completed in the shortest possible time. However, cyclic compounds containing ¹⁸ F labels were not successfully obtained by this protocol. This may be due to the formation of AgCl from compound 10 and AgOTf, which inhibited the radiofluorination reaction.

In order to solve this problem, we decided to use a one-pot two-step method for radiofluorination labeling, and obtained suitable reaction conditions by changing a series of reaction parameters. The radiofluorination reaction includes two reaction processes, that is, atomic exchange of ¹⁸ F and Cl and fluorination process. We first changed the reaction temperature of the two processes and found that the fluorination temperature had an effect on the radiochemical yield (RCY), while the ¹⁸ F-Cl exchange temperature had little effect on the radiochemical yield (RCY). Therefore, the ¹⁸ F-Cl exchange temperature and ^{the 18} F-fluorination temperature were set to 60°C and 80°C, respectively. In addition to the reaction temperature, the concentration of the reaction solution, the solvent and the type of silver salt have a greater impact on the reaction. In terms of the type of solvent and the concentration of the reaction solution, the ¹⁸ F-labeled cyclic compound can only be successfully obtained in a high-concentration compound 10 (0.24 μM) in acetonitrile solution. The reaction could not be carried out successfully when using low concentration of reaction solution or using DMSO/DMF mixed solvent system. In addition, Ag salt is indispensable in this reaction. Condition optimization found that AgSbF ₆ is the best silver salt, which can get the highest radioactivity yield. However, when the amount of _AgSbF6 was reduced to 0.5 or 0.05 equivalents, the fluorination reaction failed. In order to avoid the additional introduction of ¹⁹ F in the reaction, we used AgOTf instead of AgSbF ₆ as the catalyst for the reaction to prepare various ¹⁸ F-oxazolidin-2-ones with high radioactive purity, and the results are shown in Table 1.

Beneficial effect:

The present invention reacts hypervalent iodine chlorine compound with radioactive [ ¹⁸ F]-TBAF, introduces radioactive fluorine atoms into hypervalent iodine fluorine compound, and prepares a novel radiofluorination reagent, which is then used as a reaction intermediate in one pot and two steps This method can quickly obtain unreported radioactive fluorooxazolidinone compounds, which can be used as PET tracers to conduct non-destructive examination and disease treatment research on organisms, including the metabolic process of organisms. Non-invasive research and chemical and radiation treatment of disease.

Description of drawings

Figure 1 is a decay-corrected microPET/CT image of a nude mouse vein scan 1 hour after injection of [18F]-3a. A: coronal image, B: sagittal image);

Fig. 2 is the HPLC UV-chromatogram (upper figure) and radiation chromatogram (lower figure) of the purified [ ¹⁸ F]-3a solution co-injected with the standard sample (3a) which has no corresponding structure;

Fig. 3 is the HPLC UV-chromatogram (upper figure) and radiation chromatogram (lower figure) of the purified [ ¹⁸ F]-3b solution co-injected with the standard sample (3b);

Fig. 4 is the HPLC UV-chromatogram (upper figure) and radiation chromatogram (lower figure) of the purified [ ¹⁸ F]-3c solution co-injected with the standard sample (3c);

Fig. 5 is the HPLC UV-chromatogram (upper figure) and radiation chromatogram (lower figure) of the purified [ ¹⁸ F]-3d solution co-injected with the standard sample (3d);

Fig. 6 is the HPLC UV-chromatogram (upper figure) and radiation chromatogram (lower figure) of the purified [ ¹⁸ F]-3e solution co-injected with the standard sample (3e);

Figure 7 is the HPLC UV-chromatogram (upper figure) and radiation chromatogram (lower figure) of the purified [ ¹⁸ F]-3f solution co-injected with the standard sample (3f);

Fig. 8 is the HPLC UV-chromatogram (upper panel) and radiochromatogram (lower panel) of purified [ ¹⁸ F]-3 g solution co-injected with a standard sample (3 g).

Detailed ways

The present invention will be further described below in conjunction with specific examples.

Example 1

Standard Sample Preparation: Synthesis of Fluorinated Oxazolidinones by Catalytic Fluorine Cyclization

Substrate 2, required amount of compound 1 (1.5 eq), _AgSbF6 (0.1 eq) and DCM were introduced into the reaction flask. The mixture was stirred at a temperature of 20-60°C, and the progress of the reaction was monitored by TLC. When the completion of the reaction was observed, the reaction mixture was concentrated to dryness, extracted and separated by column chromatography to obtain oxazolidinone compound 3, which were the following eight compounds 3a-3h.

5-Benzyl-5-fluoro-3-(4-methoxyphenyl)oxazolidin-2-one (3a)

NMR(376MHz, CDCl ₃ )δ-92.52ppm. ¹³ C NMR(101MHz, CDCl ₃ )δ156.96,152.32(d,J=1.7Hz),132.23(d,J=4.2Hz),130.37,130.20,128.95,128.03 ,120.68,114.49,112.31(d,J=233.1Hz),55.58,54.10(d,J=30.6Hz),42.03(d,J=29.1Hz)ppm.IR(KBr)ν3005,2990,1771,1515, 1456,1339,1275,1360,1080,828,764,750,704.HRMS(ESI)m/z calcd.for C ₁₇ H ₁₆ FNNaO ₃ ⁺ (M+Na ⁺ ):324.1006,Found:324.1002.

5-Benzyl-5-fluoro-3-(p-tolyl)oxazolidin-2-one (3b)

152.13, 134.70, 132.25(d, J=4.3Hz), 130.42, 129.86, 129.04, 128.11, 118.69, 112.31(d, J=233.1Hz), 53.77(d, J=30.7Hz), 42.15(d, J= 29.1Hz), 20.90ppm.IR(KBr)ν3033,3006,2986,2921,2851,1774,1517,1468,1404,1335,1275,1261,1080,976,810,764,750,702.HRMS(ESI)m/z calcd.for C ₁₇ H ₁₆ FNNaO ₂ ⁺ (M+Na ⁺ ):308.1057, Found: 308.1045.

5-Benzyl-3-(4-chlorophenyl)-5-fluorooxazolidin-2-one (3c)

130.39, 130.18, 129.36, 129.08, 128.20, 119.66, 112.24(d, J=233.9Hz), 53.51(d, J=30.8Hz), 42.03(d, J=28.9Hz)ppm.IR(KBr)ν3005,2986 ,1771,1496,1338,1275,1261,1094,1080,978,826,764,750,704.HRMS(ESI)m/z calcd.for C ₁₆ H ₁₄ ClFNO ₂ ⁺ (M+H ⁺ ):306.0692,Found:306.0688.

2-(5-Benzyl-5-fluoro-2-oxazolidin-3-yl)-3-phenylpropanoic acid ethyl ester (3d)

(3H)]ppm. ¹⁹ F NMR (376MHz, CDCl ₃ ) δ-92.12, -94.35ppm. ¹³ C NMR (101MHz, CDCl ₃ ) δ 169.95, 169.81, 155.15 (d, J=1.5Hz), 154.92 (d, J＝1.4Hz), 135.71, 135.63, 132.33 (d, J＝3.2Hz), 132.31 (d, J＝4.7Hz), 130.38, 130.30, 128.92, 128.89, 128.85, 128.81, 128.69, 128.54, 127.89, 127.85, 127.36, 127.29, 113.42(d, J=234.4Hz), 113.38(d, J=234.5Hz), 61.92, 61.83, 56.63, 56.54, 50.60(d, J=29.6Hz), 50.48(d, J=30.7Hz ), 42.18(d, J=28.9Hz), 42.06(d, J=29.5Hz), 35.48, 35.18, 14.14ppm.IR(KBr)ν3005,2989,1779,1738,1456,1275,1261,1031,897,765,750,703 .HRMS(ESI)m/z calcd.for C ₂₁ H ₂₂ FNNaO ₄ ⁺ (M+Na ⁺ ):394.1425,Found:394.1425.

5-Fluoro-5-(4-fluorobenzyl)-3-(4-methoxyphenyl)oxazolidin-2-one (3e)

Hz), 130.13, 127.96(t, J=3.7Hz), 120.72, 115.93(d, J=21.4Hz), 114.56, 112.07(dd, J=233.0, 1.2Hz), 55.63, 54.19(d, J=30.6 Hz),41.32(d,J=29.6Hz)ppm.IR(KBr)ν3008,2992,2920,2845,1771,1760,1512,1275,1258,1080,826,764,750.HRMS(ESI)m/zcalcd.for C ₁₇ H ₁₆ F ₂ NO ₃ ⁺ (M+H ⁺ ):320.1093, Found: 320.1091.

5-fluoro-5-(4-methoxybenzyl)-3-(4-methoxyphenyl)oxazolidin-2-one (3f)

( d,J=29.4Hz)ppm.IR(KBr)ν3005,2984,1771,1515,1456,1339,1275,1260,764,750.HRMS(ESI)m/z calcd.forC ₁₈ H ₁₈ FNNaO ₄ ⁺ (M+ Na ⁺ ):354.1112, Found: 354.1104.

5-Fluoro-3-(4-methoxyphenyl)-5-(thiophen-3-ylmethyl)oxazolidin-2-one (3g)

7.38–7.29(m,3H),7.23(d,J=1.8Hz,1H),7.08(d,J=4.9Hz,1H),6.91–6.83(m,2H),4.01,3.92(ABq,J= 10.9Hz,1H),3.93,3.87(ABq,J＝10.9Hz,1H),3.78(s,3H),3.49–3.32(m,2H)ppm. ¹⁹ F NMR(376MHz,CDCl ₃ )δ-92.91ppm . ¹³ C NMR (101MHz, CDCl ₃ ) δ157.00, 152.27, 132.24 (d, J = 4.4Hz), 130.18, 128.99, 126.64, 124.68, 120.72, 114.53, 112.05 (d, J = 232.9Hz), 55.62, 54.19 ( d,J=30.5Hz),36.79(d,J=30.7Hz)ppm.IR(KBr)ν2920,2849,1771,1646,1515,1469,1338,1276,1255,1090,1060,830,764,750.HRMS(ESI )m/z calcd. for C ₁₅ H ₁₅ FNO ₃ S ⁺ (M+H ⁺ ):308.0751, Found: 308.0742.

5-Fluoro-3-(4-methoxyphenyl)-5-(thiophen-2-ylmethyl)oxazolidin-2-one (3h)

MHz, CDCl ₃ ) δ-93.23ppm. ¹³ C NMR (101MHz, CDCl ₃ ) δ 157.10, 152.14, 133.14 (d, J=5.2Hz), 130.17, 128.56, 127.47, 126.20, 120.82, 114.59, 111.68 (d, J =233.3Hz),55.65,54.00(d,J=30.4Hz),36.57(d,J=32.4Hz)ppm.IR(KBr)ν3006,2920,2849,1775,1646,1515,1469,1338,1275, 1257,975,829,764,750.HRMS(ESI)m/z calcd.for C ₁₅ H ₁₅ FNO ₃ S ⁺ (M+H ⁺ ):308.0751,Found:308.0747.

Example 2

The preparation of the radiofluorination reagent and the radiofluorooxazolidinone compound of the present invention:

Radioactive Fluorine Cyclization to Radioactive Fluorooxazolidinones Using One-Pot Method

Step 1, the hypervalent chloroiodide compound 1 (6 μmol) was mixed in 25 μL of anhydrous MeCN, and then the resulting solution was combined with [ ¹⁸ F]-TBAF in MeCN, and the reaction mixture was reacted at 60°C for 10 minutes to obtain radioactive iodine The fluorine compound intermediate ¹⁸ F-2 is the radiofluorination reagent, which can be directly carried out to the next reaction without further purification.

Step 2, add the acetonitrile solution of olefin precursor styrene or acrylamide compound 2 (6 μmol) and AgOTf salt (6 μmol) to the above reaction mixture, react at 80° C. for 10 minutes, and use 1 mL 1:1 (v/ v) Water: MeCN quenched, filtered through a Sep-Pak light alumina N cartridge. Then by HPLC conditions: Phenomenex, 5μm EVO C18 250×4.6mm liquid phase column. Solvent A: 0.1% TFA/water; Solvent B: 0.1% TFA/acetonitrile; 0 to 2 minutes: isocratic elution at 50% solvent B, 2 to 12 minutes, 50% to 95% solvent B. Flow rate: 1 mL/min, column temperature: 19 to 21°C) to separate and obtain the corresponding radioactive fluorooxazolidinones. Product identification is judged by comparing the retention time of the standard sample in HPLC. (Figure 2~8)

Claims (3)

1. A preparation method of radiofluorination reagent based on high-valence iodine compounds is characterized in that: mixing a solution of a high-valent chloroiodine compound in acetonitrile with the solution of [ 2 ]¹⁸F]-TBAF in acetonitrile and reacting the reaction mixture at 60 ℃ for 10 minutes to make the novel radiofluorination reagent;

the reaction formula is as follows:

2. a method of preparing a class of radiofluoro-oxazolidinone compounds using the radiofluorination reagent of claim 1, wherein the compound has the formula:

the concrete are the following eight compounds:

the preparation method adopts a one-pot method to realize radioactive fluorine cyclization reaction to obtain the radioactive fluoro oxazolidinone compound, and specifically comprises the following steps:

the method comprises the following steps: preparation of radioiodine fluoride intermediate 2

The higher chloro-iodine compound 1 was mixed in anhydrous MeCN, and the resulting solution was then mixed with [18F ]]-TBAF was combined in MeCN and the reaction mixture was reacted at 60 ℃ for 10 minutes to give a radioiodinofluoride intermediate¹⁸F-2 is a radiofluorination reagent and is directly subjected to the next reaction without further purification;

step two: synthesis of radioactive fluoro-oxazolidinone compounds by fluorine cyclization reaction

Olefin precursor styrene or acrylamide compound 2 and an acetonitrile solution of AgOTf salt are added to the above reaction mixture, reacted at 80 ℃ for 10 minutes, and reacted with 1mL of water in a volume ratio of 1: quenching MeCN, filtering by a Sep-Pak light alumina N column, and separating by HPLC to obtain corresponding radioactive fluoro oxazolidinone compounds; the reaction formula is as follows:

wherein, the structural general formula of the compound 2 is as follows:

3. the process for preparing a class of radiofluorooxazolidinones according to claim 2, wherein: the HPLC conditions are as follows: the amount of the Phenomenex is that the amount of the Phenomenex is less than the amount of the Phenomenex,5μm EVO C18a 250X 4.6mm liquid phase column; solvent A: 0.1% TFA/water; solvent B: 0.1% TFA/acetonitrile; 0 to 2 minutes: isocratic elution at 50% solvent B, 2 to 12 minutes, 50% to 95% solvent B; flow rate: 1mL/min, column temperature: 19 to 21 ℃.