Tao Guoliang from the Department of Chemistry of Wuhan University and others have given the following synthetic route: Preparation of I 0.5mmol of benzyloxycarbonyl aspartic acid, 1.5mmol of phenylalanine methyl ester hydrochloride and 2.5mL of water were added to 25mL of cone The pH value was adjusted to 6 with ammonia water, 7 mg of thermophilic protease was added, and the reaction was stirred at 40 °C for 6 h. Filter, wash with distilled water, and dry to obtain 0.29 g of white solid (I), yield 95.6%, melting point 116-118°C. Elemental analysis results: C62.96%, H6.09%. N6.65%.
(2) Preparation of II Add 0.5 g of sample I and 20 mL of 3 mol/L hydrochloric acid to a 25 mL conical flask, and stir and react at 45°C for 0.5 h. Filter, wash with distilled water, and dry to obtain 0.32 g of product II, with a yield of 92% and a melting point of 129-131 °C. Elemental analysis results: C61.45%, H5.42%, N6.82%. Preparation of III 0.2 g of palladium-carbon (10%) catalyst, 20 mL of glacial acetic acid and 5 mL of water were added to a 100 mL three-necked flask, and hydrogenated for activation for 1.5 h. 20 mL of glacial acetic acid dissolved in 0.6 g II was added, and the mixture was stirred and hydrogenated at 30 °C for 6 h. After completion of the reaction, filter and wash the catalyst with glacial acetic acid three times; the filtrate and washings were concentrated to dryness under reduced pressure, 15 mL of benzene was added, and 15 mL of benzene was added, and concentrated to dryness under reduced pressure to obtain a white solid, which was dried to obtain product III, 0.38 g, with a yield of 92.3%. , the melting point of 245 ℃. Elemental analysis results: C55.63%, H6.23%, N8.96%.
Using aspartic acid and phenylalanine as raw materials, it is synthesized through the steps of amino protection, internal anhydride, condensation, hydrolysis, and neutralization. Different protecting groups, different methyl esterification order, can have a variety of different synthetic methods. For example, using a formyl group as the protective group and the process route of post-esterification, put 27 mL of 95% methanol and 0.2 g of magnesium oxide into a 250 mL flask, and after the magnesium oxide is dissolved, add 100 mL of 98% acetic anhydride, and the temperature gradually increases. to 40°C. 67g L-aspartic acid was added, the temperature was raised to 50°C, the reaction was stirred and incubated for 2.5h, 15mL of 98% acetic anhydride was added, the reaction was continued for 2.5h, 16mL of isopropanol was added, and the reaction was continued for 1.5h. After the reaction was completed, it was cooled to room temperature. .
The above internal anhydride compound was added to a 1000mL flask, then 207mL of ethyl acetate and 66Gl-phenylalanine were added, stirred at 25~30°C for 1.5h, then 126mL of glacial acetic acid was added, and the reaction was continued for 4.5h. After the reaction was completed, the vacuum was removed. solvent until the temperature of the reaction system is 65°C.
Then, 45 mL of 35% hydrochloric acid was added, the temperature was raised to 60 °C, and the reaction was refluxed for 2 h. After the hydrolysis was completed, atmospheric distillation was carried out until the distillation temperature reached 63°C (the reaction system temperature was 73°C), 180 mL of methanol was additionally added, and the atmospheric distillation was continued until the system temperature was 85°C. After cooling to 25°C, the light components were removed in vacuo.
To the above hydrolysis reaction solution, 54 mL of 35% hydrochloric acid, 9 mL of methanol and 43 mL of water were added, and the esterification reaction was carried out at 20-30 °C for 7 d. Then suction filtration, washing with water to separate α-APM hydrochloride. It was dissolved in 600 mL of distilled water, and neutralized to Ph=4.5 with 5%-10% NaOH solution at 40°C. Cool to below 5°C, filter and wash with suction to obtain crude α-APM, which is then dissolved in 500 mL of a mixture of methanol and water (volume ratio 1:2). Crystallization by cooling, suction filtration washing, vacuum drying, the yield is 45% (calculated by L-phenylalanine).
Japanese scholars proposed an unprotected route: dissolve 90g of phenylalanine methyl ester hydrochloride in 450mL of water, neutralize it with 24g of sodium carbonate, and then extract with 2 pieces of 350mL of dichloroethylene to obtain phenylalanine methyl ester . Add 9g acetic acid and 8mL methanol to the extract, then add 15.2g aspartic anhydride hydrochloride at -20°C, keep stirring for 30min, then add 350mL hot water at 70~80°C and sodium carbonate (5.7g) solution in turn. 300mL. After the remaining phenylalanine methyl ester was extracted twice with 150 mL of dichloroethylene, the pH value of the aqueous layer was adjusted to 4.8 with dilute hydrochloric acid. The aqueous solution was measured to contain 18.2 g (60% molar yield) of α-APM and 6.1 g (20% molar yield) of β-APM by paper electrophoresis. The aqueous solution was concentrated in vacuo to 100 mL and added. 30mL of 36% hydrochloric acid, placed in the refrigerator overnight. 21.3 g of α-APM·HCl crystals were precipitated (yield 58%), and the crystals were filtered out and dissolved in 200 mL of water. The solution was stirred at 50°C, and the pH value was adjusted to 4.8 with 5% sodium carbonate solution, then placed in a refrigerator overnight, and 13.0 g of α-APM crystals were precipitated and filtered (yield 43%). The crystals were dissolved in 500 mL of water, passed through a Dowex 1×4 (acetate form) column (1×20 cm) at 45° C., and washed with 20 mL of water. The effluent and the washings were concentrated in vacuo to precipitate 11.2 g of α-APM crystals. The yield is 37%, the melting point is 235~236°C (decomposition), and the specific optical rotation αD22+32.0° (C=1, in acetic acid). Elemental analysis results: C55.30%, H6.19%, N9.36%.
