3-(o-nitrophenyl)thio-2(R)-phthalimidopropionic acid → 3-(o-aminophenyl)thio-2(R)-phthalimidopropionic acid

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Reaction Steps

In 300 ml of methanol is placed 10 g of 3-(o-nitrophenyl)thio-2(R)-phthalimidopropionic acid, which is catalytically reduced at ordinary temperature under atmospheric pressure, using 5% palladium-carbon as a catalyst. After the calculated amount of hydrogen is absorbed, the catalyst is removed, and the methanol is evaporated off under reduced pressure. Ether and petroleum ether are added to the residue, and the deposited yellowish crystalline powder is collected by filtration to give 8.4 g of 3-(o-aminophenyl)thio-2(R)-phthalimidopropionic acid. This product (8.4 g) is dissolved in 50 ml of dimethylformamide, and 5.5 g of diethyl phosphorocyanidate is added dropwise to the solution under ice-cooling with stirring. After the addition is completed, the mixture is stirred for 5 minutes, and 2.28 g of triethylamine is further added dropwise under ice-cooling. The mixture is stirred under ice-cooling for 30 minutes and then at room temperature for 1 hour. Water (200 ml) is added to the reaction solution, and the mixture is allowed to stand overnight. The deposited solid is collected by filtration and dried. This product is purified by silica-gel column chromatography (dichloromethane:ethyl acetate=2:1) to give 5.4 g of 3(R)-phthalimido-2,3-dihydro-1,5(5H)-benzothiazepine-4-one as colorless prisms, melting at 202°-205° C.

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