Enzymes and catalysts. II. Pig liver esterase-catalyzed asymmetric synthesis of (-)- and (+)-cucurbitine and its (-)-thio analogue.

The asymmetric synthesis of (-) - and (+) -cucurbitine was carried out by a method involving 1, 3-dipolar cycloaddition of the intermediary azomethine ylide and pig liver esterase (PLE) - catalyzed hydrolysis. The thio analogue, (-) -3-aminotetrahydrothiophene-3-carboxylic acid, was also synthesized.