Synthesis of a S-(Carboxymethyl)cysteine Analog of (L-2-Amino-6-adipyl)-L-cysteinyl-D-valine and its Cell Free Biosynthetic Conversion into 6-[2-(D-2-Amino-2-carboxyethyl)thio) acetamido]penicillanic Acid

A new tripeptide (dimer), bis[(L -cysteine-S-acetyl)-L -hemicystinyl(S² → S²)-D -valine] ( 6 ) was synthesized by coupling N-(tert-butoxycarbonyl)-S-carboxymethyl-L -cysteine benzyl ester ( 1 ) with S-trityl-L -cysteinyl-D -valine benzyl ester and subsequent removal of the protecting groups. After reduction of the disulfide, the free tripeptide Cys (CH₂CO-Cys-D -Val) ( Ib ) was used as a substrate of isopenicillin-N synthetase in a cell-free conversion to 6-[2-((D -2-amino-2-carboxyethyl)thio)acetamido]penicillanic acid ( IIa ).