E. R. Squibb Sons, Inc.

John Kloss

Christopher M Cimarusti

David R Kronenthal

Richard H Mueller

A process is provided for preparing (trans)-4-phenyl-DL-proline derivatives, which are useful in preparing certain angiotensin converting enzyme inhibitors, which process involves reacting an ester of the structure ##STR1## wherein X is a leaving group such as tosylate, R.sup.3 is lower alkyl, R is cyclohexyl, phenyl or substituted phenyl, and R.sup.1a is a protecting group, with a potassium amide base such as potassium hexamethyldisilazide under reduced temperatures to form the trans-4-substituted proline ester derivative of the structure ##STR2## then hydrolyzing the proline ester to the acid of the structure ##STR3## and removing the R.sup.1a nitrogen protecting group to form the unprotected acid of the structure ##STR4##

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Holland, PA, United States of America

John Kloss