To a solution of cis-5-phenyl proline hydrochloride (5.0 g., 0.022 m) and 1 N sodium hydroxide (44 ml.) at 10° C. was slowly added 3-bromopropionyl chloride (2.2 ml., 0.022 m) and 2-N sodium hydroxide (11 ml.), keeping pH between 7.5 and 9. The mixture was stirred at 25° C. for 3 hours. Potassium thiobenzoate, prepared by mixing thiobenzoic acid, 95% (3.28 g., 0.024 m) and potassium carbonate (2.02 g., 0.014 m) in water (25 ml.), was added to the reaction, which was stirred overnight at 25° C. The solution was acidified and extracted with ethylacetate. The extract was washed, dried over sodium sulfate and the solvent was evaporated off to yield the title compound as a gum which was employed as the reactant in the following example without further purification.
