5.4 ml of triethylamine and 13.5 g of the N-hydroxysuccinimide ester of N-benzyloxycarbonyl-L-proline were added to 5.6 g of methyl 1-aminocyclopentane-1-carboxylate in 50 ml of dioxane at 10° C., the reaction mixture was stirred for 2 hours at this temperature, 20 ml of water were then added and the reaction was allowed to continue for 20 hours at room temperature. The mixture was taken up in ethyl acetate, and the organic phase was washed successively with 10% strength aqueous citric acid solution, sodium carbonate solution and water, dried over sodium sulfate and evaporated down under reduced pressure. Crystallization of the solid residue gave 11.5 g (79%) of methyl N-benzyloxy-carbonyl-L-prolyl-1-aminocyclopentane-1-carboxylate.
