Trans-1-(p-Nitrobenzyloxycarbonyl)-4-hydroxy-L-proline (15.0 g) and triethylamine (13.5 ml) were dissolved in 150 ml of dry dimethylformamide, and 12.66 ml of p-methoxybenzyl chloride was dropwise added thereto under nitrogen stream, followed by stirring at 70° C. for 10 hours. The reaction mixture was diluted with 500 ml of ethyl acetate, washed with water, dried over anhydrous sodium sulfate and distilled to remove the solvent. Recrystallization of the residue from diethyl ether gave trans-1-(p-nitrobenzyloxycarbonyl)-4-hydroxy-L-proline p-methoxybenzyl ester. M.P., 83°-85° C.
