15.0 g of trans-1-(p-nitrobenzyloxycarbonyl)-4-hydroxy-L-proline and 13.5 ml of triethylamine were dissolved in 150 ml of dried dimethylformamide, and 12.66 ml of p-methoxybenzyl chloride was added dropwise to the solution under a 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 sodium sulfate and distilled off to remove the solvent. Recrystallization of the residue from diethyl ether gave trans-1-(p-nitrobenzyloxycarbonyl)-4-hydroxy-L-proline p-methoxybenzyl ester.
