3-(t-butoxycarbonyl)thiazolidine-2-carboxylic acid (1 g, 4.3 mmol) and carbonyldiimidazole (0.7 g, 4.3 mmol) are dissolved in THF (10 ml). the mixture is agitated for 1 hour at ambient temperature. 4-nitrobenzylamine (0.81 g, 4.3 mmoles) and triethylamine (0.6 ml. 0.43 g, 4.3 mmoles) in suspension in 10 ml of a THF and DMF mixture (1/1) are added to the preceding solution and the whole is heated under reflux for 5 hours. The solvents are then evaporated off under reduced pressure. The residue is taken up in 25 ml of ethyl acetate and washed 3 times with 15 ml of water. The organic phase is dried and the solvent is evaporated off under reduced pressure. The product obtained is purified on silica gel in a dichloromethane/methanol mixture (95/5). N-(4-nitrobenzyl)-3-(t-butoxycarbonyl)thiazolidine-2-carboxamide is obtained in the form of a pale yellow oil with a yield of 80% (1.25 g).
