Dissolve 2.5 g. of t-butoxycarbonyl-glycyl-glycine in dimethylformamide (20 ml.) containing 2,4,5-trichlorophenol (2.13 g.) and N-hydroxysuccinimide (1.4 g.) . Cool the solution in an ice bath and stir while adding dicyclohexylcarbodiimide (2.44 g.) in dimethylformamide (5 ml.). Allow the reaction mixture to stand at room temperature for 48 hours, filter the reaction mixture and evaporate the filtrate to dryness under reduced pressure. Chromatograh the residue on silica gel (150 g.). The desired product is eluted with 20% ethyl acetate/chloroform and crystallized from ether-hexane (m.p. 90°-91° C.).
