Polypeptides. Part V. The use of t-butyl 2,4,5-trichlorophenyl carbonate in the synthesis of N-t-butoxycarbonyl amino-acids and their 2,4,5-trichlorophenyl esters

t-Butyl 2,4,5-trichlorophenyl carbonate, conveniently prepared from phosgene in two stages, reacts cleanly with amino-acids in the presence of bases to give N-t-butoxycarbonyl amino-acids (and 2,4,5-trichlorophenol) in excellent yield. By co-extraction of the N-t-butoxycarbonyl amino-acid and 2,4,5-trichlorophenol from the acidified reaction mixture, followed by treatment of the extracts with NN′-dicyclohexylcarbodi-imide, high yields of the corresponding N-t-butoxycarbonyl amino-acid 2,4,5-trichlorophenyl esters are obtained. These active esters are mostly stable, crystalline solids which may be conveniently used in peptide synthesis.