Azido acids in a novel method of solid-phase peptide synthesis.

Azido acids were produced from alpha-branched acids by alpha-bromination with NBS followed by substitution with sodium azide and the products were used in a novel method of solid-phase synthesis. The azido acids were transformed into the highly activated acid chlorides and used synthesis of extremely hindered peptides containing up to four successive diphenyl glycine or Aib residues. By reaction of the genetically encoded amino acids with TfN(3) and then SOCl2 they were transformed into alpha-azido acid chlorides used in solid-phase peptide synthesis without racemization. (C) 1997 Elsevier Science Ltd.