Improved Solid-Phase Synthesis of Tryptophan-Containing Peptides. II. Use of Nα-t-Butyloxycarbonyl-Ni-formyltryptophan

Ni-Formyltryptophan has proved to be more resistant than tryptophan against oxidation mediated by hydrogen chloride in acetic acid. Nα-t-Butyloxycarbonyl-Ni-formyltryptophan has been synthesized via nonaqueous acylation reaction and used for the solid-phase synthesis of tryptophan-containing peptides, in combination with hydrogen chloride in formic acid as the reagent for cleavage of the t-butyloxycarbonyl group. The validity of the method has been demonstrated, on the basis of several criteria, in the synthesis of the tryptophan-containing octapeptide, Lys–Gly–Val–Leu–Ala–Gly–Trp–Leu.