[Studies on the Nin-formyl group as possible protecting group against tryptophan indole side chain tert-butylation...

Investigations on the Nin-formyl group as a protecting group of the tryptophan indole side chain under the conditions of conventional peptide synthesis using model compounds are described. The protecting group prevents the tert-butylation of tryptophan residues during acidolytic removal of tert-butyloxycarbonyl groups and allows the preparation of tryptophan tert-butylester in good yields. However, because of the observed side reactions, as hydrogenation of the indole to a 2,3-dihydroindole side chain, instability of the protecting group under various experimental conditions, the Nin-formyl group is only of limited use in peptide synthesis.