[Side-reactions in peptide synthesis, III. Synthesis and characterization of Nin-tert-butylated tryptophan derivatives (author's transl)].

It was possible to elucidate a side reaction which had long been assumed to occur during the acidolytic cleavage of protecting groups based on a ter-butyl moiety, by synthesizing Nin-tert-butyltryptophan in different ways. It was found to be absolutely identical with a "modified tryptophan" which was isolated after the total synthesis of a gastrin analogue; Nin-tert-butyl-tryptophan peptides are formed as the main products of a tert-butylation reaction, the mechanism of which is not very clear yet. The proof for a Nin-tert-butylation of tryptophan was obtained by spectroscopic methods, in particular mass spectrometry and nuclear magnetic resonance spectroscopy.