Conversion of N-hydroxytryptophans into α,β-dehydrotryptophan. An approach to the neoechinulin series

Abstract

Reaction of the N-hydroxytryptophan derivative (21b) with pyruvoyl chloride gives access to the N-hydroxydioxopiperazine (28b). O-Tosylation of the latter compound, followed by base treatment, affords the dioxopiperazine (30b), an N(1)-allyl derivative of the fungal metabolite neoechinulin B (6). The biogenetic relevance of this reaction sequence is discussed.