C(2)-Functionalized Tryptophans from 3-Acetoxyindoles and Their Possible Implication in Indole Alkaloid Biosynthesis

Article abstract of DOI:10.1021/jo00379a010

The acetoxyindoles 10 and 11 are efficiently converted (85percent-95percent) into the dihydro-1,2-oxazines 13 and 14, respectively, by reaction with the transient nitroso olefin 2, prepared in situ from ethyl α-(hydroxyimino)-β-bromopropanoate by base treatment.The cycloadducts 13 and 14 react efficiently with thiols or a hydride donor to yield (60-90percent) the 2-substituted tryptophan derivatives 9a-f.Selective reduction of the oxime function of the 2-(S-cysteinyl)tryptophan derivative 9d afforded 19, a derivative of tryptathionine.The sulfonium salt 22b derived from 2-(ethylthio)tryptophan derivative 9b was shown to undergo a thio-Claisen rearrangement to yield 26.This reaction supports Bycroft's proposal involving a thio-Claisen rearrangement in indole alkaloid biosynthesis.