On the fate of the tryptophan stereocenter during the synthesis of hexacyclic analogues of N-acetylardeemin

Add time:07/29/2019    Source:sciencedirect.com

The reaction between 6-acetyl-3-alkyl-1-ethoxy-3,4,5a,6,11,11a-hexahydro-10bH-pyrazino-[2′,1′-5,1]pyrrolo[2,3-b]indole-1,4-diones and anthranilic acid was studied from a stereochemical point of view. Various degrees of epimerization of the tryptophan and alanine stereocenters were observed in compounds with a cis relationship between their H-3 and H-11a hydrogen atoms, and stereochemistry was retained in the trans compounds. These observations are explained in terms of steric compression between the C5O, C7–alkyl and C8O groups in the hexacyclic reaction products. Acylation at N-2 with o-azidobenzoyl chloride followed by an intramolecular aza Wittig reaction afforded the target 10-acetyl-5,7,8,9a,10,14b,15,15a-octahydroindolo[3″,2″-4′,5′]pyrrolo[2′,1′-3,4]pyrazino[2,1-b]quinazoline-5,8-diones with retention of all stereocenters.

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