Synthetic Studies on Echinulin and Related Natural Products. IV. : Isolation, Structure and Synthesis of Flavoglaucin-Auroglaucin Type Natural Products isolated from Aspergillus amstelodami

Abstract

Five natural products, named E-1, E-2, E-3, E-4, and E-5, were isolated from hexane extract of freeze-dried mycelium of Aspergillus amstelodami IFO-6667. E-4 and E-5 were found to be identical with flavoglaucin (1) and auroglaucin (2), respectively, from spectroscopic and melting point data. The structure of E-3 was elucidated as 3 mainly from analysis of spectroscopic data. The structure 3 had already been given to aspergin, but the melting point of E-3 did not agree with the reported melting point of aspergin. The structure of E-3 was confirmed by its total synthesis. The structure of E-1 and E-2 was determined as 8 and 13 by analysis of spectroscopic data. The structure 8 was confirmed by its total synthesis. One-step transformation of auroglaucin (2) into E-2 was achieved by heating 2 in dimethyl sulfoxide containing Triton-B.