Malbrancheamide B, a novel compound from the fungus Malbranchea aurantiaca

A new indole alkaloid, namely malbrancheamide B (2), was isolated from the culture medium and mycelia of the ascomycete Malbranchea aurantiaca along with malbrancheamide (1). Structural elucidation of 2 was carried out by a combination of mass spectrometry (MS) and (1)H and (13)C NMR spectroscopy analyses, as well as by comparison of the NMR data with those of 1. According to the conformational studies using molecular mechanics analyses, compound 2 exists in one preferred conformation, which was optimised by density functional theory (DFT) calculations. Compound 2 is the second chlorinated indole alkaloid possessing a bicyclo [2.2.2] ring with an unusual relative configuration at C12a in the bicyclo [2.2.2] diazaoctane ring system. So far, these structural features seem to be unique for the alkaloids biosynthesised by the fungus M. aurantiaca.