Determination of Taichunamide H and Structural Revision of Taichunamide A

A new indole alkaloid, named taichunamide H (1), was obtained from cultures of the fungus Aspergillus versicolor. With observation of a carbon resonance with a chemical shift of 190.4 ppm, generally thought to be a carbonyl, the structure of 1 was initially proposed to be a diastereomer of taichunamide A that contains a unique spiro-azetidine moiety. Further analysis of compound 1 using X-ray diffraction showed that the spiro-azetidine moiety should be revised as a fused-imine-containing pyrrole ring, with the resonance at 190.4 ppm assigned as an imine carbon. Accordingly, the structure of taichunamide A was also revised.