Isolation of a new indoxyl alkaloid, Amoenamide B, from Aspergillus amoenus NRRL 35600: biosynthetic implications and correction of the structure of Speramide B.

A new prenylated indoxyl alkaloid, Amoenamide B ( 1 ), was isolated from Aspergillus amoenus NRRL 35600 along with Asperochramide A ( 2 ). Although many prenylated oxyindole alkaloids, containing bicyclo[2.2.2]diazaoctane cores, have been isolated from the fungus of the genera Aspergillus and Penicillium to date, 1 is the fourth compound with the indoxyl unit containing the cores. During the structure elucidation of 1 , we found that the planar structure matched to that of Speramide A ( 3 ), isolated from A. ochraceus KM007, but the reported structure of 3 was incorrect and turned out to be that of Taichunamide H ( 4 ), recently isolated from A. versicolor HDN11-84.