Beshanzuamide A, an unprecedented prenylated indole alkaloid produced by Aspergillus sp. Y-2 from the critically endangered conifer Abies beshanzuensis

A structurally unprecedented prenylated indole alkaloid, beshanzuamide A (1), together with five known analogues (2–6) were isolated and identified from the endophytic fungus derived from the needles of the critically endangered conifer Abies beshanzuensis. The new structure was determined by extensive spectroscopic methods and quantum chemical calculations of NMR and electronic circular dichroism (ECD) data. Compound 1 features a unique N,O-spiroketal/δ-lactone motif connected to a pyranoindole-derived bicyclo[2.2.2]diazaoctane ring. A plausible biogenetic pathway for the assembly of 1 was proposed.