Koniamborine, the first pyrano[3,2-b]indole alkaloid and other secondary metabolites from Boronella koniambiensis

Two new alkaloids,(-)-cis-1,2-dihydroxy- 1,2-dihydromedicosmine (3) and koniamborine (4), have been isolated from Boronella koniambiensis aerial parts. Their structures have been established from NMR and mass data. Koniamborine is a novel type of alkaloid, which derives from the pyrano[3,2-b]indole basic skeleton, described for the first time from nature. 6-Methoxy-1-methylisatin, also present in the plant material, can be considered biogenetically as a degradation product of the fused pyrone ring of 4.