Abstract
Phenylphenalenones (PPs) are phytoalexins protecting banana plants (Musaceae) against various pathogens. However, how plants synthesize PPs is still poorly understood. In this work, we investigated the major secondary metabolites of developing seed coats of Musella lasiocarpa to determine if this species might be a good model system to study the biosynthesis of PPs. We found that PPs are major components of M. lasiocarpa seed coats at middle and late developmental stages. Two previously undescribed PP dimers (M-4 and M-6) and a group of unreported diarylheptanoid (DH) derivatives named musellins A-F (B-7, B-9, B-10, B-12, B-14, and B-15) were isolated along with 14 known compounds. Musellin D (B-12) and musellin F (B-15) contain the first reported furo[3,2-c]pyran ring and represent a previously undescribed carbon skeleton. The chemical structures of all new compounds were characterized by spectroscopic data, including NMR, HRESIMS, and ECD analysis. Plausible biosynthetic pathways for the formation of PPs and DHs are proposed.