Antibacterial Neolignans from the Leaves of Melaleuca Bracteata.

Phytochemical study on the leaves of Melaleuca bracteata resulted in the isolation of ten compounds including three new neolignans, named melaleucins A-C (1-3). Among them, melaleucin B shares a rarely occurring nor-neolignan skeleton, and both melaleucins 13 and C bear a novel aldehyde moiety, which might also be response for the delicate fragrance of M. bracteata. Their structures were extensively assigned by spectral data interpretation and biomimetic total synthesis. Moreover, their biosynthetic pathway with oxidative radical coupling and Michael addition as critical reactions was also confirmed. The antimicrobial activity evaluation revealed that melaleucin A exhibited considerable antimicrobial activity towards methicillin-resistant Staphylococcus aureus.