Structure and antiviral properties of macrocaesalmin, a novel cassane furanoditerpenoid lactone from the seeds of Caesalpinia minax Hance

A novel cassane-type furanoditerpenoid lactone, named macrocaesalmin, possessing a ten-membered macrocyclic 1,5-diketone ring and an unprecedented cis B/D ring fusion mode, has been isolated from the seeds of Caesalpinia minax Hance. Its structure was elucidated from detailed 1D and 2D NMR spectral analyses and X-ray crystallography, and density-functional optimization showed that cis fusion of the B/D ring is more stable than the trans mode. Macrocaesalmin was found to exhibit inhibitory activity against RSV, but not for Flu-A and Para-3 viruses.