The dried leaves and the bark of the Madagascar plant Physena madagascariensis are rubbed on clothing as a repellant against terrestrial leeches that infest certain regions on the island. The crude methanolic extract of the dried leaves showed significant antibacterial activity against a variety of species. Using this activity to guide the isolation through a series of chromatographic procedures, two novel flavanones 1 and 2 were identified as the active constituents using extensive NMR and MS studies to determine the structures. The S absolute stereochemistry was established for the C2 stereogenic center using circular dichroism, but the relative stereochernistry between this center and the stereogenic center on the lavandulyl side chain could not be determined on the. parent flavanones. Acid catalyzed cyclization of 1 produced pyranoflavanone 3 quantitatively. A weak NOE was observed in the Hl"P proton upon irradiation of H2, an experiment run at CM[R at 600 MHz. The stereochernistry at H2" was then established as S on the basis of the coupling constants with the Hl" protons. 2' N 0 E OH p-TsOH H H OH 2 1: R= H 0 0 2 0 H 2: R = OH H Oil; k 0 Sk '!~; r~R A~ 3 OH 0 OH 0
NIH ExPorter
NIH ExPorter