Highly oxygenated spiro-biflavanoids from Anneslea fragrans twigs

Phytochemical investigation of the ethanolic extract of Anneslea fragrans twigs resulted the isolation of two new highly-oxygenated and sterically hindered spiro-biflavanoids, named fragranols B and C (1 and 2), together with a known compound 3-epilarixinol (3). The structural elucidation was achieved by HRFABMS, NMR spectroscopic analysis, and quantum ECD calculations. A plausible biogenetic pathway of the isolated compounds is also proposed.