Five new quassinoids from the bark of Picrasma quassioides

Five new quassinoids, named picraqualides A-E (1-5), together with eleven known ones, nigakilactone E (6), nigakilactone F (7), kusulactone (8), javanicin U (9), 12-norquassin (10), quassin (11), 2,3-didehydropicrasin B (12), nigakilactone B (13), nigakilactone C (14), picrasin B (15), and simalikalacton C (16), were isolated from the EtOH extract of the bark of Picrasma quassioides (D. DON) BENN. Their structures were determined mainly by spectroscopic methods, especially by 2D-NMR techniques and circular dichroism (CD). Some empirical rules were summarized on the basis of C-13-NMR spectral analysis to distinguish between OH (or Ac) groups attached at C(11) vs. C(13).