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 13C‐NMR spectral analysis to distinguish between OH (or Ac) groups attached at C(11) vs. C(13).
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Yang et al. (2004) studied this question.
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