Thapsakins:: possible biogenetic intermediates towards insecticidal cyclopenta[b]benzofurans from Aglaia edulis

Nine new flavaglines, cyclopenta[bc]benzopyrans (thapsakins) and benzo[b]oxepines (thapoxepines), were isolated from the lipophilic root extract of Aglaia edulis together with two known cyclopenta[b]benzofurans, aglaroxin A and pannellin. The structures were established on the basis of extensive use of NMR spectroscopic methods (C,H-COSY, NOESY, HMBC, lanthanide induced shifts). Aglaroxin A and pannellin exhibited the strongest insect toxicity toward neonate larvae of Spodoptera littoralis. Possible biogenetic connections between the three skeletal types are outlined and chemosystematic implications of flavagline formation are discussed. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.