Quantitative evaluation of annonaceous acetogenins in monthly samples of paw paw (Asimina triloba) twigs by liquid chromatography electrospray ionization tandem mass spectrometry

A quantitative liquid chromatography/tandem mass spectrometry (LC/MS/MS) me thod was established for the quality control of the Annonaceous acetogenins in the extracts of the paw paw tree, Asimina triloba (L.) Dunal. (Annonace ae). A new calibration method was developed by (a) using the diastereoisome rs of analytes present in the same extract as internal standards, and (b) a dding five different levels of pure analytes to the extract solutions to co nstruct a calibration curve. These modifications completely eliminate the m atrix and instrument variations and, thus, provide high accuracy. As an exa mple, concentrations of the three major and most active Annonaceous acetoge nins, bullatacin (1), asimicin (2) and trilobacin (3), were directly evalua ted, without any further sample preparation, in crude dichtoromethane extra cts of twigs collected monthly from a single paw paw tree. The results show ed that the contents of 1 and the mixture of 2 and 3 increased significantl y in May and June, with 1 at 12.94 and 14.55 ppm, respectively, and the mix ture of 2 and 3 at 47.05 and 51.26 ppm, respectively. The quantified conten ts of these potent acetogenins showed a good correlation with potencies obs erved in the brine shrimp test (BST), which demonstrated the highest activi ties with extracts from the May and June samples. These results suggest tha t May and June are the best time to collect paw paw twigs for maximizing pe sticidal and other bioactivities. In addition, the results obtained from bo th methods, BST and LC/MS/MS, also verify the accuracy of each other, This well-defined LC/MS/MS method can be widely applied in the quantitative anal ysis of other natural components in crude extracts. (C) 1999 John Wiley & S ons, Ltd.