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) method was established for the quality control of the Annonaceous acetogenins in the extracts of the paw paw tree, Asimina triloba (L.) Dunal. (Annonaceae). A new calibration method was developed by (a) using the diastereoisomers of analytes present in the same extract as internal standards, and (b) adding five different levels of pure analytes to the extract solutions to construct a calibration curve. These modifications completely eliminate the matrix and instrument variations and, thus, provide high accuracy. As an example, concentrations of the three major and most active Annonaceous acetogenins, bullatacin (1), asimicin (2) and trilobacin (3), were directly evaluated, without any further sample preparation, in crude dichtoromethane extracts of twigs collected monthly from a single paw paw tree. The results showed that the contents of 1 and the mixture of 2 and 3 increased significantly in May and June, with 1 at 12.94 and 14.55 ppm, respectively, and the mixture of 2 and 3 at 47.05 and 51.26 ppm, respectively. The quantified contents of these potent acetogenins showed a good correlation with potencies observed in the brine shrimp test (BST), which demonstrated the highest activities with extracts from the May and June samples. These results suggest that May and June are the best time to collect paw paw twigs for maximizing pesticidal and other bioactivities. In addition, the results obtained from both 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 analysis of other natural components in crude extracts. (C) 1999 John Wiley & Sons, Ltd.