Phytochemistry and chemotaxonomy of the Convolvulaceae -: Part 4 -: Pyrrolizidine alkaloids of Ipomoea hederifolia and related species

The common necine base of the novel pyrrolizidine alkaloids (ipangulines) isolated recently from Ipomoea hederifolia is not turneforcidine but its 1 beta-epimer, platynecine. Three novel ipangulines were isolated from the aerial parts of I. hederifolia and identified as 9-O-[2-hydroxy-3-(2-acetoxy)-2-methylbutyryl]-7-O-salicyloylplatynecine (ipanguline B-2), 9-O-[2-hydroxy-3-(2-methylbutyryloxy)-2-methylbutyryl]-platynecine (ipanguline D-10) and 9-O-salicyloylplatynecine (ipanguline D-11). Comprehensive GC-mass spectrometric analysis also revealed a great variety of > 38 platynecine monoesters and diesters. They are classified as ipangulines A (diesters with one phenylacetic acid moiety), ipangulines B (diesters with one salicylic acid moiety), ipangulines C (diesters with two aliphatic moieties) and ipangulines D (either 7- or 9-monoesters). In shoot tips and young leaves, total ipangulines concentrations are up to 0.45% ton dry wt basis). The ipangulines are stored as tertiary alkaloids and not as N-oxides. Seeds of different provenance showed similar alkaloid patterns. Taxonomically related species, such as I. neei and I. x perigrenium, also contain platynecine esters in their vegetative tissues. (C) 1998 Elsevier Science Ltd. All rights reserved.