Structural studies on alkaloids from Peripentadenia MearsII and Hedycarya Angustifolia

A detailed phytochemical investigation of the alkaloids of two plant species: Peripentadenia mearsii (Elaeocarpaceae) and Hedycarya angustifblia (Monimiaceae) has been undertaken. P. mearsii was found to be a rather rich source of alkaloids: nearly thirty different alkaloids were detected in the bark and leaf extracts. A total of twenty bases and three non-alkaloidal compounds were isolated during this investigation. The structural elucidation of the major alkaloid, peripentadenine, was carried out by spectroscopic methods and by degradation. Detailed PMR and 13C NMR spectral assignments of peripentadenine and some of its twenty derivatives or degradation products are described. Approaches to the synthesis of EZaeocarpus alkaloids are reviewed. The structure of peripentadenine was finally confirmed by two different syntheses. Structures of three minor bases from the bark: dinorperipentadenine, peripentamine and dehydroperipentamine were also established. Dinorperipentadenine was synthesised, and the other two bases were converted to one of the Hofmann degradation products of peripentadenine. Tentative structures have been assigned for three other bases (PBXM2, PLM2 and PLM3) and partial structural analysis was carried out on two further bases (PBVMD and PLM4). The identities of the non-alkaloidal compounds isolated were established by spectroscopy as dimethylsulphone, methylgallate and 2-hydroxy-6-methylacetophenone. The remaining twelve bases were isolated in minute amounts, and only their mass spectra were recorded. Possible biosynthetic origins for Peripentadenia bases have been discussed. The presence of a three-carbon unit between two nitrogens was considered to be an interesting structural feature of these alkaloids and a list of compounds with similar features has been compiled. Nine alkaloids including four new compounds were isolated from Hedycaria angustifoZia. The new compounds include a benzylisoquinoline whose structure was established by X-ray crystallography (by Professor Allan H. White, University of Western Australia), a tetrahydrobenzylisoquinoline, a phenanthrene and a dehydraporphine. The known compounds isolated are all aporphines. Two non-alkaloidal compounds, 2,3-camphanediol and eudesmol, were also isolated from the same plant. The isolation of the alkaloids of Macademia integrifolia was also attempted but a successful method could not be developed.