Chemical studies of some natural products

This Thesis is divided into four distinct and self-contained parts whose unifying theme is implicit in the general title "Chemical Studies of Some Natural Products". Part I discusses possible biogenetic routes to the vesicant principle cantharidin in which it is considered that this compound is terpenoid in origin. It indicates the expected radio-active labelling patterns that would be encountered should feeding experiments with 14C labelled mevalonic acid to the bestle Meloe proscarabeus L. lead to the incorporation of radio-activity in the cantharidin shown to be aynthesised by this insect. Chemical degradations of the theoretically possible labelled cantharidins designed to distinguish between them are discussed and a survey of the occurrence of cantharidin within the family Meloidae is given. Part II describes an attempt to prepare, from a consideration of certain theoretical factors which are briefly discussed, a compound with potentially high neuromuscular blocking activity, 3a, 17a-bis (trimethylammonium)-5-a-androstane, by Sn2 replacement of the methanesulphonyloxy groups of 3b, 17b-dimethane-sulphonyloxy-5a-androstane with trimethylamine. Part III describes a physico-chemical approach to the elucidation of the structure of the sesquiterpane y-lactone, aristolactone occurring in Aristolochia reticulate L and A. serpentaria L. Successful degradation to the parent hyurocarbon germacrane (as a mixture of diastereoisomers) is described these results permitting unequivocal assignment of the basic carbon skeleton of aristolactone. Re-examination of accumulated chemical evidence together with a number of physical measurements (I-R and n.m.r.) are employed to give a probable structure for aristolactone. A cyclisation of methyl oxoaristate, a y-keto ester derived from aristolactone, has been effected giving rise to a new derivative possessing an as yet undetermined bicyclic system. Part IV describes the elucidation of the structures of the quaternary alkaloid petaline chloride and its methane base, leonticine - compounds isolated from Leontice leontopetalum L. An attempt to synthesise one of the degradation products derived from the methane base leonticine is described but the projected synthesis failed at the last stage