Biosynthesis of Pyrrolizidine Alkaloids and Bio-Transformations of Diamines

The work presented in this thesis is divided into four sections: (a) examination of the pyrrolizidine alkaloid content of plants and transformed root cultures; (b) further biosynthetic studies on the pyrrolizidine necine bases; (c) biosynthesis of analogues of pyrrolizidine alkaloids; (d) lipase-catalysed acylation of diamines. (a) Pyrrolizidine Alkaloid Isolations Certain species of plant and root culture were examined to see which, if any, alkaloids they produced. Emilia flammea transformed root cultures produced the alkaloids senecionine (A), integerrimine (B) and emiline (C). The proportions of these alkaloids varied with the age of the culture. Senecionine was the predominant alkaloid until the culture was 21 days old when emiline became the major alkaloid. High total incorporations (ca. 11%) were observed when [1,4-14C]-1,4-diaminobutane (putrescine) dihydrochloride was fed to the cultures. Senccio vulgaris transformed root cultures contained mainly senecionine (A) with a small amount (< 5%) of integerrimine (B). When radiolabelled putrescine was fed total incorporations of about 10% were achieved. Otosenine (D), senkirkine (E) and senecionine (A) were found in the common house plant Gynura sarmentosa. (b) Biosynthesis of Necine Bases N- Acetyl [1,4-14C] p utrescine hydrochloride was synthesised and fed along with [1,4-3H]putrescine dihydrochloride to Senecio pleistocephalus and Cynoglossum australe plants, and E. flammea and S. vulgaris transformed root cultures. In all cases putrescine was incorporated more efficiently than N-acetylputrescine into the pyrrolizidine alkaloids. Efforts were made to synthesise diol (F) which is required to probe the biosynthesis of the pyrrolizidine alkaloid rosmarinine. (c) Biosynthesis of Pyrrolizidine Alkaloid Analogues The biosynthesis of pyrrolizidine alkaloids in S. vulgaris transformed root cultures was shown to be inhibited when 2-hydroxyethylhydrazine was present in the culture medium above a concentration of 1 6 mM. Retronecine (G) and trachelanthamidine (H) were taken up by the inhibited roots and transformed into senecionine. It was not clear whether the 3beta-methyl analogue of trachelanthamidine (I) was converted into an alkaloid analogue. (d) Lipase-catalysed Acylation of Diamines Putrescine, cadaverine and 1,2-diaminopropane were monoacetylated using ethyl acetate and porcine pancreatic lipase. The acetylation of 1,2-diaminopropane was regiospecific with N-acetyl-1,2-diaminopropane hydrochloride being the product. This reaction showed some stereoselectivity with the R-enantiomer predominating in the product. A number of methods were used to try and improve the stereoselectivity of the lipase-catalysed acylation of 1,2-diaminopropane