Biosynthesis of Quinolizidine Alkaloids

Brown, Alison Margaret (1989) Biosynthesis of Quinolizidine Alkaloids. PhD thesis, University of Glasgow.

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The research presented in this thesis can be divided into four main areas: (a) Biosynthesis of Quinolizidine Alkaloids; (b) Biosynthesis of Ammodendrine and Anabasine; (c) Synthesis of Cadaverine Derivatives and Testing for Biological Activity; and (d) Monoacylation of Diamines Catalysed by Lipases. (a) Biosynthesis of Quinolizidine Alkaloids Previous work had revealed that cadaverine is a good precursor of quinolizidine alkaloids. A series of cadaverines, namely (R)- and (S)-[1- 2H]cadaverine, [3,3-2H2] cadaverine, [2,2,4,4-2H4]cadaverine, [1-amino-15N, 1-13C]cadaverine and 2,2,4,4-2H4]cadaverine were synthesised by known routes and isolated as their dihydrochloride salts. The biosynthesis of matrine was studied in Sophora microphylla plants. Samples of (R)- and (S)-[l- 2H] cadaverine, (R)- and (S)- 2 2 2 [2-2H] cadaverine, [3,3-2H2]cadaverine, [2,2,4,4-2H4]cadaverine and [1-amino-15N, 1-13C]cadaverine were fed with a radioactive tracer to the plants by the wick method. After ten days the plants were macerated and the alkaloids were extracted. Matrine was separated from anagyrine, N-methylcytisine, and cytisine, using preparative t. l. c. plates. High specific incorporations were recorded and labelling patterns were established using 2H and 13C n. m. r. spectroscopy. Information about the enzymic processes involved in matrine biosynthesis was gained and a biosynthetic pathway was proposed. (b) Biosynthesis of Ammodendrine and Anabasine Samples of (R)- and (S) -[1-2H]cadaverines were used to establish the stereochemistry of the enzymic processes taking place in the biosynthesis of ammodendrine and anabasine. Ammodendrine biosynthesis was studied in cell-free extracts containing diamine oxidases and in intact leaves and petioles of Lupin us species. GC-MS analysis showed that it is the pro-S hydrogen that is lost and the pro-R hydrogen is retained on oxidation of each cadaverine unit and that similar processes occur in cell-free extracts and intact cells in the formation of ammodendrine. The biosynthesis of anabasine was investigated in Nicotiana rustica hairy root cultures produced at the A. F. R. C. Food Research Institute at Norwich. 2H N. m. r. spectroscopy revealed that (i) cadaverine is a precursor of the piperidine ring only of anabasine; (ii) it is the pro-S hydrogen that is lost in the conversion of cadaverine into 1-aminopentanal; and (iii) the nicotinic acid attacks the A'-piperideine moiety at C-2' from either the re or si face to produce racemic anabasine. (c) Synthesis of Cadaverine Derivatives and Testing for Biological Activity A series of cadaverine derivatives was prepared from the corresponding diacid by reduction to the diol followed by transformation of the diol into the diamine using hydrazoic acid, di-isopropyl azo-dicarboxylate and triphenylphosphine. These diamines were tested by other workers for biological activity against fungi and bacteria. The derivatives were also made available for testing by others as substrates for the enzyme diamine oxidase. (d) Monoacylation of Diamines Catalysed by Lipases Putrescine was successfully monoacylated in ethyl acetate using porcine pancreatic lipase (PPL) as a catalyst. Both the structure of the acyl group and the alkyl group of the solvent ester were found to have an effect on the rate of acylation. The concentration of water and temperature were also found to be significant factors affecting the reaction. Attempts were made to resolve (+/-)-trains-1,2-diaminocyclo-hexane, (+/-)-1,2-diaminopropane and (+/-)-2-methylcadaverine using the enzymic monoacylation. Some enantioselectivity was observed in the monoacylation of (+/-)-1,2-diaiminopropane when 3-methylpentan-3-ol was used as a solvent with 2 molar equivalents of ethyl acetate. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1989
Depositing User: Enlighten Team
Unique ID: glathesis:1989-78010
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:44
Last Modified: 30 Jan 2020 15:44

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