Distomadines A and B, novel 6-hydroxyquinoline alkaloids from the New Zealand ascidian, Pseudodistoma aureum
摘要:
Distomadines A and B, novel tetracyclic guanidine-containing 6-hydroxyquinoline alkaloids were isolated from the New Zealand ascidian Pseudodistoma aureum and characterised by interpretation of spectroscopic data and chemical derivatisation. Distomadine A exhibited mild antifungal activity but failed to exhibit any biological activity in a range of antitumour, cytotoxicity, anti-inflammatory, and antimycobacterial tests. The known methyl esters of fatty acids eicosapentaenoic acid (EPA), docosahexaenoic acid and eicosatetraenoic acid were also identified in the extract with EPA methyl ester exhibiting mild cytotoxicity to a non-malignant cell line. (C) 2003 Elsevier Science Ltd. All rights reserved.
The total synthesis of distomadines A and B, two structurally unique tetracyclic quinolines, is described. The route features a three-step process to access the pyranoquinoline butenolide rings via a Suzuki cross coupling of a 5-bromo-4-methoxycarbonylmethoxyquinoline with a vinyl boronate, followed by an alpha-ketohydroxylation and double cyclization by intramolecular aldol condensation and lactonization. Subsequent manipulation of the side chain to introduce the guanidine fragment completed the synthesis of distomadine B, whereas the distomadine A congener resulted from decarboxylation of a late-stage intermediate.