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Studies in Marine Natural Products : Onchidoris bilamellata, Nanaimoal and Capnellene

University of British Columbia

The following thesis is divided into three chapters. The first describes the isolation and identification of a sphingolipid L from the methanolic skin extract of the British Columbia nudibranch Onchidoris bilamellata. The long chain base has been identified as (E)-l,3-dihydroxy-2-amino-16-methyl-4-octadecene (1̲3) and the fatty acid moiety as palmitic acid (1̲2). This ceramide possesses antibacterial activity towards the microorganisms Bacillus subtilis and Staphylococcus aureus. [formula omitted] The second chapter presents our attempt to synthesize a hypothetical structure of nanaimoal (2̲4), a marine sesquiterpenoid, isolated from the British Columbia nudibranch Acanthadoris nanaimoensis. The proposed route envisaged photolysis of a 2,2,10,10-tetrasubstituted cyclodecanone. This work lend to a study of the solution photochemistry of 2,2,10-trimethyl-cyclodecanone (3̲5). [formula omitted] The last chapter outlines studies directed toward the synthesis of capnellene (5̲1), a tricyclopentanoid obtained by Djerassi and co-workers from the soft coral Capnel laimbricata. Starting with an improved synthesis of the known ketone Δ¹̕̕̕⁵-bicyclo[3.3.0] octen-2-one (1̲3̲8), an acylation method was developed for the preparation of Δ¹̕⁵-3-carboethoxybicyclo-[3.3.0] octen-2-one (1̲6̲0). The procedure is of general utility and has been extended to related ketones. This unsaturated keto-ester underwent a Michael addition with methyl vinyl ketone to give 1̲7̲8. Selective Knoevenagal condensation of the methyl ketone produced Δ¹̕⁵-3-carboethoxy-3-(dimethyl-3-methyl-3-butenyl-4,4-dicarboxylate)-bicyclo[3.3.0] octen-2-one (179). Reduction of the unsaturated ketone and dehydration of the allylic alcohol produced a 1,1,3,4-tetrasubstituted cyclopentadiene derivative 1̲8̲1. Intramolecular Diels-Alder cyclization of the latter afforded the tetracyclic tricarboxylic ester 1̲8̲2. Selective hydrolysis of the malonic estertricarboxylic ester 1̲8̲2 followed by decarboxylation led to 1̲8̲3, a key intermediate for the ultimate construction of the capnellane ring system. [formula omitted]

Text

2010-06-17

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http://hdl.handle.net/2429/25822

Chemistry

University of British Columbia

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