A number of marine metabolites have been isolated from the ascidian L. bistratum. These include the bistramide series of compounds (bistramides A-K). Bistramide A had been previously isolated and characterised, however, while the structural connectivity had been established, the relative and absolute stereochemistry was unclear. In order to allow elucidation of this, synthesis of fragments of bistramide A was undertaken. Bistramide A was dissected into three fragments (A, B and C). As part of this thesis, fragments A and B were constructed in a stereoselective manner.
The four possible enantiopure isomers of fragment A, a functionalised tetrahydropyran, were synthesised via two routes. The initial pathway, beginning with a chiral epoxide, utilized oxy-mercurycyclisation to provide the tetrahydropyran. A second, more efficient route, beginning with [3-citronellene, made use of intramolecular palladiummediated cyclisation to give access to the tetrahydropyran. Comparison of NMR spectral data of the four isomers with the natural compound allowed determination of the relative stereochemistry in bistramide A of the tetrahydropyranal unit.
Fragment B, containing two stereogenic centres was also constructed in a stereoselective manner. One diastereomer was synthesised enantioselectively utilizing aldol methodology. This involved the use of an Evans' chiral auxiliary, which was accessed from a non-racemic chiral amino acid. The alternative diastereomer was provided through the use of crotylation methodology. This provided a racemic sample of the isomer, which was then separated on chiral HPLC, to give access to the enantiopure diastereomer.
A species of canegrub, Antitrogus parvulus (the Childers canegrub), was beHeved to synthesise and utilize, methyl-branched hydrocarbons, containing 27 and 28 carbon atoms, as pheromones. While the structural connectivity was established from NMR spectral data, the relative stereochemistry was unclear. The relative stereochemistry of the partial structure was determined from comparison with NMR spectral data to a synthesised sample. The synthetic sample was constructed from syn-2,5- dimethylcyclohexanol through a series of organic transformations.