A synthetic approach to the marine cyclodepsipeptides Geodiamolide A and B is described. The synthesis is based on the construction of two key fragments: a tripeptide and a polyketide. Attempts to reproduce published procedures for the synthesis of the tripeptide were complicated by problems in protecting group manipulation and some discrepancies in spectroscopic data. The synthesis of the polyketide fragment (Philip Ashworth's route) involved a novel method for the chromatographic resolution of tetrahydropyran-2-ones which was shown to be general. Union of the tripeptide and polyketide fragments was successful and gave an advanced intermediate which had previously been converted to Geodiamolide A or B corresponding to the aromatic ring halogens.