The bioassay-guided fractionation of the Okinawan marine cyanobacterium Okeania sp. led to the isolation of the 26-membered cyclodepsipeptide odoamide (1). The gross structure of 1 was determined by 1D and 2D NMR analyses, whereas its absolute stereochemistry was determined using a variety of different methods, including synthesis and chemical degradation followed by chiral HPLC analysis. Notably,
An efficient and highly stereocontrolled synthesis of protected (2R,3R,4S)-3-hydroxy-2,4,6-trimethylheptanoic acid, the β-hydroxy acid unit that acylates the N-terminus of callipeltin A, has been devised starting from methyl (2S)-2-methyl-3-hydroxypropionate. Comparison of NMR data with the corresponding fragment obtained from the acid hydrolysate of callipeltin A indicates that the stereostructure