Absolute configuration of the alpha,omega-bifunctionalized sphingolipid leucettamol A from Leucetta microrhaphis by deconvoluted exciton coupled CD.

The configuration of leucettamol A (1), a known long-chain "two-headed" sphingolipid (dimeric sphingolipid) from the marine sponge Leucetta microrhaphis, was determined by conversion to an N,N',O,O'-tetrabenzoyl derivative, measurement of the exciton coupled circular dichroism spectrum (ECCD), and quantitative analysis by deconvolution of superposed exciton couplets. Contrary to the earlier assignment that claimed leucettamol A (1) was racemic, the CD approach unambiguously reveals the natural product is chiral and optically active and displays pseudo-C(2) symmetry. The configuration of each end of the chain has erythro stereochemistry with an absolute configuration of 2R,3S,28S,29R. We show that deconvolution ECCD reliably predicts erythro versus threo vicinal amino alcohols in all cases with greater sensitivity (<5 nmol) compared to (1)H NMR J-based methods and provides verification of optical purity and unequivocal elucidation of absolute configuration in this difficult class of natural products.