The marine polyether toxin, 45-hydroxyyessotoxin, was isolated together with yessotoxin from the scallop, Patinopecten yessoensis. The 45-hydroxy group in the side chain was esterified with (S)- and (R)-α-methoxy-α-trifluoromethylphenylacetic acids (MTPA). A detailed analysis of the 2D NMR spectra of the two esters established the R configuration at C45.
