ENANTIOSELECTIVE CONVERSION OF LINOLEATE HYDROPEROXIDE TO AN ALPHA,BETA-EPOXY ALCOHOL BY NIOBIUM ETHOXIDE

Niobium (V) ethoxide [Nb(OC2H5)(5)] catalyzed the rearrangement of met hyl 13(S)-hydroperoxy-9(Z),11 (E)-octadecadienoate (Me-HPODE) to epoxy hydroxy isomers. At low temperature (5 degrees C) in aprotic solvent, Me-HPODE was converted to the diastereomeric alpha, beta-epoxy alcoho ls, methyl 11 (R,S), 12(R,S)-epoxy-13 (S)-hydroxy-9(Z)octadecenoate. T hese products are referred to as oxylipids and structurally resemble t hose obtained from the vanadium- and epoxygenase-catalyzed rearrangeme nt of Me-HPODE but are distinct from products obtained from ferrous ir on-, hematin-, and hemoglobin-catalyzed rearrangements. Because the pr oduct of the niobium-catalyzed rearrangement of Me-HPODE was predomina ntly the erythro diastereomer, the rearrangement is distinguished from that produced by a titanium catalyst, in which the three diastereomer [methyl 11 (R), 12 (R)-epoxy-13(S)-hydroxy-9(Z)-octadecenoate] predom inates, and from that produced by a vanadium catalyst, in which both d iastereomers are produced in equal proportion. The synthesis of alcoho l epoxide by Nb(OC2H5)(5) was inhibited by traces of water, but inclus ion of molecular sieves in the reaction medium did not improve yield, as the alcohol epoxide rearranged to ketonic materials.