Absolute configuration of cis-12-oxophytodienoic acid of flaxseed: implications for the mechanism of biosynthesis from the 13(S)-hydroperoxide of linolenic acid.

摘要: cis-12-Oxophytodienoic acid (cis-12-oxo-PDA) is a C18 cyclopentenone formed from the 13-(S)-hydroperoxide of linolenic in flaxseed and other plant tissues. Although structure cis-12-oxo-PDA well established, absolute configuration side chains has not been determined. We have now measured this important parameter by two independent approaches. The CD spectrum freshly prepared showed no deviations base line--implying that product racemic. This conclusion was checked high-pressure liquid chromatography (HPLC) method capable resolving enantiomers; reduced to saturated hydroxy analogues which were each converted (-)-menthoxycarbonyl diastereomers analyzed HPLC. Each epimer resolved as peaks equal area, thus confirming their parent racemic mixture, enantiomeric at ring junctures. propose biosynthesis proceeds dehydration 13(S)-hydroperoxide an allene oxide. A major fate oxide hydrolysis alpha-ketol, always together with cis-12-oxo-PDA. also opens zwitterion, undergoes charge delocalization form planar intermediate; achiral precursor stable end pericyclic closure, viz.,