Cyclization of natural allene oxide fatty acids. The anchimeric assistance of beta, gamma-double bond beside the oxirane and the reaction mechanism.
Formation of cyclopentenones was followed from linoleic, alpha-linolenic and gamma-linolenic acid hydroperoxides (HPOD, HPOT(alpha) and HPOT(gamma), respectively) via allene oxides in the presence of flax seed allene oxide synthase. Although 13-HPOT(alpha) and 9-HPOT(gamma) were effective cyclopentenone precursors, 13-HPOD, 9-HPOD(gamma) and 9-HPOT(alpha) were not. These results suggest that the presence of a double bond in beta, gamma-position toward the hydroperoxide function causes the strong effect of anchimeric assistance, increasing the cyclization rate by 2-3 orders of magnitude. The minor 15(E) isomer was formed from 13-HPOT along with usual 12-oxo-10,15(Z)-phytodienoic acid (12-oxo-PDA). The remarkable (about 2-fold) suppression of 12-oxo-PDA formation was observed under acidic (pH 5.5) conditions in comparison to the alkaline (pH 7.8) ones. The mechanism of double bond-assisted allene oxide cyclization, comprising dipolar pericyclic ring closure in zwitterionic intermediate, is proposed.
Grechkin
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AN
Institute of Biology, Kazan Branch of Russian Academy of Sciences.
D002244:Carbon; D002851:Chromatography, High Pressure Liquid; D003517:Cyclopentanes / Q000378:metabolism; D005027:Ethylene Oxide; D005227:Fatty Acids / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000032:analysis / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D019746:Intramolecular Oxidoreductases; D007535:Isomerases / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010084:Oxidation-Reduction; D012639:Seeds
D003517:Cyclopentanes; D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; C025999:12-oxophytodienoic acid; D002244:Carbon; D007535:Isomerases; D019746:Intramolecular Oxidoreductases; C021377:hydroperoxide isomerase; D005027:Ethylene Oxide; C013905:cyclopentenone