Document Detail

Role of structure and pH in cyclization of allene oxide fatty acids: implications for the reaction mechanism.
MedLine Citation:
PMID:  12426078     Owner:  NLM     Status:  MEDLINE    
Incubations of allene oxide synthases of flax or maize with the E,E-isomers of the 13- and 9-hydroperoxides of linoleic acid (E,E-13- and E,E-9-HPOD, respectively) at pH 7.5 afforded substantial yields of trans-disubstituted cyclopentenones. Under the conditions used, (Z,E)-HPODs were converted mainly into alpha-ketols and afforded only trace amount of cyclopentenones. These findings indicated that changing the double bond geometry from Z to E dramatically increased the rate of formation of the pericyclic pentadienyl cation intermediate necessary for electrocyclization of 18:2-allene oxides and thus the yield of cyclopentenones. The well-known cyclization of the homoallylic allene oxide (12,13-EOT) derived from alpha-linolenic acid 13-hydroperoxide (E,Z-13-HPOT) into cis-12-oxo-10,15-phytodienoic acid was suppressed at pH below neutral and was not observable at pH 4.5. In contrast, cyclization of the allene oxide ((9E)-12,13-EOD) derived from (E,E)-13-HPOD was slightly favoured at low pH. The finding that the cyclizations of 12,13-EOT and (9E)-12,13-EOD were differently affected by changes in pH suggested that the mechanisms of cyclization of these allene oxides are distinct.
Alexander N Grechkin; Ivan R Chechetkin; Lucia S Mukhtarova; Mats Hamberg
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Chemistry and physics of lipids     Volume:  120     ISSN:  0009-3084     ISO Abbreviation:  Chem. Phys. Lipids     Publication Date:  2002 Dec 
Date Detail:
Created Date:  2002-11-11     Completed Date:  2003-11-04     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0067206     Medline TA:  Chem Phys Lipids     Country:  Ireland    
Other Details:
Languages:  eng     Pagination:  87-99     Citation Subset:  IM    
Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, P.O. Box 30, 420503, Kazan, Russia.
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MeSH Terms
Cyclopentanes / chemistry,  metabolism
Fatty Acids / metabolism*
Flax / enzymology
Hydrogen-Ion Concentration
Intramolecular Oxidoreductases / metabolism*
Linoleic Acid / metabolism
Molecular Structure
Zea mays / enzymology
Reg. No./Substance:
0/Cyclopentanes; 0/Fatty Acids; 0/Peroxides; 2197-37-7/Linoleic Acid; 930-30-3/cyclopentenone; EC 5.3.-/Intramolecular Oxidoreductases; EC isomerase

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