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Mechanism and Stereoselectivity of Biologically Important Oxygenation Reactions of the 7-Dehydrocholesterol Radical

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Title Mechanism and Stereoselectivity of Biologically Important Oxygenation Reactions of the 7-Dehydrocholesterol Radical
 
Creator RAJEEV, R
SUNOJ, RB
 
Subject LIPID-PEROXIDATION
OXIDATION
DISTORTION/INTERACTION
CYCLOADDITIONS
OXYSTEROLS
ACTIVATION
CHEMISTRY
PATHWAYS
MODELS
 
Description The mechanism of free radical oxygenation of 7-dehydrocholesterol (7-DHC), one of the biologically important sterols, is investigated by using density functional theory. The energetic origin of the product distribution and the stereoelectronic factors involved in various mechanistic pathways are delineated. The addition of triplet molecular oxygen to two types of conjugatively stabilized radicals, generated by the removal of the reactive allylic hydrogens from C9 or C14 positions, respectively denoted as H9 and H14 pathways, is studied. The distortion interaction analysis of the C-O bond formation transition states suggests that the energetic preference toward the a prochiral face stems from reduced skeletal distortions of the cholesterol backbone as compared to that in the corresponding beta prochiral face. This insight derived through a detailed quantitative analysis of the stereocontrolling transition states suggests that the commonly found interpretations solely based on steric interactions between the incoming oxygen and the protruding angular methyl groups (C10, C13 methyls) in the beta face calls for adequate refinement. The relative energies of the transition states for molecular oxygen addition to C9, C5, and C14 (where spin densities are higher) and the ensuing products thereof are in agreement with the experimentally reported distribution of oxygenated 7-DHCs.
 
Publisher AMER CHEMICAL SOC
 
Date 2014-10-15T12:22:51Z
2014-10-15T12:22:51Z
2013
 
Type Article
 
Identifier JOURNAL OF ORGANIC CHEMISTRY, 78(14)7023-7029
http://dx.doi.org/10.1021/jo4008496
http://dspace.library.iitb.ac.in/jspui/handle/100/14894
 
Language en