STEREOCHEMICAL ASPECTS OF THE METABOLISM OF THE ISOMERIC METHYLCYCLOHEXANOLS AND METHYLCYCLOHEXANONES

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Abstract
The 7 isomeric optically inactive forms of methylcyclohexanol (i. e. 1-, and cis-and trans-2-, -3-and-4-) are excreted by rabbits mainly as glu-curonides of the thermodynamically more stable forms of the alcohols. The eighth isomer, cyclohexylmethanol, however, undergoes aromatiza-tion in vivo, giving rise to benzoic acid and hippuric acid. The ([plus or minus])-2-, (i)-3-and 4-methylcyclohexanones are reduced in the rabbit and excreted mainly as the glucuronides of the thermodynamically more stable forms of the corresponding methylcyclohexanols. Racemic cis-and trans-2-methylcyclohexanol and 2-methylcyclohexanone are all excreted as conjugated trans-2-methylcyclohexanol. However, when the ([plus or minus])-cis-alcohol or the (-)-ketone is fed, (+)-trans-2-methylcyclohexanol is excreted, whereas when the ([plus or minus])-trans-alcohol is fed it is excreted as the (i)-trans-alcohol. Racemic cis-and trans-3-methylcyclohexanol and 3-methylcyclohexanone are all excreted as conjugated racemic cis-3-methylcyclohexanol. cis-and trans-4-Methylcyclohexanol and 4-methylcyclohexanone are all excreted as conjugated trans-4-methyl-cyclohexanol. The metabolic differences between the various methylcyclohexanols are explicable in terms of their conformations and of Vennesland'';s (1958) hypothesis of the role of NADH [reduced nicotin-amide adenine dinucleotide) in dehydrogenation reactions.