Methylation conjugation reactions

Other drugs are metabolised by Phase II synthetic reactions, catalysed typically by non-microsomal enzymes. Processes include acetylation, sulphation, glycine conjugation and methylation. Phase II reactions may be affected less frequently by ageing. Thus according to some studies, the elimination of isoniazid, rifampicin (rifampin), paracetamol (acetaminophen), valproic acid, salicylate, indomethacin, lorazepam, oxazepam, and temazepam is not altered with age. However, other studies have demonstrated a reduction in metabolism of lorazepam, paracetamol (acetaminophen), ketoprofen, naproxen, morphine, free valproic acid, and salicylate, indicating that the effect of age on conjugation reactions is variable. 

In the reaction of "carbomethoxypalladium salts with olefins, there is a marked tendency to product unsaturated esters in which the double bond is not conjugated with the carbonyl. The reaction of carbomethoxy palladium acetate with a-methylstyrene produced an 86% yield of unsaturated esters of which 96% was the non-conjugated isomer, methyl 3-phenyl-3-butenoate and only 4% was the imws-conjugated product 24>. 

Stevens JL, Bakke JE (1990) S-methylation. In Mulder GJ (ed) Conjugation reactions in drug metabolism an integrated approach. Taylor and Francis, London, p 251... 

Conjugation reactions of xenobiotics or their metabolites with endogenous substrates produce highly hydrophilic metabolites however, to a lesser extent functional groups may be also methylated or acetylated to produce less hydrophilic compounds. 

Benzoyl peroxide, the active ingredient in some shampoos for dogs, is almost completely metabolized to benzoic acid in the epidermis. Benzoic acid undergoes conjugation with glycine, primarily in the liver, and is excreted in urine as hippuric acid. Methylation of norepinephrine to epinephrine, an A-transferase-mediated conjugation reaction, in human and animal skin preparations has been reported. ... 

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