Sulfate conjugation reactions

The lactam derivative dibenz[h/]l 4-oxazepin-ll-(lOH)-one is a primary metabolic product of metabolism and a direct precursor of the urinary hydroxylated metabolites. In rats, the lactam, a dihydro-CR metabolite, an amino alcohol of CR, and an arene oxide are metabolites in CR degradation. In the rat, the major mechanism for elimination is sulfate conjugation and biliary excretion to a limited extent. Phase I metabolism by microsomal mixed fimction oxidases involves reduction of CR to the amino alcohol, oxidation to form the lactam ring, and hydroxylation to form the hydroxylactams. Phase II conjugation reactions sulfate the hydroxylactam intermediates for renal elimination. Amino alcohol intermediates are conjugated with glucuro-nide for biliary secretion. 

Dissolve HRP (Chapter 26) in 200pi 0.1 M sodium borate, pH 9.3, at a concentration of lOmg/ml. If the HRP is supplied as an ammonium sulfate suspension, all ammonium ions must be removed by extensive dialysis prior to the conjugation reaction. Add the HRP solution to the activated oligo. 

If the foreign molecule already possesses a functional group suitable for a phase 2 reaction, a phase 1 reaction will be unnecessary. Thus, if phenol is administered to an animal, then it may immediately undergo a phase 2 reaction, such as conjugation with sulfate. Alternatively it may undergo another phase 1 type of reaction. The major types of reactions are shown in Table 4.2. 

The main metabolic reaction is the deamination of amphetamine with the formation of phenylacetone, which is subsequently oxidized to benzoic acid, then conjugated with glycine to form hippuric acid. Side reactions include aromatic hydroxylation to form 4-hydroxyamphetamine (an active metabolite), the stereoselective [i-hydroxy-lation for the isomer (+) of amphetamine leading to the formation of norephedrine (phenylpropanolamine) and finally the N-oxidation leading to the formation of a hydroxylamine derivative. The products of the hydroxyl and aromatic N-oxides can be conjugated with sulfate or glucuronic acid [18]. 

Mulder GJ, Jakoby WB. Sulfation. In Mulder GJ, ed. Conjugation Reactions in Drag Metabolism. New York Taylor and Francis, 1990 107-161. 

Phase 2 conjugation, reaction of the activated molecule with a hydrophilic molecule such as glucuronic acid, glutathione or sulfate. 

A second important conjugation reaction is the sulfate conjugation. This, again, occurs predominantly with hydroxy groups and occasionally with amino groups. The sulfate donor is 3 -phosphoadenosine-5 -phosphosulfate, which is formed from ATP and inorganic sulfate. The enzyme involved is sulfotransferase. 

Phase I metabolites, together with unchanged parent compound, are excreted via bile and urine, if sufficient solubility and/or transporter specificity is given. In a second step, conjugation reactions often increase polarity even more by glucuronidation, sulfation, or glutathione conjugation (Phase II). 

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