Solid-phase synthesis of drug glucuronides by immobilized glucuronosyltransferase

Rabbit liver glucuronosyltransferase immobilized on beaded agarose has been used to synthesize glucuronic acid conjugates of meprobamate, diethylstibestrol, bilirubin, borneol, benzioc acid, and p-nitrothiophenol. The immobilized enzyme exhibited a high degree of specificity for UDPGA as cofactor when p-nitrophenol is used as substrate. Other cofactors tested were less effective, all producing less than 10% conjugation relative to UDPGA. The effects on agarose-bound enzyme activity of a variety of cosolvents and emulsifiers have been studied. Ethanol, dimethyl sulfoxide, propylene glycol, and bovine serum albumin are among the cosolvents and emulsifiers which can be used within limited concentration ranges to sulubilize lipophilic substrates for conjugation. Concentrations of calcium and magnesium cations between 1.5 and 10.0mM were found to enhance glucuronosyltransferase activity of the immobilized enzyme.