Biocatalytic Process Optimization for the Production of High-Added-Value 6-O-Hydroxy and 3-O-Hydroxy Glycosyl Building Blocks

A biocatalytic process to synthesize regioselective monohydroxy glycosyl building blocks has been optimized. Lipases immobilized on commercial supports were treated with watersoluble carbodiimide (EDC) at different concentrations. In the presence of cosolvents, the stability of lipases adsorbed on octyl-Sepharose improved after the EDC modification. The new Candida rugosa lipase (CRL) modified heterogeneous biocatalysts were tested in the production of 6-OH hydroxyl-tetraacetyl glucose by a regioselective mono-deacetylation in aqueous media. Improvements in activity and excellent regioselectivity were obtained for octyl-CRL-EDC10mM preparation, with 95% isolated yield of product on a multimilligram scale. We also observed excellent recyclability. The C-6 alcohol was transformed to a C-3 alcohol by chemical migration, and both compounds were transformed successfully in the corresponding new trichloroacetimidyl glucoderivatives. Modified CRL biocatalysts were also tested in the selective deprotection of peracetylated thymidine, and octyl-CRL-EDC10mM showed excellent specificity and improved regioselectivity to produce 3-hydroxy-5acetyl-thymidine, a precursor of azidethymidine (AZT), in 95% yield. The new Rhizomucor miehei lipase (RML)-modified heterogeneous biocatalysts showed excellent regioselectivity and recyclability in the 3-OH mono-deprotection of peracetylated lactal.