Lipase-catalyzed synthesis of l-phenylalanyl-d-glucose

Regioselective synthesis of l-phenylalanyl ester of d-glucose with unprotected l-phenylalanine and d-glucose was carried out in organic solvents using lipases from Rhizomucor miehei (RML) and porcine pancreas (PPL). The reaction was investigated in terms of free unprotected l-phenylalanine, d-glucose, RML and PPL concentrations, buffer salts (pH and concentration), enzyme reusability and incubation period. Under the experimental conditions employed, both the enzymes exhibited good esterification potentialities, with RML exhibiting better conversions (maximum yield, 98%) than PPL (maximum yield, 75.6%). Reactions in the presence of buffer salts gave about 10% higher yields than those in their absence. Two-dimensional heteronuclear single quantum coherence transfer (HSQCT) NMR spectral analysis confirmed the formation of five diastereomeric esters: three different l-phenylalanyl-d-glucose monoesters (6-O: 24.1%, 3-O: 23.3% and 2-O: 19.2%) and two different diesters (2,6-di-O: 16.6% and 3,6-di-O: 16.8%) in an esterification yield of 92.4%.