Calorimetric investigations of the lipase-catalysed hydrolysis of acylatedacyclonucleosides

Thermal power accompanying the hydrolysis of mono- and bi-acylated acyclonu cleosides: (R,S)-1-N-(1-O-acetyl-3-hydroxypropoxymethyl)-thymine (ThL), 1-N -(1,3-di-O-acetylpropoxymethyl)-thymine (ThAc), and 1-N-(1,3-di-O-acetylpro poxymethyl)-5-fluorouracil (FAc), catalysed by lipase from Candida Cylindra cea (Rugosa) was investigated by isothermal heat conduction microcalorimetr y. Changes of the thermal power in time and the total heat effects were det ermined in long-lasting measurements. Hydrolysis of these compounds was exa mined also by TLC. For all three esters the thermal power curves reveal both a relatively inte nsive and slow heat evolutions. It is suggested that this complexity result s from a superposition of: (i) a stereospecific hydrolysis of the ester bon d connected to the heterocyclic moiety by a chain endowed with an appropria te chirality, and (ii) a non-specific hydrolysis of another ester bond. A p artial chemical degradation of reactants in the buffer was also observed.