A comparative study on the substrate recognition was conducted successfully in Novozym 435-mediated acylation of various 2'- or 5-substituted nucleosides with acyl donors carrying different aliphatic chain lengths (C6, C10, and C14). The unexpected results revealed that the physicochemical property of the substituents (such as the size, hydrophobicity, and substitutional position) in nucleosides profoundly influenced the behavior of the enzyme. The different substrate-binding patterns derived from the existence of the substituents in 2'- or 5-position of the nucleosides could account for this. Moreover, another possible factor governing the regioselectivity might be ascribed to the interaction between the substituent and acyl donor in addition to the geometrical configuration of the lipase's active site. (C) 2013 Elsevier Ltd. All rights reserved.