Available online at www.sciencedirect.com J. of Supercritical Fluids 45 (2008) 88–93 Lipase-catalyzed regioselective acylation of tritylglycosides in supercritical carbon dioxide Cleofe Palocci ∗ , Mariangela Falconi, Laura Chronopoulou, Enrico Cernia Dipartimento di Chimica, Universit` a degli Studi di Roma “La Sapienza”, P.le A.Moro, 5 00185 Rome, Italy Received 27 June 2007; received in revised form 24 October 2007; accepted 9 November 2007 Abstract Candida rugosa lipase (CRL) was used to catalyze the regioselective acylation of methyl 6-O-trityl -d-glucopyranoside in supercritical CO 2 (SCCO 2 ), using vinyl acetate as the acyl donor and obtained final conversion values up to 91.4%. The effect of pressure, temperature, enzyme quantity and sugar/ester molar ratio on the catalytic efficiency and regioselectivity of CRL was evaluated. The regioselectivity of the reaction was shifted towards the synthesis of 3-O-acetyl 6-O-trityl -d-glucopyranoside and this is a function of the chemico-physical parameters of the supercritical medium employed. In fact, by varying the CO 2 pressure used in the process up to 20 MPa at constant temperature, we were able to obtain the formation of the sole 3-O-acetyl 6-O-trityl -d-glucopyranoside regioisomer. A kinetic study was also performed and the relative kinetic parameters calculated. © 2007 Elsevier B.V. All rights reserved. Keywords: Sugar esters; Lipase; Supercritical carbon dioxide; Enzymatic acylation; Regioselective reactions; Green chemistry 1. Introduction As it is well known, the use of non-aqueous media in biocatal- ysis has made accessible a range of reactions, which, like ester- ification, transesterification and aminolysis, only proceed in the presence of limited amounts of water [1–6]. In addition, by using a supercritical fluid as the reaction medium one can exploit the unique transport properties and the adjustable solvating power of this fluid [7–9]. Of the most commonly used solvents, carbon dioxide has many advantages over conventional organic solvents as reaction medium, since it is non-toxic, non-flammable, inex- pensive, easy to separate from substrate and products, and has a low viscosity and high diffusivity. However, the use of carbon dioxide in supercritical conditions as reaction medium for bio- catalyzed reactions has been restricted to only a few applications involving mainly substrates with low polarity [10–12]. Of the enzymes more widely applied in industrial transforma- tions, lipases from microbial and fungal sources find interesting applications in regioselective acylation of polyfunctional com- pounds [3,13–15]. Among these, monosaccharides represent a very promising class of molecules to be employed as new drugs ∗ Corresponding author. Fax: +39 06490324. E-mail address: cleofe.palocci@uniroma1.it (C. Palocci). [16–20]. Their chemical selective modification usually requires several protecting and deprotecting steps, since they have multiple hydroxyl groups of comparable chemical reactivity. An enzymatic acylation of monoprotected glycosides, recently described by the authors in organic media [21], highlighted the influence of chemico-physical parameters of the reaction medium on the yield and regioselectivity of lipase-catalyzed transesterification reactions. The solvent influences the yield of the reaction as well as its regioselectivity. In particular, a strong linear correlation between the enzyme selectivity towards posi- tion C-3 of the substrate and the log P ow of the organic medium was found. The results obtained in organic solvents have been rationalized on the basis of different conformational restraints imposed on the substrate by different solvent media. Supercritical carbon dioxide (SCCO 2 ) can be considered a promising alternative to conventional organic media for the enzymatic synthesis of functionalized monosaccharides. Since it is non-toxic, it can be employed in the production of interme- diates for pharmaceutical applications. With the aim of conducting an in-depth study of the behaviour of microbial lipase in the regioselective acylation of protected monosaccharides we focused our attention on the study of trans- esterification reactions catalyzed by wild type microbial lipases by using monoprotected glycosides, as substrates, in SCCO 2 as reaction medium. 0896-8446/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.supflu.2007.11.009