Carbohydrate Research 337 (2002) 1615 – 1621 www.elsevier.com/locate/carres Regioselective enzymatic hydrolysis of acetylated pyranoses and pyranosides using immobilised lipases. An easy chemoenzymatic synthesis of - and -D-glucopyranose acetates bearing a free secondary C-4 hydroxyl group Marco Terreni, a, * Raul Salvetti, a Laura Linati, a Roberto Fernandez-Lafuente, b Gloria Ferna ´ndez-Lorente, b Agatha Bastida, b, * Jose ´ M. Guisan b a Pharmaceutical Biocatalysis Laboratories, Department of Pharmaceutical Chemistry, Via Taramelli 12, Uniersity of Paia, Paia, Italy b Laboratorio de Tecnologı ´a Enzima ´tica, Departamento de Biocata ´lisis, Instituto de Cata ´lisis, CSIC, Cantoblanco, 28049 Madrid, Spain Received 15 October 2001; accepted 29 April 2002 Abstract Protected sugars with only one free hydroxyl group are useful building blocks for the synthesis of a large number of glycoderivatives. In order to avoid the problems of the classical chemical synthesis, we studied the regioselective enzymatic hydrolysis of different fully acetylated glycopyranoses and glycopyranosides. The main challenge was to obtain the hydrolysis of the substrates in only one position, with high regioselectivity, while avoiding any further hydrolysis towards partially acetylated sugars. Candida rugosa (CRL) and Pseudomonas fluorescens (PFL) lipases (EC 3.1.1.3) immobilised on octyl agarose afforded regioselective hydrolysis only in the 6- and 1-positions, respectively. Furthermore, a new one-pot chemoenzymatic approach has been developed in order to obtain - and -protected glucopyranoses bearing a free secondary C-4 hydroxyl group. For instance, 1,2,3,6-tetra-O-acetyl--D-glucopyranose was easily synthesised in good overall yield (70%) starting from 1,2,3,4,6-penta-O-acetyl- -D-glucopyranose by regioselective enzymatic hydrolysis in the 6-position, catalysed by CRL, followed by a temperature- and pH-controlled acyl migration. © 2002 Elsevier Science Ltd. All rights reserved. Keywords: Regioselective hydrolysis; Acetylated pyranosides; Lipase; Acetyl group migration For example, 1,2,3,6-tetra-O -acetyl--D-glucopyran- ose and related compounds, may be of particular inter- est due to the presence of (1 4)-glycosidic bonds in natural oligosaccharides and in those of pharmaceutical interest. However, only few papers describing suitable chemical syntheses of APs have been published. 3,4 The 1,2,3,4,6-penta-O -acetyl--D-pyranose (1) could eco- nomically be used in regioselective deacetylation for large-scale preparation of APs. Although a large num- ber of procedures has been reported, suitable processes for the chemical hydrolysis of 1 only afford the deacetylation at the anomeric position. 5 An alternative approach for obtaining protected sugars with only one free secondary hydroxyl group, including the 4-posi- tion, employs dispiroketals for regioselective protection of vicinal diols. 6 The complexity of the classical chemical approaches for regioselective protection/deprotection of sugars 1. Introduction Pure regioisomers of O -acetyl pyranosides bearing only one free hydroxyl group (AP) may be used as key intermediates for the synthesis of a large number of glycoderivatives (oligosaccharides, sugar esters, gly- copeptides, etc.). 1,2 AP intermediates can be readily and selectively modified at their free hydroxyl group and are soluble in most organic solvents. Moreover, the pro- tected final products can be easily deacetylated by very mild chemical or enzymatic processes. However, the preparation of APs with only one free hydroxyl group requires by classical chemical synthesis multistep reac- tions that may pose environmental problems for large- scale production, due to the use of organic solvents and toxic reagents. * Corresponding authors. Tel.: +39-382-507-361; fax: + 39-382-422-975 E -mail address: markt@pbl.unipv.it (M. Terreni). 0008-6215/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved. PII:S0008-6215(02)00113-1