engleski

Intramolecular Transesterification of Pivaloylated Monosaccharides

Intramolecular migrations of acyls are well known in carbohydrate chemistry. These transesterifications are most often acid or base catalysed, and the mechanism of such reactions has been described (1). Especially prone to migrations are acetyls which spontaneuosly migrate along the sugar ring even under neutral conditions, in organic solvents (2). Pivaloyl groups do not migrate easily even under basic or acidic conditions. But, intramolecular transesterifications catalysed by enzymes from mammalian sere were observed in radiolabelled dipivalates of glucose (3). In this work we describe enzymically catalyzed migrations of monopivalates. Thus, the sense of migrations was determined by using 14C-labelled methyl 2- and 6- O-pivaloyl-alpha-D-glucopyranosides as substrates. Source of enzymes were mammalian sera. Futhermore, several migrations of pivaloyls were observed in partially pivaloylated mannose, xylose and galactose series of sugars, caused by reaction medium and changes of temperature, and without the presence of enzymes. (1). T. Horrobin, Ch.H. Tran, D. Crout, J.. Chem. Perkin Trans I (1998)1069- 1080. (2). S. Tomić, Đ. Ljevaković, J. Tomašić, Tetrahedron 49 (1993) 10977-10986. (3). S. Tomić, Lj. Sesartić, J. Tomašić, Comp. Biochem. Physiol. 92B (1989) 681-684.

monosaccharides ; enzymes ; transesterification

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