Polymer-supported enzymic synthesis on a preparative scale

Abstract

A number of feasible approaches for the solid-phase synthesis of oligosaccharides, using protecting group chemistry, have been published in recent years [l-4]. Nevertheless, a widespread use of these approaches suffers from the fact that there is no chemical glycosylation method that is generally applicable for the synthesis of any glycosidic linkage. Enzymic glycosylation, on the other hand, represents a strategy applicable for any glycosidic linkage once the appropriate enzyme is available. Glycosylations using glycosyltransferases have proved to be an attractive alternative to protecting group chemistry in numerous examples [ 5,6] ; the method is therefore ideally suited to apply to a solid-phase synthesis. An additional reason for the application of solid-phase synthesis in enzymic glycosylations is the ease of work-up and separation in the solid-phase approach. This is especially advantageous in enzymic systems that use complex mixtures of a multitude of enzymes and cofactors for regeneration of substrates. A method for the attachment and release of the saccharide acceptor onto the polymer suitable for enzymic glycosylations has been developed by Zehavi et al. [ 731. This approach utilises a photocleavable bond for the linkage of the acceptor to the polymer and was used with several enzyme systems [ 91. The incorporation yields obtained in these reactions vary with the polymers and the enzymic systems applied. In recent studies [lo], we have developed some insoluble polymers that carry feasible spacers for the attachment of the saccharide. These polymers were effective supports for enzymic glycosylation with galactosyltransferase, which was demonstrated by small-scale synthesis using radioactively labelled donors. The use of radioactive labelling is very advisable in the development of polymeric supports because of the high costs of cofactors and enzymes. In order to demonstrate the feasibility of the solid-phase approach, we now report a polymer-supported enzymic synthesis on a preparative scale, including the photochemical release and isolation