Glycosidation enzymatic methods

Glycosides of ergot alkaloids were isolated as naturally occurring products [40] and a large series of them has been prepared by chemical and enzymatic methods [41]. 

In recent years enzymatic methods for certain glycosidations have been applied to the construction of a number of oligosaccharides [20,21], With their proved advantages of... 

Recently, a large series of glycosides of ergot alkaloids was prepared using both chemical and enzymatic methods [131,132,133,134]. Preliminary results obtained indicate that some of these derivatives could have very interesting activities compared to their aglycons. 

Biocatalytic synthetic pathways are very attractive as they have many advantages such as mild reaction conditions, high enantio-, regio-, chemoselectivity and are nontoxic natural catalysts. In enzymatic methods for glycoside and saccharide synthesis no selective protection/deprotection steps are necessary and control of configuration at newly formed anomeric centers is absolute. 

The polymerization of 1 mentioned above should be compared with the enzymatic synthesis of chitin reported by Kobayashi and coworkers, in which an oxazoline derivative of A, A -diacetylchitobiose, the repeating unit of chitin was polymerized in the presence of chitinase enzyme via ring-opening addition process to give an artihcial chitin (Scheme 6) [5]. The method using an enzyme, however, may not enable synthesis of nonnatural-type aminopolysaccharide because the reaction catalyzed by chitinase enzyme is limited to the formation of (1 4)-P-glycosidic linkage. 

The structures of oligosaccharides and polysaccharides are usually determined by a combination of methods specific enzymatic hydrolysis to determine stereochemistry and produce smaller fragments for further analysis methylation analysis to locate glycosidic bonds and stepwise degradation to determine sequence and configuration of anomeric carbons. 

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