3. Stereochemistry of glycosyl transfer: interaction with "glucose" active site of the enzyme

The analysis of stereochemical details of the transglycosylation reaction can be pointed out by taking into consideration the importance of the interaction of the OH-containing molecule with active site of the glycosyl-enzyme during enzymatic process Ref.17. This study conducted using polyols of Fig.1B

is very informative in that these structures mimic the glucose molecule in the interaction at the glucopyranose binding site of the enzyme Ref.18. The effectiveness of these interactions for the enzyme from Sulfolobus is based experimentally from the results of salicin glycosylation (R'OH = salicin, Scheme 1.

The analysis of disaccharides formed shows that the glucose molecule is always transferred to the free -OH groups of original glucose of salicin with a certain degree of selectivity (C-6, 63%) and not to the free hydroxymethilene of aglycone present on the aromatic ring. This result indicates a possible role of interactions of original glucose of substrate with active site of the enzyme in drawing its hydroxymethilene group far from the glycosylating site of the enzyme Ref.15. However, this -CH2OH is the only glycosylated group when the aglycone (R'OH = 2-OH benzyl alcohol, Scheme 1) is used as acceptor.

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