Transglycosylic Reactions of Deoxysugars. Biosynthesis of Deoxy Analogues of Starch

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Abstract
The biosynthesis of starch was investigated in the reaction catalyzed by plant α(1→4)‐glucan phosphorylase using α‐d‐glucopyranosyl phosphate and its deoxy analogues as substrates. It was found that the hydroxyl groups at the positions C‐2, C‐3, C‐4 and C‐6 in the glucose moiety of the molecule of α‐d‐glucopyranosyl phosphate are not essential for its substrate properties in the transglycosylic reaction. The affinity of plant α(1→4)‐glucan phosphorylase and the rate of hexose incorporation into α(1→4)‐glucan decreases in the following sequence: α‐d‐glucopyranosyl phosphosphate, 2‐deoxy‐, 6‐deoxy, 4‐deoxy, and 3‐deoxy‐α‐d‐glucopyranosyl phosphate. The deoxyglucosyl analogues of α‐d‐glucosylpyranosyl phosphate act as competitive inhibitors on the elongation reaction of the α(1→4) chains of starch. It was found that more than one residue of 2‐deoxy‐d‐glucose or 6‐deoxy‐d‐glucose can be incorporated into the nonreducing terminus of α(1→4)‐glucan chains of starch.