Previously it has been shown that glycerol can be regioselectively glucosylated by sucrose phosphorylase from Leuconostoc mesenteroides to form 2-O-alpha-D-glucopyranosyl-glycerol (Coedl et al., Angew. Chem. Int. Ed. 47 (2008) 10086-10089). A series of compounds related to glycerol were investigated by us to determine the scope of the alpha-glucosylation reaction of sucrose phosphorylase. Both sucrose and glucose 1-phosphate (GIP) were applied as glucosyl donor. Mono-alcohols were not accepted as substrates but several 1,2-diols were readily glucosylated, proving that the vicinal diol unit is crucial for activity. The smallest substrate that was accepted for glucosylation appeared to be ethylene glycol, which was converted to the monoglucoside for 69%. Using high acceptor and donor concentrations :up to 2.5 M), sucrose or GIP hydrolysis (with H2O being the 'acceptor') can be minimised. In the study cited above, a preference for glucosylation of glycerol on the 2-position has been observed. For 1,2-propanediol however, the regiochemistry appeared to be dependent on the configuration of the substrate. The (R)enantiomer was preferentialy glucosylated on its 1-position (ratio 2.5:1), whereas the 2-glucoside is the major product for (S)-1,2-propanediol (1:4.1). d.e.(p)s of 71-83% were observed with a preference for the (S)-enantiomer of the glucosides of 1,2-propanediol and 1,2-butanediol and the (R)-enantiomer of the glucoside of 3-methoxy-1,2-propanediol. This is the first example of stereoselective glucosylation of a non-natural substrate by sucrose phosphorylase. 3-Amino-1,2-propanediol, 3-chloro-1,2-propanediol, 1-thioglycerol and glyceraldehyde were not accepted as substrates. Generally, the glucoside yield is higher when sucrose is used as a donor rather than GIP. due to the fact that the released phosphate is a stronger inhibitor of the enzyme (in case of Cl P) than the released fructose (in case of sucrose). Essentially the same results are obtained with sucrose phosphorylase from Blfidobacterium adolescentis.
- catalyzed synthesis
- water activity