Intramolecular acyl migration and enzymatic hydrolysis of a novel monoacylated ascorbic acid derivative, 6-O-dodecanoyl-2-O-α-d-glucopyranosyl-l-ascorbic acid

Increased yield of 2-O-α-d-glucopyranosyl-l-ascorbic acid synthesis by α-glucosidase using rational design that regulating the ground state of enzyme and substrate complex

BACKGROUND

α-Glucosidase (AG) is a bifunctional enzyme, it has a capacity to synthesize 2-O-α-d-glucopyranosyl-l-ascorbic acid (AA-2G) from l-ascorbic acid (L-AA) and low-cost maltose under mild conditions, but it can also hydrolyze AA-2G, which leads to low synthesis efficiency of AA-2G.

MAIN METHODS AND MAJOR RESULTS

This study introduces a rational molecular design strategy to regulate enzymatic reactions based on inhibiting the formation of ground state of enzyme-substrate complex. Y215 was analyzed as the key amino acid site affecting the affinity of AG to AA-2G and L-AA. For the purpose of reducing the hydrolysis efficiency of AA-2G, the mutant Y215W was obtained by analyzing the molecular docking binding energy and hydrogen bond formation between AG and the substrates. Compared with the wild-type, isothermal titration calorimetry (ITC) results showed that the equilibrium dissociation constant (KD ) of the mutant for AA-2G was doubled; the Michaelis constant (Km ) for AA-2G was reduced by 1.15 times; and the yield of synthetic AA-2G was increased by 39%.

CONCLUSIONS AND IMPLICATIONS

Our work also provides a new reference strategy for the molecular modification of multifunctional enzymes and other enzymes in cascade reactions system.

Intramolecular acyl migration and enzymatic hydrolysis of 2-O-α-D-glucopyranosyl-6-O-(2-pentylheptanoyl)-L-ascorbic acid

2-O-α-D-Glucopyranosyl-6-O-(2-pentylheptanoyl)-L-ascorbic acid (6-bDode-AA-2G) underwent an intramolecular acyl migration to yield approximately 12% of 2-O-α-D-glucopyranosyl-5-O-(2-pentylheptanoyl)-L-ascorbic acid (5-bDode-AA-2G) in neutral solutions for 3 days. In small intestine homogenate from guinea pigs for 12h, 6-bDode-AA-2G, which hardly underwent acyl migration to give 5-bDode-AA-2G, was predominantly hydrolyzed with α-glucosidase and then with esterase to ascorbic acid.

Regioselective monoacylation of 2-O-α-D-glucopyranosyl-L-ascorbic acid by a polymer catalyst in N,N-dimethylformamide

6-O-Dodecanoyl-2-O-α-D-glucopyranosyl-L-ascorbic acid (6-sDode-AA-2G) was synthesized from 2-O-α-D-glucopyranosyl-L-ascorbic acid and lauric anhydride with a polymer catalyst, poly(4-vinylpyridine), in N,N-dimethylformamide without the introduction of protecting groups. The optimum reaction conditions enabled 6-sDode-AA-2G to be synthesized in a yield of 49.7%. The yield and the regioselectivity in this method were far superior to those in our previous method by using an enzyme. The polymer catalyst could be recycled more than five times without any significant activity loss.