Enzymatic synthesis and antitumor evaluation of mono- and diesters of 3-O-β-D-galactopyranosyl-sn-glycerol

Lipase-catalyzed synthesis of mono- and diesters of 3-O-β-D-galactopyranosyl-sn- glycerol (β-GG) with caproic acid was performed in acetone. The simultaneous production of 1(6’)-monoesters and 1,6’-diesters of β-GG was achieved in this reaction. In order to improve the yield of β-GG esters, four process parameters, enzyme concentration (15 ∼ 25 mg/mL), and substrate molar ratio (caproic acid: β-GG= 1.60 ∼ 2.00 mmol: 0.10 mmol), reaction temperature (40 ∼ 60 °C), and reaction time (8 ∼ 12 h), were optimized via response surface methodology (RSM) employing a three-level-four-variable central composite design. Results showed that enzyme concentration had the most significant (p < 0.0001) effect on the synthesis of β-GG esters. The optimal reaction conditions in acetone were given as follows: Novozyme435 concentration 18.65 mg/mL, molar rate of caproic acid to β-GG 19.46:1, reaction temperature 48 °C, and reaction time 9.83 h. The yield of β-GG esters reached 88.08% under above optimized conditions, which was very close to the predicted value 87.95%. The molar ratio of monoester to diesters was 0.39:0.61. β-GG esters with other fatty acyl chains were synthesized based on the optimized conditions. In vitro antitumor activity indicated that the antitumor activity of β-GG esters was dependent on the nature of fatty acids, such as the length of acyl chain, the degree of saturation, as well as the number of acyl chain.