Purification of PAGs
To verify the universality of the enzymatic esterification method, the optimal conditions of synthesis of CG obtained above were used to synthesize FG and p -HCG. The optimal conditions were as follows: 0.01 mol PAs (CA, FA, orp -HCA) was reacted with 1.5 mol of glycerol catalyzed by 25 % of Lipozyme 435 (relative to the weight of total substrates) at 80oC under 86.7 kPa for 10 h. Then the enzyme was filtered off. The filtrate was extracted with ethyl acetate (reaction mixture/ethyl acetate, 1:1, V/V) for three times. The extracted organic phase was combined and concentrated using a rotary evaporator at 50oC. When the liquid change to be turbid, the liquid was crystallized at ambient temperature for 24 h. The solid was carefully separated after centrifugation (3,000 rpm) for 10 min. Then washed with distilled water and subsequently freezing dried. The liquid was concentrated and separated by silica gel column chromatography using chloroform/ toluene/ methanol/ acetate acid (CG, 32:20:10:1; FG andp -HCG, 32:20:1.5:1) as mobile phase. After vacuum evaporation, the white solid was obtained. Combined with the freeze dried solid, 2.16 g of CG (85.0 % of isolated yield), 2.20 g of FG (82.1 % of isolated yield) and 1.92 g of p -HCG (80.7% of isolated yield) were obtained respectively. The purity of isolated PAGs were reconfirmed by TLC and HPLC.