Qingxun Song

Repeated use of immobilized Gluconobacter oxydans cells for conversion of glycerol to dihydroxyacetone.

Abstract Dihydroxyacetone (DHA) is of great interest in the fine chemical and pharmaceutical industry; therefore, the discovery of suitable biocatalysts for the efficient production of it is very necessary. In the experiment, Gluconobacter oxydans was immobilized in polyvinyl alcohol (PVA). Various parameters of the immobilized cells were investigated. The results have shown that the optimal conversion conditions by the immobilized cells were at 30°C and pH 6.0. The immobilized cells remained very active over the period of 14 days for storage and only lost 10% of its original activity. Repeated use of immobilized cells for conversion of glycerol to DHA was carried out in a 1.5 L stirred tank reactor, the average conversion rate was about 86%. Despite the high shear stress, bead shape was not affected, even after five consecutive conversion cycles. The regenerated biocatalyst could recover 90% of its initial activity.

Preparation of Optically Pure tert‐Leucine by Penicillin G Acylase‐Catalyzed Resolution

Abstract Penicillin G acylase, from Kluyvera citrophila, was used in kinetic resolution of DL‐ tert‐leucine. N‐phenylacetylated‐DL‐tert‐leucine, chemically synthesized from DL‐ tert‐leucine, was enantioselctively hydrolyzed by penicillin G acylase to obtain L‐tert‐leucine, D‐ tert‐leucine was prepared by acid‐catalyzed hydrolysis of the remaining substrate. The total yields of D‐ tert‐leucine and L‐tert‐leucine are 80.6% and 83.1%, respectively. The enantiomeric excess of the two products, D‐ tert‐leucine and L‐tert‐leucine, are 98.5% and 99%. This is a practical way for the preparation of D‐ tert‐leucine and L‐tert‐leucine.

Production of Gluconobacter oxydans Cells from Low‐cost Culture Medium for Conversion of Glycerol to Dihydroxyacetone

Abstract Gluconobacter oxydans could be immobilized as a biocatalyst for the conversion of glycerol to dihydroxyacetone. To reduce the production cost, the cells were produced from agricultural byproducts. Corn meal hydrolysate and corn steep liquor were employed to replace of sorbitol and yeast extract as medium for G. oxydans cell production. The optimal medium contained 80 g/L reducing sugar, 25 g/L corn steep liquor, and 10 g/L glycerol. The cell mass was about 4.22 g/L and the glycerol dehydrogenase activity was about 5.23 U/mL. For comparison, the cell mass was about 4.0 g/L and the glycerol dehydrogenase activity was about 5.35 U/mL cultured in sorbitol and yeast extract medium. These studies shown the corn meal hydrolysate and corn steep liquor medium was similar in performance to a nutrient‐rich medium, but the cost of production was only 15% of that cultured in sorbitol and yeast extract medium. It was an economical process for the production of G. oxydans cells as biocatalyst for the conversion of glycerol to dihydroxyacetone in industry.

Optimisation of enzymatic synthesis of cefaclor with in situ product removal and continuous acyl donor feeding

Enzymatic synthesis of cefaclor by penicillin acylase (PA) was carried out under kinetic control with in situ product removal (ISPR). We present a continuous acyl donor feeding strategy for enzymatic reactions. Using this strategy, the conversion of the antibiotic nucleus was improved from 65 to 91%, and the hydrolysis of phenylglycine methyl ester (PGME) was decreased. Side product (phenylglycine) production was less than half of that in the control batch. The ratio of synthesis to hydrolysis (S/H) in the process was kept stable for longer and at a higher level than in the control. This is a practical method for enzymatic synthesis of cefaclor.

Study of ibuprofen glucopyranoside derivative synthesis by Candida antarctica lipase in organic solvent.

Abstract The direct esterification of ibuprofen and methyl α‐D‐glucopyranoside in organic solvent by Novozym 435 was investigated in terms of the main variables controlling the process, including initial water activity (aw, 0.05–0.75), incubation time, (0‐168 h) and substrate concentration. The results showed that the lower initial aw values resulted in higher enzymatic activity and bioconversion yield. The most appropriate initial aw and incubation time were 0.06 and 144 h, respectively. The results also showed that the optimal ratio of ibuprofen to methyl α‐D‐glucopyranoside was 2.0. By optimizing these parameters, the yield increased about 50%. In addition, the product was confirmed to be methyl 6‐O‐(2′‐(4′‐isobutylphenyl) propionyl) D‐α‐glucopyranoside.

Enzymatic synthesis of ethyl-glucoside monooleate with lipase in solvent-free medium

Ethylglucoside monooleate was synthesized by esterification between ethylglucoside and oleic acid with immobilized lipase from Candida antarctica in a solvent-free system. It was shown that a stirred tank reactor was suitable for the enzymatic reaction process involving substrates with low miscibility, in which the biocatalyst was recycled five times without significant activity loss. Removal of the co-product, water, from the reaction medium by carrying out the reaction under reduced pressure benefited the esterification reaction and increased the monooleate yield up to 97% within 8 hours.