Enzymatic Synthesis of Glucose‐ and Xylose Laurate Esters Using Different Acyl Donors, Higher Substrate Concentrations, and Membrane Assisted Solvent Recovery

Abstract

Glucose‐ and xylose laurate esters are enzymatically synthesized using equimolar substrate concentrations in 2‐methyl‐2‐butanol, comparing free lauric acid with methyl‐ and vinyl‐laurate as acyl donors. All reactions result in ≥70% acyl donor conversions after 72 h but the activated donors are also partially hydrolyzed to lauric acid, highlighting the difficulty in controlling water presence in this particular reaction system. The esterification of xylose generates a complex product profile, with several regioisomers of monoesters and diesters. The esterification of glucose is quite selective, forming mainly the 6‐O monoester (≥96%) with a small presence of two diester isomers (4%). Increasing substrate concentration up to 800 millimoles kg−1 results in lower conversion values (down to 58%) but shows that the reaction proceeds successfully even in the presence of high amounts of insoluble glucose. However, the reaction is less selective and the proportion of diester increases, becoming up to 46% (molar fraction) of the final product. Solvent recovery after esterification can be achieved by organic solvent nanofiltration through a polymeric membrane able to retain ≥80% of all reaction substrates and products. Practical Applications: The use of high substrate concentrations during the enzymatic synthesis of sugar ester biosurfactants leads to product titers that are more industrially appealing, without the need to find a solvent that can solubilize all initial substrate. The sustainability of the enzymatic conversion at mild temperatures can be enhanced by recycling of the reaction solvent through organic solvent nanofiltration, an energy efficient alternative to other traditional methods like distillation.

Improving the environmental compatibility of enzymatic synthesis of sugar-based surfactants using green reaction media

“…1.7-yield increase) and regioselectivity towards monoesterification on the primary hydroxyl of glucose. Moreover, the yields obtained in MeTHF-3-one were competitive compared to the rates obtained previously and more recently in 2M2B [41,43].…”

“…In all cases, glucose laurate mono-ester (C18H34O7) is evidenced by RT = 2.88 -2.98 min, [M + Na] + m/z 385.220 and [MM+Na] + m/z 785.445 with the presence of both anomers [27] (Figure S3). 2021) reporting up to 4% of diester synthesized in 2M2B [43]. In MeTHF-3-one, the selectivity of the reaction seems exclusively orientated toward monoester synthesis.…”

“…2M2B has often been presented as a reference solvent for this type of reaction. It seems to receive a renewed interest in recent studies despite physicochemical properties far away from durability criteria [42,43]. Based on literature data, we firstly set the following experimental conditions as a basis for comparison with 2M2B: equimolar ratio of lauric acid/glucose, 100 g.L -1 of molecular sieve, 25 g.L -1 of Novozym435 ® , 50 °C, 350 rpm.…”

Ultrasound-assisted enzymatic synthesis of xylitol fatty acid esters in solvent-free conditions

“…Analogous results were obtained for both 1:1 and 1:2 (mol/mol) xylitol/fatty acid ratios. Similarly, it was described how the acyl donor with the longest alkyl chain provided the highest conversion rate in the biocatalytic synthesis of fatty acid glucose esters from different fatty acyl donors [9] . At this point, it should be noted that Candida antarctica lipase B (CALB) contains a flexible lid that undergoes a large conformational change when transforming hydrophobic substrates [32].…”

“… Entry Acyl acceptor Acyl donor Product Solvent Reaction conditions Yield (%) Ref. 1 Glucose Vinyl palmitate Glucosyl palmitate ACN, THF or Acetone 45 °C, 72 h 100 [9] 2 Glucose Vinyl Laurate Mixture of glucosyl mono- and di-laurate 2-methyl-2-butanol 60 °C, 120 h 96 (83) b [10] 3 Xylitol Butanoic anhydride Xylityl 1,5-di-butyrate ACN or THF 35 °C, 12 h 80 [11] 4 Xylitol Oleic acid Mixture of Xylityl monoacyl-, diacyl- and triacyl esters 2-Methyl-2-propanol/DMSO 80:20 (v/v) 45 °C, 24 h 100 (73) b [12] 5 Xylitol Decanoic acid Lauric acid Myristic acid Mixture of xylityl monoacyl- and diacyl esters t-Butanol/Pyridine, 45:55 (v/v) 45 °C, 20 h 41 (30) b [13] 6 Xylitol a Lauric acid Butiric acid Xyliltyl monoacyl ester t-Butanol 45 °C, 24 h 86 [14] 7 Glucose Vinyl laurate Vinyl mirstate Palmitic acid Glucosyl monoacyl ester [Bmim][BF 4 ] / t-Butanol, 60:40 (v/v) [Bmim][PF 6 ] / t-Butanol, 60:40 (v/v) 60 °C, 72 h 90 [15] 8 Glucose Fructose Sucrose Vinyl laurate Monolaurate of sugar [Bmim][Tf ...…”