Enzymatic production of modified 2‐dodecyl‐sophorosides (biosurfactants) and their characterization

Alkyl sophorosides, a special type of sophorolipids, can be produced using Candida bombicola cultures with glucose as main carbon source and 2-dodecanol as co-substrate. The dominating component, 2-dodecyl-sophoroside SL-E2-12, was purified via medium pressure liquid chromatography (MPLC) and used as substrate for further enzymatic modifications. Using β-glucuronidase in aqueous media the first modification gave a glycosidic cleavage of the acetyl glucose unit leading to 2-dodecyl-glucoside GL-A2-12. In a subsequent lipase-catalyzed acylation with sebacic acid in toluene this compound was functionalized regioselectively at the primary C-6′ position of glucose. Similar lipase-catalyzed reactions in toluene, but now using SL-E2-12 as acyl acceptor and unusual hydroxyl fatty acids – 3-hydroxy decanoic acid and 17-hydroxy stearic acid – as acyl donors, resulted in mono- and diacylations of primary hydroxyl positions of the sophorose unit (C-6′ and C-6′′) as shown by NMR and MS studies. In physicochemical characterization experiments the new glycoconjugates lowered the surface tension of water from 72 to 27–32 mN/m. Moreover it was observed that the new products inhibit the growth of particular Gram-positive bacteria. Additionally they indicate potential for anti-tumor promoting activity. Practical applications: According to literature data 2-alkyl-sophorosides can be produced using Candida bombicola cultures with yields of more than 20 g/L. Based on this starting material, 2-dodecyl-sophoroside, several regioselective enzymatic modifications were performed. Initially, β-glucuronidase catalysis in aqueous buffer solution gave 2-dodecyl-glucoside which was then successfully acylated at the C-6 position of glucose by lipase catalysis using a common dicarboxylic acid, sebacic acid. The resulting free carboxylic function of the acidic derivative opens up the possibility of achieving additional chemo-enzymatic reactions at this position for conversion, for instance, into polyesters. In addition lipase catalysis in organic solvents of 2-dodecyl-sophoroside allows acylation with unusual hydroxyl fatty acids of microbial origin. Physicochemical studies showed that these new glycoconjugates may be of interest for the cosmetic industry due to moisture conservation of the skin. For practical applications the conditions of the above biocatalytic reactions have been improved and scaled up.