Enzymatic synthesis of 6- and 6′-O-linoleyl-α-d-maltose: From solvent-free to binary ionic liquid reaction media

The eco-efficient lipase catalyzed synthesis of sugar fatty acid ester surfactants from renewable commodities is a stimulating challenge in biotransformation. The biocatalytic investigations went from solvent-free and minimal ionic liquid use to bulk organic solvents, and binary solvents thereof. Disaccharide maltose was acylated with linoleic acid (C18:2) on the primary O-6,6′ hydroxyl functions. The ionic liquid [emim][MeSO3] and the potentially renewable acetone enabled best conversions. Binary solvents like acetone/DMF and [emim][MeSO3]/[bmpyr][PF6] tended to double conversions. The lipase selection is also crucial and the enzymes Pseudomonas cepacia and immobilized Candida antarctica allowed highest yields in a screening with 10 different lipases. Also other non-solvent parameters such as reaction time and molecular sieve content improved maltose transformation further up to 82%. Analysis by HPLC, ESI-MS, and NMR indicated the formation of mono-6 or 6′-O-linoleyl-α-d-maltose as a mixture of two regioisomers in a 1.4:1 ratio. From an applied point of view, the best solvent is acetone. Unlike ionic liquids and binary mixtures, it is easily removable from reaction mixtures. Moreover, acetone is to some degree a green solvent as it can be produced directly from renewable feedstock.