Regioselective synthesis and characterization of 6-O-alkanoylgluconolactones

6-O-Alkanoylgluconolactones, a novel class of carbohydrate ester-linked surfactants containing a lactone head group, have been synthesized enzymatically from the unprotected aldonolactone. The synthesis was accomplished by regioselective esterification of glucono-1,5-lactones at C-6 by porcine pancreatic lipase in the solvent pyridine. These compounds were found to exhibit a sharp increase in solubility at 90–96°C but remained soluble well below their initial dissolution temperature, precipitating at 30–37°C. To determine the cause of this unusual solubility behavior, the composition of the precipitate was characterized by 1H and 13C NMR, and GC-MS. Analysis of the precipitates identified the material as a hydrolysate containing alkanoylglucono-1,5-lactone, alkanoylglucono-1,4-lactone and alkanoylgluconic acid. The hydrolysis and isomerization of the lactone gave a mixture of compounds that are more soluble than the corresponding pure alkanoylglucon-δ-lactone.