Biocatalytic synthesis of ultra-long-chain fatty acid sugar alcohol monoesters

Abstract

An array of ultra-long-chain fatty acid sugar alcohol monoesters, with behenic acid as an acyl representative and sugar alcohols altered from ethylene glycol to glycerol, erythritol, pentaerythritol, arabitol, xylitol and sorbitol, were enzymatically synthesized in high purity and selectivity. The molecular structures of the synthetic compounds were confirmed by ¹H NMR, FT-IR and MS analysis, and the thermal properties were primarily characterized by DSC analysis. The molecular packing and thermal properties of synthetic sugar alcohol monobehenates (SAMBs) were investigated by Temp-Ramp-FT-IR. For in vivo application purposes, the enzymatic lipolysis of synthesized SAMBs was examined by a PPL (porcine pancreatic lipase)-mediated in vitro digestion test, and improved resistance of most SAMBs to enzymatic lipolysis, in comparison to glycerol monopalmitate, was observed. FT-IR spectroscopic analysis of the thermotropic phase transitions of the synthetic SAMBs indicated that the thermal collapse temperatures do not vary significantly as the polar head alters, suggesting their thermostabilities are largely governed by hydrophobic interactions among the alkanyl chains, while the size, properties and volume of the polar heads may determine the packing patterns. Systemic mapping of the structure–property–function relationship of SAMBs revealed the potential of these compounds for multipurpose applications. Ethylene glycol and glycerol monobehenates enable orthorhombic packing, and could find applications in cosmetic formulation, whereas sorbitol monobehenate is capable of forming stable surfactant-free nanoparticles, which could be excellent excipients for solid lipid nanoparticles for use as delivery cargo for drugs and food ingredients.