Abstract
An efficient and convenient chemoenzymatic route for the synthesis of novel phenolic mono-, di- and oligosaccharide esters is described. Acetal derivatives of glucose, sucrose, lactose and inulin were obtained by chemical synthesis. The fully characterized pure sugar acetals were subjected to enzymatic esterification with 3-(4-hydroxyphenyl) propionic acid (HPPA) in the presence of Novozyme 435 lipase as a biocatalyst. The aromatic esters of alkyl glycosides and glucose acetal were obtained with good esterification yields, characterized by mass spectrometry (MALDI-TOF MS), infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (1H NMR, 13C NMR). The synthesis of aromatic esters of disaccharide acetals was successful only for the enzymatic esterification of sucrose acetal. The new chemoenzymatic route allowed the synthesis of novel aromatic esters of inulin as the inulin monoacetal monoester and diester and the inulin diacetal monoester with a polymerization degree of two, as well as the inulin monoacetal monoester with a degree of polymerization of three, were obtained by enzymatic acylation of inulin acetals with HPPA. These compounds could represent a new class of sugar ester surfactants with enhanced bioactivity, antioxidative and antimicrobial properties and with potential application in drug delivery systems.
Highlights
Synthetic strategies for sugar esters are needed because the isolation, profiling, characterization and quantification of naturally occurring acylated sugars, important metabolites of plants, are difficult and laborious processes that require complex protocols [1]
Acylations were performed in 2 mL glass vials, charged with a mixture of 1-octanol (0.05 m/mol), aromatic compound (HPPA, HPPME, ferulic acid, caffeic acid, p-coumaric, gallic acid, vanillic acid, ethyl ferulate, propyl gallate or protocatechuic acid ethyl ester) (0.15 m/mol), n-decosan as internal standard (1 mg), tert-butanol (1 mL) and native lipase from C. antarctica B, C. rugosa, T. lanuginosus, A. niger, R. oryzae, pig pancreas or wheat germ (10 mg)
Prior to the enzymatic esterification of sugar derivatives, several aromatic substrates and lipases were screened in reaction conditions resulting from preliminary experiments
Summary
Synthetic strategies for sugar esters are needed because the isolation, profiling, characterization and quantification of naturally occurring acylated sugars, important metabolites of plants, are difficult and laborious processes that require complex protocols [1]. As chemical pathways are not environmentally friendly and require harsh reaction conditions that can lead to multiple secondary products, the use of biocatalysts could be an alternative route [2,3]. Due to their unique properties, enzymes offer effective and sustainable possibilities for utilization in the carbohydrate field. The use of immobilized lipases is Processes 2020, 8, 1638; doi:10.3390/pr8121638 www.mdpi.com/journal/processes
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