Selective Enzymatic Esterification of Lignin-Derived Phenolics for the Synthesis of Lipophilic Antioxidants.

Lignin is an abundant and renewable source of phenolic compounds that can be used as natural antioxidants to substitute synthetic, petroleum-based alternatives. The development of lignin depolymerization techniques has improved the accessibility of low-molecular-weight phenolic fractions with enhanced antioxidant activity compared to native lignin. The selective esterification of the aliphatic OH groups in these compounds is necessary in order to increase their compatibility with hydrophobic product matrixes, while preserving their antioxidant capacity.

Aldehyde-Assisted Lignocellulose Fractionation Provides Unique Lignin Oligomers for the Design of Tunable Polyurethane Bioresins.

Thanks to chemical stabilization, aldehyde-assisted fractionation (AAF) of lignocellulosic biomass has recently emerged as a powerful tool for the production of largely uncondensed lignin. Depolymerization of AAF lignin via ether cleavage provides aromatic monomers at near theoretical yields based on ether cleavage and an oligomeric fraction that remains largely unexploited despite its unique material properties. Here, we present an in-depth analytical characterization of AAF oligomers derived from hardwood and softwood in order to elucidate their molecular structures.

Synthesis of Enantiopure Constrained α,β-Cycloaliphatic Cystines via Diels-Alder Reaction with Homochiral Thiazolines.

The behavior of homochiral 2,3-dihydrothiazoles, easily available from l-cysteine in Diels-Alder reaction with different dienes, "en route" to sterically constrained modified cystines, has been studied. The oxidation level of the sulfur atom of the heterocyclic ring was crucial for the course of the reaction. Whereas 2,3-dihydrothiazoles did not lead to Diels-Alder adducts, 1-oxide and 1,1-dioxide derivatives afforded the exo adduct enantiopurely in high yields and diastereoselectivities.