Synthesis and fundamental HSQC NMR data of monolignol β-glycosides, dihydromonolignol β-glycosides and p-hydroxybenzaldehyde derivative β-glycosides for the analysis of phenyl glycoside type lignin-carbohydrate complexes (LCCs)

Abstract

Abstract Twelve monolignol (coniferyl alcohol, sinapyl alcohol and p-coumaryl alcohol) β-glycosides (β-glucosides, β-galactosides, β-xylosides and β-mannosides) were synthesised to obtain fundamental NMR data for the analysis of phenyl glycoside type lignin-carbohydrate complexes (LCCs). That is, the 1,2-trans glycosides (the β-glucosides, β-galactosides and β-xylosides) and the 1,2-cis glycosides (the β-mannosides) were synthesized by means of Koenig-Knorr glycosylation and β-selective Mitsunobu glycosylation strategies, respectively. In addition, dihydromonolignol and p-hydroxybenzaldehyde derivative β-glycosides were also prepared from the corresponding monolignol glycosides and their intermediates, respectively. The correlation observed for the C1β-H1β bonds of the sugar moieties in the HSQC spectra of the all β-glycosides varied and were in the range of δC/δH 96–104/4.7–5.4 ppm. Especially, it was found that the correlations derived from the C1β-H1β bonds of the guaiacyl and p-hydroxyphenyl β-mannosides were close to those derived from the C1α-H1α bonds of the 4-O-methyl-α-D-glucuronic acid moieties described in the literature.