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)

Twelve monolignol (coniferyl alcohol, sinapyl alcohol and p-coumaryl alcohol) beta-glycosides (beta-glucosides, beta-galactosides, beta-xylosides and beta-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 beta-glucosides, beta-galactosides and beta-xylosides) and the 1,2-cis glycosides (the beta-mannosides) were synthesized by means of Koenig-Knorr glycosylation and beta-selective Mitsunobu glycosylation strategies, respectively. In addition, dihydromonolignol and p-hydroxybenzaldehyde derivative beta-glycosides were also prepared from the corresponding monolignol glycosides and their intermediates, respectively. The correlation observed for the C-1 beta-H-1 beta bonds of the sugar moieties in the HSQC spectra of the all beta-glycosides varied and were in the range of delta(C)/alpha(H) 96-104/ 4.7-5.4 ppm. Especially, it was found that the correlations derived from the C-1 beta-H-1 beta bonds of the guaiacyl and p-hydroxyphenyl beta-mannosides were close to those derived from the C-1 alpha-H-1 alpha bonds of the 4-O-methyl-alpha-D-glucuronic acid moieties described in the literature.