LIGNIN MODEL GLYCOSIDES - PREPARATION AND OPTICAL RESOLUTION

Synthetic protocols for the preparation of the hydroxy-3-methoxyphenyl )-2(2-methoxyphenoxy)propyl beta-D-glucopyranosides and corresponding xylopyranosides have been developed. Glycosylation of racemic xyphenyl )-3-hydroxy-2-(2-methyoxyphenoxy)propanone with the per-benzoylated py ranosyl bromides of D-glucose and D-xylose affords diastereomeric mixt ures of the beta-glycosides in up to 92% yield. Stereoselective reduct ion of the benzoyl ketone with Zn(BH4)(2) gives the protected erythro diastereomers (2R,3S and 2S,3R) of ydroxy-3-methoxyphenyl)-2-(2-methox yphenoxy)propyl beta-D-gluco- and -xylo-pyranosides. Reduction with ()- or (-)-DIP chloride affords the protected threo diastereomers (2S,3 S and 2R,3R) without any significant enantioselectivity. Deprotection then gives the desired lignin dimer-glycosides. The use of the pyranos ide to provide diastereomers leads to the enrichment (>90%) of several individual enantiomers using silica gel chromatography, and also allo ws the rapid assessment of enantiomeric purity by H-1 NMR spectroscopy .