SELECTIVE CARBON-13 ENRICHMENT OF SIDE-CHAIN CARBONS OF GINKGO LIGNINTRACED BY CARBON-13 NUCLEAR-MAGNETIC-RESONANCE

Although carbon 13 nuclear magnetic resonance spectroscopy (C-13-NMR) is widely used in lignin structural studies, serious difficulties are encountered in the assignments of C-13 signals because of their extens ive overlaps resulting from the complex structure of lignin and of del icate detection of minor structures. To overcome these difficulties, s pecifically C-13-enriched precursors of lignin biosynthesis, coniferin -[side chain-beta-C-13] and coniferin-[side chain-gamma-C-13], were ad ministered to growing stems of ginkgo (Ginkgo biloba). The NMR analysi s of the milled wood lignins isolated from the newly formed xylem show ed that selective enrichment of specific carbons of protolignin in the cell wall was achieved without seriously disturbing the lignin biosyn thesis. The presence of saturated methylene side chains in the protoli gnin was shown for the first time by this selective enrichment techniq ue in combination with NMR analysis.