ON THE BEHAVIOR OF MONOLIGNOL GLUCOSIDES IN LIGNIN BIOSYNTHESIS .2. SYNTHESIS OF MONOLIGNOL GLUCOSIDES LABELED WITH H-3 AT THE HYDROXYMETHYL GROUP OF SIDE-CHAIN, AND INCORPORATION OF THE LABEL INTO MAGNOLIA AND GINKGO LIGNIN

For selective radio-labeling of specific structural units of protolignin in the cell wall, three kinds of precursor of lignin biosynthesis, p-glucocoumaryl alcohol, coniferin and syringin labeled with H-3 at the hydroxymethyl group of side chain (gamma-position) were synthesized, and administered to magnolia and ginkgo trees. The newly formed radioactive lignin gave thioacidolysis products in which radioactivities were distributed not only in the C6-C3 units corresponding to the administered precursor but also other C6-C3 units. These results indicate that the modification of aromatic ring moiety occurs among the intermediates which retain the gamma-H-3. It suggests a new mechanism of modification of aromatic ring may participate in the pathway of lignin biosynthesis.