Lignin labeled precursors

Noguchi et al. (8) synthesized precursors of lignin biosynthesis (i.e., coniferyl and sinapyl alcohols) in which the side chain and methoxy groups were doubly labeled by and H, prepared the DHP (synthetic lignin) from them, and treated the DHP with the laccase. These results showed that about 25% of Hs of the a- and -positions were removed in a ratio of one to one, respectively, and that the methoxyl group of a syringyl unit was de-methylated easier than that of a guaiacyl. 

Table I. Use of Doubly labeled Guaiacyl Lignin Precursors in Lignin Biosynthesis Studies...

The role of coniferyl alcohol as the immediate precursor of softwood lignin has been demonstrated by using 14C labeling. Administration of labeled coniferyl alcohol as /3-glucoside (coniferin) to seedlings of spruce results in the exclusive formation of radioactive lignin. 

Hydrogenolysis has also found use in a lignin biosynthesis study in which 14C-labeled lignin precursors were administered to wheat plants and maple twigs and ultimately recovered in the form of the typical lignin hydrogenolysis products, dihydroconiferyl and dihydrosinapyl alcohols (Brown and Neish 1959). 

Lignin Models. l-(4-Hydroxy-3-methoxyphenyl)-2-(2-methoxyphcnoxy)propan-1,3-diol (VII). The 4-benzyloxy-a-keto precursor to VII was prepared as previously described (16), Treatment of this compound (70 mg, 0.17 mmole) in THF(2 mL)/H2O(0.1 mL) with 10% Pd/C under H2 (balloon), with stirring, for 3 hours gave a colorless oil (49 mg, 91%) which was shown to be VII by comparison (TLC and NMR) with authentic material. A 70 30 erythroAhreo ratio was indicated by 13C-NMR. The XH and 13C-chemical shifts (CDCI3) have been previously published (17), Compound VII enriched with 13C at Ca was prepared from labeled acetovanillone, which was prepared from guaiacol and acetic acid-l-13C by a procedure analogous with that described previously (16), The 7-13C enriched compound was made by simply utilizing 13C-formaldehyde in the synthesis. 

The use of methionine doubly labeled in the methyl group was subsequently extended to experiments with higher plants by Byerrum, Ball, and their co-workers. It was shown that the methyl group of methionine was a precursor of the N-methyl of nicotine in tobacco (Dewey et al., 1954), the methyl ether groups of lignin in barley and tobacco (Byerrum et al., 1954), and the methyl esters of pectinic acid in radish (Sato et ah, 1957). In none of these methylations was the deuterium ratio in... 

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