Untersuchungen über den Einbau methylierter Vorstufen in die Isoflavone der Kichererbse

In order to determine at what stage in the biosynthesis of biochanin A (5.7-dihydroxy-4′-methoxyisoflavone) and formononetin (7-hydroxy-4′-methoxyisoflavone) the methylation of the 4′-hydroxygroup occurs, the incorporation of p-methoxy-cinnamic acid-[3-14C-methyl-T], 4-methoxy-2′.4′-dihydroxychalcone- [β-14C-methyl-T] and a number of unmethylated precursors into the isoflavones of chana seedlings (Cicer arietinum L.) was compared. p-Methoxy-cinnamic acid and 4.2′.4′-Trihydroxychalcone were found to be the best precursors. Although the incorporation of p-methoxy-cinnamic acid was very good (incorporation rate 6.2%) the T/14C ratio dropped by 95% upon incorporation into the isoflavones, a fact which showed that a rapid demethylation takes place in the plants. In addition, kinetic experiments were carried out with p-methoxycinnamic acid- [3-14C-methyl-14C-methyl-T] and 4-methoxy-2′.4′-dihydroxychalcone- [β-14C-methyl-14C-methyl-T]. But in this case also the rapid demethylation did not permit a definite conclusion to be drawn as to the stage in the biosynthesis at which the methylation step occurs. The very good incorporation of 4.2′.4′-trihydroxycalcone- [β-14C] into the isoflavones (5,3% incorporation, dilution 61), however, shows that methylation can occur at a late stage in the biosynthesis.