Isolation of 6-hydroxykynurenic acid from the tobacco leaf

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Abstract
6 -Hydroxyknurenic acid (4,6-dihydroxyquinoline-2-carboxylic acid, 6-HKA) was isolated in crystalline form from both green and cured tobacco leaves. A method for the determination of 6-HKA by paper chromatography and fluorimetry is described. The content of 6-HKA in the flowers, stem and roots of the tobacco plant was much lower than that in the leaf. The 6-HKA content increased throughout leaf development and senescence. 6-HKA was detected in the leaves of plants representing 11 out of 27 families sampled. 6-HKA was found to be devoid of antibacterial and antifungal activity, and was inactive in the Avena-coleoptile and cress-seed-germination tests. The presence of 6-HKA is taken as evidence in plants of the trypto-phan-catabolic pathway already known in mammals and microorganisms.