4-Hydroxy-3-methyl-2(1)-quinolone, originally discovered from a plant, produced by a soil bacterium of the genus sp.: determination of a preferred tautomer and antioxidant activity.

4-Hydroxy-3-methyl-2(1)-quinolone (), a molecule known for a long time and recently discovered from a plant without providing sufficient evidence to support the structure, was isolated from a fermentation extract of sp. 3Y-MMP isolated from a soil by a Zn enrichment culture. Detailed spectroscopic analyses by MS and NMR, combined with C chemical shift comparison with literature values of the related compounds and a synthetic preparation of , allowed its first full NMR characterization and identification of 2-quinolone but not 2-quinolinol () as the preferred tautomer for this heterocyclic system. While the metal-chelating activity was negligible, compound at 10 μM, a concentration lower than that in liquid production cultures, quenched hydroxy radical-induced chemiluminescence emitted by luminol by 86%. Because some species are pathogenic to plants and animals, the above result suggests that is a potential antioxidant to counteract reactive oxygen species-based immune response in the host organisms.