Biosynthesis of a Cyclic Tautomer1of (3-Methylmaleyl)acetone from 4-Hydroxy-3,5-dimethylbenzoate byPseudomonassp. HH35 but Not byRhodococcus rhodochrousN75

Here we report that the bacterial catabolism of 4-hydroxy-3,5-dimethylbenzoic acid 1 takes a different course inRhodococcus rhodochrousN75 andPseudomonassp. strain HH35. The former organism accumulates a degradation metabolite of the acid which we isolated and identified as 2,6-dimethylhydroquinone 2. The latter bacterial strain converts the acid and the hydroquinone into a dead-end metabolite. This novel compound was characterised unequivocally by mass spectrometry and1H and13C NMR and UV spectroscopy as 4-acetonyl-4-hydroxy-2-methylbut-2-en-1,4-olide 4, a cyclic tautomer of (3-methylmaleyl)acetone, which exists as the enol carboxylate form 3 in aqueous solution.