Oxidative transformation of aminodinitrotoluene isomers by multicomponent dioxygenases

The electron-withdrawing nitro substituents of 2,4,6-trinitrotoluene (TNT) make the aromatic ring highly resistant to oxidative trans formation. The t ypical biological transformation of TNT involves reduction of one or more o f the nitro groups of the ring to produce the corresponding amine. Reductio n of a single nitro substituent of TNT to an amino substituent increases th e electron density of the aromatic nucleus considerably. The comparatively electron-dense nuclei of the aminodinitrotoluene (ADNT) isomers would be ex pected to be more susceptible to oxygenase attack than TNT. The hypothesis was tested by evaluating three nitroarene dioxygenases for the ability to h ydroxylate the ADNT isomers. The predominant reaction was dioxygenation of the ring to yield nitrite and the corresponding aminomethylnitrocatechol. A secondary reaction was benzylic monooxygenation to form aminodinitrobenzyl alcohol. The substrate preferences and catalytic specificities of the thre e enzymes differed considerably. The discovery that the ADNT isomers are su bstrates for the nitroarene dioxygenases reveals the potential for extensiv e bacterial transformation of TNT under aerobic conditions.