Fig 3.

Identification of the 228.0768 m/z product. (A) The MS/MS fragmentation pattern of the [M+H]⁺ molecular ion 228.0768 m/z from urine is consistent with potential products that would arise from fragmentation of an INH-nicotinamide adduct (4-INN). The masses noted for the structures of the fragmentation products are the predicted m/z of the positive ion. All of the observed fragmentation masses were within 6 ppm of the predicted masses. (B) The hypothesized hydrolysis of an INH-NAD⁺ adduct would lead to an INH-nicotinamide adduct in an open (4-INN) or cyclic {1-hydroxy-1-(pyridin-4-yl)-1H-pyrrolo[3,4-c]pyridin-3(2H)-one} configuration.