1H and 13C NMR study of 2‐aminothiazole urinary tract carcinogens

Abstract

AbstractUsing 1H and 13C NMR, 13C‐labelled modifications of 2‐amino‐4‐(5‐nitro‐2‐furyl)thiazole (ANFT) and its N‐formyl analogue N‐[4‐(5‐nitro‐2‐furyl)‐2‐thiazolyl]formamide (FANFT), as well as the 5‐(S)‐substituted glutathione and N‐acetylcysteine conjugates of prostaglandin H synthase‐catalyzed peroxidative metabolism of ANFT were studied. 1H and 13C NMR chemical shifts, heteronuclear coupling constants, spin–lattice relaxation times (T1) and nuclear Overhauser enhancements (NOE) were obtained. Three‐bond coupling constants of the 13C‐labelled nucleus with the C‐5 protons of ANFT and FANFT were in close agreement but were absent in the conjugates owing to the 5‐substitution. Two‐bond coupling of the 13C‐labelled nucleus was observed with the amide proton of FANFT, but not with ANFT because of rapid exchange of the amine protons. Values of T1 were smaller in the conjugates than in FANFT or ANFT owing to their larger molecular weights. 1H spectra and NOEs provide further support for the prevalence of the 2‐aminothiazole tautomer over the 2‐iminothiazoline tautomer. Evidence is presented for a proton transfer of the C‐5 proton of ANFT, which proceeds over a time of the order of weeks in dimethyl sulphoxide and is autocatalytic. FANFT showed a different proton‐transfer reaction involving the amide proton, which occurs on a time scale of the order of days in dimethyl sulphoxide. The FANFT molecule revealed no evidence for transfer of its C‐5 proton, in contradistinction to ANFT. From a calculation of the percentage of the 13C relaxation due to the dipole–dipole mechanism, it can be concluded that for this class of sp2‐hybridized carbon (the C‐2 position of the 2‐aminothiazole system) a considerable portion of the relaxation is due to mechanisms other than dipolar.