H-1-NMR STUDIES ON THE METHYLATION, PROTONATION, AND HYDRATION SITES IN SOME BENZO[B]NAPHTHYRIDINES (AZAACRIDINES)

The 300.13 MHz H-1 NMR spectra of the methylated and protonated 6(9)-m ethylbenzo[b][1,x]naphthyridines (x=5, 6, 7, 8) (5-methylazaacridines) were collected at 298 K in deuterated dimethyl sulfoxide and chlorofo rm, respectively. The methylation and protonation sites were assigned by comparisons of these data with those of the free bases. The results were compared with similar data for related heterocycles and showed t hat both methylation and protonation occur at the nitrogen in the oute r pyrido ring in all four series. The hydration site in some 2- and 3- azaacridines was determined by specific line broadening in their H-1 N MR spectra to be the same nitrogen as that involved in methylation and protonation. Variable temperature H-1 NMR demonstrated that the speci fic line broadening results from some changes of N-14 quadrupolar rela xation produced by the slow chemical exchange between unhydrated and h ydrated species. Deuterium exchange experiments indicated that the dir ect spin-spin interaction of a water proton and the protons alpha to t he hydrated nitrogen may also have some contribution.