NMR Spectra of Tetracyclines: Assignment of Additional Protons

The pH dependence of carbon-13 nuclear magnetic resonance shifts of tetracycline. Microscopic dissociation constants

“…The pH dependences of the C-l 1, C-l la, C-12, and C-12a carbon signals are shown in Figures 2, 3, and 4. In the pH [6][7][8][9][10][11][12][13] range the C-l 1 and C-lla signals were shifted upfield 10.4 and 4.5 ppm, respectively, while the C-12 and C-12a signals were shifted downfield 13.0 and 2.8 ppm, respectively. Since the C-12 signal was observed to have a very large shift in this pH range, it seems reasonable to assign the deprotonation to the C-12 hydroxyl rather than the C-10 hydroxyl as reported by Rigler et al 12 Deprotonation of the C-10 hydroxyl would be expected to manifest itself by a shift of greater than 0.4 ppm because the hydroxyl bearing carbon in phenol has been reported to shift 11 ppm over pH 1-13.26 The carbon signals that were observed to have very small shifts over the entire pH range were the C-6, C-6 methyl, and C-10.…”

Three new complexes of platinum(II) with doxycycline, oxytetracycline and chlortetracycline and their antimicrobial activity

“…[17][18][19][20][21][22][23] Two regions in Dox 1 H NMR spectrum are of special interest for the attribution of metal coordination sites: the D ring aromatics and the dimethylamino, C4, C4a, and C6 protons on ring A. These protons are not labile and their chemical shift, which is very sensitive to metal coordination, can be distinguished if the coordination occurs through O10 and O12 sites or through A ring sites.…”