Studies related to antitumor antibiotics. Part XXIV. High field 1H nmr analysis and conformations of saframycins A and C

Abstract
A detailed analysis of the high field (400 MHz) 1H nmr spectra of the basic antitumor antibiotics saframycin A and C in CDCl3, C6D6, and in aqueous DMSO solutions has been carried out. Selective double irradiation experiments permitted the unambiguous assignment of all the proton chemical shifts and coupling constants. Consideration of the magnitudes of the latter together with specific nOe experiments permits assignment of molecular geometry and average conformations in solution. Selective shifts occurring in DMSO–D2O solutions upon addition of CF3COOD identified the 12-N atom as the site of protonation which result bears directly on the acid promoted binding of these antibiotics to DNA templates as part of their cytotoxic action.