1H and13C NMR spectra of 2-substituted 5-nitrofurans and conformation of chemotherapeutic preparations of the 5-nitrofuran series

Abstract

The1H and13NMR spectra of t-nitrofuran and 17 2-substituted 5-nitrofurans were investigated. The Δ1H and Δ13C substituent increments [Δ = δ(2-X-5-nitrofuran) δ(5-nitrofuran)] in the spectra of these compounds were analyzed by comparison with the analogous 5-methylfuran and furan derivatives, and the change in the sensitivity of the chemical shifts of the ring protons and the carbon atoms to the effects of substituents X as a function of the electronic character of substituent R was also analyzed. The chemical shifts and the spin-spin coupling constants were used to determine the preferred orientation of the substituents relative to the furan ring. It was found that medicinal preparations of the 5-nitrofuran series (5-nitrofurfurylidenehydrazones) exist in the form of s-trans conformers in solutions in dimethyl sulfoxide and water, whereas furagin has primarily the structure of the E s-trans form.