Structure and NMR properties of 6‐substituted‐5,6‐dihydrobenzo[c]phenanthridine alkaloids

Abstract

We report a preparation of new 6-substituted-5,6-dihydrobenzo[c]phenanthridines by the reaction of azoles with quaternary benzo[c]phenanthridine alkaloids sanguinarine and chelerythrine. The prepared compounds have been characterized by NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. Conformational behaviors of carbazole derivatives in solution have been investigated by low-temperature NMR experiments. Barriers to rotation around newly formed C6-N bonds were determined to be 12-13 kcal/mol. Quantum chemical calculations have been used to reproduce the experimental observations. Large structural effects on several 1 H NMR resonances were observed experimentally, analyzed by Density Functional Theory (DFT) calculations at B3LYP/6-311+G(d,p)/PCM level, and interpreted by ring-current effects of the benzo[c]phenanthridine and carbazole units.

Theoretical insights of solvent effect on tautomerism, stability, and electronic properties of 6‐ketomethylphenanthridine

“…Phenanthridine scaffolds are an essential class of nitrogen‐bonded heterocyclic compounds with extensive applications in chemical, medicinal, and biological industries. [ 1–6 ] For example, their biological properties can be considered as antitumor, [ 1 ] antiviral, [ 3 ] and anti‐hepatitis agents. [ 5 ] Especially, these heterocycles have extensively been investigated for efficient DNA‐binding bioactive compounds.…”