Synthesis, characterisation, conformational preferences, dynamic NMR studies and antimicrobial evaluation of N-nitroso- and N-formyl-c-3,t-3-dimethyl-r-2,c-7-diphenyl-1,4-diazepan-5-ones

•N-nitroso- and N-formyl-1,4-diazepan-5-ones were synthesized.•Assignment of 1H & 13C NMR signals are made using 2D NMR spectra.•N-nitroso-1,4-diazepan-5-one prefers chair conformation with diaxial phenyl groups.•X-ray crystal structure of N-nitroso compound has been solved.•Energy barriers for N–NO & N–CO rotations are calculated using dynamic NMR spectra.

The stereochemical preferences of N-nitroso- and N-formyl-c-3,t-3-dimethyl-r-2,c-7-diphenyl-1,4-diazepan-5-ones 3 & 4, respectively, have been determined using 1D and 2D NMR spectral techniques. Interestingly, the N-nitroso compound 3 is found to prefer an equilibrium between alternate chair conformations with diaxial phenyl groups, while the N-formyl compound 4 prefers flattened boat conformation. This is stereochemically a novel report on the flexible rings adopting a chair conformation with diaxial phenyl groups. The X-ray crystal structure of N-nitroso-c-3,t-3-dimethyl-r-2,c-7-diphenyl-1,4-diazepan-5-one (3) also supports the chair conformation with diaxial phenyl groups. Dynamic 1H NMR spectral studies have been carried out on the N-nitroso and N-formyl diazepan-5-ones 3 & 4 and the energy barriers for N–NO and N–CO rotations are found to be 88.7 and 75.7 kJ/mol, respectively. The antimicrobial activities have been determined for the compounds 2–4 and it is found that all the compounds exhibit significant antibacterial and antifungal activities when compared to the standard chloramphenicol.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide