Synthesis, spectral, theoretical, and antimicrobial screening of some heterocyclic oximes

In a wide research program toward new and efficient antimicrobial agents, a series of substituted N-nitroso-3-alkyl piperidone oximes were synthesized and their antibacterial activity against Staphylococcus aureus, Pseudomonas aerugonisa, Escherichia coli, and Klbesiella pneumoniae and antifungal activity against Aspergillus niger, Aspergillus flavus, and Rhizopus were evaluated. Their structure and stereochemistry were characterized by high-resolution ¹H NMR, mass and elemental analysis. The spectra of all N-nitroso oximes reveal the presence of two isomers labeled as E (–NOH group is anti to N–N=O moiety) and Z (–NOH group is syn to N–N=O moiety) in solution and the coupling constants ruled out the possibility of normal chair conformation. From the theoretical studies and coupling constant values, it was found that all N-nitroso oximes exist as an equilibrium mixture of CA boat conformation (B ₁) and the major isomer was found to be E isomer. The molecular structure of N-nitroso oximes were also determined by semiempirical and Gaussian-03 calculation and the results are in agreement with the experimental studies.