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 1 H 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.