Sterically Hindered N‐Heterocyclic Salts Utilized as Antimicrobial Agents

By the adoption of annulated ring systems for their steric bulkiness, a new series of symmetric N ‐heterocyclic imidazolium and perimidium salts were synthesized. Also, corresponding asymmetric ferrocenyl N ‐functionalized series were prepared as salts. All the reported salts were fully characterized. The reported X‐ray structure of 4,5‐diphenyl‐1,3‐dimethyl‐1H ‐imidazol‐3‐ium iodide ( 2a ) shows that it crystallized in the orthorhombic space group P 2₁2₁2₁. Low to moderate antimicrobial activities were observed with both sets of salts against important clinical isolates of Staphylococcus aureus , Bacillus subtilis , and Enterococcus faecalis and Escherichia coli , Pseudomonas aeruginosa , and Salmonella enterica . The results were benchmarked against meropenem. Both 1,3‐propyl‐1H ‐phenanthro9,10‐d ]imidazol‐3‐ium iodide ( 3b ) and 1‐ferrocenyl‐3‐propyl‐1H ‐perimidin‐3‐ium iodide ( 9b ) showed high antimicrobial activities against all tested Gram‐positive bacterial strains, with minimum inhibitory concentration values ranging from 8 to 4 μg/mL (meropenem = 0.5–0.125 μg/mL), while all the salts showed little or no activity against Gram‐negative bacterial strains. In general, the asymmetric ferrocenyl‐containing salts exhibited higher activities than the symmetric ones.