Chlamydia pneumoniae-IN-1 (compound 55), a benzimidazole, shows high activity against the bacterium. Chlamydia pneumoniae-IN-1 has 99% inhibition of C. pneumoniae Growth at 10 μM, and has 95% inhibition effect on the viability of the host cells at 10 μM. Chlamydia pneumoniae-IN-1 inhibits the growth of the CV-6 strain with a MIC of 12.6 μM. Chlamydia pneumoniae-IN-1 has antichlamydial efficiency[1].