Impact of tetracationic calix[4]arene conformation - from conic structure to expanded bolaform- on their antibacterial and antimycobacterial activities.

The four possible conformers of a new tetra-guanidino calix[4]arene thought to interact deleteriously with bacterial membrane were synthesized, characterized and evaluated for their in vitro antibacterial activity against various reference Gram negative and Gram positive bacteria: E. coli, P. aeruginosa, S. aureus, E. faecalis as well as M. tuberculosis. Their cytotoxicity was also evaluated in order to estimate their potential use. It appears that the transition from the cone conformation to partial cone and alternate analogues results in a significant gain of activity. This can be attributed to the evolution towards bolaform structures prone to interact deeper with the bacterial membrane. Indeed, the 1,3-alternate conformer 16 exhibits the most interesting antibacterial activity (MIC < 1.0 µg·mL-1 on S. aureus). Moreover, 16 displays very good antibacterial activities against isoniazid-resistant strain of M. tuberculosis (MIC = 0.8 µg·mL-1), associated to the lowest cytotoxicity, making it the most potent compound of the series; this can open new ways of research in the field of anti-infective drugs development to face the huge current demand.