Figure 1: Chemical structure of Chemically Modified Tetracycline (COL-3). While all tetracyclines present an octahydrotetracene-2-carboxamide skeleton, they differ from each other by the presence of chloride, methyl, and hydroxyl groups. COL-3 differs from other tetracyclines in the absence of the dimethylamino group from carbon 4 in the A ring, which confers it the characteristic of a non-antibacterial tetracycline.