The invention encompasses an active metabolite of the 18-membered macrocyclic antimicrobial agents, specifically, a metabolite of tiacumicin B and in certain embodiments, R-Tiacumicin B or and its related compounds. In particular, the invention encompasses a compound that acts as a potent antibiotic agent for the treatment of bacterial infections, specifically GI infections caused by toxin producing strains of Clostridium difficile (C. difficile) and Clostridium perfringens (C. perfringens).