MX-100 (also known as PL-100) is a benzenesulfonamide derivative patented by Pharmacor Inc as HIV aspartyl protease inhibitor. MX-100 retained excellent antiviral activity against almost all of these protease inhibitor-resistant viruses and that its performance in this regard was superior to those of atazanavir, amprenavir, indinavir, lopinavir, nelfinavir, and saquinavir. In almost every case, the increase in the EC50 for MX-100 observed with viruses containing multiple mutations in protease was far less than that obtained with the other drugs. Preclinical studies showed that MX-100 possessed suboptimal solubility and pharmacokinetic, (PK) properties, possibly hindering further development. MX-100 successfully completed preclinical and clinical development (phase I in healthy volunteers) and have been licensed to Merck in 2006