Maintaining potent HTLV-I protease inhibition without the P3-cap moiety in small tetrapeptidic inhibitors

The human T cell lymphotropic/leukemia virus type 1 (HTLV-I) causes adult T cell lymphoma/leukemia. The virus is also responsible for chronic progressive myelopathy and several inflammatory diseases. To stop the manufacturing of new viral components, in our previous reports, we derived small tetrapeptidic HTLV-I protease inhibitors with an important amide-capping moiety at the P3 residue. In the current study, we removed the P3-cap moiety and, with great difficulty, optimized the P3 residue for HTLV-I protease inhibition potency. We discovered a very potent and small tetrapeptidic HTLV-I protease inhibitor (KNI-10774a, IC50 = 13 nM).