10-Hydroxy-7,8-dihydropyrazino[1',2':1,5]pyrrolo[2,3-d]pyridazine-1,9(2H,6H)-diones: potent, orally bioavailable HIV-1 integrase strand-transfer inhibitors with activity against integrase mutants.

A series of 10-hydroxy-7,8-dihydropyrazino[1',2':1,5]pyrrolo[2,3-d]pyridazine-1,9(2H,6H)-diones was synthesized and tested for their inhibition of HIV-1 replication in cell culture. Structure-activity studies indicated that high antiviral potency against wild-type virus as well as viruses containing integrase mutations that confer resistance to three different structural classes of integrase inhibitors could be achieved by incorporation of small aliphatic groups at certain positions on the core template. An optimal compound from this study, 16, inhibits integrase strand-transfer activity with an IC(50) value of 10 nM, inhibits HIV-1 replication in cell culture with an IC(95) value of 35 nM in the presence of 50% normal human serum, and displays modest pharmacokinetic properties in rats (i.v. t(1/2)=5.3 h, F=17%).

Design and Synthesis of Piperazine Sulfonamide Cores Leading to Highly Potent HIV-1 Protease Inhibitors.

Using the HIV-1 protease binding mode of MK-8718 and PL-100 as inspiration, a novel aspartate binding bicyclic piperazine sulfonamide core was designed and synthesized. The resulting HIV-1 protease inhibitor containing this core showed an 60-fold increase in enzyme binding affinity and a 10-fold increase in antiviral activity relative to MK-8718.

Discovery of MK-8718, an HIV Protease Inhibitor Containing a Novel Morpholine Aspartate Binding Group.

A novel HIV protease inhibitor was designed using a morpholine core as the aspartate binding group. Analysis of the crystal structure of the initial lead bound to HIV protease enabled optimization of enzyme potency and antiviral activity. This afforded a series of potent orally bioavailable inhibitors of which MK-8718 was identified as a compound with a favorable overall profile.

Discovery of potent, selective 4-fluoroproline-based thrombin inhibitors with improved metabolic stability.

Previous reports from our laboratories described potent tripeptide thrombin inhibitors which incorporate heterocycle-substituted chlorophenyl groups in the P1 position. Using these as lead compounds for further optimization, we identified sites of metabolism and designed analogs with 4-fluoroproline in P2 and cyclopropane-containing side chains in P3 as an approach to reducing metabolism and improving their oral pharmacokinetic performance. The large (300-fold) difference in potency between analogs containing (4R)- and (4S)-4-fluoroproline was rationalized by analyzing inhibitor-enzyme interactions in crystal structures of related compounds and by molecular modeling which indicated that the more potent (4R)-4-fluoroproline isomer stabilizes a proline ring conformation that is preferred for binding to the enzyme. An optimal compound from this work, 41, exhibits high potency in a coagulation assay in human plasma (2xAPTT=190 nM), excellent selectivity versus the digestive enzyme trypsin (K(i)=3300 nM), and excellent oral bioavailability in dogs with moderate clearance (F=100%, CL=12 mL/min/kg).