Novel P2 Tris-tetrahydrofuran Group in Antiviral Compound 1 (GRL-0519) Fills the S2 Binding Pocket of Selected Mutants of HIV-1 Protease

GRL-0519 (1) is a potent antiviral inhibitor of HIV-1 protease (PR) possessing tris-tetrahydrofuran (tris-THF) at P2. The high resolution X-ray crystal structures of inhibitor 1 in complexes with single substitution mutants PRR8Q, PRD30N, PR150V, PR154M, and PRV82A were analyzed in relation to kinetic data. The smaller valine side chain in PR150V eliminated hydrophobic interactions with inhibitor and the other subunit consistent with 60-fold worse inhibition. Asn30 in PRD30N showed altered interactions with neighboring residues and 18-fold worse inhibition. Mutations V82A and I54M showed compensating structural changes consistent with 6-7-fold lower inhibition. Gln8 in PRR8Q replaced the ionic interactions of wild type Arg8 with hydrogen bond interactions without changing the inhibition significantly. The carbonyl oxygen of Gly48 showed two alternative conformations in all structures likely due to the snug fit of the large tris-THF group in the S2 subsite in agreement with high antiviral efficacy of 1 on resistant virus.