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Optimization of pyridine-based noncatalytic site integrase inhibitors (NCINIs) based on compound 2 has led to the discovery of molecules capable of inhibiting virus harboring N124 variants of HIV integrase (IN) while maintaining minimal contribution of enterohepatic recirculation to clearance in rat. Structure-activity relationships at the C6 position established chemical space where the extent of enterohepatic recirculation in the rat is minimized. Desymmetrization of the C4 substituent allowed for potency optimization against virus having the N124 variant of integrase. Combination of these lessons led to the discovery of compound 20, having balanced serum-shifted antiviral potency and minimized excretion in to the biliary tract in rat, potentially representing a clinically viable starting point for a new treatment option for individuals infected with HIV.

A scaffold replacement approach was used to identifying the pyridine series of noncatalytic site integrase inhibitors. These molecules bind with higher affinity to a tetrameric form compared to a dimeric form of integrase. Optimization of the C6 and C4 positions revealed that viruses harboring T124 or A124 amino acid substitutions are highly susceptible to these inhibitors, but viruses having the N124 amino acid substitution are about 100-fold less susceptible. Compound 20 had EC50 values10 nM against viruses having T124 or A124 substitutions in IN and800 nM in viruses having N124 substitions. Compound 20 had an excellent in vitro ADME profile and demonstrated reduced contribution of biliary excretion to in vivo clearance compared to BI 224436, the lead compound from the quinoline series of NCINIs.

An assay recapitulating the 3' processing activity of HIV-1 integrase (IN) was used to screen the Boehringer Ingelheim compound collection. Hit-to-lead and lead optimization beginning with compound 1 established the importance of the C3 and C4 substituent to antiviral potency against viruses with different aa124/aa125 variants of IN. The importance of the C7 position on the serum shifted potency was established. Introduction of a quinoline substituent at the C4 position provided a balance of potency and metabolic stability. Combination of these findings ultimately led to the discovery of compound 26 (BI 224436), the first NCINI to advance into a phase Ia clinical trial.