Potent Long-Acting Inhibitors Targeting the HIV-1 Capsid Based on a Versatile Quinazolin-4-one Scaffold.

Long-acting (LA) human immunodeficiency virus-1 (HIV-1) antiretroviral therapy characterized by a ≥1 month dosing interval offers significant advantages over daily oral therapy. However, the criteria for compounds that enter clinical development are high. Exceptional potency and low plasma clearance are required to meet dose size requirements; excellent chemical stability and/or crystalline form stability is required to meet formulation requirements, and new antivirals in HIV-1 therapy need to be largely free of side effects and drug-drug interactions. In view of these challenges, the discovery that capsid inhibitors comprising a quinazolinone core tolerate a wide range of structural modifications while maintaining picomolar potency against HIV-1 infection in vitro, are assembled efficiently in a multi-component reaction, and can be isolated in a stereochemically pure form is reported herein. The detailed characterization of a prototypical compound, GSK878, is presented, including an X-ray co-crystal structure and subcutaneous and intramuscular pharmacokinetic data in rats and dogs.

Discovery and Preclinical Profiling of GSK3839919, a Potent HIV-1 Allosteric Integrase Inhibitor.

Allosteric HIV-1 integrase inhibitors (ALLINIs) have been of interest recently because of their novel mechanism of action. Strategic modifications to the C5 moiety of a class of 4-(4,4-dimethylpiperidinyl)-2,6-dimethylpyridinyl ALLINIs led to the identification of a tetrahydroisoquinoline heterocycle as a suitable spacer element to project the distal hydrophobic aryl ring. Subsequent optimization of the aryl substitutions identified 12 as an ALLINI with single-digit nanomolar inhibitory potency and low clearance across preclinical species. In preclinical toxicology studies with 12 in rats, lipid hepatocellular vacuolation was observed. Removal of the C6 methyl group resulted in GSK3839919 (22), which exhibited a reduced incidence and severity of lipid vacuolation in both in vitro assays and in vivo studies while maintaining the potency and pharmacokinetic (PK) properties of the prototype. The virology, PK, and toxicology profiles of 22 are discussed.

Scaffold modifications to the 4-(4,4-dimethylpiperidinyl) 2,6-dimethylpyridinyl class of HIV-1 allosteric integrase inhibitors.

Allosteric integrase inhibitors (ALLINIs) of HIV-1 may hold promise as a novel mechanism for HIV therapeutics and cure. Scaffold modifications to the 4-(4,4-dimethylpiperidinyl) 2,6-dimethylpyridinyl class of ALLINIs provided a series of potent compounds with differentiated 5/6 fused ring systems. Notably, inhibitors containing the 1,2,4-triazolopyridine and imidazopyridine core exhibited single digit nM antiviral potency and low to moderate clearance after intravenous (IV) dosing in rat pharmacokinetic (PK) studies. The 1,2,4-triazolopyridines showed a higher oral exposure when compared to the imidazopyridines. Further modifications to the C5 substituent of the 1,2,4-triazolopyridines resulted in a new lead compound, which had improved rat IV/PO PK compared to the former lead compound GSK3739936, while maintaining antiviral potency. Structure-activity relationships (SAR) and rat pharmacokinetic profiles of this series are discussed.

DNA-Model-Based Design and Execution of Some Fused Benzodiazepine Hybrid Payloads for Antibody-Drug Conjugate Modality.

A new series with the tetrahydroisoquinoline-fused benzodiazepine (TBD) ring system combined with the surrogates of (1-methyl-1H-pyrrol-3-yl)benzene ("MPB") payloads were designed and executed for conjugation with a monoclonal antibody for anticancer therapeutics. DNA models helped in rationally identifying modifications of the "MPB" binding component and guided structure-activity relationship generation. This hybrid series of payloads exhibited excellent in vitro activity when tested against a panel of various cancer cell lines. One of the payloads was appended with a lysosome-cleavable peptide linker and conjugated with an anti-mesothelin antibody via a site-specific conjugation method mediated by the enzyme bacterial transglutaminase (BTGase). Antibody-drug conjugate (ADC) 50 demonstrated good plasma stability and lysosomal cleavage. A single intravenous dose of ADC 50 (5 or 10 nmol/kg) showed robust efficacy in an N87 gastric cancer xenograft model.

Structure-based amelioration of PXR transactivation in a novel series of macrocyclic allosteric inhibitors of HIV-1 integrase.

Previous studies have identified a series of imidazo[1,2-a]pyridine (IZP) derivatives as potent allosteric inhibitors of HIV-1 integrase (ALLINIs) and virus infection in cell culture. However, IZPs were also found to be relatively potent activators of the pregnane-X receptor (PXR), raising the specter of induction of CYP-mediated drug disposition pathways. In an attempt to modify PXR activity without affecting anti-HIV-1 activity, rational structure-based design and modeling approaches were used. An X-ray cocrystal structure of (S,S)-1 in the PXR ligand binding domain (LBD) allowed an examination of the potential of rational structural modifications designed to abrogate PXR. The introduction of bulky basic amines at the C-8 position provided macrocyclic IZP derivatives that displayed potent HIV-1 inhibitory activity in cell culture with no detectable PXR transactivation at the highest concentration tested.

Heterocycle amide isosteres: An approach to overcoming resistance for HIV-1 integrase strand transfer inhibitors.

A series of heterocyclic pyrimidinedione-based HIV-1 integrase inhibitors was prepared and screened for activity against purified integrase enzyme and/or viruses modified with the following mutations within integrase: Q148R, Q148H/G140S and N155H. These are mutations that result in resistance to the first generation integrase inhibitors raltegravir and elvitegravir. Based on consideration of drug-target interactions, an approach was undertaken to replace the amide moiety of the first generation pyrimidinedione inhibitor with azole heterocycles that could retain potency against these key resistance mutations. An imidazole moiety was found to be the optimal amide substitute and the observed activity was rationalized with the use of calculated properties and modeling. Rat pharmacokinetic (PK) studies of the lead imidazole compounds demonstrated moderate clearance and moderate exposure.

5,6,7,8-Tetrahydro-1,6-naphthyridine Derivatives as Potent HIV-1-Integrase-Allosteric-Site Inhibitors.

A series of 5,6,7,8-tetrahydro-1,6-naphthyridine derivatives targeting the allosteric lens-epithelium-derived-growth-factor-p75 (LEDGF/p75)-binding site on HIV-1 integrase, an attractive target for antiviral chemotherapy, was prepared and screened for activity against HIV-1 infection in cell culture. Small molecules that bind within the LEDGF/p75-binding site promote aberrant multimerization of the integrase enzyme and are of significant interest as HIV-1-replication inhibitors. Structure-activity-relationship studies and rat pharmacokinetic studies of lead compounds are presented.

General Method for the Preparation of Electron-Deficient Imidazo[1,2-a]pyridines and Related Heterocycles.

A new annulation method for the preparation of the imidazo[1,2-a]pyridine ring system under mild conditions is presented. Treatment of a 2-aminopyridine with a dimethylketal tosylate in acetonitrile at elevated temperature (80-140 °C) in the presence of catalytic Sc(OTf)3 provides the imidazo[1,2-a]pyridine product in good yield. The annulation method is broadly applicable to electron-poor 2-aminopyridines and displays a complementary profile to the classic preparation of the imidazo[1,2-a]pyridine ring system by reaction of a bromoketone with electron-rich and -neutral substrates. The scope of the process and mechanistic considerations are discussed.

Tandem ring-closing metathesis/transfer hydrogenation: practical chemoselective hydrogenation of alkenes.

An operationally simple chemoselective transfer hydrogenation of alkenes using ruthenium metathesis catalysts is presented. Of great practicality, the transfer hydrogenation reagents can be added directly to a metathesis reaction and effect hydrogenation of the product alkene in a single pot at ambient temperature without the need to seal the vessel to prevent hydrogen gas escape. The reduction is applicable to a range of alkenes and can be performed in the presence of aryl halides and benzyl groups, a notable weakness of Pd-catalyzed hydrogenations. Scope and mechanistic considerations are presented.

New first and second generation inhibitors of human immunodeficiency virus-1 integrase.

INTRODUCTION: The use of inhibitors of HIV-1 integrase for treating HIV-1 infection has proven to be very beneficial. Raltegravir, a strand transfer inhibitor, has been approved for use both as a first-line therapy and in treatment-experienced patients. A second compound in this class, elvitegravir, is in Phase III clinical trials and is being developed as part of a once daily fixed dose combination pill. With widespread use of raltegravir, viral resistance has emerged with surprising facility. Attempts to use raltegravir on a once daily dosing regimen have been unsuccessful whilst elvitegravir cannot be delivered daily without the aid of a pharmacokinetic (PK)-enhancing agent. Thus, there is a need for second generation compounds to address these issues. AREAS COVERED: Patent applications claiming compounds useful as inhibitors of HIV-1 integrase are reviewed in this paper, along with compounds related to the strand transfer inhibitors. EXPERT OPINION: The field appears to be more focused on developing compounds which address the issues identified for the first generation compounds, raltegravir and elvitegravir. Patent activity around new strand transfer inhibitors claims compounds active against first generation resistant mutations and having PK profiles suitable for daily dosing. Advancements in this area have been rapid and several compounds described in these patent applications are currently in clinical trials. Bolstered by recent mechanistic discoveries, compounds inhibiting processes other than strand transfer have begun to emerge. It is foreseeable that a second generation integrase inhibitor could be approved for treatment in the coming years.

Asymmetric synthetic access to the hetisine alkaloids: total synthesis of (+)-nominine.

A dual cycloaddition strategy for the synthesis of the hetisine alkaloids has been developed, illustrated by a concise asymmetric total synthesis of (+)-nominine (7). The approach relies on an early-stage intramolecular 1,3-dipolar cycloaddition of a 4-oxido-isoquinolinium betaine dipole with an ene-nitrile dipolarophile. Subsequent late-stage pyrrolidine-induced dienamine isomerization/Diels-Alder cascade allows for rapid construction of the carbon--nitrogen polycyclic skeleton within this class of C(20)-diterpenoid alkaloids.

Efficient synthetic access to the hetisine C20-diterpenoid alkaloids. A concise synthesis of nominine via oxidoisoquinolinium-1,3-dipolar and dienamine-Diels-Alder cycloadditions.

A concise synthetic approach to the hetisine C20-diterpenoid alkaloids is reported. The total synthesis of (+/-)-nominine was accomplished in a 15-step sequence employing a dual cycloaddition strategy. Key features of the synthesis include a reversible intramolecular 4-oxidoisoquinolinium betaine dipolar cycloaddition in conjunction with a pyrrolidine-induced dienamine isomerization/Diels-Alder cascade.

Structure-activity relationships of triazolopyridine oxazole p38 inhibitors: identification of candidates for clinical development.

The synthesis, structure-activity relationship, in vivo activity, and metabolic profile for a series of triazolopyridine-oxazole based p38 inhibitors are described. The deficiencies of the lead structure in the series, CP-808844, were overcome by changes to the C4 aryl group and the triazole side-chain culminating in the identification of several potential clinical candidates.

Enantioselective approach to the hetisine alkaloids. Synthesis of the 3-methyl-1-aza-tricyclo[5.2.1.0(3,8)]decane core via intramolecular dipolar cycloaddition.

[structure: see text]. An efficient, enantioselective approach to the hetisine class of the C(20)-diterpenoid alkaloids is described. The strategy involves an intramolecular oxidopyridinium dipolar cycloaddition as the key transformation, in which simultaneous formation of the C5-C6 and C10-C20 bonds in the 3-methyl-1-aza-tricyclo[5.2.1.0(3,8)]decane core of the hetisine alkaloids is effected.

Benzimidazolone p38 inhibitors.

The synthesis and in vitro p38 alpha activity of a novel series of benzimidazolone inhibitors is described. The p38 alpha SAR is consistent with a mode of binding wherein the benzimidazolone carbonyl serves as the H-bond acceptor to Met109 of p38 alpha in a manner analogous to the pyridine nitrogen of prototypical pyridylimidazole p38 inhibitors. Potent p38 alpha activity comparable to that of several previously reported p38 inhibitors is observed for this novel chemotype.

Glutathione s-transferase omega 1-1 is a target of cytokine release inhibitory drugs and may be responsible for their effect on interleukin-1beta posttranslational processing.

Stimulus-induced posttranslational processing of human monocyte interleukin-1beta (IL-1beta) is accompanied by major changes to the intracellular ionic environment, activation of caspase-1, and cell death. Certain diarylsulfonylureas inhibit this response, and are designated cytokine release inhibitory drugs (CRIDs). CRIDs arrest activated monocytes so that caspase-1 remains inactive and plasma membrane latency is preserved. Affinity labeling with [(14)C]CRIDs and affinity chromatography on immobilized CRID were used in seeking potential protein targets of their action. Following treatment of intact human monocytes with an epoxide-bearing [(14)C]CRID, glutathione S-transferase (GST) Omega 1-1 was identified as a preferred target. Moreover, labeling of this polypeptide correlated with irreversible inhibition of ATP-induced IL-1beta posttranslational processing. When extracts of human monocytic cells were chromatographed on a CRID affinity column, GST Omega 1-1 bound selectively to the affinity matrix and was eluted by soluble CRID. Recombinant GST Omega 1-1 readily incorporated [(14)C]CRID epoxides, but labeling was negated by co-incubation with S-substituted glutathiones or by mutagenesis of the catalytic center Cys(32) to alanine. Peptide mapping by high performance liquid chromatography-mass spectrometry also demonstrated that Cys(32) was the site of modification. Although S-alkylglutathiones did not arrest ATP-induced IL-1beta posttranslational processing or inhibit [(14)C]CRID incorporation into cell-associated GST Omega 1-1, a glutathione-CRID adduct effectively demonstrated these attributes. Therefore, the ability of CRIDs to arrest stimulus-induced IL-1beta posttranslational processing may be attributable to their interaction with GST Omega 1-1.