Synthesis, Structure-Activity Relationships, and In Vivo Evaluation of Novel C-17 Amine Derivatives Based on GSK3640254 as HIV-1 Maturation Inhibitors with Broad Spectrum Activity.

An investigation of the structure-activity relationships of a series of HIV-1 maturation inhibitors (MIs) based on GSK3640254 (4) was conducted by incorporating novel C-17 amine substituents to reduce the overall basicity of the resultant analogues. We found that replacement of the distal amine on the C-17 sidechain present in 4 with a tertiary alcohol in combination with either a heterocyclic ring system or a cyclohexyl ring substituted with polar groups provided potent wild-type HIV-1 MIs that also retained excellent potency against a T332S/V362I/prR41G variant, a laboratory strain that served as a surrogate to assess HIV-1 polymorphic virus coverage. Compound 26 exhibited broad-spectrum HIV-1 activity against an expanded panel of clinically relevant Gag polymorphic viruses and had the most desirable overall profile in this series of compounds. In pharmacokinetic studies, 26 had low clearance and exhibited 24 and 31% oral bioavailability in rats and dogs, respectively.

The Discovery of GSK3640254, a Next-Generation Inhibitor of HIV-1 Maturation.

GSK3640254 is an HIV-1 maturation inhibitor (MI) that exhibits significantly improved antiviral activity toward a range of clinically relevant polymorphic variants with reduced sensitivity toward the second-generation MI GSK3532795 (BMS-955176). The key structural difference between GSK3640254 and its predecessor is the replacement of the para-substituted benzoic acid moiety attached at the C-3 position of the triterpenoid core with a cyclohex-3-ene-1-carboxylic acid substituted with a CH2F moiety at the carbon atom α- to the pharmacophoric carboxylic acid. This structural element provided a new vector with which to explore structure-activity relationships (SARs) and led to compounds with improved polymorphic coverage while preserving pharmacokinetic (PK) properties. The approach to the design of GSK3640254, the development of a synthetic route and its preclinical profile are discussed. GSK3640254 is currently in phase IIb clinical trials after demonstrating a dose-related reduction in HIV-1 viral load over 7-10 days of dosing to HIV-1-infected subjects.

GSK3640254 Is a Novel HIV-1 Maturation Inhibitor with an Optimized Virology Profile.

HIV-1 maturation inhibitors (MIs) offer a novel mechanism of action and potential for use in HIV-1 treatment. Prior MIs displayed clinical efficacy but were associated with the emergence of resistance and some gastrointestinal tolerability events. Treatment with the potentially safer next-generation MI GSK3640254 (GSK'254) resulted in up to a 2-log10 viral load reduction in a phase IIa proof-of-concept study. In vitro experiments have defined the antiviral and resistance profiles for GSK'254. The compound displayed strong antiviral activity against a library of subtype B and C chimeric viruses containing Gag polymorphisms and site-directed mutants previously shown to affect potency of earlier-generation MIs, with a mean protein-binding adjusted 90% effective concentration (EC90) of 33 nM. Furthermore, GSK'254 exhibited robust antiviral activity against a panel of HIV-1 clinical isolates, with a mean EC50 of 9 nM. Mechanistic studies established that bound GSK'254 dissociated on average 7.1-fold more slowly from wild-type Gag virus-like particles (VLPs) than a previous-generation MI. In resistance studies, the previously identified A364V Gag region mutation was selected under MI pressure in cell culture and during the phase IIa clinical study. As expected, GSK'254 inhibited cleavage of p25 in a range of polymorphic HIV-1 Gag VLPs. Virus-like particles containing the A364V mutation exhibited a p25 cleavage rate 9.3 times higher than wild-type particles, providing a possible mechanism for MI resistance. The findings demonstrate that GSK'254 potently inhibits a broad range of HIV-1 strains expressing Gag polymorphisms.

Discovery of new indole-based acylsulfonamide Nav1.7 inhibitors.

Screening of 100 acylsulfonamides from the Bristol-Myers Squibb compound collection identified the C3-cyclohexyl indole 6 as a potent Nav1.7 inhibitor. Replacement of the C2 furanyl ring of 6 with a heteroaryl moiety or truncation of this group led to the identification of 4 analogs with hNav1.7 IC50 values under 50 nM. Fluorine substitution of the truncated compound 12 led to 34 with improved potency and isoform selectivity. The inverted indole 36 also maintained good activity. Both 34 and 36 exhibited favorable CYP inhibition profiles, good membrane permeability and a low efflux ratio and, therefore, represent new leads in the search for potent and selective Nav1.7 inhibitors to treat pain.

Design, Synthesis, and SAR of C-3 Benzoic Acid, C-17 Triterpenoid Derivatives. Identification of the HIV-1 Maturation Inhibitor 4-((1 R,3a S,5a R,5b R,7a R,11a S,11b R,13a R,13b R)-3a-((2-(1,1-Dioxidothiomorpholino)ethyl)amino)-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-2,3,3a,4,5,5a,5b,6,7,7a,8,11,11a,11b,12,13,13a,13b-octadecahydro-1 H-cyclopenta[ a]chrysen-9-yl)benzoic Acid (GSK3532795, BMS-955176).

GSK3532795, formerly known as BMS-955176 (1), is a potent, orally active, second-generation HIV-1 maturation inhibitor (MI) that advanced through phase IIb clinical trials. The careful design, selection, and evaluation of substituents appended to the C-3 and C-17 positions of the natural product betulinic acid (3) was critical in attaining a molecule with the desired virological and pharmacokinetic profile. Herein, we highlight the key insights made in the discovery program and detail the evolution of the structure-activity relationships (SARs) that led to the design of the specific C-17 amine moiety in 1. These modifications ultimately enabled the discovery of 1 as a second-generation MI that combines broad coverage of polymorphic viruses (EC50 <15 nM toward a panel of common polymorphisms representative of 96.5% HIV-1 subtype B virus) with a favorable pharmacokinetic profile in preclinical species.

The design, synthesis and structure-activity relationships associated with C28 amine-based betulinic acid derivatives as inhibitors of HIV-1 maturation.

The design and synthesis of a series of C28 amine-based betulinic acid derivatives as HIV-1 maturation inhibitors is described. This series represents a continuation of efforts following on from previous studies of C-3 benzoic acid-substituted betulinic acid derivatives as HIV-1 maturation inhibitors (MIs) that were explored in the context of C-28 amide substituents. Compared to the C-28 amide series, the C-28 amine derivatives exhibited further improvements in HIV-1 inhibitory activity toward polymorphisms in the Gag polyprotein as well as improved activity in the presence of human serum. However, plasma exposure of basic amines following oral administration to rats was generally low, leading to a focus on moderating the basicity of the amine moiety distal from the triterpene core. The thiomorpholine dioxide (TMD) 20 emerged from this study as a compound with the optimal antiviral activity and an acceptable pharmacokinetic profile in the C-28 amine series. Compared to the C-28 amide 3, 20 offers a 2- to 4-fold improvement in potency towards the screening viruses, exhibits low shifts in the EC50 values toward the V370A and ΔV370 viruses in the presence of human serum or human serum albumin, and demonstrates improved potency towards the polymorphic T371A and V362I virus variants.

Discovery of a Potent Acyclic, Tripeptidic, Acyl Sulfonamide Inhibitor of Hepatitis C Virus NS3 Protease as a Back-up to Asunaprevir with the Potential for Once-Daily Dosing.

The discovery of a back-up to the hepatitis C virus NS3 protease inhibitor asunaprevir (2) is described. The objective of this work was the identification of a drug with antiviral properties and toxicology parameters similar to 2, but with a preclinical pharmacokinetic (PK) profile that was predictive of once-daily dosing. Critical to this discovery process was the employment of an ex vivo cardiovascular (CV) model which served to identify compounds that, like 2, were free of the CV liabilities that resulted in the discontinuation of BMS-605339 (1) from clinical trials. Structure-activity relationships (SARs) at each of the structural subsites in 2 were explored with substantial improvement in PK through modifications at the P1 site, while potency gains were found with small, but rationally designed structural changes to P4. Additional modifications at P3 were required to optimize the CV profile, and these combined SARs led to the discovery of BMS-890068 (29).

Discovery of BMS-955176, a Second Generation HIV-1 Maturation Inhibitor with Broad Spectrum Antiviral Activity.

HIV-1 maturation inhibition (MI) has been clinically validated as an approach to the control of HIV-1 infection. However, identifying an MI with both broad polymorphic spectrum coverage and good oral exposure has been challenging. Herein, we describe the design, synthesis, and preclinical characterization of a potent, orally active, second generation HIV-1 MI, BMS-955176 (2), which is currently in Phase IIb clinical trials as part of a combination antiretroviral regimen.

Identification and Characterization of BMS-955176, a Second-Generation HIV-1 Maturation Inhibitor with Improved Potency, Antiviral Spectrum, and Gag Polymorphic Coverage.

BMS-955176 is a second-generation human immunodeficiency virus type 1 (HIV-1) maturation inhibitor (MI). A first-generation MI, bevirimat, showed clinical efficacy in early-phase studies, but ∼50% of subjects had viruses with reduced susceptibility associated with naturally occurring polymorphisms in Gag near the site of MI action. MI potency was optimized using a panel of engineered reporter viruses containing site-directed polymorphic changes in Gag that reduce susceptibility to bevirimat (including V362I, V370A/M/Δ, and T371A/Δ), leading incrementally to the identification of BMS-955176. BMS-955176 exhibits potent activity (50% effective concentration [EC50], 3.9 ± 3.4 nM [mean ± standard deviation]) toward a library (n = 87) of gag/pr recombinant viruses representing 96.5% of subtype B polymorphic Gag diversity near the CA/SP1 cleavage site. BMS-955176 exhibited a median EC50 of 21 nM toward a library of subtype B clinical isolates assayed in peripheral blood mononuclear cells (PBMCs). Potent activity was maintained against a panel of reverse transcriptase, protease, and integrase inhibitor-resistant viruses, with EC50s similar to those for the wild-type virus. A 5.4-fold reduction in EC50 occurred in the presence of 40% human serum plus 27 mg/ml of human serum albumin (HSA), which corresponded well to an in vitro measurement of 86% human serum binding. Time-of-addition and pseudotype reporter virus studies confirm a mechanism of action for the compound that occurs late in the virus replication cycle. BMS-955176 inhibits HIV-1 protease cleavage at the CA/SP1 junction within Gag in virus-like particles (VLPs) and in HIV-1-infected cells, and it binds reversibly and with high affinity to assembled Gag in purified HIV-1 VLPs. Finally, in vitro combination studies showed no antagonistic interactions with representative antiretrovirals (ARVs) of other mechanistic classes. In conclusion, BMS-955176 is a second-generation MI with potent in vitro anti-HIV-1 activity and a greatly improved preclinical profile compared to that of bevirimat.

Inhibitors of HIV-1 maturation: Development of structure-activity relationship for C-28 amides based on C-3 benzoic acid-modified triterpenoids.

We have recently reported on the discovery of a C-3 benzoic acid (1) as a suitable replacement for the dimethyl succinate side chain of bevirimat (2), an HIV-1 maturation inhibitor that reached Phase II clinical trials before being discontinued. Recent SAR studies aimed at improving the antiviral properties of 2 have shown that the benzoic acid moiety conferred topographical constraint to the pharmacophore and was associated with a lower shift in potency in the presence of human serum albumin. In this manuscript, we describe efforts to improve the polymorphic coverage of the C-3 benzoic acid chemotype through modifications at the C-28 position of the triterpenoid core. The dimethylaminoethyl amides 17 and 23 delivered improved potency toward bevirimat-resistant viruses while increasing C24 in rat oral PK studies.

The discovery of asunaprevir (BMS-650032), an orally efficacious NS3 protease inhibitor for the treatment of hepatitis C virus infection.

The discovery of asunaprevir (BMS-650032, 24) is described. This tripeptidic acylsulfonamide inhibitor of the NS3/4A enzyme is currently in phase III clinical trials for the treatment of hepatitis C virus infection. The discovery of 24 was enabled by employing an isolated rabbit heart model to screen for the cardiovascular (CV) liabilities (changes to HR and SNRT) that were responsible for the discontinuation of an earlier lead from this chemical series, BMS-605339 (1), from clinical trials. The structure-activity relationships (SARs) developed with respect to CV effects established that small structural changes to the P2* subsite of the molecule had a significant impact on the CV profile of a given compound. The antiviral activity, preclincial PK profile, and toxicology studies in rat and dog supported clinical development of BMS-650032 (24).

Discovery and early clinical evaluation of BMS-605339, a potent and orally efficacious tripeptidic acylsulfonamide NS3 protease inhibitor for the treatment of hepatitis C virus infection.

The discovery of BMS-605339 (35), a tripeptidic inhibitor of the NS3/4A enzyme, is described. This compound incorporates a cyclopropylacylsulfonamide moiety that was designed to improve the potency of carboxylic acid prototypes through the introduction of favorable nonbonding interactions within the S1' site of the protease. The identification of 35 was enabled through the optimization and balance of critical properties including potency and pharmacokinetics (PK). This was achieved through modulation of the P2* subsite of the inhibitor which identified the isoquinoline ring system as a key template for improving PK properties with further optimization achieved through functionalization. A methoxy moiety at the C6 position of this isoquinoline ring system proved to be optimal with respect to potency and PK, thus providing the clinical compound 35 which demonstrated antiviral activity in HCV-infected patients.

Developments in antiviral drug design, discovery and development in 2004.

This article summarizes key aspects of progress made during 2004 toward the design, discovery and development of antiviral agents for clinical use. Important developments in the identification, characterization and clinical utility of inhibitors of human immunodeficiency virus; the hepatitis viruses, hepatitis B, hepatitis C; the herpes family of viruses, herpes simplex viruses 1 and 2, varicella zoster virus, Epstein-Barr virus and human cytomegalovirus; the respiratory viruses, influenza, respiratory syncytial virus, human metapneumovirus, picornaviruses, measles and the severe acute respiratory syndrome coronavirus; human papilloma virus; rotavirus; Ebola virus and West Nile virus, are reviewed.

3-Thio-quinolinone maxi-K openers for the treatment of erectile dysfunction.

A series of Maxi-K openers for the treatment of erectile dysfunction based on the 3-thio-quinolinone core is described. Significant levels of channel opening (up to 550% of control) are seen in transfected oocytes. Functional activity in rabbit corpus cavernosum tissue strips confirms the potential to effect therapy for ED, the effect being maximal for the 3-amino-2-hydroxy thiol side chain.

Synthesis and SAR exploration of dinapsoline analogues.

Dinapsoline is a full D(1) dopamine receptor agonist that produces robust rotational activity in the unilateral 6-OHDA rat model. This compound is orally active, and shows a low tendency to cause tolerance in rat models. The active enantiomer was determined to have the S-(+) configuration, and the opposite enantiomer is essentially devoid of biological activity. Taken together, dinapsoline has significant metabolic and pharmacological advantages over previous D(1) agonists. In an attempt to define the structure-activity relationships (SARs) and to map out the key elements surrounding the unique structure of dinapsoline, core analogues and substitution analogues of the parent tetracyclic condensed ring structure were prepared. Based on a recently developed synthesis of dinapsoline and its enantiomers, both core and substitution analogues on all four rings (A, B', C and D ring) of dinapsoline were synthesized. It was found that affinity for both D(1)and D(2) receptors was decreased by most substituents on the A, B', and C rings, whereas D ring substitutions preserved much of the dopamine receptor binding activity.

(+)-Dinapsoline: an efficient synthesis and pharmacological profile of a novel dopamine agonist.

A highly convergent synthesis was developed for the novel dopamine agonist dinapsoline (12) (Ghosh, D.; Snyder, S. E.; Watts, V. J.; Mailman, R. B.; Nichols, D. E. 8,9-Dihydroxy-2,3,7, 11b-tetrahydro-1H-naph[1,2,3-de]isoquinoline: A Potent Full Dopamine D(1) Agonist Containing a Rigid beta-Phenyldopamine Pharmacophore. J. Med. Chem. 1996, 39 (2), 549-555). The crucial step in the new synthesis was a free radical-initiated cyclization to give the complete dinapsoline framework. The improved synthesis required half as many steps as the original procedure (Nichols, D. E.; Mailman, R.; Ghosh, D. Preparation of novel naphtho[1,2,3-de]isoquinolines as dopamine receptor ligands. PCT Int. Appl. WO 9706799 A1, Feb 27, 1997). One of the late-stage intermediates (11) was resolved into a pair of enantiomers. From there, the (R)-(+)-12 (absolute configuration by X-ray) of dinapsoline was identified as the active enantiomer. In unilateral 6-hydroxydopamine (6-OHDA)-lesioned rats, (+)-dinapsoline showed robust rotational behavior comparable to that of an external benchmark, trans-4,5,5a,6,7,11b-hexahydro-2-propyl-benzo[f]thieno[2,3-c]quinoline-9,10-diol, hydrochloride 18 (Michaelides, M. R.; Hong, Y. Preparation of heterotetracyclic compounds as dopamine agonists. PCT Int. Appl. WO 9422858 A1, Oct 13, 1994).

Novel dihydropyrazine analogues as NPY antagonists.

The dihydropyridine is currently one of the lead compounds in the neuropeptide-Y(1) (NPY-Y(1)) receptor antagonist program. Compound is a selective, high affinity ligand at the NPY-Y(1) receptors (IC(50)=4.2 nM) in SK-N-MC cells. To further expand the SAR study surrounding this dihydropyridine core structure we succeeded in synthesizing an analogous series of dihydropyrazine derivatives. This structural modification yielded compounds substantially different from the parent molecules in terms of molecular polarization and electron distribution while the overall molecular structure was generally preserved. This altered property should therefore provide us with additional SAR information on the optimal binding requirement with NPY receptors.