Synthesis and biological properties of amino acid amide ligand-based pyridinioalkanoyl thioesters as anti-HIV agents

NCp7: targeting a multitasking protein for next-generation anti-HIV drug development part 1: covalent inhibitors

The major internal component of the HIV virion core is the nucleocapsid protein 7 (NCp7), a small, highly basic protein that is essential for multiple stages of the viral replicative cycle, and whose structure is preserved in all viral strains, including clinical isolates from therapy-experienced patients. This key protein is recognised as a potential target for an effective next-generation antiretroviral therapy, because it could offer the possibility to develop broad-spectrum agents that are less prone to select for resistant strains. Here, we provide a comprehensive overview of the covalent NCp7 inhibitors that have emerged over the past 25 years of drug discovery campaigns, emphasising, where possible, their structure-activity relationships (SARs) and pharmacophoric features.

Synthesis, characterization and biological evaluation of novel α, β unsaturated amides

Three derivatives of α,β unsaturated amides have been successfully synthesized via Ugi-four component (U-4CR) reaction. The interactions of the amides with calf thymus deoxyribonucleic acid (ct-DNA) have been investigated in the Tris-HCl buffer (pH=7.4) using viscometric, spectroscopic, thermal denaturation studies, and also molecular docking. By UV-Vis absorption spectroscopy studies, adding CT-DNA to the compound solution caused the hypochromism indicates that there are interactions between the compounds and DNA base pairs. In competitive fluorescence with methylene blue as an intercalator probe, adding compounds to DNA-MB solution caused an increase in emission spectra of the complex. This could be because of compound replacing, with similar binding mode of MB, between the DNA base pairs due to release of bonded MB molecules from DNA-MB complex. Thermal denaturation studies and viscometric experiments also indicated that all three investigated compounds bind to CT-DNA by non-classical intercalation mode. Additionally, molecular docking technique predicted partial intercalation binding mode for the compounds. Also, the highest binding energy was obtained for compound 5a. These results are in agreement with results obtained by empirical methods.

The next generation of HIV/AIDS drugs: novel and developmental antiHIV drugs and targets

There are presently 42 million people worldwide living with HIV/AIDS, the majority of which have limited access to antiretrovirals. Even if worldwide penetration was possible, our current chemotherapeutic strategies still suffer from issues of cost, patient compliance, deleterious acute and chronic side effects, emerging single and multidrug resistance, and generalized treatment and economic issues. Even our best antiretroviral therapeutic strategy, highly active antiretroviral therapy (HAART), falls short of completely suppressing HIV replication. Therefore, expansion of current therapeutic options by discovering new antiretrovirals and targets will be critical in the coming years. This review addresses the current status of reverse transcriptase and protease inhibitor development, and summarizes the progress in emerging classes of HIV inhibitors, including entry (T-20, T-1249), coreceptor (SCH-C, SCH-D), integrase (beta-Diketos) and p7 nucleocapsid Zn finger inhibitors (thioesters and PATEs). In addition, the processes of virus entry, PIC transport to the nucleus, HIV interaction with nuclear pores, Tat function, Rev function and virus budding (Tsg101 and ubiquitination) are examined, and proof of concept inhibitors and potential antiviral targets discussed.

Synthesis and Antifungal Studies of (2E)-N-Benzyl-N′-phenylbut-2-enediamide and (2E)-N,N′-Dibenzylbut-2-enediamide Analogues

A series of eleven butanediamine analogues, of which nine were new, were synthesized by the nucleophilic substitution of aromatic amines and benzylamines with maleic anhydride and tested on four yeast strains ofCandidaspecies using the broth microdilution method. Compounds3aand3cwith an unsubstituted phenyl ring and a 3-methoxyphenyl ring, respectively, are the most active against the fungal species with MIC values ranging from 20.2 to 80.6 μM forC. albicansandC. parapsilosisand 178.5 and 161.2 μM forC. krusei, respectively.

Conjugating drug candidates to polymeric chains does not necessarily enhance anti-influenza activity

Using the plaque reduction assay, relatively simple bicyclic quinone molecules, as well as multiple copies thereof covalently attached to a long polyglutamate-based polymeric chain, were examined as new inhibitors of various naturally occurring strains of influenza A virus. The polymer-conjugated inhibitors were found to have a far greater potency (for some as high as two orders of magnitude when a long spacer arm was employed) than their corresponding parent molecules against the human Wuhan influenza strain. However, such polymeric inhibitors failed to exhibit higher potency compared with their small molecule predecessors against the human Puerto Rico and avian turkey influenza strains. These observations, further explored by means of molecular modeling, reveal the previously unrecognized unpredictability of the benefits of multivalency, possibly because of poor accessibility of the viral targets to polymeric agents.

HIV type 1 Gag as a target for antiviral therapy

The Gag proteins of HIV-1 are central players in virus particle assembly, release, and maturation, and also function in the establishment of a productive infection. Despite their importance throughout the replication cycle, there are currently no approved antiretroviral therapies that target the Gag precursor protein or any of the mature Gag proteins. Recent progress in understanding the structural and cell biology of HIV-1 Gag function has revealed a number of potential Gag-related targets for possible therapeutic intervention. In this review, we summarize our current understanding of HIV-1 Gag and suggest some approaches for the development of novel antiretroviral agents that target Gag.

A one-pot preparation of N-2-mercaptobenzoyl-amino amides

The HIV-1 nucleocapsid (NCp7), structurally defined by zinc-binding domains, participates in crucial stages of the HIV-1 lifecycle and is mutationally nonpermissive, making it an attractive anti-HIV target. Mode of action studies have shown that the secondary structure and activity of NCp7 can be disrupted by acyl transfer from N-2-mercaptobenzoyl-amino amides. We have developed an improved one-pot reaction that affords N-2-mercaptobenzoyl-amino acids on multi-gram scales. This synthetic route allows for rapid modular construction and has greatly expanded the scope of easily accessible potential NCp7 inhibitors.

Novel approaches to inhibiting HIV-1 replication

Considerable success has been achieved in the treatment of HIV-1 infection, and more than two-dozen antiretroviral drugs are available targeting several distinct steps in the viral replication cycle. However, resistance to these compounds emerges readily, even in the context of combination therapy. Drug toxicity, adverse drug-drug interactions, and accompanying poor patient adherence can also lead to treatment failure. These considerations make continued development of novel antiretroviral therapeutics necessary. In this article, we highlight a number of steps in the HIV-1 replication cycle that represent promising targets for drug discovery. These include lipid raft microdomains, the RNase H activity of the viral enzyme reverse transcriptase, uncoating of the viral core, host cell machinery involved in the integration of the viral DNA into host cell chromatin, virus assembly, maturation, and budding, and the functions of several viral accessory proteins. We discuss the relevant molecular and cell biology, and describe progress to date in developing inhibitors against these novel targets. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

Optimization of unique, uncharged thioesters as inhibitors of HIV replication

A combinatorial chemistry approach was employed to prepare a restricted library of N-substituted S-acyl-2-mercaptobenzamide thioesters. It was shown that many members of this chemotype display anti-HIV activity via their ability to interact with HIV-1, HIV-2, SIV-infected cells, cell-free virus, and chronically and latently infected cells in a manner consistent with targeting of the highly conserved HIV-1 NCp7 zinc fingers. Compounds were initially screened using two different in vitro antiviral assays and evaluated for stability in neutral buffer containing 10% pooled human serum using a spectrophotometric assay. These data revealed that there was no significant correlation between thioester stability and antiviral activity, however, a slight inverse correlation between serum stability and virucidal activity was noted. Based on the virucidal capability and the ability to select lead compounds to inhibit virus expression from latently infected TNFalpha-induced U1 cells, we next determined if these compounds could prevent HIV cell-to-cell transmission. Several thioesters demonstrated potent inhibition of HIV cell-to-cell transmission with EC50 values in the 80-100 nM range. Thus, we have optimized a series of restricted thioesters and provided evidence that serum stability is not required for antiviral activity. Moreover, selected compounds show potential for development as topical microbicides.

Synthesis, resolution, and determination of the absolute configuration of the enantiomers of cis-4,5-dihydroxy-1,2-dithiane 1,1-dioxide, an HIV-1NCp7 inhibitor

The anti-HIV activity of (+/-)-cis-4,5-dihydroxy-1,2-dithiane 1,1-dioxide [(+/-)-cis-1,1-dioxo-[1,2]-dithiane-4,5-diol, NSC-624151] and its attack on the zinc finger domain of the HIV-1 nucleocapsid p7 (NCp7) protein has been established [Rice, W. G.; Baker, D. C.; Schaeffer, C. A.; Graham, L.; Bu, M.; Terpening, S.; Clanton, D.; Schultz, R.; Bader, J. P.; Buckheit, R. W.; Field, L.; Singh, P. K. Turpin, J. A. Antimicrob. Agents Chemother. 1997, 41, 419]. In order to determine which enantiomer of NSC-624151 is the more active component, the compound was resolved via its bis-'Mosher ester', which was prepared via its reaction with two equiv of (-)-(R)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride. The diastereoisomeric esters were separated, and each ester was hydrolyzed to yield enantiomers with (D)(21) +151 degrees (c 0.5, MeOH) and (D)(21) -146 degrees (c 0.5, MeOH). Single-crystal X-ray analysis of the (-)-bis-'Mosher ester' showed that the (-)-enantiomer is the (4S, 5R)-compound. The (-)-enantiomer (NSC 693195) was ca. twice as active (EC(50) 8.8+/-0.2 microM) as its (+)-counterpart (NSC 693194) (EC(50) 16.2+/-2.4 microM) in the XTT assay against HIV-1. All three compounds were found to be approximately equally effective in promoting Zn ejection from the NCp7 zinc finger. As the more anti-HIV active enantiomer is only slightly more active than the racemic form, it appears to offer no advantages over the racemic form.

In vivo antiviral activity of novel human immunodeficiency virus type 1 nucleocapsid p7 zinc finger inhibitors in a transgenic murine model

Control of human immunodeficiency virus through the use of inexpensive chemotherapeutics, with minimal side effects and decreased potential for engendering resistant virus, is a long-term therapeutic goal. In principle, this goal can be accomplished if viral replication in reservoirs of chronically and latently infected cells is addressed. As a first step, we have developed novel antiviral compounds based on a 2-mercaptobenzamide thioester chemotype, including the pyridinioalkanoyl thioesters, which specifically target the zinc fingers of the human immunodeficiency virus nucleocapsid protein (NCp7). Using these compounds in a murine transgenic model, in which infectious human immunodeficiency virus is induced from an integrated provirus, we show inhibition of transgenic spleen cell p24 expression with potencies comparable to acute infection assays using human peripheral blood lymphocytes. More importantly, transgenic mice treated in vivo with two 2-mercaptobenzamide thioesters expressed significantly lower plasma p24, and splenocytes from these animals produced fewer infectious virions. Thus, these thioesters may provide an effective means for inhibiting the expression of human immunodeficiency virus from integrated viral reservoirs.