Synthesis and biological evaluation of prodrug-type anti-HIV agents: ester conjugates of carboxylic acid-containing dipeptide HIV protease inhibitors and a reverse transcriptase inhibitor

The Use of Zidovudine Pharmacophore in Multi-Target-Directed Ligands for AIDS Therapy

The concept of polypharmacology embraces multiple drugs combined in a therapeutic regimen (drug combination or cocktail), fixed dose combinations (FDCs), and a single drug that binds to different targets (multi-target drug). A polypharmacology approach is widely applied in the treatment of acquired immunodeficiency syndrome (AIDS), providing life-saving therapies for millions of people living with HIV. Despite the success in viral load suppression and patient survival of combined antiretroviral therapy (cART), the development of new drugs has become imperative, owing to the emergence of resistant strains and poor adherence to cART. 3'-azido-2',3'-dideoxythymidine, also known as azidothymidine or zidovudine (AZT), is a widely applied starting scaffold in the search for new compounds, due to its good antiretroviral activity. Through the medicinal chemistry tool of molecular hybridization, AZT has been included in the structure of several compounds allowing for the development of multi-target-directed ligands (MTDLs) as antiretrovirals. This review aims to systematically explore and critically discuss AZT-based compounds as potential MTDLs for the treatment of AIDS. The review findings allowed us to conclude that: (i) AZT hybrids are still worth exploring, as they may provide highly active compounds targeting different steps of the HIV-1 replication cycle; (ii) AZT is a good starting point for the preparation of co-drugs with enhanced cell permeability.

Hybrid Molecules as Potential Drugs for the Treatment of HIV: Design and Applications

Human immunodeficiency virus (HIV) infection is a major problem for humanity because HIV is constantly changing and developing resistance to current drugs. This necessitates the development of new anti-HIV drugs that take new approaches to combat an ever-evolving virus. One of the promising alternatives to combination antiretroviral therapy (cART) is the molecular hybrid strategy, in which two or more pharmacophore units of bioactive scaffolds are combined into a single molecular structure. These hybrid structures have the potential to have higher efficacy and lower toxicity than their parent molecules. Given the potential advantages of the hybrid molecular approach, the development and synthesis of these compounds are of great importance in anti-HIV drug discovery. This review focuses on the recent development of hybrid compounds targeting integrase (IN), reverse transcriptase (RT), and protease (PR) proteins and provides a brief description of their chemical structures, structure–activity relationship, and binding mode.

Polypharmacology in HIV inhibition: can a drug with simultaneous action against two relevant targets be an alternative to combination therapy?

HIV infection still has a serious health and socio-economical impact and is one of the primary causes of morbidity and mortality all over the world. HIV infection and the AIDS pandemic are still matters of great concern, especially in less developed countries where the access to highly active antiretroviral therapy (HAART) is limited. Patient compliance is another serious drawback. Nowadays, HAART is the treatment of choice although it is not the panacea. Despite the fact that it suppresses viral replication at undetectable viral loads and prevents progression of HIV infection into AIDS HAART has several pitfalls, namely, long-term side-effects, drug resistance development, emergence of drug-resistant viruses, low compliance and the intolerance of some patients to these drugs. Moreover, another serious health concern is the event of co-infection with more than one pathogen at the same time (e.g. HIV and HCV, HBV, herpes viruses, etc). Currently, the multi-target drug approach has become an exciting strategy to address complex diseases and overcome drug resistance development. Such multifunctional molecules combine in their structure pharmacophores that may simultaneously interfere with multiple targets and their use may eventually be more safe and efficacious than that involving a mixture of separate molecules because of avoidance or delay of drug resistance, lower incidence of unwanted drug-drug interactions and improved compliance. In this review we focus on multifunctional molecules with dual activity against different targets of the HIV life cycle or able to block replication, not only of HIV but also of other viruses that are often co-pathogens of HIV. The different approaches are documented by selected examples.

Viral proteinases: targets of opportunity

During antiviral drug development, any essential stage of the viral life cycle can serve as a potential drug target. Since most viruses encode specific proteases whose cleavage activity is required for viral replication, and whose structure and activity are unique to the virus and not the host cell, these enzymes make excellent targets for drug development. Success using this approach has been demonstrated with the plethora of protease inhibitors approved for use against HIV. This discussion is designed to review the field of antiviral drug development, focusing on the search for protease inhibitors, while highlighting some of the challenges encountered along the way. Protease inhibitor drug discovery efforts highlighting progress made with HIV, HCV, HRV, and vaccinia virus as a model system are included. Drug Dev. Res. 67:501–510, 2006. © 2006 Wiley‐Liss, Inc.

Nucleophilic acyl substitutions of anhydrides with protic nucleophiles catalyzed by amphoteric, oxomolybdenum species

[reaction: see text] Among six different group VIb oxometallic species examined, dioxomolybdenum dichloride and oxomolybdenum tetrachloride were the most efficient catalysts to facilitate nucleophilic acyl substitution (NAS) of anhydrides with a myriad array of alcohols, amines, and thiols in high yields and high chemoselectivity. In contrast to the well-recognized redox chemical behaviors associated with oxomolybdenum(VI) species, the catalytic NAS was unprecedented and tolerates virtually all kinds of functional groups. By using benzoic anhydride as a mediator for in situ generation of an incipient mixed anhydride-MoO(2)Cl(2) adduct with a given functional alkanoic acid, one can achieve oleate, dipeptide, diphenylmethyl, N-Fmoc-alpha-amino, pyruvic, and tert-butylthio ester, N-tert-butylamide, and trityl methacrylate syntheses with appropriate protic nucleophiles. The amphoteric character of the Mo=O unit in oxomolybdenum chlorides was found to be responsible for the catalytic NAS profile as supported by a control NAS reaction of using an authentic adduct-MoOCl(2)(O(2)CBu(t)())(2) between pivalic anhydride and MoO(2)Cl(2) as the catalyst.

Chemoenzymatic syntheses of homo- and heterodimers of AZT and d4T, and evaluation of their anti-HIV activity

Homo- and heterodimers of AZT and d4T, possessing carbonate and carbamate linkers, have been synthesized with the aim to enhance the antiviral activity of their components. Homo- and heterodimer carbamates showed weak anti-HIV activity. On the other hand, dinucleoside carbonates showed marked antiviral activity.

Plasmepsin II inhibition and antiplasmodial activity of Primaquine-Statine 'double-drugs'

Statine-based inhibitors of Plasmepsin II (PLMII) coupled with Primaquine have been designed using the 'double-drug' approach. The IC50 values for PLMII inhibition ranged from 0.59 to 400 nM and the best IC50 value for inhibition of Plasmodium falciparum growth in vitro was 0.4 microM, which represent a remarkable improvement compared to other statine-based PLMII inhibitors.

New bicyclam-GalCer analogue conjugates: synthesis and in vitro anti-HIV activity

The synthesis of bipharmacophore anti-HIV compounds which, in a single molecule, combine two ligands, that is, the bicyclam AMD3100 and a GalCer analogue, that might inhibit several steps of the complex virus/cell cascade interactions has been performed. The 'double-drug' Gal-AMD3100 conjugates elicited inhibitory effects on T (or X4)-tropic HIV-1 replication in all CXCR4 expressing cell lines with EC(50) values ranging from 0.25 to 6.0 microM which were however approximately 40- to 125-fold lower than that of AMD3100. Concerning the mechanism of inhibition of the Gal-AMD3100 conjugates, experiments performed with X4 or R5HIV-1 strains and GHOST cells genetically modified to express CD4 and CXCR4 or CCR5 indicated clearly that the conjugates interact with CXCR4 and not with CCR5.

New water-soluble prodrugs of HIV protease inhibitors based on O-->N intramolecular acyl migration

To improve the low water-solubility of HIV protease inhibitors, we synthesized water-soluble prodrugs of KNI-272 and KNI-279 which are potent HIV-1 protease inhibitors consisting of an Apns-Thz core structure (Apns; allophenylnorstatine, Thz; thiazolidine-4-carboxylic acid) as an inhibitory machinery. The prodrugs, which contained an O-acyl peptidomimetic structure with an ionized amino group leading to the increase of water-solubility, were designed to regenerate the corresponding parent drugs based on the O-->N intramolecular acyl migration reaction at the alpha-hydroxy-beta-amino acid residue, that is allophenylnorstatine. The synthetic prodrugs 3, 4, 6, and 7 improved the water-solubility (>300mg/mL) more than 4000-fold in comparison with the parent compounds, which is the practically acceptable value as water-soluble drugs. These prodrugs were stable as an HCl salt and in a strongly acidic solution corresponding to gastric juice (pH 2.0), and could be converted to the parent compounds promptly in the aqueous condition from slightly acidic to basic pH at 37 degrees C, with the suitable migration rate, via a five-membered ring intermediate. Using a similar method, we synthesized a prodrug (12) of ritonavir, a clinically useful HIV-1 protease inhibitor as an anti-AIDS drug. In contrast to the prodrugs 3, 4, 6, and 7, the prodrug 12 was very slowly converted to ritonavir probably through a six-membered ring intermediate, with the t(1/2) value of 32h that may not be suitable for practical use.

Design, synthesis, and biological evaluation of anti-HIV double-drugs. conjugates of HIV protease inhibitors with a reverse transcriptase inhibitor through spontaneously cleavable linkers

Based on the prodrug concept as well as the combination of two different classes of anti-HIV agents, we designed and synthesized a series of anti-HIV double-drugs consisting of HIV protease inhibitors conjugated with a nucleoside reverse transcriptase inhibitor in an effort to enhance the antiviral activity. For the conjugation, a series of linkers that conjoins the two different classes of inhibitors has been investigated. Double-drugs using a succinyl amino acid linker were shown to release the parent drugs via spontaneous imide formation at a faster rate compared to compounds using a glutaryl amino acid linker, as expected from the energetically favorable cyclization to the five-membered ring. Among the double-drugs, KNI-1039 (3b) with a glutarylglycine linker exhibited extremely potent anti-HIV activity compared with that of the individual components. Double-drug 3b was relatively stable in culture medium, whereas it regenerated active species in cell homogenate. These results suggested that the synergistic enhancement of anti-HIV activities of 3b may be due to their ability to penetrate into the target cell and subsequent regeneration of two different classes of anti-HIV agents in the cytoplasm.