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Of the 38.6 million people living with HIV/AIDS globally, almost 25 million (65%) live in sub-Saharan Africa. Preventive strategies and measures fall short, often simply because they are not available or are largely male-controlled. A preventive HIV vaccine is still far away; hence the drive to develop alternative prevention technologies, such as microbicides and oral pre-exposure prophylaxis, that could be female controlled. There are, at present, twenty-two anti-HIV drugs which have been formally licensed for clinical use in the treatment of HIV infections (AIDS): zidovudine, didanosine, zalcitabine, stavudine, lamivudine, abacavir, emtricitabine, tenofovir, nevirapine, delavirdine, efavirenz, saquinavir, ritonavir, indinavir, nelfinavir, amprenavir, lopinavir, atazanavir, fosamprenavir, tipranavir, darunavir and enfuvirtide. These compounds, in combination, form the basis of HAART (highly active antiretroviral therapy), which has led to the development of a single daily pill existing of the combination of tenofovir disoproxil fumarate, emtricitabine and efavirenz, which has to be taken orally once daily for the treatment of AIDS. Beyond development of new drugs and clinical evaluation of existing medications, several companies within the pharmaceutical industry have established innovative policies that provide HIV medications at affordable prices in the least-developed countries. Reduced pricing is not alone a solution, and thus companies are actively working in partnership with the World Health Organization and other multinational groups to address roadblocks such as complex registration and procurement systems. Even in this period of successful anti-HIV therapy via HAART, a growing number of patients is cycling through the various remaining therapeutic options and are increasingly becoming dependent of the availability of newly developed anti-HIV agents. It is of concern that existing and future therapies will have to be effective against newly evolving (including drug-resistant) HIV variants in patients who currently face many years, if not decades, of chronic anti-HIV drug treatment. In spite of continuous long-term interventions to promote safer sexual behaviour, HIV prevalence is high and still rising in many parts of the world. The face of the epidemic is now black, female, young and poor..., and female controlled methods are urgently needed. Female controlled methods such as microbicides and cervical barrier methods provide hopeful perspectives when condom use is low due to social, cultural and/or economic factors, but, after all, the oral administration of a single daily pill would seem the most convenient way to prevent HIV infection, as its protective activity may be independent of the route of viral transmission.
The acyclic nucleoside phosphonates [HPMPC: cidofovir, Vistide; PMEA: adefovir dipivoxil, Hepsera; and PMPA: tenofovir, Viread] have proven to be effective in vitro (cell culture systems) and in vivo (animal models and clinical studies) against a wide variety of DNA virus and retrovirus infections, for example, cidofovir against herpesvirus [herpes simplex virus type 1 and 2, varicella-zoster virus, cytomegalovirus, Epstein-Barr virus, human herpesvirus type 6, 7 and 8), polyoma-, papilloma-, adeno- and poxvirus (variola virus, cowpox virus, vaccinia virus, molluscum contagiosum virus and orf) infections; adefovir against herpesvirus, hepadnavirus [human hepatitis B virus] and retrovirus [HIV type-1 and 2, simian immunodeficiency virus and feline immunodeficiency virus] infections; and tenofovir against both hepadna- and retrovirus infections. Cidofovir has been officially approved for the treatment of cytomegalovirus retinitis in AIDS patients, tenofovir disoproxil fumarate (Viread) for the treatment of HIV infections (i.e., AIDS) and adefovir dipivoxil for the treatment of chronic hepatitis B.
In our previous studies, we combined the pharmacophoric group of etravirine and VRX-480773 using structure-guided molecular hybridization strategy, which led to the identification of <italic>S</italic>-DAPYs with an amide subunit that exhibited moderate potency against wild-type HIV-1 strain. However, Maurizo's discovering of <italic>S</italic>-DAPYs without the amide subunit showed excellent potency against HIV-1. To investigate the effect of the amide subunit on antiviral activity, a series of novel <italic>S</italic>-DAPYs derivatives without the amide subunit were synthesized and evaluated for their anti-HIV activities in MT-4 cell cultures. Biological results showed that three compounds (<bold>6g</bold>, <bold>6m</bold> and <bold>6s</bold>) exhibited moderate inhibitory activities against wild-type HIV-1 strain with EC<sub>50</sub> values ranging from 6.5 to 15.4 μmol/L, but inferior to that of the corresponding derivatives with the amide subunit. Molecular simulation revealed that a hydrogen bond was formed between the C=O of the amide moieties and the NH group of Lys103, and it provides ideas for more drug research in the treatment of AIDS.