Browsing by Author "Pribut, Nicole"

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    The design and synthesis of novel HIV-1 non-nucleoside reverse transcriptase inhibitors
    (Stellenbosch : Stellenbosch University, 2015-04) Pribut, Nicole; Pelly, Stephen Christopher; Van Otterlo, Willem A. L.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Since its discovery in the 1980’s, HIV has affected the lives of millions of individuals around the globe. Despite obvious need and an enormous amount of research a cure has remained elusive due to the rapid onset of mutated forms of the virus. However, there has been considerable success in reducing viral levels of infected individuals through the use of highly active antiretroviral therapy (HAART). The first-line regimen HAART mainly targets reverse transcriptase (RT) through the employment of two nucleoside RT inhibitors (NRTIs) and a nonnucleoside RT inhibitor (NNRTI). NNRTIs target an allosteric pocket situated about 10 Å from the catalytic site and cause a conformational change in the enzyme upon binding, leading to the inhibition of viral replication. There are currently 5 FDA approved NNRTIs on the market which successfully inhibit viral replication, but the use of these drugs is becoming limited due to the onset of drug resistant strains of the virus. In light of this need for the development of novel NNRTIs, we set out to explore new territory in NNRTI drug design with a goal of maintaining efficacy in the presence of both wild-type and mutated forms of HIV-1. To this end we designed three different NNRTI scaffolds along three different research thrusts. The first of these focused on the synthesis of 15 novel flexible triazole containing compounds. With these compounds we sought to achieve π-π stacking interactions with conserved amino acid residue Trp229 in the hope that we would be able to maintain efficacy in the presence of mutated forms of the virus. An additional feature included hydrogen bonding interactions to the backbone of Lys103. However, despite having thoroughly explored the triazole ring with multiple substitution arrangements, these compounds had very poor to no activity against whole cell HIV-1. Secondly we focused on the synthesis of a 4-hydroxyindole scaffold as a potential NNRTI. The focus here was to achieve interactions to Trp229 and simultaneously achieve hydrogen bonding interactions to the backbone of Lys101 at the entrance of the pocket. This was a novel concept in this class of compounds. We were able to successfully synthesize the indole core as a proofof-concept using the Knoevenagel-Hemetsberger method however; this compound had no activity against HIV-1. Lastly, in our quest to synthesize a novel NNRTI that could maintain efficacy against HIV-1 we decided to attempt to improve upon the stability of a lead indole-based compound synthesized previously within our research group. The lead compound was found to be potent with an IC50 of 1 nM but was unstable in acidic media due to the presence of a methoxy functionality situated at the 3-position on the indole. We sought to overcome this issue by introducing a substituted aryl amine functionality at this position. We were successful in synthesizing our desired compound but unfortunately it was significantly less active against whole cell HIV-1 than the lead compound. However, we were not completely deterred as there are a number of unexplored bioiososteres as possibilities to improve upon the stability of the lead compound while maintaining its excellent activity profile.
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    Design and Synthesis of potent benzimidazolone HIV Non-nucleoside reverse transcriptase inhibitors
    (Stellenbosch : Stellenbosch University, 2018-12) Pribut, Nicole; Pelly, Stephen C; Van Otterlo, Willem A. L.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Since the 1980’s, HIV has plagued the population on a global scale, with millions of newly infected individuals reported every year. However, with the introduction of combination therapy, which can significantly suppress viremia to almost undetectable levels in the infected populace, the disease can be managed to a point where the infected population can live almost normal lives. Unfortunately, although able to improve quality of life and prevent the onset of AIDS, combination therapy is not curative as issues related to drug resistance and adherence can lead to the re-emergence of high viremia, AIDS and, inevitably, death. Consequently, there remains a need for the continued development of new and superior ARVs that are effective against wild-type and resistant strains of HIV and are well tolerated for chronic use. In an effort to address this need, our group has focused on the design and synthesis of new NNRTIs. In the clinic, NNRTIs are an important part of first-line regimens employed in the treatment of HIV. In particular, our group focused on the synthesis of a series of small benzimidazolone-containing NNRTIs which were initially designed to address lability issues exhibited by a series of potent indole-based NNRTIs. These first-generation benzimidazolones were readily synthesized over five steps and, following evaluation in an HIV whole cell assay, were found to be potent inhibitors of HIV RT, but were susceptible to clinically relevant resistant strains such as K103N and Y181C. As a result, we synthesized a series of second-generation benzimidazolone NNRTIs which were designed to overcome, specifically, the Y181C resistant strain. Starting from 2-amino-3-nitrophenol, the benzimidazolone precursor for these compounds was synthesized over six steps. This precursor was then coupled to various aryl or heteroaryl halides by way of an Ullmann reaction or SNAr. Of this small library, one compound in particular was found to be potent (with low nanomolar activity), not only against wildtype, but also against Y181C, Y188C and the double mutant K103N/Y181C. Furthermore, this compound, 3-chloro-5-((3-ethyl-2-oxo-1-((2-trimethylsilyl)ethoxy)methyl)-2,3-dihydro-1H-benzo[d]imidazol-4- yl)oxy)benzonitrile, exhibited only low levels of susceptibility against the most problematic K103N resistant strain. We envisaged that by introducing additional electrostatic interactions between our potent lead compound and the NNIBP we would succeed in optimizing the efficacy of our compound against wild-type and resistant strains of HIV. In order to achieve these additional interactions we adopted two different approaches. The first approach focused on targeting a lysine residue located at the top of a narrow hydrophobic chimney towards the back of the NNIBP. To this end, we installed a cyanovinyl substituent onto our lead compound which, based on docking studies, would protrude into the chimney and form a hydrogen bond with the targeted lysine. Installation of the cyanovinyl substituent was achieved using the well-established Heck coupling reaction. Although this compound, (E)-3-(2-cyanovinyl)-5-((3-ethyl-2-oxo-2,3-dihydro-1Hbenzo[ d]imidazol-4-yl)oxy)benzonitrile, was also a potent inhibitor of HIV RT, it was unfortunately not significantly more potent than our existing lead compound. The second approach employed a molecular hybridization technique to form a combination of our lead compound and efavirenz, in order to achieve additional hydrogen bonding to the backbone of Lys101. This new hybrid compound, 3-chloro-5-((4,4-dimethyl-2-oxo-1,4-dihydro-2H-benzo[d][1,3]oxazin-5- yl)oxy)benzonitrile, was successfully synthesized over seven steps and found to be slightly more potent than our lead compound with an improved selectivity index.