Abstracts Category : Other

Lead optimisation of an indole based HIV-1 non-nucleoside reverse transcriptase inhibitor

by Siobhan Ernan Brigg

ENGLISH ABSTRACT: HIV-1 remains the worst pandemic faced by mankind since its discovery as the causative agent of AIDS in the early 1980s. An enormous amount of research has been done to find a cure, but to date there has been no success and resistance is widespread among the available treatment. This project focused on the development of novel non-nucleoside reverse transcriptase inhibitors (NNRTIs) using a rational design approach. The lead compound, ethyl 5-chloro-3-(methoxy(phenyl)methyl)-1H-indole-2-carboxylate, was shown to have low nano-molar potency against HIV-1 (IC50 = 16 nM), however it had two main shortcomings which needed to be addressed; poor resistance profile and poor acid stability. Previous research had shown the resistance profile could be improved by introducing meta substitution on the phenyl moiety which interacts with Tyr181 of the NNRTI binding pocket (NNIBP). We were successful in synthesising several meta substituted phenyl derivatives of the lead compound and these were shown to be equally as potent as the lead compound. Their activity against resistant strains is yet to be determined as we are awaiting the results from biological testing. The presence of an acid labile methyl ether functionality on the molecule which was susceptible to an acid catalysed indole mediated SN1 substitution in aqueous acidic medium meant that the lead compound could never be considered as a candidate for an orally available drug. The methyl ether moiety was exchanged for a sulfide moiety and several of these derivatives were successfully synthesised. Acid stability tests showed that we were successful in our endeavour to improve the acid stability, offering an advantage over the lead compound despite a slight reduction in potency. However to completely eliminate the possibility of substitution, we replaced the methyl ether moiety for an ethyl group, successfully synthesising ethyl 5-chloro-3-(1-phenylpropyl)-1H-indole-2-carboxylate and 5-chloro-3-(1-phenylpropyl)-1H-indole-2-carboxamide and we are currently awaiting the results from biological testing to determine whether this derivative is active against HIV-1. The functionality in the 2-position of the indole was also investigated through the synthesis of 5-chloro-3-(methoxy(phenyl)methyl)-1H-indole and 5-chloro-3-((methylthio),(phenyl)methyl)-1H-indole. These derivatives lacking a group in the 2-position of the indole showed significant reduction in potency. Replacement of the ethyl ester for an isobutyl ester to give isobutyl 5-chloro-3-((3,5-dimethylphenyl),(methylthio)methyl)-1H-indole-2-carboxylate, showed some maintenance of potency, however the larger side chain was not well accommodated in the NNIBP.The presence of a chiral centre on the lead compound, and all derivatives synthesised in the project, resulted in our final aim; we set out to develop a method for resolving these enantiomers. Unfortunately, although we employed a variety of different strategies, including the use of chiral auxiliaries and the classical resolution method of attempting toAdvisors/Committee Members: Pelly, Stephen, C., Blackie, Margeret, A. L., Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science..