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Alkaloids are a class of organic compounds with a wide range of biological properties, including anti-HIV activity. The 1,2,3,4-tetrahydroisoquinoline is a ubiquitous structural motif of many alkaloids. Using a short and an efficient route for synthesis, a series of 1,2,3,4-tetrahydroisoquinolines/isoquinolines was developed. These compounds have been analysed for their ability to inhibit an important interaction between HIV-1 integrase enzyme (IN) and human LEDGF/p75 protein (p75) which assists in the viral integration into the active genes. A lead compound 6d is found to inhibit the LEDGF/p75-IN interaction in vitro with an IC of ~10 μm. Molecular docking analysis of the isoquinoline 6d reveals its interactions with the LEDGF/p75-binding residues of IN. Based on an order of addition experiment, the binding of 6d or LEDGF/p75 to IN is shown to be mutually exclusive. Also, the activity of 6d in vitro is found to be unaffected by the presence of a non-specific DNA. As reported earlier for the inhibitors of LEDGF/p75-IN interaction, 6d exhibits a potent inhibition of both the early and late stages of HIV-1 replication. Compound 6d differing from the known inhibitors in the chemical moieties and interactions with CCD could potentially be explored further for developing small molecule inhibitors of LEDGF/p75-IN interaction having a higher potency.

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Lens-epithelium-derived-growth factor (LEDGF/p75) is an essential host protein for integration of HIV-1 DNA into host genome. Earlier alanine scanning mutational analysis has revealed that residues I365, D366 and F406 in the integrase binding domain (IBD) of p75 are critical for interaction with HIV-1 integrase (IN), while K364, V408 have intermediate effect and residues N367, L368, R405, K407 show wild type binding with IN. To gain insight into contribution of side chains of L368 and V408 that are adjacent to critical residues I365 and F406, respectively, site directed mutation of these residues to Ile/Leu, Met and Phe has been performed and characterized in this study. In contrast to alanine substitution, L368F mutation showed a ∼25% decrease, while V408L and V408F showed wild type binding, to IN. Docking analysis of I365, D366 and F406 mutants of IBD with IN predicts that interaction between residue M178(IN) and I365(IBD) might lead to an encounter complex formation. Accordingly, M178I mutant of IN failed to interact with IBD. Interestingly, a L368F/V408F double mutant of IBD restored binding to M178I mutant of IN, indicating that altered hydrophobicity in the inter helical loops of IBD might make I365 more accessible for interaction with IN.