Tino Sanchez

From Ligand to Complexes. Part 2. Remarks on Human Immunodeficiency Virus type 1 Integrase Inhibition by β-Diketo Acid Metal Complexes

Previously, we synthesized a series of beta-diketo acid metal complexes as novel HIV-1 integrase (IN) inhibitors (J. Med. Chem. 2006, 46, 4248-4260). Herein, a further extension of this study is reported. First, detailed docking studies were performed in order to investigate the mode of binding in the active site of the free ligands and of their metal complexes. Second, a series of potentiometric measurements were conducted for two diketo acids chosen as model ligands, with Mn(2+) and Ca(2+), in order to outline a speciation model. Third, we designed and synthesized a new set of complexes with different stoichiometries and tested them in an in vitro assay specific for IN. Finally, we obtained the first X-ray structure of a metal complex with HIV-1 IN inhibition activity. Analysis of these results supports the hypothesis that the diketo acids could act as complexes and form complexes with the metal ions on the active site of the enzyme.

Development of the next generation of HIV-1 integrase inhibitors: Pyrazolone as a novel inhibitor scaffold

HIV-1 integrase (IN), one of the essential enzymes in HIV infection, has been validated as a target for HIV treatment. While more than 20 drugs have been approved by the FDA to treat HIV/AIDS, only one drug, Raltegravir (1), was approved as an IN inhibitor. The rapid mutation of the virus, which leads to multidrug resistant HIV strains, presents an urgent need to find potent compounds that can serve as second-generation IN inhibitors. The pyrazolone scaffold, predicted by a computational modeling study using GS-9137(2) as a pharmacophoric model, has shown to inhibit the IN catalytic activities in low micromolar range. We have synthesized various analogs based on the pyrazolone scaffold and performed SAR studies. This paper will showcase the up-to-date result of this scaffold as a promising HIV-1 IN inhibitor.

Design and synthesis of novel dihydroquinoline-3-carboxylic acids as HIV-1 integrase inhibitors

Previously, we discovered linomide analogues as novel HIV-1 integrase (IN) inhibitors. Here, to make possible structure-activity relationships, we report on the design and synthesis of a series of substituted dihydroquinoline-3-carboxylic acids. The crystal structure of the representative compound 2c has also been solved. Among the eight new analogues, 2e showed a potency in inhibiting IN strand transfer catalytic activity similar to the reference diketo acid inhibitor L-731,988 (IC(50)=0.9 microM vs. 0.54 microM, for 2e and L-731,988, respectively). Furthermore, none of the compounds showed significant cytotoxicity in two tested cancer cell lines. These compounds represent an interesting prototype of IN inhibitors, potentially involved in a metal chelating mechanism, and further optimization is warranted.

Efficient synthesis and utilization of phenyl-substituted heteroaromatic carboxylic acids as aryl diketo acid isosteres in the design of novel HIV-1 integrase inhibitors

Three new types of aryl diketo acid (ADK) isosteres were designed by conversion of the biologically labile 1,3-diketo unit into heteroaromatic motif such as isoxazole, isothiazole, or 1H-pyrazole to improve the physicochemical property of ADK-based HIV-1 integrase (IN) inhibitors. The synthesis of the heteroaromatic carboxylic acids was established by employing phenyl beta-diketoester or benzaldehyde as the starting material and 1,3-dipolar cycloaddition as the key reaction. Of the compounds tested, the 3-benzyloxyphenyl-substituted isoxazole carboxylic acid displayed the best IN inhibitory and antiviral activities, with N-hydroxylamidation enhancing the in vitro and in vivo potency. These findings are important for further optimization of ADK-based IN inhibitors.

HIV-1 in strand transfer chelating inhibitors: A focus on metal binding

Most active and selective strand transfer HIV-1 integrase (IN) inhibitors contain chelating functional groups that are crucial feature for the inhibition of the catalytic activities of the enzyme. In particular, diketo acids and their derivatives can coordinate one or two metal ions within the catalytic core of the enzyme. The present work is intended as a contribution to elucidate the mechanism of action of the HIV-IN inhibitors by studying the coordinative features of H₂L¹ (L-708,906), an important member of the diketo acids family of inhibitors, and H₂L₂, a model for S-1360, another potent IN inhibitor. Magnesium(II) and manganese(II) complexes of H₂L¹ and H₂L² were isolated and fully characterized in solution and in the solid state. The crystal structures of the manganese complex [Mn(HL₂)₂(CH₃OH)₂]·2CH₃OH were solved by X-ray diffraction analysis. Moreover, the speciation models for H₂L₂ with magnesium(II) and manganese(II) ions were performed and the formation constants of the complexes were measured. M(HL₂)₂ (M = Mg²+, Mn²+) was the most abundant species in solution at physiological pH. All the synthesized compounds were tested for their anti-IN activity, showing good results both for the ligand and the corresponding complexes. From analysis of the speciation models and of the biological data we can conclude that coordination of both metal cofactors could not be strictly necessary and that inhibitors can act as complexes and not only as free ligands.

Investigating the Role of Metal Chelation in HIV-1 Integrase Strand Transfer Inhibitors

HIV-1 integrase (IN) has been validated as an attractive target for the treatment of HIV/AIDS. Several studies have confirmed that the metal binding function is a crucial feature in many of the reported IN inhibitors. To provide new insights on the metal chelating mechanism of IN inhibitors, we prepared a series of metal complexes of two ligands (HL1 and HL2), designed as representative models of the clinically used compounds raltegravir and elvitegravir. Potentiometric measurements were conducted for HL2 in the presence of Mg(II), Mn(II), Co(II), and Zn(II) in order to delineate a metal speciation model. We also determined the X-ray structures of both of the ligands and of three representative metal complexes. Our results support the hypothesis that several selective strand transfer inhibitors preferentially chelate one cation in solution and that the metal complexes can interact with the active site of the enzyme.

Repositioning HIV-1 Integrase Inhibitors for Cancer Therapeutics: 1,6-Naphthyridine-7-carboxamide as a Promising Scaffold with Drug-like Properties

Among a large number of HIV-1 integrase (IN) inhibitors, the 8-hydroxy-[1,6]naphthyridines (i.e., L-870,810) were one of the promising class of antiretroviral drugs developed by Merck Laboratories. In spite of its remarkable potency and efficacy, unfortunately upon completion of phase I clinical studies, development of L-870,810 was halted. Because of its desirable pharmacological and pharmaceutical properties we were intrigued to design novel analogues of L-870,810 with goals to (1) improve upon limitations of naphthyridine-7-carboxamides as antiviral agents and (2) to reposition their use as innovative cytotoxic agents for cancer therapeutics. Herein, we report on the design and synthesis of a series of 1,6-naphthyridine-7-carboxamides with various substitutions at the 5- and 8-positions. All the new 5-substituted-8-hydroxy-[1,6]naphthyridines were potent IN inhibitors and the 5-substituted-8-amino-[1,6]naphthyridines were significantly cytotoxic. Further optimization of the 5,8-disubstituted-[1,6]naphthyridines with structural variation on 7-carboxamide delivered novel compounds with significant cytotoxicity in a panel of cancer cell lines and effective inhibition against select oncogenic kinases.

Novel dimeric aryldiketo containing inhibitors of HIV-1 integrase: Effects of the phenyl substituent and the linker orientation

Aryl diketoacids (ADK) and their bioisosteres are among the most promising HIV-1 integrase (IN) inhibitors. Previously, we designed a series of ADK dimers as a new class of IN inhibitors that were hypothesized to target two divalent metal ions on the active site of IN. Herein we present a further structure-activity relationship (SAR) study with respect to the substituent effect of the ADK and the dimerization with conformationally constrained linkers such as piperazine, 4-amino-piperidine, piperidin-4-ol, and trans-cyclohexan-1,4-diamine. The substituents on the phenyl ring as well as the spatial orientation of the two diketo units were observed to play important roles in the IN inhibitory potency. The hydrophobic group was an optimal substitution at the 3-position of the aryl ring. The piperazine and 4-amino-piperidine linkers brought about the most potent analogs among the hydrophobic group or halogen substituted ADK dimers. The docking studies suggested that the bulky hydrophobic substitution at 3-phenyl ring and the linker of 4-amino-piperidine were beneficial for adopting an active conformation to achieve strong interactions with the active site Mg(2+) and the key residue E152 within the catalytic core domain. This study is a significant extension of our previous report on the dimeric ADK-containing IN inhibitors, providing a new promising template for further lead optimization.

Ruthenium arene complexes as HIV-1 integrase strand transfer inhibitors

The quinolone HL(1) and the hydroxypyrimidine-carboxamide HL(2) were designed and synthesized as models of the HIV integrase strand transfer inhibitors Elvitegravir and Raltegravir (brand name Isentress), with the aim to study their complexing behavior and their biological activity. The Ru(arene) complexes [RuCl(η(6)-p-cym)L(1)], [RuCl(η(6)-p-cym)L(2)] and [RuCl(hexamethylbenzene)L(2)] were also synthesized and spectroscopically characterized and their X-ray diffraction structures were discussed. The ligands and the complexes showed inhibition potency in the sub/low-micromolar concentration range in anti-HIV-1 integrase enzymatic assays, with selectivity toward strand transfer catalytic process, without any significant cytotoxicity on cancer cells.

Discovery and structure-activity relationship studies of a unique class of HIV-1 integrase inhibitors

HIV‐1 integrase (IN) is an essential enzyme for viral replication and a validated target for the development of drugs against AIDS. Currently there are no approved drugs that target IN. However, new IN inhibitors are under clinical investigation. As more IN inhibitors enter human drug trials, there is a growing need for the design of novel lead compounds with diverse structural scaffolds and promising pharmacokinetic properties to counteract the difficulties observed with first‐generation IN inhibitors. We have identified a novel class of IN inhibitors through the systematic exploration of structure–activity relationships in a series of linomide analogues. The predicted bound conformation of the most active analogues inside the IN active site also supports the observed structure–activity correlation in this new compound class.