Bis-(pentafluorophenyl)boryl ferrocene, 1, was prepared via borylation of ferrocene with HB(C6F5)2 or via a transmetallation reaction involving FcHgCl and ClB(C6F5)2 in 87–91% yield. The compound is characterized by a deep maroon colour. A significant intramolecular iron–boron interaction is manifested in the solution spectroscopic (Fe [Formula: see text] B charge transfer band at ~230 nm, ε = 1.33 × 104) and solid-state crystallographic data (Fe-B = 2.924 Å) This interaction has an impact on the Lewis acidity of the boron center which, unlike the related compound B(C6F5)3, does not strongly bind Lewis bases such as acetone, THF, or acetonitrile. However, an adduct between the stronger base PMe3 and 1 forms readily and this complex (2) was fully characterized. The electron withdrawing -B(C6F5)2 group causes 1 to be oxidized at +450 mV relative to ferrocene. Oxidation of 1 with [NO][BF4], AgOSO2CF3, or AgC6F5 leads to the zwitterionic ferrocenium borates 3-F, 3-OTf, and 3-C6F5, respectively. Each of these compounds was characterized spectroscopically and via X-ray crystallography. The properties of these compounds relative to 1 suggest that oxidation of the iron center significantly enhances the Lewis acidity of the boron center. Due to the σ-donating ability of the borate substituents, zwitterions 3 are weaker oxidizing agents than unsubstituted ferrocenium salts.Key words: organoboranes, ferrocene derivatives, Lewis acids.

Based on the attrition rate of CCR5 small molecule antagonists in the clinic the discovery and development of next generation antagonists with an improved pharmacology and safety profile is necessary. Herein, we describe a combined molecular modeling, CCR5-mediated cell fusion, and receptor site-directed mutagenesis approach to study the molecular interactions of six structurally diverse compounds (aplaviroc, maraviroc, vicriviroc, TAK-779, SCH-C and a benzyloxycarbonyl-aminopiperidin-1-yl-butane derivative) with CCR5, a coreceptor for CCR5-tropic HIV-1 strains. This is the first study using an antifusogenic assay, a model of the interaction of the gp120 envelope protein with CCR5. This assay avoids the use of radioactivity and HIV infection assays, and can be used in a high throughput mode. The assay was validated by comparison with other established CCR5 assays. Given the hydrophobic nature of the binding pocket several binding models are suggested which could prove useful in the rational drug design of new lead compounds.

An efficient and convergent four-step synthetic route to the CXCR4 chemokine receptor antagonist AMD070 (1) has been developed which employs only a single chromatographic step in the entire sequence. Novel reductive amination methods have been developed for the coupling of 2 and 3 in which a dehydrative imine formation is followed by reduction with an attenuated borohydride reagent (zinc chloride and sodium borohydride). Selective extraction methods were employed to purify synthetic intermediates and remove reagents and impurities. A procedure has also been developed to isolate 1 in a pure crystalline form.

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A series of CCR5 antagonists representing the thiophene-3-yl-methyl ureas were designed that met the pharmacological criteria for HIV-1 inhibition and mitigated a human ether-a-go-go related gene (hERG) inhibition liability. Reducing lipophilicity was the main design criteria used to identify compounds that did not inhibit the hERG channel, but subtle structural modifications were also important. Interestingly, within this series, compounds with low hERG inhibition prolonged the action potential duration (APD) in dog Purkinje fibers, suggesting a mixed effect on cardiac ion channels. KEYWORDS: HIV-1, hERG, CCR5, chemokine receptor Recently, we reported 5 on the identification of pyridin-2-ylmethylaminopiperidin-1-ylbutyl amides (1) as a novel class of CCR5 antagonists that exhibited potent inhibition of R5 HIV-1 (BaL) replication in PBMC (Figure 1). These compounds were identified based on our initial redesign efforts of Schering C. 6 Although these compounds met most of the criteria for further development, they were found to have a significant hERG liability (also reported by the GSK 7 and Pfizer 8 groups), which we sought to mitigate by reducing the lipophilicity through the design of compounds 2 (Figure 1). The antiviral activity was used to determine a structure−activity relationship (SAR), and it was measured utilizing the R5 HIV-1 PBMC assay. 9 In addition, we also utilized a gp120/CCR5 cell fusion assay 10 as a first pass screen to select compounds for antiviral screening since the fusion data were found to be a reliable predictor of antiviral activity.On the basis of the recognition that compound 1a containing an anilino nitrogen (R 1 = phenyl) had potent antiviral activity, we reasoned that the most expedient way to address the hERG liability was to replace the substituted phenyl group on the left had side with an amide or urea that would reduce the lipophilicity 11 as measured by cLog P. Initially, the 4-methyl pyridine moiety on the top left-hand side was retained, but these compounds were substantially less potent than the corresponding thiophene analogues, 5 so the thiophene moiety was utilized for further optimization (Table 1). For example, comparison of the tetrahydropyranyl esters 1b and 2b showed that the thiophene 2b provided a 44-fold enhancement in potency as compared to the 4-methyl pyridine 1b based on CCR5 fusion inhibition. Similarly, comparison of the pyridinyl ureas 1c and 2c showed a 130-fold increase in potency for 2c as compared to the 4-methyl pyridine 1c.Several amide analogues of compound 2 were prepared (Table 2). Aside from maintaining antiviral potency, the important properties that were measured to distinguish the analogues was fusion inhibition shift in the presence of α-1-acid glycoprotein (AGP), human plasma protein binding, and hERG inhibition based on % inhibition and/or IC 50 . The simple methyl amide 2d containing the optimum 2-chloro-4,6-