This study addresses the hypothesis that the lack of anesthetic activity for (3α,5α)-3-hydroxypregn-16-ene-11,20-dione (Δ16-alphaxalone) is explained by the steroid Δ16 double bond constraining the steroid 20-carbonyl group to a position that prevents it from favorably interacting with γ-aminobutyric acid type A (GABAA) receptors. A series of Δ16 and Δ17(20) analogues of Δ16-alphaxalone was prepared to evaluate this hypothesis in binding, electrophysiological and tadpole anesthesia experiments. The results obtained failed to support the hypothesis. Instead, the results indicate that it is the presence of the C-21 methyl group in Δ16-alphaxalone, not the location of the constrained C-20 carbonyl group, which prevents Δ16-alphaxalone from interacting strongly with the GABAA receptor and having anesthetic activity. Consistent with this conclusion, a Δ17(20) analogue of Δ16-alphaxalone without a C-21 methyl group was found to be very similar to the anesthetic steroid (3α,5α)-3-hydroxypregnane-11,20-dione (alphaxalone) with regard to time of onset and rate of recovery from anesthesia when administered to mice by tail vein injection.
Recently, covalent drugs have attracted great interest in the drug discovery community, with successful examples that have demonstrated their therapeutic effects. Here, we focus on the covalent inhibition of the fatty acid amide hydrolase (FAAH), which is a promising strategy in the treatment of pain and inflammation. Among the most recent and potent FAAH inhibitors (FAAHi), there are the cyclic piperidine/piperazine aryl ureas. FAAH hydrolyzes efficiently the amide bond of these compounds, forming a covalent enzyme-inhibitor adduct. To rationalize this experimental evidence, we performed an extensive computational analysis centered on the piperidine-based PF750 (1) and the piperazine-based JNJ1661010 (2), two potent lead compounds used to generating covalent inhibitors as clinical candidates. We found that FAAH induces a distortion of the amide bond of the piperidine/piperazine aryl ureas. QM/MM ΔELUMO-HOMO energies indicate that the observed enzyme-induced distortion of the amide bond favors the formation of a covalent FAAH- inhibitor adduct. These findings could help in the rational structure-based design of novel covalent FAAHi.
We previously reported that substituted 4-aminoquinolines with a phenylether substituent at the 7-position of the quinoline ring and the capability of intramolecular hydrogen bonding between the protonated amine on the side chain and a hydrogen bond acceptor on the amine’s alkyl substituents exhibited potent antimalarial activity against the multi-drug resistant strain P. falciparum W2. We employed a parallel synthetic method to generate diaryl ether, biaryl, and alkylaryl 4-aminoquinoline analogs, in the background of a limited number of side chain variations that had previously afforded potent 4-aminoquinolines. All subsets were evaluated for their antimalarial activity against the chloroquine-sensitive strain 3D7 and the chloroquine-resistant K1 and cytotoxicity mammalian cell lines. While all three arrays showed good antimalarial activity, only the biaryl-containing subset showed consistently good potency against the drug-resistant K1strain good selectivity with regard to mammalian cytotoxicity. Overall, our data indicate that the biaryl-containing series contains promising candidates for further study.
The androgen receptor (AR) is the best studied drug target for the treatment of prostate cancer. While there are a number of drugs that target the AR, they all work through the same mechanism of action and are prone to the development of drug resistance. There is a large unmet need for novel AR inhibitors which work through alternative mechanism(s). Recent studies have identified a novel site on the AR called Binding Function 3 (BF3) that is involved into AR transcriptional activity. In order to identify inhibitors that target the BF3 site, we have conducted a large-scale in-silico screen followed by experimental evaluation. A number of compounds were identified that effectively inhibited the AR transcriptional activity with no obvious cytotoxicity. The mechanism of action of these compounds was validated by biochemical assays and x-ray crystallography. These findings lay a foundation for the development of alternative or supplementary therapies capable of combating prostate cancer even in its anti-androgen resistant forms.
anti-androgens; androgen receptor; virtual screening; prostate cancer; drug resistance; protein-protein interactions; protein-protein interactions; co-regulation
A structure-based approach was used to design irreversible, cysteine-targeted inhibitors of the human centrosomal kinase, Nek2. Potent inhibition of Nek2 kinase activity in biochemical and cell-based assays required a noncatalytic cysteine residue (Cys22), located near the glycine-rich loop in a subset of human kinases. Elaboration of an oxindole scaffold led to our most selective compound, oxindole propynamide 16 (JH295). Propynamide 16 irreversibly inhibited cellular Nek2 without affecting the mitotic kinases, Cdk1, Aurora B, or Plk1. Moreover, 16 did not perturb bipolar spindle assembly or the spindle assembly checkpoint. To our knowledge, 16 is the first small molecule shown to inactivate Nek2 kinase activity in cells.
1-Deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) is a novel target for developing new antibacterial (including anti-tuberculosis) and antimalaria drugs. 41 lipophilic phosphonates, representing a new class of DXR inhibitors, were synthesized, among which 5-phenylpyridin-2-ylmethylphosphonic acid possesses the most activity against E. coli DXR (EcDXR) with a Ki of 420 nM. Structure activity relationships (SAR) are discussed, which can be rationalized using our EcDXR:inhibitor structures, and a predictive quantitative SAR (QSAR) model is also developed. Since inhibition studies of DXR from Mycobacterium tuberculosis (MtDXR) have not been well performed, 48 EcDXR inhibitors with a broad chemical diversity were found, however, to generally exhibit considerably reduced activity against MtDXR. The crystal structure of a MtDXR:inhibitor complex reveals the flexible loop containing the residues 198–208 has no strong interactions with the 3,4-dichlorophenyl group of the inhibitor, representing a structural basis for the reduced activity. Overall, these results provide implications in the future design and development of potent DXR inhibitors.
We have identified naturally occurring 2-benzylidenebenzofuran-3-ones (aurones) as new templates for non-nucleoside hepatitis C virus (HCV) RNA-dependent RNA polymerase (RdRp) inhibitors. The aurone target site, identified by site-directed mutagenesis, is located in Thumb Pocket I of HCV RdRp. The RdRp inhibitory activity of 42 aurones was rationally explored in an enzyme assay. Molecular docking studies were used to determine how aurones bind to HCV RdRp and to predict their range of inhibitory activity. Seven aurone derivatives were found to have potent inhibitory effects on HCV RdRp, with IC50s below 5 μM and excellent selectivity. The most active aurone analogue was (Z)-2-((1-butyl-1H-indol-3-yl)methylene)-4,6-dihydroxybenzofuran-3(2H)-one (compound 51), with an IC50 of 2.2 μM. Their potent RdRp inhibitory activity, together with their low toxicity, make these molecules attractive candidate direct-acting anti-HCV agents.
Antiviral Agents; chemical synthesis; pharmacology; Benzofurans; chemical synthesis; pharmacology; Hepacivirus; enzymology; Models, Molecular; RNA Replicase; antagonists & inhibitors; metabolism
We synthesized 2,6-Diisopropyl-4-[3-(3-methyl-3H-diazirin-3-yl)-propyl]-phenol (p-(4-azipentyl)-propofol), or p-4-AziC5-Pro, a novel photoactivable derivative of the general anesthetic propofol. p-4-AziC5-Pro has an anesthetic potency similar to propofol. Like propofol, the compound potentiates inhibitory GABAA receptor current responses and allosterically modulates binding to both agonist and benzodiazepine sites, assayed on heterologously expressed GABAA receptors. p-4-AziC5-Pro inhibits excitatory current responses of nACh receptors expressed in Xenopus oocytes and photoincorporates into native nACh receptor-enriched Torpedo membranes. Thus p-4-AziC5-Pro is a functional general anesthetic that both modulates and photoincorporates into Cys-loop ligand-gated ion channels, making it an excellent candidate for use in identifying propofol binding sites.
The structure activity relationship (SAR) of 1,2,4-triazolo[1,5-a]-1,3,5-triazine derivatives related to ZM241385 as antagonists of the A2A adenosine receptor (AR) was explored through the synthesis of analogues substituted at the 5 position. The A2A AR X-ray structure was used to propose a structural basis for the activity and selectivity of the analogues and to direct the synthetic design strategy to provide access to solvent-exposed regions. Thus, we have identified a point of substitution for the attachment of solubilizing groups to enhance both aqueous solubility and physicochemical properties, maintaining potent interactions with the A2A AR and, in some cases, receptor subtype selectivity. Among the most potent and selective novel compounds were a long-chain ether-containing amine congener 20 (Ki 11.5 nM) and its urethane-protected derivative 14 (Ki 17.8 nM). Compounds 20 and 31 (Ki 11.5 and 16.9 nM, respectively) were readily water soluble up to 10 mM. The analogues were docked in the crystallographic structure of the hA2A AR and in a homology model of the hA3 AR, and the per residue electrostatic and hydrophobic contributions to the binding were assessed and stabilizing factors were proposed.
G protein-coupled receptor; purines; molecular modeling; structure activity relationship; radioligand binding; adenylyl cyclase
Sixteen new anilide derivatives of the natural trioxane artemisinin were prepared and evaluated for antimalarial efficacy in Plasmodium berghei-infected mice. Of these sixteen new anilides administered orally as one 6 mg/kg dose combined with 18 mg/kg mefloquine hydrochloride, only sulfide 3-arteSanilide 12d was completely curative: on day 30 after infection, all mice in this group had no detectable parasitemia, gained as much weight as the uninfected control mice, and behaved normally.
Antimalarial thioethers, sulfoxides, and sulfones; Artemisinin-derived trioxanes; Trioxane monomers SAR
Compounds that coordinate to the heme-iron of cytochrome P450 (CYP) enzymes are assumed to increase metabolic stability. However, recently we observed that the type II binding quinoline carboxamide (QCA) compounds were metabolically less stable. To test if the higher intrinsic clearance of type II binding compounds relative to type I binding compounds is general for other metabolic transformations, we synthesized a library of QCA compounds that could undergo N-dealkylation, O-dealkylation, benzylic hydroxylation and aromatic hydroxylation. The results demonstrated that type II binding QCA analogs were metabolically less stable (2 to 12 fold) at sub-saturating concentration compared to type I binding counterparts for all the transformations. When the rates of different metabolic transformations between type I and type II binding compounds were compared, they were found to be in the order of N-demethylation>benzylic hydroxylation> O-demethylation> aromatic hydroxylation. Finally, for the QCA analogs with aza-heteroaromatic rings, we did not detect metabolism in aza-aromatic rings (pyridine, pyrazine, pyrimidine) indicating electronegativity of the nitrogen can change regioselectivity in CYP metabolism.
Cytochrome P450 3A4; Drug metabolism; Metabolic stability; Type I binding; Type II binding; Regioselectivity
Vigabatrin, a GABA aminotransferase (GABA-AT) inactivator, is used to treat infantile spasms and refractory complex partial seizures and is in clinical trials to treat addiction. We evaluated a novel GABA-AT inactivator (CPP-115) and observed that it does not exhibit other GABAergic or off-target activities and is rapidly and completely orally absorbed and eliminated. Using in vivo microdialysis techniques in freely moving rats and micro-PET imaging techniques, CPP-115 produced similar inhibition of cocaine-induced increases in extracellular dopamine and in synaptic dopamine in the nucleus accumbens at 1/300–1/600th the dose of vigabatrin. It also blocks expression of cocaine-induced conditioned place preference at a dose 1/300th that of vigabatrin. Electroretinographic (ERG) responses in rats treated with CPP-115, at doses 20–40 times higher than those needed to treat addiction in rats, exhibited reductions in ERG responses, which were less than the reductions observed in rats treated with vigabatrin at the same dose needed to treat addiction in rats. In conclusion, CPP-115 can be administered at significantly lower doses than vigabatrin, which suggests a potential new treatment for addiction with a significantly reduced risk of visual field defects.
GABA aminotransferase; Enzyme inactivator; Addiction; Cocaine; Visual field defect; Pharmacokinetics; Micro-PET imaging; Conditioned place preference
Molecular modeling of agonist binding to the human A2A adenosine receptor (AR) was assessed and extended in light of crystallographic structures. Heterocyclic adenine nitrogens of co-crystallized agonist overlayed corresponding positions of the heterocyclic base of a bound triazolotriazine antagonist, and ribose moiety was coordinated in a hydrophilic region, as previously predicted based on modeling using the inactive receptor. Automatic agonist docking of 20 known potent nucleoside agonists to agonist-bound A2AAR crystallographic structures predicted new stabilizing protein interactions, to provide a structural basis for previous empirical structure activity relationships consistent with previous mutagenesis results. We predicted binding of novel C2 terminal amino acid conjugates of A2AAR agonist CGS21680 and used these models to interpret effects on binding affinity of newly-synthesized agonists. D-Amino acid conjugates were generally more potent than L- stereoisomers, and free terminal carboxylates more potent than corresponding methyl esters. Amino acid moieties were coordinated close to extracellular loops 2 and 3. Thus, molecular modeling is useful in probing ligand recognition and rational design of GPCR–targeting compounds with specific pharmacological profiles.
G protein-coupled receptor; nucleosides; purines; radioligand binding; docking; X-ray crystallography
A variety of ammosamide B analogues have been synthesized and evaluated as inhibitors of quinone reductase 2 (QR2). The potencies of the resulting series of QR2 inhibitors range from 4.1 to 25,200 nM. The data provide insight into the structural parameters necessary for QR2 inhibitory activity. The natural product ammosamide B proved to be a potent QR2 inhibitor, and the potencies of the analogues generally decreased as their structures became more distinct from that of ammosamide B. Methylation of the 8-amino group of ammosamide B was an exception, resulting in an increase in quinone reductase 2 inhibitory activity from IC50 of 61 nM to IC50 4.1 nM.
The rocaglates/ rocaglamides are a class of natural products known to display potent anticancer activity. One such derivative, silvestrol, has shown activity comparable to taxol in certain settings. Here, we report the synthesis of various rocaglamide analogs and identification of a hydroxamate derivative (-)-9 having activity similar to silvestrol in vitro and ex vivo for inhibition of protein synthesis. We also show that (-)-9 synergizes with doxorubicin in vivo to reduce Eμ-Myc driven lymphomas.
silvestrol; rocaglamide; hydroxamate; lymphoma; eIF4A; translation initiation; Myc
Tubulin, the major structural component of microtubules, is a target for the development of anticancer agents. Two series of 1,5-diaryl substituted 1,2,3,4-tetrazoles were concisely synthesized, using a palladium-catalyzed cross-coupling reaction, and identified as potent antiproliferative agents and novel tubulin polymerization inhibitors that act at the colchicine site. SAR analysis indicated that compounds with a 4-ethoxyphenyl group at the N-1 or C-5 position of the 1,2,3,4-tetrazole ring exhibited maximal activity. Several of these compounds also had potent activity in inhibiting the growth of multidrug resistant cells overexpressing P-glycoprotein. Active compounds induced apoptosis through the mitochondrial pathway with activation of caspase-9 and caspase-3. Furthermore, compound 4l significantly reduced in vivo the growth of the HT-29 xenograft in a nude mouse model, suggesting that 4l is a promising new antimitotic agent with clinical potential.
Enoyl-acyl carrier protein (ACP) reductase, FabI, is a key enzyme in the bacterial fatty acid biosynthesis pathway (FAS II). FabI is an NADH-dependent oxidoreductase that acts to reduce enoyl-ACP substrates in a final step of the pathway. The absence of this enzyme in humans makes it an attractive target for the development of new antibacterial agents. FabI is known to be unresponsive to structure-based design efforts due to a high degree of induced fit and a mobile flexible loop encompassing the active site. Here we discuss the development, validation, and careful application of a ligand-based virtual screen used for the identification of novel inhibitors of the Francisella tularensis FabI target. In this study, four known classes of FabI inhibitors were used as templates for virtual screens that involved molecular shape and electrostatic matching. The program ROCS was used to search a high-throughput screening library for compounds that matched any of the four molecular shape queries. Matching compounds were further refined using the program EON, which compares and scores compounds by matching electrostatic properties. Using these techniques, 50 compounds were selected, ordered, and tested. The tested compounds possessed novel chemical scaffolds when compared to the input query compounds. Several hits with low micromolar activity were identified and follow-up scaffold-based searches resulted in the identification of a lead series with sub-micromolar enzyme inhibition, high ligand efficiency, and a novel scaffold. Additionally, one of the most active compounds showed promising whole-cell antibacterial activity against several Gram-positive and Gram-negative species, including the target pathogen. The results of a preliminary structure-activity relationship analysis are presented.
Truncated N6-substituted-4′-oxo- and 4′-thioadenosine derivatives with C2 or C8 substitution were studied as dual acting A2A and A3 adenosine receptor (AR) ligands. The lithiation-mediated stannyl transfer and palladium-catalyzed cross coupling reactions were utilized for functionalization of the C2 position of 6-chloropurine nucleosides. An unsubstituted 6-amino group and a hydrophobic C2 substituent were required for high affinity at the hA2AAR, but hydrophobic C8 substitution abolished binding at the hA2AAR. However, most of synthesized compounds displayed medium to high binding affinity at the hA3AR, regardless of C2 or C8 substitution, and low efficacy in a functional cAMP assay. Several compounds tended to be full hA2AAR agonists. C2 substitution probed geometrically through hA2AAR-docking, was important for binding in order of hexynyl > hexenyl > hexanyl. Compound 4g was the most potent ligand acting dually as hA2AAR agonist and hA3AR antagonist, which might be useful for treatment of asthma or other inflammatory diseases.
lithiation-mediated stannyl transfer; structure-activity relationship; adenosine receptors; truncated adenosine; palladium-catalyzed cross coupling; dual-acting ligands
Competitive N-methyl-D-aspartate receptor (NMDAR) antagonists bind to the GluN2 subunit, of which there are four types (GluN2A-D). We report that some N1-substituted derivatives of cis-piperazine-2,3-dicarboxylic acid display improved relative affinity for GluN2C and GluN2D versus GluN2A and GluN2B. These derivatives also display subtype-selectivity among the more distantly related kainate receptor family. Compounds 18i and (−)-4 were the most potent kainate receptor antagonists and 18i was selective for GluK1 versus GluK2, GluK3 and AMPA receptors. Modeling studies revealed structural features required for activity at GluK1 subunits and suggested that S674 was vital for antagonist activity. Consistent with this hypothesis, replacing the equivalent residue in GluK3 (alanine) with a serine imparts 18i antagonist activity. Antagonists with dual GluN2D and GluK1 antagonist activity may have beneficial effects in various neurological disorders. Consistent with this idea, antagonist 18i (30 mg/Kg i.p.) showed antinociceptive effects in an animal model of mild nerve injury.
Many factors are implicated in age-related CNS disorders making it unlikely that modulating only a single factor will provide effective treatment. Perhaps a better approach is to identify small molecules that have multiple biological activities relevant to the maintenance of brain function. Recently, we identified an orally active, neuroprotective and cognition-enhancing molecule, the flavonoid fisetin, that is effective in several animal models of CNS disorders. Fisetin has direct antioxidant activity and can also increase the intracellular levels of glutathione (GSH), the major endogenous antioxidant. In addition, fisetin has both neurotrophic and anti-inflammatory activity. However, its relatively high EC50 in cell based assays, low lipophilicity, high tPSA and poor bioavailability suggest that there is room for medicinal chemical improvement. Here we describe a multi-tiered approach to screening that has allowed us to identify fisetin derivatives with significantly enhanced activity in an in vitro neuroprotection model while at the same time maintaining other key activities.
Two estrogen receptor (ER) subtypes, ERα and ERβ, mediate the actions of estrogens in diverse reproductive and non-reproductive target tissues. ER subtype-selective ligands, which bind to and activate these subtypes differentially, have proved to be useful in elucidating which actions of estrogens proceed through ERα vs. ERβ. Some of these ligands show potential as novel therapeutic agents. Diarylpropionitrile (DPN), an ERβ selective ligand that we developed, is a chiral molecule, but it has been studied almost exclusively as the racemic mixture (rac-DPN, 1). Herein we report the development of an efficient enantioselective synthesis of the two isomers, R-DPN (3) and S-DPN (2), and we have compared the in vitro ligand binding affinities, coactivator binding affinities and recruitment potencies, and cellular transcriptional potencies of these isomers. Both enantiomers show a very high affinity and potency preference for ERβ over ERα, typically in the range of 80-300 fold. Although the enantioselectivity is only modest (3-4 fold), the R-enantiomer is the higher affinity and more potent isomer. While ERβ can be effectively and selectively stimulated by rac-DPN or by either R-DPN or S-DPN, R-DPN might be the preferred member of this isomeric series for biological studies of ERβ function.
Redox-active metalloporphyrins represent the most well characterized class of catalysts capable of attenuating oxidative stress in vivo through the direct interception and decomposition of superoxide and peroxynitrite. While many interesting pharmacological probes have emerged from these studies, few catalysts have been developed with pharmaceutical properties in mind. Herein we describe our efforts to identify new Mn(III)-porphyrin systems with enhanced membrane solubilizing properties. To this end seven new Mn(III)-tetracyclohexenylporphyin (TCHP) analogues 7, 10, 12, 15, 16a–c have been prepared in which the beta-fused cyclohexenyl rings provide a means to shield the charged metal center from the membrane during passive transport. Compounds 7, 15, and 16a–c have been shown to be orally active and potent analgesics in a model of carrageenan-induced thermal hyperalgesia. In addition oral administration of compound 7 (10–100 mg/kg, n = 5) has been shown to dose dependently reverse mechano-allodynia in the CCI model of chronic neuropathic pain.
Neuronal nicotinic receptors have been implicated in several diseases and disorders such as: autism, Alzheimer’s disease, Parkinson’s disease, epilepsy, and various forms of addiction. To understand the role of nicotinic receptors in these conditions, it would be beneficial to have selective molecules that target specific nicotinic receptors in vitro and in vivo. Our laboratory has previously identified novel negative allosteric modulators of human α4β2 (Hα4β2) and human α3β4 (Hα3β4) nicotinic receptors. In the following studies, the effects of novel sulfonylpiperazine analogs that act as negative allosteric modulators on both Hα4β2 nAChRs and Hα3β4 nAChRs were investigated. This work, through structure-activity relationship (SAR) studies, describes the chemical features of these molecules that are important for both potency and selectivity on Hα4β2 nAChRs.
Inhibition of amyloid β-protein (Aβ)-induced toxicity is a promising therapeutic strategy for Alzheimer’s disease (AD). Previously, we reported that the C-terminal tetrapeptide Aβ(39–42) is a potent inhibitor of neurotoxicity caused by Aβ42, the form of Aβ most closely associated with AD. Here, initial structure-activity relationship studies identified key structural requirements, including chirality, side-chain structure, and a free N-terminus, which control Aβ(39–42) inhibitory activity. To elucidate the binding site(s) of Aβ(39–42) on Aβ42, we used intrinsic tyrosine (Y) fluorescence and solution-state NMR. The data suggest that Aβ(39–42) binds at several sites, of which the predominant one is located in the N-terminus of Aβ42, in agreement with recent modeling predictions. Thus, despite the small size of Aβ(39–42) and the hydrophobic, aliphatic nature of all four side-chains, the interaction of Aβ(39–42) with Aβ42 is controlled by specific intermolecular contacts requiring a combination of hydrophobic and electrostatic interactions and a particular stereochemistry.
Alzheimer’s disease; amyloid β-protein; C-terminal fragment; tetrapeptide; structure-activity relationship; NMR; toxicity; intrinsic fluorescence