Catalytic, Enantioselective ß-Protonation through a Cooperative Activation Strategy.

The NHC-catalyzed transformation of unsaturated aldehydes into saturated esters through an organocatalytic homoenolate process has been thoroughly studied. Leveraging a unique "Umpolung"-mediated ß-protonation, this process has evolved from a test bed for homoenolate reactivity to a broader platform for asymmetric catalysis. Inspired by our success in using the ß-protonation process to generate enals from ynals with good E/Z selectivity, our early studies found that an asymmetric variation of this reaction was not only feasible, but also adaptable to a kinetic resolution of secondary alcohols through NHC-catalyzed acylation. In-depth analysis of this process determined that careful catalyst and solvent pairing is critical for optimal yield and selectivity; proper choice of nonpolar solvent provided improved yield through suppression of an oxidative side reaction, while employment of a cooperative catalytic approach through inclusion of a hydrogen bond donor cocatalyst significantly improved enantioselectivity.

Potent and selective inhibitors of the TASK-1 potassium channel through chemical optimization of a bis-amide scaffold.

TASK-1 is a two-pore domain potassium channel that is important to modulating cell excitability, most notably in the context of neuronal pathways. In order to leverage TASK-1 for therapeutic benefit, its physiological role needs better characterization; however, designing selective inhibitors that avoid the closely related TASK-3 channel has been challenging. In this study, a series of bis-amide derived compounds were found to demonstrate improved TASK-1 selectivity over TASK-3 compared to reported inhibitors. Optimization of a marginally selective hit led to analog 35 which displays a TASK-1 IC50=16 nM with 62-fold selectivity over TASK-3 in an orthogonal electrophysiology assay.

Lifting the mask: identification of new small molecule inhibitors of uropathogenic Escherichia coli group 2 capsule biogenesis.

Uropathogenic Escherichia coli (UPEC) is the leading cause of community-acquired urinary tract infections (UTIs), with over 100 million UTIs occurring annually throughout the world. Increasing antimicrobial resistance among UPEC limits ambulatory care options, delays effective treatment, and may increase overall morbidity and mortality from complications such as urosepsis. The polysaccharide capsules of UPEC are an attractive target a therapeutic, based on their importance in defense against the host immune responses; however, the large number of antigenic types has limited their incorporation into vaccine development. The objective of this study was to identify small-molecule inhibitors of UPEC capsule biogenesis. A large-scale screening effort entailing 338,740 compounds was conducted in a cell-based, phenotypic screen for inhibition of capsule biogenesis in UPEC. The primary and concentration-response assays yielded 29 putative inhibitors of capsule biogenesis, of which 6 were selected for further studies. Secondary confirmatory assays identified two highly active agents, named DU003 and DU011, with 50% inhibitory concentrations of 1.0 µM and 0.69 µM, respectively. Confirmatory assays for capsular antigen and biochemical measurement of capsular sugars verified the inhibitory action of both compounds and demonstrated minimal toxicity and off-target effects. Serum sensitivity assays demonstrated that both compounds produced significant bacterial death upon exposure to active human serum. DU011 administration in mice provided near complete protection against a lethal systemic infection with the prototypic UPEC K1 isolate UTI89. This work has provided a conceptually new class of molecules to combat UPEC infection, and future studies will establish the molecular basis for their action along with efficacy in UTI and other UPEC infections.

A selective ATP-binding cassette subfamily G member 2 efflux inhibitor revealed via high-throughput flow cytometry.

Chemotherapeutics tumor resistance is a principal reason for treatment failure, and clinical and experimental data indicate that multidrug transporters such as ATP-binding cassette (ABC) B1 and ABCG2 play a leading role by preventing cytotoxic intracellular drug concentrations. Functional efflux inhibition of existing chemotherapeutics by these pumps continues to present a promising approach for treatment. A contributing factor to the failure of existing inhibitors in clinical applications is limited understanding of specific substrate/inhibitor/pump interactions. We have identified selective efflux inhibitors by profiling multiple ABC transporters against a library of small molecules to find molecular probes to further explore such interactions. In our primary screening protocol using JC-1 as a dual-pump fluorescent reporter substrate, we identified a piperazine-substituted pyrazolo[1,5-a]pyrimidine substructure with promise for selective efflux inhibition. As a result of a focused structure-activity relationship (SAR)-driven chemistry effort, we describe compound 1 (CID44640177), an efflux inhibitor with selectivity toward ABCG2 over ABCB1. Compound 1 is also shown to potentiate the activity of mitoxantrone in vitro as well as preliminarily in vivo in an ABCG2-overexpressing tumor model. At least two analogues significantly reduce tumor size in combination with the chemotherapeutic topotecan. To our knowledge, low nanomolar chemoreversal activity coupled with direct evidence of efflux inhibition for ABCG2 is unprecedented.

High-throughput screening identifies a bisphenol inhibitor of SV40 large T antigen ATPase activity.

The authors conducted a high-throughput screening campaign for inhibitors of SV40 large T antigen ATPase activity to identify candidate antivirals that target the replication of polyomaviruses. The primary assay was adapted to 1536-well microplates and used to screen the National Institutes of Health Molecular Libraries Probe Centers Network library of 306 015 compounds. The primary screen had an Z value of ~0.68, signal/background = 3, and a high (5%) DMSO tolerance. Two counterscreens and two secondary assays were used to prioritize hits by EC(50), cytotoxicity, target specificity, and off-target effects. Hits that inhibited ATPase activity by >44% in the primary screen were tested in dose-response efficacy and eukaryotic cytotoxicity assays. After evaluation of hit cytotoxicity, drug likeness, promiscuity, and target specificity, three compounds were chosen for chemical optimization. Chemical optimization identified a class of bisphenols as the most effective biochemical inhibitors. Bisphenol A inhibited SV40 large T antigen ATPase activity with an IC(50) of 41 µM in the primary assay and 6.2 µM in a cytoprotection assay. This compound class is suitable as probes for biochemical investigation of large T antigen ATPase activity, but because of their cytotoxicity, further optimization is necessary for their use in studying polyomavirus replication in vivo.

Impact of solvent polarity on N-heterocyclic carbene-catalyzed beta-protonations of homoenolate equivalents.

N-Heterocyclic carbenes have been demonstrated to react through divergent pathways under the same conditions. Experimental and computational evidence demonstrates that the ability to favor generation of homoenolate equivalents from alpha,beta-unsaturated aldehydes versus the oxidation of aldehydes to esters is highly dependent upon the choice of solvent. The solvation environment plays an important role due to the mechanistic differences in these processes, with polar protic solvent favoring the oxidation process due to solvation of intermediates with greater charge separation.

Single-flask synthesis of N-acylated indoles by catalytic dehydrogenative coupling with primary alcohols.

Indoles and alcohols can be coupled in a dehydrogenative process catalyzed by tetrapropylammonium perruthenate. This efficient approach to indolylamides proceeds in a single flask under mild conditions. By employing substituted indoles and alkyl, branched, or benzylic alcohols, a variety of indolylamides can be formed. Aryl indolylamides can be functionalized through an additional dehydrogenative coupling to furnish elaborated polycyclic heterocycles similar to biologically active structures previously reported.

N-Heterocyclic Carbene-Catalyzed Oxidations.

N-Heterocyclic carbenes catalyze the oxidation of allylic and benzylic alcohols as well as saturated aldehydes to esters with manganese(IV) oxide in excellent yields. A variety of esters can be synthesized, including protected carboxylates. The oxidation proceeds under mild conditions, with low loadings of a simple triazolium salt pre-catalyst in the presence of base. Substrates containing potentially epimerizable centers are oxidized while preserving stereochemical integrity. The acyl triazolium intermediate generated under catalytic conditions can be employed as a chiral acylating agent in the desymmetrization of meso-diols.

N-heterocyclic carbene-catalyzed oxidation of unactivated aldehydes to esters.

N-Heterocyclic carbenes catalyze the oxidation of unactivated aldehydes to esters with manganese(IV) oxide in excellent yield. The reaction proceeds through a transient activated alcohol, which when generated in situ allows for the selective oxidation of the aldehyde under mild conditions. These conditions successfully oxidize potentially epimerizable aldehydes and alcohols while preserving stereochemical integrity. A variety of ester derivatives can be synthesized with variation of the acylated alcohol as well as the unactivated aldehyde.

Protonation of Homoenolate Equivalents Generated by N-Heterocyclic Carbenes.

Homoenolate equivalents are generated by Lewis basic N-heterocyclic carbene catalysts and then protonated to generate efficiently saturated esters from unsaturated aldehydes. This reactivity is extended to the generation of ß-acylvinyl anions from alkynyl aldehydes. The asymmetric protonation of a homoenolate equivalent generated from a ß,ß-disubstituted aldehyde can be accomplished with a chiral N-heterocyclic carbene.

Tandem oxidation of allylic and benzylic alcohols to esters catalyzed by N-heterocyclic carbenes.

N-heterocyclic carbenes catalyze the oxidation of allylic, propargylic, and benzylic alcohols to esters with manganese(IV) oxide in excellent yields. A variety of ester derivatives can be synthesized, including protected carboxylates. This one-pot tandem oxidation represents the first organocatalytic oxidation of alcohols to esters. Saturated esters can also be accessed from aldehydes using this method. Through the utilization of a chiral catalyst, the acyl-heteroazolium intermediate becomes a chiral acylating agent, which can desymmetrize meso-1,2-diols. [reaction: see text].