Many bacterial pathogens rely on a conserved membrane histidine sensor kinase, QseC, to respond to host adrenergic signaling molecules and bacterial signals in order to promote the expression of virulence factors. Using a high-throughput screen, we identified a small molecule, LED209, that inhibits the binding of signals to QseC, preventing its autophosphorylation and consequently inhibiting QseC-mediated activation of virulence gene expression. LED209 is not toxic and does not inhibit pathogen growth; however, this compound markedly inhibits the virulence of several pathogens in vitro and in vivo in animals. Inhibition of signaling offers a strategy for the development of broad-spectrum antimicrobial drugs.A key challenge for medicine is to develop new drugs against pathogens that are resistant to current antimicrobial agents (1,2). A promising strategy is to identify agents that inhibit microbial virulence without inhibiting growth, because these present less selective pressure for the generation of resistance (3-5). Many bacterial pathogens recognize the host environment by sensing and responding to the host adrenergic signaling molecules epinephrine and norepinephrine (NE) in order to promote the expression of virulence factors (6,7). These pathogens appear to use the same membrane-embedded sensor histidine kinase, QseC (7), to recognize both host-derived adrenergic signals and the bacterial aromatic signal autoinducer-3 (AI-3) to activate their virulence genes (5,6). Upon sensing any of these signaling molecules, QseC autophosphorylates and subsequently phosphorylates a transcription factor, QseB (Fig. 1A) (7), which initiates a relay to a complex regulatory cascade and leads to the transcription of key virulence genes (Fig. 1B) (5-8).QseC homologs are present in at least 25 important human and plant pathogens (table S1), and qseC mutants of enterohemorrhagic Escherichia coli (EHEC) (Fig. 1C and fig. S1) (7), Salmonella typhimurium ( Fig. 2A) (8), and Francisella tularensis (9) are attenuated in infected †To whom correspondence should be addressed.

An organocatalytic, enantioselective oxy-Michael addition to achiral γ-and δ-hydroxy-α,β-enones was developed. The key transformation is an unprecedented, asymmetric conjugate addition triggered by complexation between an in situ generated boronic acid hemiester and a chiral amine catalyst. Functionally, the intermediate amine-boronate complex acts as a chiral hydroxide surrogate or synthon. The resultant chiral β-hydroxy-ketones are obtained in good to excellent yields and high ee following mild oxidative removal of the cyclic boronate. Natural products (R,12Z,15Z)-2-hydroxy-4-oxohenicosa-12,15-dienyl acetate and (+)-(S)-Streptenol A were synthesized to demonstrate the utility of this reaction.Structural motif 1 is present in a wide range of natural products and synthetic intermediates. 1 While Michael additions of hydroxide or synthetic equivalents to α,β-unsaturated carbonyls represent an attractive approach to this moiety, 2 the strong basicity of the former and generally poor nucleophilicity or lability of the latter often render this option problematic. In its place, the intramolecular oxy-Michael addition of hemiacetal/hemiketal-derived alkoxides has emerged as a popular alternative strategy, 3 although the resultant cyclic acetals/ketals can be difficult to remove. In some instances, satisfactory diastereoselectivity has been attained via exploitation of adjacent secondary hydroxy or amino stereocenters. 4,5 In 2001, Watanabe et al 6 introduced an asymmetric version of the oxy-Michael addition utilizing chiral hemiketals derived from D-glucose and D-fructose in the more challenging case of achiral γ/δ-hydroxy-α,β-enones. Herein, we reported an unprecedented organocatalytic, enantioselective oxyMichael addition to achiral γ/δ-hydroxy-α,β-enones and its use in the preparation of 1 (eq 1). 7 The key transformation is the asymmetric conjugate addition triggered by complexation between boronic acid hemiester 3, generated in situ from γ/δ-hydroxy-α,β-enones, and a chiral amine catalyst. Functionally, the intermediate amine-boronate complex acts as a chiral hydroxide surrogate or synthon. Mild, oxidative removal of the boronate moiety from the dioxaborolane (n = 0) or dioxaborinane (n = 1) adduct 2 furnishes 1 in good to excellent overall yield and % ee.Recently, this 8 and other laboratories 9 have highlighted the nucleophilic properties of organoboronic acids and the unique stereospecific reactions of their borate complexes. Despite E-mail: j.falck@UTSouthwestern.edu. NIH Public AccessAuthor Manuscript J Am Chem Soc. Author manuscript; available in PMC 2009 January 9. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript expectations, when model compound (E)-4-hydroxy-1-phenyl-2-buten-1-one (4) was mixed with equimolar phenylboronic acid and activated 4Å molecular sieves in CH 2 Cl 2 (Table 1, entry 1), no intramolecular Michael addition was observed, even though the hemiester (3: R= Ph, n = 0) could be detected by 1 H and 13 C NMR. Inclusion of some common bases, viz., bicarbonat...

Prochiral ketones are reduced to enantioenriched, secondary alcohols using catecholborane and a family of air-stable, bifunctional thiourea-amine organocatalysts. Asymmetric induction is proposed to arise from the in situ complexation between the borane and chiral thiourea-amine organocatalyst resulting in a stereochemically biased boronate-amine complex. The hydride in the complex is endowed with enhanced nucleophilicity while the thiourea concomitantly embraces and activates the carbonyl.The enantioselective reduction of prochiral ketones is a mainstay in the production of enantioenriched, secondary alcohols. 1 As in other areas of chiral synthetic methodology, the trend has been away from stoichiometric reductants 2 towards more economic and environmentally friendly catalytic processes 3 and, in recent years, has embraced organocatalysis. 4,5 One of the most prominent and frequently applied members of this latter category is the Corey-Bakshi-Shibata (CBS) catalyst, a chiral oxazaborolidine pioneered by Itsuno 6 and further developed by Corey 7 and other investigators. 8 However, the sensitivity of oxazaborolidines to oxygen and moisture as well as the need in conjunction with a current project for a highly enantioselective reducing agent compatible with a challenging combination of highly sensitive functionality, prompted us to explore the utility of urea-/ thiourea-based organocatalysts as an alternative to CBS oxazaborolidines. 9,10 Whilst chiral ureas and thioureas have emerged as efficacious catalysts for a variety of nucleophilic conjugate additions 11 and 1,2-carbonyl additions, e.g., hydrocyanation, 12 Henry reaction, 13 15,16 However, the insights gained developing asymmetric oxy-Michael additions of boronic acids with α,β-unsaturated ketones 17 revealed several unique attributes that we felt could be harnessed for enantioselective carbonyl reductions. Specifically, we envisioned that the union between a borane and a chiral thiourea-amine organocatalyst would result in a stereochemically biased boronate-amine complex. 18 The hydride in the complex is endowed with enhanced nucleophilicity (the push) while the thiourea concomitantly embraces and activates the carbonyl (the pull) ( Figure 1). As proof-of-concept, we developed of a family of robust, bifunctional thiourea-amine catalysts and describe herein their exploitation for the stereodefined reduction of prochiral ketones to enantioenriched, secondary alcohols.Despite its outstanding performance catalyzing the aforementioned oxy-Michael additions, 17 thiourea catalyst A 19 furnished (S)-(−)-1-phenylethanol (2) in poor yield and low enantioselectivity at room temperature in THF (Table 1, entry 1) using acetophenone (1) and BH 3 ·THF as the model substrate and hydride source, respectively. Reasoning that the cinchona alkaloid moiety might be responsible, it was replaced with the simpler (R,R)-trans-N,N′-dimethylcyclohexane-1,2-diamine. The resultant monobasic catalyst B provided a modest improvement in yield and enantioselectivity, albeit d...