Single site OH to F substitution at the termini of maltotetraose leads to significantly improved ... more Single site OH to F substitution at the termini of maltotetraose leads to significantly improved hydrolytic stability towards alpha-amylase and alpha-glucosidase relative to the natural compound. Stability enhancements of around 1 order of magnitide result from these subtle point mutations. In both scenarios, modification of the monosaccharide furthest from the site of enzymatic cleavage leads to the greatest improvement in stability, and the configuration of the fluorine-bearing stereocenter has a clear impact on catalysis. This pre-clinical evaluation provides valuable guidelines for the development of tracer candidates for non-invasive bacterial imaging.
Target-directed dynamic combinatorial chemistry (tdDCC) enables the identification, as well as op... more Target-directed dynamic combinatorial chemistry (tdDCC) enables the identification, as well as optimization of ligands for un(der)explored targets such as the anti-infective target 1‑deoxy‑d‑xylulose-5-phosphate synthase (DXS). We report the unprecedented use of tdDCC to first identify and subsequently optimize inhibitors of the anti-infective target DXS. Using tdDCC, we were able to generate acylhydrazone-based inhibitors for DXS. The tailored tdDCC runs also provided insights into the structure–activity relationship of this novel class of DXS inhibitors. This approach holds the potential to expedite the drug discovery process and could be generally applied to a range of biological targets.
Nearly quantitative yields and high enantiomeric purity (89-95% ee) were attained in the course o... more Nearly quantitative yields and high enantiomeric purity (89-95% ee) were attained in the course of 100 reaction cycles of a polystyrene resin-supported Cinchona alkaloid organocatalyst in the enantioselective α-amination of 2-oxindoles with diethyl azodicarboxylate. The catalytic material proved stable for> 5300 h operation time over eight months.
The enantioselective organocatalytic methanolysis of cis-1,2,3,6-tetrahydrophthalic anhydride med... more The enantioselective organocatalytic methanolysis of cis-1,2,3,6-tetrahydrophthalic anhydride mediated by quinidine derivatives with pyridazine or anthraquinone core was investigated, carrying out a detailed nuclear magnetic resonance study of the conformational preferences of the alkaloid catalysts in the pure solvent and in the presence of the reaction substrates and products. No significant interaction between the meso-anhydride and the alkaloid derivatives was detected. In contrast, evidence for a considerable influence of the alcohol reactant on the conformational state of some of the chiral organocatalysts could be obtained, which lends support to the hypothesis of general-base catalysis mechanism, as opposed to the nuclephilic one. The catalytic properties of the studied derivatives showed no obvious correlation with their conformational prevalence in the resting state, suggesting that the alkaloid 9-O substituent should have a more active role than merely enforcing the chiral fragments to adopt a preferential reactive conformation. A strong enantioselective interaction between the enantiomers of the hemiester product and the alkaloid derivatives was also observed, leading to the conclusion that in the actual reaction conditions a relatively large fraction of the latter is in the protonated form.
Catalytic asymmetric conjugate addition reactions represent a powerful strategy to access chiral ... more Catalytic asymmetric conjugate addition reactions represent a powerful strategy to access chiral molecules in contemporary organic synthesis. However, their applicability to conjugated alkenyl-N-heteroaromatic compounds, of particular interest in medicinal chemistry, has lagged behind applications to other substrates. We report a highly enantioselective and chemoselective catalytic transformation of a wide range of β-substituted conjugated alkenyl-N-heteroaromatics to their corresponding chiral alkylated products. This operationally simple methodology can introduce linear, branched, and cyclic alkyl chains, as well as a phenyl group, at the β-carbon position. The key to this success was enhancement of the reactivity of alkenyl-heteroaromatic substrates via Lewis acid activation, in combination with the use of readily available and highly reactive Grignard reagents and a copper catalyst coordinated by a chiral chelating diphosphine ligand.
To address the global challenge of emerging antimicrobial resistance, the hitherto most successfu... more To address the global challenge of emerging antimicrobial resistance, the hitherto most successful strategy to new antibiotics has been the optimization of validated natural products; most of these efforts rely on semisynthesis. Herein, we report the semisynthetic modification of amidochelocardin, an atypical tetracycline obtained via genetic engineering of the chelocardin producer strain. We report modifications at C4, C7, C10, and C11 by the application of methylation, acylation, electrophilic substitution, and oxidative C-C coupling reactions. The antibacterial activity of the reaction products was tested against a panel of Gram-positive and Gram-negative0 pathogens. The emerging structure-activity relationships (SARs) revealed that positions C7 and C10 are favorable anchor points for the semisynthesis of optimized derivatives. The observed SAR was different from that known for tetracyclines, which underlines the pronounced differences between the two compound classes.
Fluorinated motifs have a venerable history in drug discovery, but as C(sp3)−F‐rich 3D scaffolds ... more Fluorinated motifs have a venerable history in drug discovery, but as C(sp3)−F‐rich 3D scaffolds appear with increasing frequency, the effect of multiple bioisosteric changes on molecular recognition requires elucidation. Herein we demonstrate that installation of a 1,3,5‐stereotriad, in the substrate for a commonly used lipase from Pseudomonas fluorescens does not inhibit recognition, but inverts stereoselectivity. This provides facile access to optically active, stereochemically well‐defined organofluorine compounds (up to 98 % ee). Whilst orthogonal recognition is observed with fluorine, the trend does not hold for the corresponding chlorinated substrates or mixed halogens. This phenomenon can be placed on a structural basis by considering the stereoelectronic gauche effect inherent to F−C−C−X systems (σ→σ*). Docking reveals that this change in selectivity (H versus F) with a common lipase results from inversion in the orientation of the bound substrate being processed as a consequence of conformation. This contrasts with the stereochemical interpretation of the biogenetic isoprene rule, whereby product divergence from a common starting material is also a consequence of conformation, albeit enforced by two discrete enzymes.
We present a study on sequential conjugate addition of Grignard reagents to alkenyl-heteroarenes... more We present a study on sequential conjugate addition of Grignard reagents to alkenyl-heteroarenes followed by trapping of the resulting enolates, yielding moderate to good diastereoselectivities. Contrary to conventional wisdom, one-pot conjugate addition/trapping using two reactive Michael acceptors in combination with Grignard reagents can proceed via conjugate addition to the least reactive Michael acceptor. This unusual chemoselectivity is triggered by the presence of a Lewis acid, reverting the usual reactivity order of Michael acceptors.
Catalytic asymmetric conjugate addition reactions represent a powerful strategy to access chiral ... more Catalytic asymmetric conjugate addition reactions represent a powerful strategy to access chiral molecules in contemporary organic synthesis. However, their applicability to conjugated alkenyl-N-heteroaromatic compounds, of particular interest in medicinal chemistry, has lagged behind applications to other substrates. We report a highly enantioselective and chemoselective catalytic transformation of a wide range of β-substituted conjugated alkenyl-N-heteroaromatics to their corresponding chiral alkylated products. This operationally simple methodology can introduce linear, branched, and cyclic alkyl chains, as well as a phenyl group, at the β-carbon position. The key to this success was enhancement of the reactivity of alkenyl-heteroaromatic substrates via Lewis acid activation, in combination with the use of readily available and highly reactive Grignard reagents and a copper catalyst coordinated by a chiral chelating diphosphine ligand.
General methods to prepare chiral pyridine derivatives are greatly sought after due to their sign... more General methods to prepare chiral pyridine derivatives are greatly sought after due to their significance in medicinal chemistry. Here, we report highly enantioselective catalytic transformations of poorly reactive β-substituted alkenyl pyridines to access a wide range of alkylated chiral pyridines. The simple methodology involves reactivity enhancement via Lewis acid (LA) activation, the use of readily available and highly reactive Grignard reagents, and a copper-chiral diphosphine ligand catalyst. Apart from allowing the introduction of different linear, branched, cyclic, and functionalised alkyl chains at the β-position of alkenyl pyridines, the catalytic system also shows high functional group tolerance.
Single site OH to F substitution at the termini of maltotetraose leads to significantly improved ... more Single site OH to F substitution at the termini of maltotetraose leads to significantly improved hydrolytic stability towards alpha-amylase and alpha-glucosidase relative to the natural compound. Stability enhancements of around 1 order of magnitide result from these subtle point mutations. In both scenarios, modification of the monosaccharide furthest from the site of enzymatic cleavage leads to the greatest improvement in stability, and the configuration of the fluorine-bearing stereocenter has a clear impact on catalysis. This pre-clinical evaluation provides valuable guidelines for the development of tracer candidates for non-invasive bacterial imaging.
Target-directed dynamic combinatorial chemistry (tdDCC) enables the identification, as well as op... more Target-directed dynamic combinatorial chemistry (tdDCC) enables the identification, as well as optimization of ligands for un(der)explored targets such as the anti-infective target 1‑deoxy‑d‑xylulose-5-phosphate synthase (DXS). We report the unprecedented use of tdDCC to first identify and subsequently optimize inhibitors of the anti-infective target DXS. Using tdDCC, we were able to generate acylhydrazone-based inhibitors for DXS. The tailored tdDCC runs also provided insights into the structure–activity relationship of this novel class of DXS inhibitors. This approach holds the potential to expedite the drug discovery process and could be generally applied to a range of biological targets.
Nearly quantitative yields and high enantiomeric purity (89-95% ee) were attained in the course o... more Nearly quantitative yields and high enantiomeric purity (89-95% ee) were attained in the course of 100 reaction cycles of a polystyrene resin-supported Cinchona alkaloid organocatalyst in the enantioselective α-amination of 2-oxindoles with diethyl azodicarboxylate. The catalytic material proved stable for> 5300 h operation time over eight months.
The enantioselective organocatalytic methanolysis of cis-1,2,3,6-tetrahydrophthalic anhydride med... more The enantioselective organocatalytic methanolysis of cis-1,2,3,6-tetrahydrophthalic anhydride mediated by quinidine derivatives with pyridazine or anthraquinone core was investigated, carrying out a detailed nuclear magnetic resonance study of the conformational preferences of the alkaloid catalysts in the pure solvent and in the presence of the reaction substrates and products. No significant interaction between the meso-anhydride and the alkaloid derivatives was detected. In contrast, evidence for a considerable influence of the alcohol reactant on the conformational state of some of the chiral organocatalysts could be obtained, which lends support to the hypothesis of general-base catalysis mechanism, as opposed to the nuclephilic one. The catalytic properties of the studied derivatives showed no obvious correlation with their conformational prevalence in the resting state, suggesting that the alkaloid 9-O substituent should have a more active role than merely enforcing the chiral fragments to adopt a preferential reactive conformation. A strong enantioselective interaction between the enantiomers of the hemiester product and the alkaloid derivatives was also observed, leading to the conclusion that in the actual reaction conditions a relatively large fraction of the latter is in the protonated form.
Catalytic asymmetric conjugate addition reactions represent a powerful strategy to access chiral ... more Catalytic asymmetric conjugate addition reactions represent a powerful strategy to access chiral molecules in contemporary organic synthesis. However, their applicability to conjugated alkenyl-N-heteroaromatic compounds, of particular interest in medicinal chemistry, has lagged behind applications to other substrates. We report a highly enantioselective and chemoselective catalytic transformation of a wide range of β-substituted conjugated alkenyl-N-heteroaromatics to their corresponding chiral alkylated products. This operationally simple methodology can introduce linear, branched, and cyclic alkyl chains, as well as a phenyl group, at the β-carbon position. The key to this success was enhancement of the reactivity of alkenyl-heteroaromatic substrates via Lewis acid activation, in combination with the use of readily available and highly reactive Grignard reagents and a copper catalyst coordinated by a chiral chelating diphosphine ligand.
To address the global challenge of emerging antimicrobial resistance, the hitherto most successfu... more To address the global challenge of emerging antimicrobial resistance, the hitherto most successful strategy to new antibiotics has been the optimization of validated natural products; most of these efforts rely on semisynthesis. Herein, we report the semisynthetic modification of amidochelocardin, an atypical tetracycline obtained via genetic engineering of the chelocardin producer strain. We report modifications at C4, C7, C10, and C11 by the application of methylation, acylation, electrophilic substitution, and oxidative C-C coupling reactions. The antibacterial activity of the reaction products was tested against a panel of Gram-positive and Gram-negative0 pathogens. The emerging structure-activity relationships (SARs) revealed that positions C7 and C10 are favorable anchor points for the semisynthesis of optimized derivatives. The observed SAR was different from that known for tetracyclines, which underlines the pronounced differences between the two compound classes.
Fluorinated motifs have a venerable history in drug discovery, but as C(sp3)−F‐rich 3D scaffolds ... more Fluorinated motifs have a venerable history in drug discovery, but as C(sp3)−F‐rich 3D scaffolds appear with increasing frequency, the effect of multiple bioisosteric changes on molecular recognition requires elucidation. Herein we demonstrate that installation of a 1,3,5‐stereotriad, in the substrate for a commonly used lipase from Pseudomonas fluorescens does not inhibit recognition, but inverts stereoselectivity. This provides facile access to optically active, stereochemically well‐defined organofluorine compounds (up to 98 % ee). Whilst orthogonal recognition is observed with fluorine, the trend does not hold for the corresponding chlorinated substrates or mixed halogens. This phenomenon can be placed on a structural basis by considering the stereoelectronic gauche effect inherent to F−C−C−X systems (σ→σ*). Docking reveals that this change in selectivity (H versus F) with a common lipase results from inversion in the orientation of the bound substrate being processed as a consequence of conformation. This contrasts with the stereochemical interpretation of the biogenetic isoprene rule, whereby product divergence from a common starting material is also a consequence of conformation, albeit enforced by two discrete enzymes.
We present a study on sequential conjugate addition of Grignard reagents to alkenyl-heteroarenes... more We present a study on sequential conjugate addition of Grignard reagents to alkenyl-heteroarenes followed by trapping of the resulting enolates, yielding moderate to good diastereoselectivities. Contrary to conventional wisdom, one-pot conjugate addition/trapping using two reactive Michael acceptors in combination with Grignard reagents can proceed via conjugate addition to the least reactive Michael acceptor. This unusual chemoselectivity is triggered by the presence of a Lewis acid, reverting the usual reactivity order of Michael acceptors.
Catalytic asymmetric conjugate addition reactions represent a powerful strategy to access chiral ... more Catalytic asymmetric conjugate addition reactions represent a powerful strategy to access chiral molecules in contemporary organic synthesis. However, their applicability to conjugated alkenyl-N-heteroaromatic compounds, of particular interest in medicinal chemistry, has lagged behind applications to other substrates. We report a highly enantioselective and chemoselective catalytic transformation of a wide range of β-substituted conjugated alkenyl-N-heteroaromatics to their corresponding chiral alkylated products. This operationally simple methodology can introduce linear, branched, and cyclic alkyl chains, as well as a phenyl group, at the β-carbon position. The key to this success was enhancement of the reactivity of alkenyl-heteroaromatic substrates via Lewis acid activation, in combination with the use of readily available and highly reactive Grignard reagents and a copper catalyst coordinated by a chiral chelating diphosphine ligand.
General methods to prepare chiral pyridine derivatives are greatly sought after due to their sign... more General methods to prepare chiral pyridine derivatives are greatly sought after due to their significance in medicinal chemistry. Here, we report highly enantioselective catalytic transformations of poorly reactive β-substituted alkenyl pyridines to access a wide range of alkylated chiral pyridines. The simple methodology involves reactivity enhancement via Lewis acid (LA) activation, the use of readily available and highly reactive Grignard reagents, and a copper-chiral diphosphine ligand catalyst. Apart from allowing the introduction of different linear, branched, cyclic, and functionalised alkyl chains at the β-position of alkenyl pyridines, the catalytic system also shows high functional group tolerance.
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Papers by Dr. Ravindra P. Jumde