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Herein we report the discovery of 2,4-1H-imidazole carboxamides as novel, biochemically potent, and kinome selective inhibitors of transforming growth factor β-activated kinase 1 (TAK1). The target was subjected to a DNA-encoded chemical library (DECL) screen. After hit analysis a cluster of compounds was identified, which was based on a central pyrrole-2,4-1H-dicarboxamide scaffold, showing remarkable kinome selectivity. A scaffold-hop to the corresponding imidazole resulted in increased biochemical potency. Next, X-ray crystallography revealed a distinct binding mode compared to other TAK1 inhibitors. A benzylamide was found in a perpendicular orientation with respect to the core hinge-binding imidazole. Additionally, an unusual amide flip was observed in the kinase hinge region. Using structure-based drug design (SBDD), key substitutions at the pyrrolidine amide and the glycine resulted in a significant increase in biochemical potency.

p38 mitogen-activated protein kinases are key mediators of environmental stress response and are promising targets for treatment of inflammatory diseases and cancer. Numerous efforts have led to the discovery of several potent inhibitors; however, so far no highly selective type-II inhibitors have been reported. We previously identified VPC-00628 as a potent and selective type-II inhibitor of p38α/β with few off-targets. Here we analyzed the chemical building blocks of VPC-00628 that played a key role in achieving potency and selectivity through targeting an inactive state of the kinases induced by a unique folded P-loop conformation. Using a rapid, systematic combinatorial synthetic approach, we identified compound 93 (SR-318) with excellent potency and selectivity for p38α/β, which potently inhibited the TNF-α release in whole blood. SR-318 therefore presents a potent and selective type-II inhibitor of p38α/β that can be used as a chemical probe for targeting this particular inactive state of these two p38 isoforms.

Targeting the “undruggable” proteome remains one of the big challenges in drug discovery. Recent innovations in the field of targeted protein degradation and manipulation of the ubiquitin-proteasome system open up new therapeutic approaches for disorders that cannot be targeted with conventional inhibitor paradigms. Proteolysis targeting chimeras (PROTACs) are bivalent ligands in which a compound that binds to the protein target of interest is connected to a second molecule that binds an E3 ligase via a linker. The E3 protein is usually either Cereblon or Von Hippel-Lindau. Several examples of selective PROTAC molecules with potent effect in cells and in vivo models have been reported. The degradation of specific proteins via these bivalent molecules is already allowing for the study of biochemical pathways and cell biology with more specificity than was possible with inhibitor compounds. In this review, we provide a comprehensive overview of recent developments in the field of small molecule mediated protein degradation, including transcription factors, kinases and nuclear receptors. We discuss the potential benefits of protein degradation over inhibition as well as the challenges that need to be overcome., Graphical Abstract Unlabelled Image

[Image: see text] Herein we report the discovery of 2,4-1H-imidazole carboxamides as novel, biochemically potent, and kinome selective inhibitors of transforming growth factor β-activated kinase 1 (TAK1). The target was subjected to a DNA-encoded chemical library (DECL) screen. After hit analysis a cluster of compounds was identified, which was based on a central pyrrole-2,4-1H-dicarboxamide scaffold, showing remarkable kinome selectivity. A scaffold-hop to the corresponding imidazole resulted in increased biochemical potency. Next, X-ray crystallography revealed a distinct binding mode compared to other TAK1 inhibitors. A benzylamide was found in a perpendicular orientation with respect to the core hinge-binding imidazole. Additionally, an unusual amide flip was observed in the kinase hinge region. Using structure-based drug design (SBDD), key substitutions at the pyrrolidine amide and the glycine resulted in a significant increase in biochemical potency.

A comprehensive study on the synthesis and ring-closing metathesis (RCM) of α,β-dehydroamino acids is described. This sequence has led to the formation of a range of biologically relevant functionalized nitrogen heterocycles. The incorporation of chiral building blocks in the RCM precursors eventually resulted in the formation of optically active 4-substituted cyclic dehydroamino acids. In addition, olefin isomerization under metathesis conditions was observed for a number of compounds, which could be successfully inhibited either by the introduction of allylic substituents or by the addition of a ruthenium hydride scavenger.

The rhodium-catalyzed asymmetric hydrogenation of several β-substituted itaconic acid mono-esters, using a library of monodentate phosphoramidite and phosphite ligands is described. Two β-alkyl-substituted substrates were readily hydrogenated by the rhodium complex Rh(COD)2BF4 in combination with (S)-PipPhos as a ligand resulting in ees of 99%. In contrast, the corresponding more hindered β-aryl-substituted substrates did not exhibit acceptable enantioselectivities under these conditions. However, the use of a 48-membered ligand library led to the identification of several suitable ligands for these substrates, resulting in ees of 89–99%. The resulting optically active succinic acid derivatives are potentially useful building blocks for more elaborate compounds, because of the ability to differentiate between the carboxylic acid and the ester groups on either side of the molecule.

Novel, efficient synthetic pathways to DAH, KDO, and 2-deoxy-beta-KDO are described. Ring-closing metathesis (RCM) of highly functionalized alpha-alkoxyacrylate fragments resulted in a series of synthetically versatile oxygen heterocyclic intermediates. Further functionalization of the resulting enol ether double bond and subsequent deprotection provided the natural products in high overall yields, starting from commercially available protected sugars.

The steric influence of extended aryl substituents on 2,2′-bis(1,3-oxazoline) ligands was investigated in a series of asymmetric catalytic reactions such as Mukaiyama aldol and Michael reactions, hetero-Diels–Alder processes, and allylic alkylation reactions. 4,4′-(2-Naphthyl)- and 4,4′-(9-anthryl)-substituted isopropylidene-bridged 2,2′-bis(1,3-oxazolines) were synthesized and their enantioselective and catalytic properties in combination with different metals evaluated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Ring-closing metathesis reactions of α-ester-substituted enol ethers are described. In the case of unsubstituted terminal olefins, isomerization prior to cyclization was observed as an undesired side reaction, which could not be completely inhibited. Furthermore, this methodology was applied to a formal synthesis of KDO, which now represents the shortest synthetic pathway to KDO and its deoxy analogue. Interestingly, in this route olefin isomerization was not observed, presumably due to the increased steric environment of the double bond. Finally, an efficient two-step conversion to transform an alcohol into an α-alkoxy acrylate is also described.

A number of cobalt(II) chloride complexes of pyridine/amine N3 and N4 donors have been prepared and structurally characterised. Even though they are paramagnetic, assignment of the 1H NMR signals was possible in several cases. With the exception of tpa, which formed a cationic monochloride complex, all new complexes have cis-coordinated chlorides. Nevertheless, only the relatively rigid pyp ligands gave rise to (low) ethene polymerisation activity on activation with MAO. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

A comprehensive study on the synthesis and ring-closing metathesis (RCM) of α,β-dehydroamino acids is described. This sequence has led to the formation of a range of biologically relevant functionalized nitrogen heterocycles. The incorporation of chiral building blocks in the RCM precursors eventually resulted in the formation of optically active 4-substituted cyclic dehydroamino acids. In addition, olefin isomerization under metathesis conditions was observed for a number of compounds, which could be successfully inhibited either by the introduction of allylic substituents or by the addition of a ruthenium hydride scavenger.

The rhodium-catalyzed asymmetric hydrogenation of several β-substituted itaconic acid mono-esters, using a library of monodentate phosphoramidite and phosphite ligands is described. Two β-alkyl-substituted substrates were readily hydrogenated by the rhodium complex Rh(COD)2BF4 in combination with (S)-PipPhos as a ligand resulting in ees of 99%. In contrast, the corresponding more hindered β-aryl-substituted substrates did not exhibit acceptable enantioselectivities under these conditions. However, the use of a 48-membered ligand library led to the identification of several suitable ligands for these substrates, resulting in ees of 89–99%. The resulting optically active succinic acid derivatives are potentially useful building blocks for more elaborate compounds, because of the ability to differentiate between the carboxylic acid and the ester groups on either side of the molecule.

The steric influence of extended aryl substituents on 2,2′-bis(1,3-oxazoline) ligands was investigated in a series of asymmetric catalytic reactions such as Mukaiyama aldol and Michael reactions, hetero-Diels–Alder processes, and allylic alkylation reactions. 4,4′-(2-Naphthyl)- and 4,4′-(9-anthryl)-substituted isopropylidene-bridged 2,2′-bis(1,3-oxazolines) were synthesized and their enantioselective and catalytic properties in combination with different metals evaluated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Both enantiomers of 1-naphthylglycine were obtained in 99% ee by enzymatic resolution of the corresponding racemic amino acid amide, giving access to the novel ligands (R)- and (S)-naphthylbis(oxazoline). Initial studies provided insight into the scope and limitations of the (S)-naphthyl-substituted bis(oxazoline) and its steric influence compared to other bis(oxazolines) in catalytic asymmetric synthesis. (© Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003)