Ring contraction in synthesis of functionalized carbocycles

Carbocycles are a key and widely present structural motif in organic compounds. The construction of structurally intriguing carbocycles, such as highly-strained fused rings, spirocycles or highly-functionalized carbocycles with congested stereocenters, remains challenging in organic chemistry. Cyclopropanes, cyclobutanes and cyclopentanes within such carbocycles can be synthesized through ring contraction. These ring contractions involve re-arrangement of and/or small molecule extrusion from a parental ring, which is either a carbocycle or a heterocycle of larger size. This review provides an overview of synthetic methods for ring contractions to form cyclopropanes, cyclobutanes and cyclopentanes en route to structurally intriguing carbocycles

Cascade aza-Wittig/6π-electrocyclization in the synthesis of 1,6-dihydropyridines

A metal-free protocol for the synthesis of substituted 1,6-dihydropyridines with quaternary stereogenic centers via a cascade aza-Wittig/6π-electrocyclization process has been developed. The high functional group compatibility and broad scope of this method were demonstrated by using a wide range of easily available vinyliminophosphoranes and ketones, with yields up to 97%. A modification of the obtained products allowed for an increase in complexity and chemical diversity. Finally, attempts for asymmetric synthesis of 1,6-dihydropyridines are demonstrated

Stereoselective synthesis of cyclobutanes by contraction of pyrrolidines

Here we report a contractive synthesis of multisubstituted cyclobutanes containing multiple stereocenters from readily accessible pyrrolidines using iodonitrene chemistry. Mediated by a nitrogen extrusion process, the stereospecific synthesis of cyclobutanes involves a radical pathway. Unprecedented unsymmetrical spirocyclobutanes were prepared successfully, and a concise, formal synthesis of the cytotoxic natural product piperarborenine B is reported

Enantioselective synthesis of five-membered-ring atropisomers with a chiral Rh(III) complex

Axially chiral atropisomeric compounds are widely applied in asymmetric catalysis and medicinal chemistry, and efficient methods for their synthesis are in high demand. This applies in particular to atropisomers derived from five-membered aromatic rings because their lower barrier for rotation among the biaryl axis limits their asymmetric synthesis. We report here an enantioselective C–H functionalization method using our chiral RhJasCp complex for the synthesis of the biaryl atropisomer types that can be accessed from three different five-membered-ring heterocycles

Dynamic catalytic highly enantioselective 1,3‐dipolar cycloadditions

In dynamic covalent chemistry, reactions follow a thermodynamically controlled pathway through equilibria. Reversible covalent-bond formation and breaking in a dynamic process enables the interconversion of products formed under kinetic control to thermodynamically more stable isomers. Notably, enantioselective catalysis of dynamic transformations has not been reported and applied in complex molecule synthesis. We describe the discovery of dynamic covalent enantioselective metal-complex-catalyzed 1,3-dipolar cycloaddition reactions. We have developed a stereodivergent tandem synthesis of structurally and stereochemically complex molecules that generates eight stereocenters with high diastereo- and enantioselectivity through asymmetric reversible bond formation in a dynamic process in two consecutive Ag-catalyzed 1,3-dipolar cycloadditions of azomethine ylides with electron-poor olefins. Time-dependent reversible dynamic covalent-bond formation gives enantiodivergent and diastereodivergent access to structurally complex double cycloadducts with high selectivity from a common set of reagents

Probing embryonic development enables the discovery of unique small-molecule bone morphogenetic protein potentiators

We report on the feasibility to harness embryonic development in vitro for the identification of small-molecule cytokine mimetics and signaling activators. Here, a phenotypic, target-agnostic, high throughput assay is presented that probes bone morphogenetic protein (BMP) signaling during mesodermal patterning of embryonic stem cells. The temporal discrimination of BMP- and transforming growth factor-β (TGFβ)-driven stages of cardiomyogenesis underpins a selective, authentic orchestration of BMP cues that can be recapitulated for the discovery of BMP activator chemotypes. Proof of concept is shown from a chemical screen of 7000 compounds, provides a robust hit validation workflow, and afforded 2,3 disubstituted 4H-chromen-4-ones as potent BMP potentiators with osteogenic efficacy. Mechanistic studies suggest that Chromenone 1 enhances canonical BMP outputs at the expense of TGFβ-Smads in an unprecedented manner. Pharmacophoric features were defined, providing a set of novel chemical probes for various applications in (stem) cell biology, regenerative medicine, and basic research on the BMP pathway

The highly potent AhR agonist picoberin modulates Hh-dependent osteoblast differentiation

Identification and analysis of small molecule bioactivity in target-agnostic cellular assays and monitoring changes in phenotype followed by identification of the biological target are a powerful approach for the identification of novel bioactive chemical matter in particular when the monitored phenotype is disease-related and physiologically relevant. Profiling methods that enable the unbiased analysis of compound-perturbed states can suggest mechanisms of action or even targets for bioactive small molecules and may yield novel insights into biology. Here we report the enantioselective synthesis of natural-product-inspired 8-oxotetrahydroprotoberberines and the identification of Picoberin, a low picomolar inhibitor of Hedgehog (Hh)-induced osteoblast differentiation. Global transcriptome and proteome profiling revealed the aryl hydrocarbon receptor (AhR) as the molecular target of this compound and identified a cross talk between Hh and AhR signaling during osteoblast differentiation

The pseudo‐natural product rhonin targets RHOGDI

For the discovery of novel chemical matter generally endowed with bioactivity, strategies may be particularly efficient that combine previous insight about biological relevance, e.g., natural product (NP) structure, with methods that enable efficient coverage of chemical space, such as fragment-based design. We describe the de novo combination of different 5-membered NP-derived N-heteroatom fragments to structurally unprecedented “pseudo-natural products” in an efficient complexity-generating and enantioselective one-pot synthesis sequence. The pseudo-NPs inherit characteristic elements of NP structure but occupy areas of chemical space not covered by NP-derived chemotypes, and may have novel biological targets. Investigation of the pseudo-NPs in unbiased phenotypic assays and target identification led to the discovery of the first small-molecule ligand of the RHO GDP-dissociation inhibitor 1 (RHOGDI1), termed Rhonin. Rhonin inhibits the binding of the RHOGDI1 chaperone to GDP-bound RHO GTPases and alters the subcellular localization of RHO GTPases

The pseudo‐natural product rhonin targets RHOGDI

For the discovery of novel chemical matter generally endowed with bioactivity, strategies may be particularly efficient that combine previous insight about biological relevance, e.g., natural product (NP) structure, with methods that enable efficient coverage of chemical space, such as fragment-based design. We describe the de novo combination of different 5-membered NP-derived N-heteroatom fragments to structurally unprecedented “pseudo-natural products” in an efficient complexity-generating and enantioselective one-pot synthesis sequence. The pseudo-NPs inherit characteristic elements of NP structure but occupy areas of chemical space not covered by NP-derived chemotypes, and may have novel biological targets. Investigation of the pseudo-NPs in unbiased phenotypic assays and target identification led to the discovery of the first small-molecule ligand of the RHO GDP-dissociation inhibitor 1 (RHOGDI1), termed Rhonin. Rhonin inhibits the binding of the RHOGDI1 chaperone to GDP-bound RHO GTPases and alters the subcellular localization of RHO GTPases

Metal-catalyzed oxidative coupling of ketones and ketone enolates

Recent years have witnessed a significant advancement in the field of radical oxidative coupling of ketones towards the synthesis of highly useful synthetic building blocks, such as 1,4-dicarbonyl compounds, and biologically important heterocyclic and carbocyclic compounds. Besides oxidative homo- and cross-coupling of enolates, other powerful methods involving direct C(sp3)–H functionalizations of ketones­ have emerged towards the synthesis of 1,4-dicarbonyl compounds. Moreover, direct α-C–H functionalization of ketones has also allowed an efficient access to carbocycles and heterocycles. This review summarizes all these developments made since 2008 in the field of metal-catalyzed/promoted radical-mediated functionalization of ketones at the α-position.1 Introduction2 Synthesis of 1,4-Dicarbonyl Compounds3 Synthesis of Heterocyclic Scaffolds4 Synthesis of Carbocyclic Scaffolds5 Conclusion</jats:p