Generation of Polar Semi-Saturated Bicyclic Pyrazoles for Fragment-Based Drug-Discovery Campaigns

Couple-close construction of polycyclic rings from diradicals

Heteroarenes are ubiquitous motifs in bioactive molecules, conferring favourable physical properties when compared to their arene counterparts1-3. In particular, semisaturated heteroarenes possess attractive solubility properties and a higher fraction of sp3 carbons, which can improve binding affinity and specificity. However, these desirable structures remain rare owing to limitations in current synthetic methods4-6. Indeed, semisaturated heterocycles are laboriously prepared by means of non-modular fit-for-purpose syntheses, which decrease throughput, limit chemical diversity and preclude their inclusion in many hit-to-lead campaigns7-10. Herein, we describe a more intuitive and modular couple-close approach to build semisaturated ring systems from dual radical precursors. This platform merges metallaphotoredox C(sp2)-C(sp3) cross-coupling with intramolecular Minisci-type radical cyclization to fuse abundant heteroaryl halides with simple bifunctional feedstocks, which serve as the diradical synthons, to rapidly assemble a variety of spirocyclic, bridged and substituted saturated ring types that would be extremely difficult to make by conventional methods. The broad availability of the requisite feedstock materials allows sampling of regions of underexplored chemical space. Reagent-controlled radical generation leads to a highly regioselective and stereospecific annulation that can be used for the late-stage functionalization of pharmaceutical scaffolds, replacing lengthy de novo syntheses.

Modular, automated synthesis of spirocyclic tetrahydronaphthyridines from primary alkylamines

Spirocyclic tetrahydronaphthyridines (THNs) are valuable scaffolds for drug discovery campaigns, but access to this 3D chemical space is hampered by a lack of modular and scalable synthetic methods. We hereby report an automated, continuous flow synthesis of α-alkylated and spirocyclic 1,2,3,4-tetrahydro-1,8-naphthyridines ("1,8-THNs"), in addition to their regioisomeric 1,6-THN analogues, from abundant primary amine feedstocks. An annulative disconnection approach based on photoredox-catalysed hydroaminoalkylation (HAA) of halogenated vinylpyridines is sequenced in combination with intramolecular SNAr N-arylation. To access the remaining 1,7- and 1,5-THN isomers, a photoredox-catalysed HAA step is telescoped with a palladium-catalysed C-N bond formation. Altogether, this provides a highly modular access to four isomeric THN cores from a common set of unprotected primary amine starting materials, using the same bond disconnections. The simplifying power of the methodology is illustrated by a concise synthesis of the spirocyclic THN core of Pfizer's MC4R antagonist PF-07258669.

A close look into the biological and synthetic aspects of fused pyrazole derivatives

The fusion of pyrazole scaffold with other skeletons creates a class of attractive molecules, demonstrating significant biological and chemical potentiality in the development of medicinal chemistry. Over the past few decades, numerous biologically active molecules featuring fused pyrazole moieties have been excavated and synthesized, some of which represented by sildenafil have been marketed as drugs, and the biological importance together with chemical synthesis strategies of fused pyrazole compounds, including structural modification based on lead compounds, have been steadily progressing. In this review, we focused our attention on the biological importance of fused pyrazoles and highlighted recent progress in the synthesis of this framework over the past 10 years. What' s more, the limitations, challenges, and future prospects were proposed, wishing to provide references for the development of pyrazole fused frameworks in the field of medicinal chemistry. Contents.

Efficient unified synthesis of diverse bridged polycyclic scaffolds using a complexity-generating 'stitching' annulation approach

Regioselective and stereospecific directed C-H arylation of simple amine substrates, and cyclisation, delivered 30 diverse, three-dimensional scaffolds. The unified approach significantly expanded the range of bridged ring systems that contain both a nitrogen atom and an aromatic ring.