Stereochemical and skeletal complexity are particularly important vis‐à‐vis the cross‐talks between a small molecule and a complementary active site of a biological target. This intricate harmony is known to increase selectivity, reduce toxicity, and increase the success rate in clinical trials. Therefore, the development of novel strategies for establishing underrepresented chemical space that is rich in stereochemical and skeletal diversity is an important milestone in a drug discovery campaign. In this review, we discuss the evolution of interdisciplinary synthetic methodologies utilized in chemical biology and drug discovery that has revolutionized the discovery of first‐in‐class molecules over the last decade with an emphasis on complexity‐to‐diversity and pseudo‐natural product strategies as a remarkable toolbox for deciphering next‐generation therapeutics. We also report how these approaches dramatically revolutionized the discovery of novel chemical probes that target underrepresented biological space. We also highlight selected applications and discuss key opportunities offered by these tools and important synthetic strategies used for the construction of chemical spaces that are rich in skeletal and stereochemical diversity. We also provide insight on how the integration of these protocols has the promise of changing the drug discovery landscape.
The de novo assembly of stereochemically and skeletally diverse scaffolds is a powerful tool for the discovery of novel chemotypes. Hence, the development of modular, step- and atom-economic synthetic methods to access stereochemically and skeletally diverse compound collection is particularly important. Herein, we show a metal-free, stereodivergent build/couple/pair strategy that allows access to a unique collection of benzo[5,6][1,4]oxazino[4,3-a]quinazoline, quinolino[1,2-a]quinazoline and benzo[b]benzo [4,5]imidazo[1,2-d][1,4]oxazine scaffolds with complete diastereocontrol and wide distribution of molecular architectures. This metal-free process proceeds via desymmetrization of phenol derivatives. The cascade unites Mannich with aza-Michael addition reactions, providing expeditious entries to diverse classes of molecular shapes in a single operation.
A one-pot, metal-free, light-driven [4+2]-cycloaddition reaction is described by accessing a diverse collection of chromeno [4,3-b]quinoline and chromeno [4,3-b][1,8]naphthyridine scaffolds in a diastereoselective manner. This process delivered stereoisomers, which were challenging to produce by an inverse-demand Diels−Alder reaction. The tetracyclic products were provided in good yields, promoted by rose bengal and blue light in a single operation. The developed protocol proceeded efficiently without the need for expensive photosensitizers such as Ir or Ru complexes. The cascade is modular and step-economic, and the substrate scope is wide. Polycyclic architectures can be assembled from readily available aniline, aminoazine, indole, and salicylaldehyde derivatives.
Azepino [3,4,5-cd]indole derivatives represent the core scaffold of important natural products and biologically relevant compounds. Therefore, the establishment of step-and atomeconomic strategies to access this class of compounds is of paramount importance. To this end, complexity-to-diversity (CtD) strategy has become one of the most important tools that transforms complex molecules into diverse skeleta. However, many of the reactions that could be employed in CtD are restricted by the functional handles exist in these molecules. This limits the achievement of the desired skeletal diversity.Herein, an efficient and step-economic strategy to access a diverse collection of azepino-[3,4,5-cd]indole architectures through a cascade that combines Pictet-Spengler with Michael addition, is described. This was achieved by reacting cyclohexadienone acetaldehydes 2 a-2 d with indolyl-4-ethyl amine 1. Employing a CtD strategy on the developed azepino-[3,4,5cd]indoles, a rapid rearrangement reaction that provided a modular, chemo-and diastereoselective access to diverse collection of spiro azepinocarbazole nature-inspired frameworks, was encountered.
The development of robust and step-economic strategies to access structurally diverse drug-like compound collections remains a challenge. A distinct structural option that constitutes the core scaffold of many biologically significant molecules is the quinazolinone ring system. Several members of this family of privileged substructures have gained attention due to their diverse biological activities. In this context, the development of an efficient strategy for their access is needed. Herein, we report a divergent metal-free operation to access a diverse collection of C6-substituted pyrrolo[4′,3′,2′:4,5]isoquinolino[1,2-b]quinazolin-8(6H)-one and pyrrolo[4′,3′,2′:4,5]isoquinolino[2,1-a]quinazolin-12(6H)-one architectures. The described cascade unites Friedel–Crafts and aza-Michael addition reactions. This operationally simple protocol enables a rapid access to these scaffolds and is compatible with a wide scope of starting materials. In addition, the cascade features a promising approach for the design of unique compound libraries for drug design and discovery programs.
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