The availability of high-quality screening compounds is of paramount importance for the discovery of innovative new medicines. Natural product (NP) frameworks can inspire the design of productive compound libraries. Here, we describe the design and synthesis of four compound libraries based on scaffolds that have broad NP-like features, but that are only distantly related to specific NPs. The optimisation of syntheses of the scaffolds using [5 + 2] cycloaddition chemistry is detailed, together with methods to yield exemplar decorated screening compounds. In each case, a library was nominated for production, leading to a total of >2900 screening compounds that augmented the Joint European Compound Library of the European Lead Factory.

Efficient access to diverse screening compounds with desirable, lead‐like properties can be a bottleneck in early drug discovery and chemical biology. Herein we present an efficient, rapid route to three structurally distinct classes of compounds (A–C) from a single precursor, which in turn is available through a one‐pot Petasis 3‐component reaction/Diels–Alder cascade reaction. We demonstrate the versatility of the approach through the synthesis of 35 exemplary compounds from the three classes, as well as by the production of 2188 final compounds, which have been included in the Joint European Compound Library of the European Lead Factory.

The PRMT5-MEP50 methyltransferase is a major target for anticancer drug discovery, and modulators of its interactions with different regulatory proteins are in high demand because they modulate PRMT5 substrate selectivity. We describe a strategy for the development of a PRMT5/adaptor protein PPI inhibitor, which includes the design and synthesis of macrocyclic peptides based on the motif for the interaction of PRMT5 with its adaptor protein RioK1. After the initial exploration of different macrocycle sizes and cyclization linkages, analysis of a peptide library identified hot spots for the variation of the amino acid structure. The incorporation of nonproteinogenic amino acids into the macrocyclic peptide led to a potent cyclic PRMT5 binding peptide (K i = 66 nM), which selectively inhibits the interaction of PRMT5 with the adaptor proteins RioK1 and pICln (IC 50 = 654 nM) but not with the alternative adaptor protein MEP50. The inhibitor is a promising tool for further biological investigation of this intriguing protein interface.

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A new effective strategy for the synthesis of sp3‐rich small molecules for library production is presented. The key steps to generate complexity involve a Petasis three‐component reaction followed by an intramolecular Diels–Alder and cyclization to generate a densely enriched tricyclic or tetracyclic scaffolds with 3–4 stereocenters and three handles for decoration. The strategy was used for the production of 143 molecules for the European Lead Factory.