Expanding the ligand spaces for E3 ligases for the design of protein degraders.

Targeted protein degradation (TPD) has recently emerged as an exciting new drug modality. However, the strategy of developing small molecule-based protein degraders has evolved over the past two decades and has now established molecular tags that are already in clinical use, as well as chimeric molecules, PROteolysis TArgeting Chimeras (PROTACs), based mainly on ligand systems developed for the two E3 ligases CRBN and VHL. The large size of the human E3 ligase family suggests that PROTACs can be developed by targeting a large diversity of E3 ligases, some of which have restricted expression patterns with the potential to design disease- or tissue-specific degraders. Indeed, many new E3 ligands have been published recently, confirming the druggability of E3 ligases. This review summarises recent data on E3 ligases and highlights the challenges in developing these molecules into efficient PROTACs rivalling the established degrader systems.

5-Amino-1-phenyl-1H-pyrazole-4-carboxylic acid.

In the mol-ecule of the title compound, C(10)H(9)N(3)O(2), the pyrazole ring is approximately coplanar with the amino and carboxyl groups. The phenyl group is twisted by 48.13 (3)° relative to this plane. An intra-molecular N-H⋯O hydrogen bond stabilizes the planar conformation of the mol-ecule. The mol-ecules are linked into two-dimensional sheets by two strong inter-molecular N-H⋯N and O-H⋯O hydrogen bonds. The latter forms the classic carboxylic acid dimer motif.