LDN-209929 dihydrochloride is a potent and selective inhibitor of haspin kinase (IC50= 55 nM), demonstrating 180-fold selectivity versus DYRK2 (IC50= 9.9 μM).

Haspin, a Haploid Germ Cell-Specific Nuclear Protein Kinase, is a serine/threonine kinase, expressed across various tissues, including testis, bone marrow, thymus, and spleen. It is crucial for mitotic processes, especially for phosphorylating histone H3 at Thr-3 (H3T3) during G2/early prophase. Its activity peaks in prometaphase/metaphase and decreases by anaphase [1]. DYRKs, part of the CMGC family of ePKs, are categorized into class 1 (DYRK1A and 1B) and class 2 (DYRK2, 3, and 4) kinases. Their functionality relies on the autophosphorylation of a vital activation loop tyrosine during protein synthesis [1].