Design and development of 5′-modified 7-substituted 4′-thionucleosides as potent Haspin inhibitors: Synthesis and biological evaluation

Haspin, a serine/threonine kinase essential for proper chromosome alignment during mitosis, has emerged as a promising anticancer target due to its selective function in proliferating cells. In our previous study, we identified LJ-4827, a 7-acetylene-substituted 4′-thionucleoside analog bearing a 5′-azido group, as a potent Haspin inhibitor with significant antiproliferative effects. To further optimize activity, we synthesized a series of novel 4′-thionucleoside analogs with 7-substituted scaffolds and diverse 5′-position modifications, as well as selected 6-position derivatives. SAR analysis revealed that incorporation of a 7-cyano group together with small, polar 5′-substituents such as azido ( 1c ) or amino ( 1d ) provided the most potent Haspin inhibition, with compound 1c achieving subnanomolar potency (IC₅₀ = 0.26 nM). Importantly, the 5′-amino analog 1d exhibited moderate Haspin inhibition (IC₅₀ = 18 nM), together with a highly selective kinase inhibition profile and markedly improved aqueous solubility relative to 1c . These properties enabled in vivo evaluation, where 1d significantly suppressed tumor growth in a colorectal cancer xenograft model, with comparable efficacy observed following either intraperitoneal or oral administration. These findings highlight 1d as a particularly promising Haspin-targeted anticancer agent that combines potent activity with favorable drug-like properties.