"(S)-3'-amino Blebbistatin, retaining the active stereochemistry of the less stable and more phototoxic (–)-blebbistatin, serves as a refined selective cell-permeable inhibitor of non-muscle myosin II ATPases. This compound efficaciously inhibits the Mg-ATPase activity and in vitro motility of non-muscle myosin IIA and IIB across several species with IC50s ranging from 0.5-5 µM, and exhibits minimal inhibition against smooth muscle myosin (IC50= 80 µM). Its primary functions include obstructing apoptosis-related bleb formation, directed cell migration, and cytokinesis in vertebrate cells. (S)-3'-amino Blebbistatin overcomes (–)-blebbistatin's limitation of rapid degradation under blue light (450-490 nm) exposure, which generates cytotoxic intermediates, thus posing a challenge for fluorescent live cell imaging applications. The introduction of a 3'-amino group to its structure notably reduces fluorescence while maintaining (–)-blebbistatin's activity, making it a superior alternative for research purposes."