para-amino-Blebbistatin is a more water-soluble form of (S)-4'-nitro-blebbistatin , which is a more stable and less phototoxic form of (-)-blebbistatin .1,2,3 (-)-Blebbistatin is a selective cell-permeable inhibitor of non-muscle myosin II ATPases that rapidly and reversibly inhibits Mg-ATPase activity and in vitro motility of non-muscle myosin IIA and IIB for several species (IC50s = 0.5-5 μM), while poorly inhibiting smooth muscle myosin (IC50 = 80 μM).2,3,4 Through these effects, it blocks apoptosis-related bleb formation, directed cell migration, and cytokinesis in vertebrate cells. However, prolonged exposure to blue light (450-490 nm) results in degradation of blebbistatin to an inactive product via cytotoxic intermediates, which may be problematic for its use in fluorescent live cell imaging applications.5,6 The addition of a 4'-amino group increases its water solubility, decreases the inherent fluorescence, stabilizes the molecule to circumvent its degradation by prolonged blue light exposure, and decreases its phototoxicity while retaining the in vitro and in vivo activity of blebbistatin.7 para-amino-Blebbistatin has the same stereochemistry as the active (-)-blebbistatin enantiomer.

|1. V?rkuti, B.H., K?pir?, M., Horv?th, I.?., et al. A highly soluble, non-phototoxic, non-fluorescent blebbistatin derivative. Sci. Rep. 6:26141, (2016).|2. Straight, A.F., Cheung, A., Limouze, J., et al. Dissecting temporal and spatial control of cytokinesis with a myosin II inhibitor. Science 299(5613), 1743-1747 (2003).|3. Kov?cs, M., T?th, J., Het?nyi, C., et al. Mechanism of blebbistatin inhibition of myosin II. J. Biol. Chem. 279(34), 35557-35563 (2004).|4. Limouze, J., Straight, A.F., Mitchison, T., et al. Specificity of blebbistatin, an inhibitor of myosin II. J. Muscle Res. Cell Motil. 25(4-5), 337-341 (2004).|5. Kolega, J. Phototoxicity and photoinactivation of blebbistatin in UV and visible light. Biochem. Biophys. Res. Commun. 320(3), 1020-1025 (2004).|6. Sakamoto, T., Limouze, J., Combs, C.A., et al. Blebbistatin, a myosin II inhibitor, is photoinactivated by blue light. Biochemistry 44(2), 584-588 (2005).|7. Verhasselt, S., Roman, B.I., Bracke, M.E., et al. Improved synthesis and comparative analysis of the tool properties of new and existing D-ring modified (S)-blebbistatin analogs. Eur. J. Med. Chem. 136, 85-103 (2017).