(S)-4'-nitro-Blebbistatin is a more stable and less phototoxic form of (-)-blebbistatin , which is a selective cell-permeable inhibitor of non-muscle myosin II ATPases.^1,2(-)-Blebbistatin rapidly and reversibly inhibits Mg-ATPase activity andin vitromotility of non-muscle myosin IIA and IIB for several species (IC₅₀s = 0.5-5 µM), while poorly inhibiting smooth muscle myosin (IC₅₀= 80 µM).³Through 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 productviacytotoxic intermediates, which may be problematic for its use in fluorescent live cell imaging applications.^4,5The addition of a 4'-nitro group decreases the inherent fluorescence, stabilizes the molecule to circumvent its degradation by prolonged blue light exposure, and decreases its phototoxicity while retaining thein vitroandin vivoactivity of (-)-blebbistatin.^6,7(S)-4'-nitro-Blebbistatin has the same stereochemistry as the active (-)-blebbistatin enantiomer.

1.Straight, A.F., Cheung, A., Limouze, J., et al.Dissecting temporal and spatial control of cytokinesis with a myosin II inhibitorScience299(5613)1743-1747(2003) 2.KovÁcs, M., TÓth, J., HetÉnyi, C., et al.Mechanism of blebbistatin inhibition of myosin IIJ. Biol. Chem.279(34)35557-35563(2004) 3.Limouze, J., Straight, A.F., Mitchison, T., et al.Specificity of blebbistatin, an inhibitor of myosin IIJ. Muscle Res. Cell Motil.25(4-5)337-341(2004) 4.Kolega, J.Phototoxicity and photoinactivation of blebbistatin in UV and visible lightBiochem. Biophys. Res. Commun.320(3)1020-1025(2004) 5.Sakamoto, T., Limouze, J., Combs, C.A., et al.Blebbistatin, a myosin II inhibitor, is photoinactivated by blue lightBiochemistry44(2)584-588(2005) 6.KÉpirÓ, M., VÁrkuti, B.H., VÉgner, L., et al.para-Nitroblebbistatin, the non-cytotoxic and photostable myosin II inhibitorAngew Chem. Int. Ed. Engl.53(31)8211-8215(2014) 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 analogsEur. J. Med. Chem.13685-103(2017)