Design and Synthesis of A Caged Zn²⁺ Probe, 8-Benzenesulfonyloxy-5-N,N-dimethylaminosulfonylquinolin-2-ylmethyl-pendant 1,4,7,10-Tetraazacyclododecane, and Its Hydrolytic Uncaging upon Complexation with Zn²⁺

8-Benzenesulfonyloxy-5- N,N-dimethylaminosulfonylquinolin-2-ylmethyl-pendant cyclen (BS-caged-L(4), BS = benzenesulfonyl) was designed and synthesized as a "caged" derivative of a previously described Zn(2+) fluorophore, 8-hydroxy-5- N,N-dimethylaminosulfonylquinolin-2-ylmethyl-pendant cyclen (L(4)) (cyclen = 1,4,7,10-tetraazacyclododecane). In the absence of metal ions and in the dark, BS-caged-L(4) (10 microM) showed negligible fluorescence emission at pH 7.4 (10 mM HEPES with I = 0.1 (NaNO3)) and 25 degrees C (excitation at 328 nm). Addition of Zn(2+) induced an increase in the UV/vis absorption of BS-caged-L(4) (10 microM) at 258 nm and a significant increase in fluorescence emission at 512 nm. These responses are results from the formation of Zn(H-1L(4)) by the hydrolysis of the sulfonyl ester at the 8-position of the quinoline unit promoted by the Zn(2+)-bound HO(-). Improvement of cell membrane permeation in comparison with L(4) is also described.