Abstract: Two approaches were explored toward the goal of synthesizing physiologically useful Caz+-selective chelators whose Ca2+ affinities increase markedly upon photolysis. In the first approach, the known Ca2+-selective chelator 1, 2-bis (o-aminophenoxy) ethane-N, N, N', N'-tetraacetic acid (BAPTA) was masked with a variety of photoremovable protecting groups on one of its four carboxyl groups, reducing its affinity for Ca2+ to-lo5 M-'. Upon ...