Synthesis of New BAPTA Calcium Chelators

Abstract A series of new 1,2-bis-(2-aminophenoxyethane) N,N,N′,N′-tetraacetic acid (BAPTA) chelators were designed and synthesized to form novel and improved fluorescent indicators. Substituted 2-nitrophenol, acting as the material, reacted in five steps to give BAPTA-derived chelators. The Ca2+ affinity of BAPTA chelators could increase significantly by addition of electron-donating groups and decrease by electron-withdrawing groups. Compounds 3a–e were treated with iron powder instead of hydrogenation, obtaining a satisfying yield. The structures of all compounds were characterized by infrared, 1H NMR, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) spectra.