Calix[4]arene methylenebisphosphonic acids as calf intestine alkaline phosphatase inhibitors

Calix[4] arenes bearing one or two methylenebisphosphonic acid fragments were prepared via addition of diethylphosphite to the parent calix[4] arene aldehydes. The resulting compounds displayed stronger inhibition of calf intestine alkaline phosphatase than simple methylenebisphosphonic or 4-hydroxyphenyl methylenebisphosphonic acids. The action of these phosphorylated calix[4] arenes is concordant with partial mixed-type inhibition. The inhibition constants K-i and K-i'. for the calix[4] arene bis(methylenebisphosphonic) acid in Tris-HCl buffer at pH 9 are 0.38 muM and 2.8 muM respectively. The replacement of the phosphoric acid moieties on the macrocycle with diethylphosphonates results in a sharp decrease of its inhibitory action. Preorganizing phosphonic acid fragments using a calixarene platform therefore provides a promising approach for the design of efficient alkaline phosphatase inhibitors.