Calix[4]arenes, functionalized at the wide rim with two or four N-2-sulfonylamidine groups were prepared. In the crystalline state, the bowl shaped calix [4]arene-bis-N-sulfonyltrifluoromethylacetamidine 3b is associated through intermolecular hydrogen bonds, (NHO)-O-...=S, while the phenyl rings of the Ph-SO2-fragments are hosted in the cavities of the nearby molecules of 3b. Calixarene 4b influences Ca2+ transport in Mg2+, ATP-dependent calcium pumps. (c) 2005 Elsevier Ltd. All rights reserved.