Multivalent benzene polyphosphate derivatives are non-Ca-mobilizing Ins(1,4,5)P receptor antagonists.

Inositol 1,4,5-trisphosphate [Ins(1,4,5)P] mobilizes intracellular Ca through the Ins(1,4,5)P receptor [InsPR]. Although some progress has been made in the design of synthetic InsPR partial agonists and antagonists, there are still few examples of useful small molecule competitive antagonists. A "multivalent" approach is explored and new dimeric polyphosphorylated aromatic derivatives were designed, synthesized and biologically evaluated. The established weak InsPR ligand benzene 1,2,4-trisphosphate [Bz(1,2,4)P] is dimerized through its 5-position in two different ways, first directly as the biphenyl derivative biphenyl 2,2',4,4',5,5'-hexakisphosphate, [BiPh(2,2',4,4',5,5')P] and with its regioisomeric biphenyl 3,3',4,4',5,5'-hexakisphosphate [BiPh(3,3',4,4',5,5')P]. Secondly, a linker motif is introduced in a flexible ethylene-bridged dimer () with its corresponding 1,2-bisphosphate dimer (), both loosely analogous to the very weak antagonist 1,2-bis(2-aminophenoxy)ethane-'-tetraacetic acid (BAPTA ). In permeabilized L15 fibroblasts overexpressing type 1 InsPR, BiPh(2,2',4,4',5,5')P () inhibits Ins(1,4,5)P-induced Ca release in a apparently competitive fashion [IC 187 nM] and the Bz(1,2,4)P dimer () is only slightly weaker [IC 380 nM]. Compounds were also evaluated against type I Ins(1,4,5)P 5-phosphatase. All compounds are resistant to dephosphorylation, with BiPh(2,2',4,4',5,5')P (), being the most effective inhibitor of any biphenyl derivative synthesized to date [IC 480 nM] and the Bz(1,2,4)P ethylene dimer () weaker [IC 3.55 μM]. BiPh(3,3',4,4',5,5')P () also inhibits 5-phosphatase [IC 730 nM] and exhibits unexpected Ca releasing activity [EC 800 nM]. Thus, relocation of only a single mirrored phenyl phosphate group in () from that of antagonist () does not markedly change enzyme inhibitory activity, but elicits a dramatic switch in Ca-releasing activity. Such new agents demonstrate the power of the multivalent approach and may be useful to investigate the chemical biology of signaling through InsPR and as templates for further design.