Multivalent benzene polyphosphate derivatives are non-Ca2+-mobilizing Ins(1,4,5)P3 receptor antagonists.

Inositol 1,4,5-trisphosphate [Ins(1,4,5)P₃1] mobilizes intracellular Ca²⁺ through the Ins(1,4,5)P₃ receptor [InsP₃R]. Although some progress has been made in the design of synthetic InsP₃R 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 InsP₃R ligand benzene 1,2,4-trisphosphate [Bz(1,2,4)P₃2] 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')P₆8] and with its regioisomeric biphenyl 3,3',4,4',5,5'-hexakisphosphate [BiPh(3,3',4,4',5,5')P₆11]. Secondly, a linker motif is introduced in a flexible ethylene-bridged dimer (9) with its corresponding 1,2-bisphosphate dimer (10), both loosely analogous to the very weak antagonist 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA 7). In permeabilized L15 fibroblasts overexpressing type 1 InsP₃R, BiPh(2,2',4,4',5,5')P₆ (8) inhibits Ins(1,4,5)P₃-induced Ca²⁺ release in a apparently competitive fashion [IC₅₀ 187 nM] and the Bz(1,2,4)P₃ dimer (9) is only slightly weaker [IC₅₀ 380 nM]. Compounds were also evaluated against type I Ins(1,4,5)P₃ 5-phosphatase. All compounds are resistant to dephosphorylation, with BiPh(2,2',4,4',5,5')P₆ (8), being the most effective inhibitor of any biphenyl derivative synthesized to date [IC₅₀ 480 nM] and the Bz(1,2,4)P₃ ethylene dimer (9) weaker [IC₅₀ 3.55 μM]. BiPh(3,3',4,4',5,5')P₆ (11) also inhibits 5-phosphatase [IC₅₀ 730 nM] and exhibits unexpected Ca²⁺ releasing activity [EC₅₀ 800 nM]. Thus, relocation of only a single mirrored phenyl phosphate group in (11) from that of antagonist (8) does not markedly change enzyme inhibitory activity, but elicits a dramatic switch in Ca²⁺-releasing activity. Such new agents demonstrate the power of the multivalent approach and may be useful to investigate the chemical biology of signaling through InsP₃R and as templates for further design.