Synthetic D‐ and L‐enantiomers of 2,2‐difluoro‐2‐deoxy‐myo‐inositol 1,4,5‐trisphosphate interact differently with myo‐inositol 1,4,5‐trisphosphate binding proteins: Identification of a potent small molecule 3‐kinase inhibitor

Abstract

The ability of two enantiomeric fluoro‐analogues of D‐myo‐inositol 1,4,5‐trisphosphate [Ins(1,4,5)P₃] to mobilize intracellular Ca²⁺ stores in SH‐SY5Y neuroblastoma cells has been investigated. (—)‐D‐2,2‐difluoro‐2‐deoxy‐myo‐Ins(1,4,5)P₃ [D‐2,2‐F₂‐Ins(1,4,5)P₃] was a full agonist [EC₅₀ 0.21 μM] and slightly less potent than D‐Ins(1,4,5)P₃ [EC₅₀ 0.13 μM]. (+)‐L‐2,2‐F₂Ins(1,4,5)P₃ was a very poor agonist, confirming the stereospecificity of the Ins(1,4,5)P₃ receptor. D‐2,2‐F₂‐Ins(1,4,5)P₃ mobilized Ca²⁺ with broadly similar kinetics to Ins(1,4,5)P₃ and was a substrate for Ins(1,4,5)P₃ 3‐kinase inhibiting Ins(1,4,5)P₃ phosphorylation (apparent K_i = 10.2 μM) but was recognised less well than Ins(1,4,5)P₃. L‐2,2‐F₂‐Ins(1,4,5)P₃ was a potent competitive inhibitor of 3‐kinase (K_i = 11.9 μM). Whereas D‐2,2‐F₂‐Ins(1,4,5)P₃ was a good substrate for Ins(1,4,5)P₃ 5‐phosphatase, L‐2,2‐F₂Ins(1,4,5)P₃ was a relatively potent inhibitor (K_i = 19.0 μM).