An efficient route toD-myo-inositol 1,3,4-triphosphate andD-myo-inositol 1,3,4,5-tetrakisphosphate

Sulfonate protecting groups. Regioselective sulfonylation of myo-inositol orthoesters-improved synthesis of precursors of D- and L-myo-inositol 1,3,4,5-tetrakisphosphate, myo-inositol 1,3,4,5,6-pentakisphosphate and related derivatives

The regioselectivity of sulfonylation of myo-inositol orthoesters was controlled by the use of different bases to obtain the desired sulfonate. Monosulfonylation of myo-inositol orthoesters in the presence of one equivalent of sodium hydride or triethylamine resulted in the sulfonylation of the 4-hydroxyl group. The use of pyridine as a base for the same reaction resulted in sulfonylation of the 2-hydroxyl group. Disulfonylation of these orthoesters in the presence of excess sodium hydride yielded the 4,6-di-O-sulfonylated orthoesters. However, the use of triethylamine or pyridine instead of sodium hydride yielded the 2,4-di-O-sulfonylated orthoester. Sulfonylated derivatives of myo-inositol orthoesters were stable to conditions of O-alkylation but were cleaved using magnesium/methanol or sodium methoxide in methanol to regenerate the corresponding myo-inositol orthoester derivative. These new methods of protection-deprotection have been used: (i) for the efficient synthesis of enantiomers of 2,4-di-O-benzyl-myo-inositol, which are precursors for the synthesis of D- and L-myo-inositol 1,3,4,5-tetrakisphosphate; (ii) for the preparation of 2-O-benzyl-myo-inositol which is a precursor for the preparation of myo-inositol 1,3,4,5,6-pentakisphosphate.

A membrane-permeant, bioactivatable derivative of Ins(1,3,4)P3 and its effect on Cl(-)-secretion from T84 cells

The synthesis of rac-2,5,6-tri-O-butyryl-myo-inositol 1,3,4-trisphosphate hexakis(acetoxymethyl) ester [Bt3-Ins(1,3,4)P3/AM, 1], a membrane-permeant derivative of myo-inositol 1,3,4-trisphosphate [Ins(1,3,4)P3] is reported. 1 inhibited calcium-mediated chloride secretion of T84 cells, suggesting a regulatory link of Ins(1,3,4)P3 and the biosynthesis of the known inhibitor myo-inositol 3,4,5,6-tetrakisphosphate.

Binding and activity of the nine possible regioisomers of myo-inositol tetrakisphosphate at the inositol 1,4,5-trisphosphate receptor

All 9 racemic regioisomers (15 enantiomerically) of myo-inositol tetrakisphosphates (IP4s): DL-Ins(1,2,4,5)P4 [A], DL-Ins(1,2,4,6)P4 [B], Ins(1,2,3,5)P4 [C], Ins(1,3,4,6)P4 [D], Ins(2,4,5,6)P4 [E], DL-Ins(1,3,4,5)P4 [F], DL-Ins(1,2,5,6)P4 [G], DL-Ins(1,2,3,4)P4 [H] and DL-Ins(1,4,5,6)P4 [I] [Chung S-K., Chang Y-T. Synthesis of all possible regioisomers of myo-inositol tetrakisphosphate. J Chem Soc Chem Commun 1995; 11-13] were investigated for their ability to bind to the D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] receptor in bovine adrenal cortical membranes, and for their ability to mobilize 45Ca2+ from Ins(1,4,5)P3-sensitive Ca2+ stores in permeabilized Chinese hamster ovary (CHO) cells. DL-Ins(1,2,4,5)P4 (Ki = 11 nM) bound to Ins(1,4,5)P3 receptors with an affinity only 2-fold lower than Ins(1,4,5)P3 (Ki = 6 nM). Ins(1,2,3,5)P4, Ins(1,3,4,6)P4, Ins(2,4,5,6)P4, DL-Ins(1,3,4,5)P4, DL-Ins(1,2,3,4)P4 and DL-Ins(1,4,5,6)P4 bound with affinities of between 0.4-0.7 microM. DL-Ins(1,2,4,6)P4 and DL-Ins(1,2,5,6)P4 bound to the Ins(1,4,5)P3 receptor with low affinity (approximately 2-3 microM). All but one of the IP4s mediated release of 45Ca2+ from stores of permeabilized CHO cells with a similar rank order of potency as that for Ins(1,4,5)P3 receptor binding, being between 16-fold and 50-fold less potent at releasing 45Ca2+ compared with their apparent binding affinities to the Ins(1,4,5)P3 receptor. The notable exception was Ins(1,2,3,5)P4, which showed an approximately 200-fold lower potency compared with its affinity for the Ins(1,4,5)P3 receptor. Ins(1,2,3,5)P4 may be a useful lead compound for the rational design of novel synthetic Ins(1,4,5)P3 analogues possessing structure-activity profiles with relatively high binding affinity, but low intrinsic efficacy, and hence partial agonists and antagonists at the Ins(1,4,5)P3 receptor.

D-myo-inositol 1,4,5-trisphosphate analogues as useful tools in biochemical studies of intracellular calcium mobilization

Two types of structural variants of D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] were prepared by a chemoenzymatic route. These 6-O-substituted analogues retained the biological activity of Ins(1,4,5)P3, and were able to elicit Ca2+ release from porcine brain microsomes. Moreover, these derivatives allowed the preparation of Ins(1,4,5)P3-based immunogens and affinity matrix which were successfully applied to the preparation and purification of antibodies against Ins(1,4,5)P3. These antibodies displayed discriminative affinity towards Ins(1,4,5)P3, and provide a useful tool to study intracellular Ca2+ mobilization.

Myo-inositol 1,3,4,5-tetrakisphosphate can independently mobilise intracellular calcium, via the inositol 1,4,5-trisphosphate receptor: studies with myo-inositol 1,4,5-trisphosphate-3-phosphorothioate and myo-inositol hexakisphosphate

Myo-inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] acts as a full agonist for Ca2+ release in saponin-permeabilised SH-SY5Y neuroblastoma cells. Studies were conducted in the presence of myo-inositol hexakisphosphate (InsP6, 10 microM), to inhibit the Ins(1,3,4,5)P(4)-3-phosphatase catalysed back conversion of Ins(1,3,4,5)P4 to Ins(1,4,5)P3. HPLC analysis confirmed that Ins(1,3,4,5)P4 releases the entire content of Ins(1,4,5)P3-sensitive intracellular Ca2+ stores, independent of 3-phosphatase activity. Further we utilised racemic myo-inositol 1,4,5-trisphosphate-3-phosphorothioate [DL-Ins(1,3,4,5)P(4)-3S], a novel intrinsically Ins(1,3,4,5)P(4)-3-phosphatase resistant Ins(1,3,4,5)P4 analogue. DL-Ins(1,3,4,5)P(4)-3S specifically displaced [3H]Ins(1,4,5)P3 from bovine adrenal cortex Ins(1,4,5)P3 binding sites (IC50 = 889 nM, compared to Ins(1,4,5)P3, IC50 = 4.4 nM and Ins(1,3,4,5)P4, IC50 = 152 nM). DL-Ins(1,3,4,5)P(4)-3S was a full agonist for Ca2+ release (EC50 = 4.7 microM), being 90- and 2-fold less potent than Ins(1,4,5)P3 and Ins(1,3,4,5)P4 (with InsP6), respectively. DL-Ins(1,3,4,5)P(4)-3S will be an important tool for identification of potentially exclusive Ins(1,3,4,5)P4 second messenger functions, since its resistance to 3-phosphatase action precludes the inconvenient artefact of steady state Ins(1,4,5)P3 generation.