A versatile intermediate, d-4,5-bis(dibenzyl phosphoryl) -myo-inositol derivative for synthesis of inositol phosphates. Synthesis of 1,2-cyclic-4,5-,1,4,5-, and 2,4,5-trisphosphate

Synthesis of D- and L-myo-inositol 2,4,5-trisphosphate and trisphosphorothioate: structural analogues of D-myo-inositol 1,4,5-trisphosphate

The preparation of D- and L-myo-inositol 2,4,5-trisphosphate is described, together with the phosphorothioate counterparts. The known chiral diols D- and L-1,4-di-O-benzyl-5,6-bis-O-p-methoxybenzyl-myo-inositol were regioselectively protected at the 3-position using a benzyl group via a 2,3-O-stannylene acetal. Removal of the p-methoxybenzyl groups of each enantiomer gave D- and L-1,3,6-tri-O-benzyl-myo-inositol. Phosphitylation with bis(benzyloxy)diisoproplyaminophosphine and 1H-tetrazole gave the trisphosphite intermediate for each enantiomer. Oxidation with 3-chloroperoxybenzoic acid gave the fully protected D- and L-myo-inositol 2,4,5-trisphosphates. Sulphoxidation of the D- and L-2,4,5-trisphosphite intermediates gave the fully protected D- and L-myo-inositol 2,4,5-trisphosphorothioate compounds. The fully protected trisphosphates were deblocked using hydrogenolysis and the phosphorothioates were deprotected using sodium in liquid ammonia. The individual compounds were then purified using ion exchange chromatography to afford pure D- and L-myo-inositol 2,4,5-trisphosphates together with the corresponding phosphorothioates.

Studies on Steric and Electronic Control of 2'-3' Phosphoryl Migration in 2'-Phosphorylated Uridine Derivatives and Its Application to the Synthesis of 2'-Phosphorylated Oligouridylates

For the synthesis of 2'-phosphorylated oligouridylates by use of new phosphoramidite building units, several masked phosphoryl groups have been examined as 2'-phosphate precursors, which should not be migrated to the 3' position when the 3' hydroxy protecting group must be removed to introduce a phosphoramidite residue into the 3'-position. As a consequence, bis(2-cyano-1,1-dimethylethoxy)thiophosphoryl (BCMETP) was found to be the most suitable 2'-phosphate precursor. This thiophosphoryl group could be introduced into the 2'-hydroxyl of 3',5'-silylated uridine derivative 7 by phosphitylation with bis(2-cyano-1,1-dimethylethoxy)(diethylamino)phosphine followed by sulfurization. Treatment of the 2'-thiophosphorylated product 15 with (HF)(x)().Py in THF gave exclusively the 3',5'-unprotected uridine derivative 16a. Compound 16a was converted to the phosphoramidite unit 22 via a two-step reaction. This building block was used for the solution phase synthesis of U(2'-p)pU (29) and U(2'-ps)pU (30). Both the 2-cyano-1,1-dimethylethyl and 2-cyanoethyl groups were effectively removed from the fully protected derivative 25 by treatment with DBU in the presence of N,O-bis(trimethylsilyl)acetamide (BSA). The resulting 2'-thiophosphoryl group was successfully converted to a phosphoryl group by iodine treatment to give U(2'-p)pU (29). U(2'-ps)pU (30) was also synthesized by a modified procedure without the iodine treatment. Reaction of 29 with a new biotinylating reagent in aqueous solution in the presence of MgCl(2) gave a biotin-labeled product 35 having a pyrophosphate bridge at the 2' position. Reaction of 30 with monobromobimane gave the 2'-S-alkylated product 33 in aqueous solution. Application of the phosphoramidite unit 22 to the solid phase synthesis using aminopropyl CPG gel gave successfully [U(2'-p)p](n)()U (n = 1, 3, 5). It was found that stability of the succinate linker between the CPG and oligouridylates was unaffected by the treatment with DBU when BSA was present. Several enzymatic properties of the synthetic 2'-phosphorylated and 2'-thiophosphorylated oligouridylates are also described.

Synthesis and biological properties of 2-substituted myo-inositol 1,4,5-trisphosphate analogues directed toward affinity chromatography and photoaffinity labeling

A series of myo-inositol 1,4,5-trisphosphate analogues with the 2-acyl substituents p-aminobenzoyl (7), p-azidobenzoyl (8), 4-(5-[2-(benzamido)ethyl]-2-hydroxyphenylazo)benzoyl (9), and cis,trans-4-aminocyclohexylcarbonyl (10) were synthesised and examined for their effects on the 5-phosphatase, the 3-kinase, the tritiated trisphosphate-binding activity, and the Ca(2+)-releasing activity. Each analogue inhibited the hydrolysis of D-[5-32P]Ins(1,4,5)P3 and the phosphorylation of D-[3H]Ins(1,4,5)P3, catalysed by erythrocyte ghosts and brain cytosol, respectively. The analogues acted as full agonists in releasing Ca2+ from permeabilised cells and also inhibited the binding of D-[3H]Ins(1,4,5)P3 to cerebellum microsomes. The analogues 7 and 10 were utilised for immobilisation of the trisphosphate on Sepharose and the subsequent affinity chromatography effected purification of the above proteins. A photoaffinity probe, the appendage of which acted as the photoaffinity probe as well as a non-radioactive molecular marker, was also derived from the analogue 7.

Preparation and application of an affinity matrix for phosphatidylinositol-specific phospholipase C

A non-hydrolyzable phosphonate analogue of phosphatidyl inositol, racemic myo-inosityl-(1)-5-oxa-16-trifluoroacetamidohexadecyl phosphonate, was synthesized. This phosphonate inhibited the activity of phosphatidyl inositol-specific phospholipase C (PI-PLC) from Bacillus cereus with an IC50 of approximately 10 mM. Removal of the trifluoroacetyl blocking group followed by covalent binding of the phosphonate to cyanogen bromide activated Sepharose 4B via the amino group produced an affinity matrix specific for the PI-PLC from B. cereus. This affinity matrix was used to purify the phospholipase C from a complex mixture of proteins in a single step. Competition experiments with myo-inositol in the elution medium indicated that specific binding of the enzyme to the matrix most likely involves the enzyme active site. The inositol phosphonate derivatized matrix was stable over several months in neutral and alkaline media and was used repeatedly without loss of binding capacity. These results show that affinity matrices employing myo-inositol phosphonate ligands are useful for isolation and binding studies of PI-PLC and possibly of other enzymes interacting with phosphoinositides or myo-inositol phosphate derivatives.

Phosphatidylinositol-specific phospholipase C from Bacillus cereus combines intrinsic phosphotransferase and cyclic phosphodiesterase activities: a 31P NMR study

The inositol phosphate products formed during the cleavage of phosphatidylinositol by phosphatidylinositol-specific phospholipase C from Bacillus cereus were analyzed by 31P NMR. 31P NMR spectroscopy can distinguish between the inositol phosphate species and phosphatidylinositol. Chemical shift values (with reference to phosphoric acid) observed are 0.41, 3.62, 4.45, and 16.30 ppm for phosphatidylinositol, myo-inositol 1-monophosphate, myo-inositol 2-monophosphate, and myo-inositol 1,2-cyclic monophosphate, respectively. It is shown that under a variety of experimental conditions this phospholipase C cleaves phosphatidylinositol via an intramolecular phosphotransfer reaction producing diacylglycerol and D-myo-inositol 1,2-cyclic monophosphate. We also report the new and unexpected observation that the phosphatidylinositol-specific phospholipase C from B. cereus is able to hydrolyze the inositol cyclic phosphate to form D-myo-inositol 1-monophosphate. The enzyme, therefore, possesses phosphotransferase and cyclic phosphodiesterase activities. The second reaction requires thousandfold higher enzyme concentrations to be observed by 31P NMR. This reaction was shown to be regiospecific in that only the 1-phosphate was produced and stereospecific in that only D-myo-inositol 1,2-cyclic monophosphate was hydrolyzed. Inhibition with a monoclonal antibody specific for the B. cereus phospholipase C showed that the cyclic phosphodiesterase activity is intrinsic to the bacterial enzyme. We propose a two-step mechanism for the phosphatidyl-inositol-specific phospholipase C from B. cereus involving sequential phosphotransferase and cyclic phosphodiesterase activities. This mechanism bears a resemblance to the well-known two-step mechanism of pancreatic ribonuclease, RNase A.

Phospholipids chiral at phosphorus. Stereochemical mechanism of reactions catalyzed by phosphatidylinositide-specific phospholipase C from Bacillus cereus and guinea pig uterus

(Rp)- and (Sp)-1,2-dipalmitoyl-sn-glycero-3-thiophosphoinositol (DPPsI) were synthesized as a mixture and their configurations assigned on the basis of the stereospecific hydrolysis catalyzed by phospholipase A2 (PLA2) from bee venom. PLA2 is known to be stereospecific to the Rp isomer of 1,2-dipalmitoyl-sn-glycero-3-thiophosphocholine (DPPsC) and 1,2-dipalmitoyl-sn-glycero-3-thiophosphoethanolamine (DPPsE). Since the configurations of (Rp)- and (Sp)-DPPsI correspond to those of (Sp)- and (Rp)-DPPsC, respectively, due to a change in priority, the isomer specifically hydrolyzed by PLA2 was assigned to (Sp)-DPPsI. The DPPsI analogues were then used to probe the mechanism and to elucidate the steric course of the reaction catalyzed by phosphatidylinositide-specific phospholipase C (PI-PLC) from Bacillus cereus and for both isozyme I and isozyme II of PI-PLC from guinea pig uterus. It was found that the Rp isomer of DPPsI is the preferred substrate for all three PI-PLCs. Thus PI-PLC shows the same stereospecificity as phosphatidylcholine-specific PLC (PC-PLC), which prefers the Sp isomer of DPPsC. The ratio of the two products inositol 1,2-cyclic phosphorothioate (cIPs) and inositol phosphorothioate (IPs) was not significantly perturbed by the use of phosphorothioate analogue for all three PI-PLCs, which implies that IPs is not produced by enzyme-mediated ring opening of cIPs and supports a parallel pathway for the formation of both products. In order to elucidate the steric course of the cyclization reaction, exo and endo isomers of cIPs were synthesized and their absolute configurations at phosphorus were determined by nuclear magnetic resonance and other techniques. It was found that exo-cIPs is the product produced by all three PI-PLCs. Thus the steric course of the conversion DPPsI to cIPs catalyzed by all three PI-PLCs was inversion of configuration at phosphorus. These results taken together suggest that the reaction catalyzed by PI-PLC most likely proceeds via direct attack by the 2-OH group to generate the cyclic product, and parallelly by water to generate the noncyclic inositol phosphates, without involving a covalent enzyme-phosphoinositol intermediate.