Esters phosphate monoesters

Esterification. The hydroxyl groups of sugars can react with organic and inorganic acids just as other alcohols do. Both natural and synthetic carbohydrate esters are important in various apphcations (1,13). Phosphate monoesters of sugars are important in metabohc reactions. An example is the enzyme-catalyzed, reversible aldol addition between dibydroxyacetone phosphate [57-04-51 and D-ylyceraldehyde 3-phosphate [591-57-1 / to form D-fmctose 1,6-bisphosphate [488-69-7],... 

Compound (1) phosphorylates phosphate monoesters and alcohols, although with the latter a considerable excess of alcohol is necessary to obtain satisfactory yields. In the absence of mercuric ions the milder phosphorylating species (3) can be isolated which converts monoalkyl phosphates to pyrophosphate diesters in good yield but does not react appreciably with alcohols unless catalytic amounts of boron trifluoride are added. Amine salts of (3) are converted to phosphoramidates on heating. In the presence of silver ions, O-esters of thiophosphoric acid behave as phosphorylating agents and a very mild and convenient procedure suitable for preparing labile unsymmetrical pyrophosphate diesters, such as the... 

A structurally characterized example of a dinuclear zinc complex with a bridging phosphate monoester was provided by Kitajima and co-workers using the tris(pyrazolyl)borate ligand system. The P—O bond in a tris- or bis-phosphate ester is cleaved by a hydroxo zinc complex resulting in the monoester compound.443... 

Two dinuclear complexes, with five-coordinate zinc centers, derived from tris((2-pyridyl)-methyl) amine were synthesized and bridging phosphate or phosphate ester groups. The X-ray structure of the phosphate monoester complex shows a syn-anti bridging mode in contrast to alkaline phosphatase in which it is syn-syn 448 Fenton and co-workers have also studied other related dizinc species of compartmental ligands 449... 

The mechanism of phosphate ester hydrolysis by hydroxide is shown in Figure 1 for a phosphodiester substrate. A SN2 mechanism with a trigonal-bipyramidal transition state is generally accepted for the uncatalyzed cleavage of phosphodiesters and phosphotriesters by nucleophilic attack at phosphorus. In uncatalyzed phosphate monoester hydrolysis, a SN1 mechanism with formation of a (POj) intermediate competes with the SN2 mechanism. For alkyl phosphates, nucleophilic attack at the carbon atom is also relevant. In contrast, all enzymatic cleavage reactions of mono-, di-, and triesters seem to follow an SN2... 

The phosphitylation procedure (step a) proceeds in the presence of EtN(i-Pr)2 (DPEA) and the subsequent oxidation by TBHP (step b). The cyclic phosphate is deprotected stepwise (steps c and d) and serves as a model for the physiological milieu . It has been possible to deliver phosphate monoesters via steps c and d in a controllable manner from cyclic phosphotri-esters at physiological pH. 

Cellulose Sulfates and Phosphates. Conversion of cellulose to sulfate or phosphate monoesters produces soluble derivatives. These ester groups are highly hydrated, offer steric interference to molecular fit, and are ionized at all PH levels so they continually produce coulombic repulsion. 

Almost all the starches investigated contain some phosphorus.124-126 In addition to phospholipids, phosphorus is also commonly found in starch as monostarch phosphate esters.6,7 Inorganic phosphate is present in some starches.124-126 Monostarch phosphate esters and phospholipids have different effects on starch paste properties.133,135 Monostarch phosphate esters, found in potato, shoti and other starches,6,7,136-140 increase paste clarity and paste viscosity.79 Little phosphate monoester is found in cereal starch.121,124,141,142 Phospholipids, found in normal cereal starches (e.g. wheat, rice and maize) decrease paste clarity and viscosity.133 31P-nmr spectroscopy has... 

Introduction of a phosphate monoester and removal of its protecting groups was a serious impediment in a synthesis of the serine-threonine phosphatase inhibitor Calyculin A by Evans and co-workers [Scheme 7,22].38 The four phosphate protecting groups evaluated were 2-cyanoethyl and 2-(trimethylsi]y])ethyl (see below), benzyl and p-methoxybenzyl. Of these, the p-methoxybenzyl phosphate ester offered the best compromise between base stability (it survived a Wittig reaction in the presence of a metal amide base) and acid lability required for the final deprotection step in which three secondary terf-butyldimethylsiiyl... 

Protection of phosphates as 2-(trimethylsilyl)ethyl esters was first developed by the Masamune group as part of their efforts to synthesise Calyculin A with its highly hindered phosphate monoester.77 A diallyi phosphate was evaluated in a model compound, but it was rejected because of incomplete deprotection under Pd(0)-catalysis, The corresponding bis-[2-(trimethylsilyl)ethyl] ester 37 1, on the... 

Fig. 1 From left to right, the structures of a phosphate monoester, diester, and triester. Depending upon pH, monoesters may be neutral, monoanionic, or dianionic diesters may be neutral or anionic. The first pKa of an alkyl phosphomonoester, and the pKa of a dialkyl diester, is 2. The second pKa of an alkyl monoester is 6.8. Oxygen atoms bonded to ester groups (OR) are called bridging oxygen atoms the other oxygen atoms are nonbridging. Thus, a triester has one nonbridging oxygen atom, an ionized diester has two, and a fully ionized monoester has three.

Both, alkyl phosphates and alkyl ether phosphates are made by treating the fatty alcohol or alcohol ethoxylates with a phosphorylating agent, usually phosphorous pentoxide, P4OJQ. The reaction yields a mixture of monoesters and diesters of phosphoric acid, with the ratio of the two esters being determined by the ratio of the reactants and the amount of water present in the reaction mixture. The physico-chemical properties of the alkyl phosphate surfactants depend on the ratio of the esters. Phosphate surfactants are used in the metal-working industry, due to their anticorrosive properties. 

As noted previously, the stereochemical course of the hydrolysis of a phosphate monoester can be studied only if an oxygen chiral phosphorothioate ester is used a substrate so that an enantiomer of 0-labeled chiral thiophos-... 

As noted previously, studies of the mechanisms of phosphate monoester solvolysis have been extended to the mechanisms of the analogous phosphorothioate ester solvolysis because the thiometaphosphate anion is believed to be more stable than the metaphosphate anion. Thus, a general method based upon P NMR spectroscopy for the configurational analysis of chiral thiophosphate monoesters (see Fig. 10) was described recently by Cullis and co-workers (38). 

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