Phosphate monoesters Phosphates

Phosphate monoesters, phosphate diesters and phosphonates soluble or sorbed to soil particles. 

Uncatalyzed Reactions of Phosphate Monoesters. Phosphate monoesters in physiologically relevant pH ranges exist as either the monoanion or dianion. A large body of evidence indicates that uncatalyzed phosphoryl transfer reactions of both ionic forms takes place by loose transition states that are characterized by extensive bond cleavage to the leaving group and a small degree of bond formation to the nucleophile (for reviews of the evidence, see References (3,4)). Despite loose transition states, these reactions are concerted, and free metaphosphate is not formed in protic solvents (5). 

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],... 

Starch sodium phosphate monoesters [11120-02-8] are prepared by heating mixtures of 10% moisture starch and sodium monohydrogen and dihydrogen phosphates or sodium tripolyphosphate. Starch phosphate monoesters are used primarily in foods, such as pudding starches and with oH-in-water emulsions. 

Phosphoric acid diesters are prepared by treating a liquid slurry of phosphate monoester with epoxides in the presence of alkali compounds. Thus a mixture of monolauryl phosphate sodium salt and triethyl amine in water was treated with glycidol at 80°C for 8 h to give 98% lauryl(2,3-dihydroxypropyl)phosphate sodium salt [13]. 

Monoester salts of phosphoric acid derived from fatty alcohol ethylene oxide adduct or alkylphenol ethylene oxide adduct useful as surfactants are prepared by addition of R(OCH2CH2) OH, alkali fluoride and (C12P0)20 in a molar ratio of 0.9-1.5 0.05-1 1.0 at -50 to + 10°C and hydrolysis of the Cl-containing intermediates with a base. The monoester phosphates showed comparable or better washing and foaming efficiency than commercial products [12]. 

Staphylococcal nuclease (SNase) is a single-peptide chain enzyme consisting of 149 amino acid residues. It catalyzes the hydrolysis of both DNA and RNA at the 5 position of the phosphodiester bond, yielding a free 5 -hydroxyl group and a 3 -phosphate monoester... 

Gani D, Wilkie J (1997) Metal Ions in the Mechanism of Enzyme Catalysed Phosphate Monoester Hydrolyses. 89 133-176... 

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... 

Phosphorylation of cholesterol followed by the normal hydrolytic work-up gives the phosphate monoester, not the symmetrical pyrophosphate diester as previously claimed. Cholesteryl phosphorodichloridate and some related steroidal phosphorodichloridates have been prepared from the action of pyrophosphoryl chloride on the appropriate alcohol ... 

Other workers have concluded that, for the solvolysis of phosphate monoesters, the bonding between nucleophile and mecaphosphate is not far developed in the transition state and... 

The involvement of monomeric metaphosphate in the phosphoryl transfer from phosphate monoesters, and of pentaco-ordinate intermediates from phosphotriesters represent two extremes in the mechanistics of the phosphoryl transfer process. Between the extremes are the (S 2)p processes involving transition states having various bond orders, but no true... 

Access to diphosphates (pyrophosphates) and triphosphates is provided through the reaction of phosphoric mono- or diimidazolides with a monoester phosphate. 

With [32P]phosphoric diimidazolide, prepared from sulfinyldiimidazole or CDI and H332P04, the 5 -terminal monoester phosphate groups in various RNAs could be selectively phosphorylated (radioactive labeling method) 1571,1581... 

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... 

Figure 4. Possible mechanisms of phosphate monoester hydrolysis by protein phosphatase 1.

A similar reaction mechanism was proposed by Chin et al. [32] for the hydrolysis of the biological phosphate monoester adenosine monophosphate (AMP) by the complex [(trpn) Co (OH2)]2+ [trpn = tris(ami-nopropyl)amine]. Rapid cleavage is observed only in the presence of 2 equiv metal complex. It is evident from 31P NMR spectra that on coordination of 1 equiv (trpn)Co to AMP a stable four-membered chelate complex 4 is formed. The second (trpn)Co molecule may bind to another oxygen atom of the substrate (formation of 5) and provide a Co-OH nucleophile which replaces the alkoxy group. The half-life of AMP in 5 is about 1 h at pD 5 and 25 °C. 

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