Cyclic phosphate diester

Phenoxide ion is released relatively rapidly from tetrahydrofuran-a r-2,3-diol phenyl phosphate [15] at 50° (Usher et al., 1970 Oakenfull et al., 1967). A cyclic phosphate diester intermediate is formed with pronounced general species catalysis. The pH-rate... 

Cyclic phosphate diesters can be hydrolyzed selectively with RNases and phosphodiesterases to give the corresponding phosphate monoesters (Table 13-10, entries 1 and 2). 

Table 4 Rates for hydrolysis of cyclic phosphate diesters and triesters relative to acyclic diesters and triesters.

Several structures of PDEs complexed to various ligands are available and have been reviewed (24). The structure of 5 -AMP bound to PDE4D2 (25) (Fig. 17.7) reveals direct coordination of the phosphate to two divalent metal ions as well as His-160, Asp-201, and Asp-318. This enzyme product complex is suggestive of a potential catalytic mechanism in which the cyclic phosphate diester undergoes nucleophilic attack from a metal-bound hydroxide ion (Fig. 17.8), which then displaces the 3 -hydroxyl leaving group. According to this mechanism, His-160 is ... 

RNA is easily hydrolyzed in both acid and alkaline solutions. The reaction products from alkaline hydrolysis have been shown to be mixtures of 2 and 3 nucleotides. The reaction mechanism by which these are formed involves the splitting of the phosphate bond with the primary alcohol (C-5 ) and the simultaneous formation of a 2 bond. This produces a cyclic phosphate diester (II). 

The resulting cyclic phosphate diester is hydrolyzed readily in acid or alkali to the phosphate monoester. 

Several alternative procedures have been developed for chemical synthesis of 41. Acetals of the dimer of 47 can be phosphoryated using phosphoroxy chloride [184] or diphenyl chlorophosphate [185], or by phosphitylation then oxidation [186]. After phosphate deprotection, free 41 is obtained, by acid hydrolysis, in overall yields of up to 60%. New procedures have recently been developed by controlled successive substitutions of dibromoacetone [187, 188] or by controlled hydrolysis of a cyclic phosphate diester of 47 [189]. 

An estimate of the rate enhancement associated with the intramolecular phosphorylation can be made by using isopropyl p-nitrophenyl methyl-phosphonate as a model for the covalent intermediate formed in the initial step of the reaction of cycloheptaamylose with bis (p-nitrophenyl) me thy 1-phosphonate. The first-order rate constant for the alkaline hydrolysis of isopropyl p-nitrophenyl methylphosphonate at pH 9.86 can be obtained from the data of van Hooidonk and Groos (1970) kun = 1.4 X 10-5 sec-1. This value may be compared with the maximal rate constant for the reaction of cycloheptaamylose with bis(p-nitrophenyl) methylphosphonate— k2 = 1.59 X 10-1 sec-1 at pH 9.86—which must be a minimal value for the rate of the intramolecular phosphorylation. This comparison implies a kinetic acceleration of at least 104 which is similar to rate enhancements associated with the formation of cyclic phosphates from nucleoside phosphate diesters. 

The most convincing evidence in favor of a uniform 3,5-diester linkage between nucleotides has been obtained by the action of various enzymes on synthetic diesters of known constitution.218 217 Ribonuclease and spleen extracts were found to act only on nucleoside 3-(benzyl hydrogen phosphates), but not on other isomers, to give nucleoside cyclic phosphates which are broken down further to give nucleoside 3-phosphates. It is concluded, by analogy, that polynucleotides, which are substrates for these enzymes, also possess ester groupings at the 3-positions, rather than at the... 

A novel synthesis of D-glucose 6-phosphate (in 55% yield) has been reported it involves alcoholysis of the cyclic phosphate of catechol with 1,2-O-isopropylidene-a-D-glucofuranose, followed by acid hydrolysis of the so-formed phosphoric diester.192 The reagent... 

Fig. 9.10. Partial metabolic scheme of tris(2-methylphenyl) phosphate (9.44) showing hydrolysis to the diester 9.45, the monoester, and phosphate. Also shown is a reaction of oxidation to the hydroxymethyl analogue 9.46, followed by cyclization to the toxic cyclic phosphate 9.47...

Perhaps the most important signaling molecule in human biochemistry is the phosphate diester cyclic adenosine monophosphate, commonly known as cAMP. cAMP is part of many signahng pathways, a sequence of steps in which some physiological signal—say the arrival of a hormone molecule at a cell surface— is translated into a physiological outcome. Here is its stracture ... 

Phosphate diesters resist acid hydrolysis, and they are only inefficiently hydrolyzed in alkaline solutions. The exception is any five-membered ring containing a phos-phodiester, such as that formed upon alkaline treatment of RNA. Such five-membered cyclic phosphodiesters are rapidly hydrolyzed in alkaline solutions. 

These were differently affected by different procedures. For example, when the enzyme was activated at 55°, the increment in ki was slight, but k2 increased 3.5-fold. Similarly, in the presence of EDTA, fc, and k2 values decreased independently, suggesting that the sites for both activities were different. Center and Behai (5) found that with the P. mirabilis enzyme, cyclic 2, 3 -UMP competitively inhibited the hydrolysis of bis(p-nitrophenyl) phosphate. The Ki was 40 pAf very close to the Km for the cyclic nucleotide (Km, 75 yM) which indicated that the two compounds could serve as alternate substrates being hydrolyzed at the same active site. In contrast, 3 -AMP was a mixed inhibitor of cyclic 2, 3 -UMP and bis(p-nitrophenyl) phosphate hydrolysis. Adenosine was a mixed inhibitor of bis(p-nitrophenyl) phosphate hydrolysis but a competitive inhibitor of 3 -AMP hydrolysis. From such kinetic studies Center and Behai (5) suggested that two separate and adjacent sites A and B are involved in the hydrolysis of the diester and phos-phomonoester substrates. Site A serves as a binding site for hydrolysis of ribonucleoside 2, 3 -cyclic phosphates and together with site B catalyzes the hydrolysis of the diester bond. During this reaction 3 -... 

A portion of an RNA chain, indicating points of cleavage by pancreatic ribonuclease. Pyr refers to a pyrimidine Base can be either a purine or a pyrimidine. The 2, 3, and 5 carbon atoms are labeled. The enzymatic reaction proceeds in two steps, with a cyclic 2, 3 -phosphate diester as an intermediate. 

Silicon containing analogues of nucleoside cyclic phosphates are also readily prepared by reaction of the nucleoside with di-/-butylsilicon diesters (Equation (6)) <90CL97>. 

Configurational assignment to cyclic [l80]phosphodiesters is made by alkylating the phosphate group to a mixture of axially and equatorially alkylated phosphate diesters. The triesters in Equation 9 exemplify the nature of the product mixture ... 

In the case of phosphates, the triesters are most susceptible to nucleophilic attack and hence the base-catalyzed reaction generally predominates in the pH-rate profile of these esters. Phosphate diesters, with the exception of small ring cyclic ones, are relatively unreactive in neutral... 

Under acidic conditions, the hydrolysis of phosphodiesters takes place via the neutral species, and a pentacoordinate intermediate is formed. The phosphoryl cleavage and migration reactions of dinucleotide-3 -phosphate diesters and related compounds have been examined by several groups, most recently by Lonnberg and co-workers.56,57 Under acidic conditions, alkylphosphate migration (to form a 21-phosphate diester) and cyclization (to the cyclic 21,3 phosphate) (Fig. 11) proceed at... 

The kinetic stability of monoesters and diesters is due largely to their negative charge when ionized, which repels nucleophiles. Thus, it is not surprising that as neutral compounds, triesters are the most reactive of the three classes of phosphate esters. A significant portion of the mechanistic studies on triesters have been carried out using six-membered ring cyclic triesters (Fig. 12).46 Such esters react at comparable rates to their acyclic counterparts, in contrast to five-membered cyclic phosphate esters, which react at much faster rates. 

Ribonucleoside 2 3 -cyclic phosphate are far more liable toward alkali and acid than are the noncyclic phospho-diesters. Hydrolysis of ribonucleoside 2 3 -cyclic phosphate produces a mixture of 2 - and 3 -phos-phates in approximately equal amoimts. Acid- and alkali-catalyzed alcoholysis of these cyclic phosphates also produces a mixture of the 2 -and 3 -alkyl phosphates, - - and the reactions are apparently reversible. " This behavior is a rather general characteristic of five-mem-bered, cyclic phosphates. [[Six-membered, cyclic phosphates, namely (25), (28), and (28a), are relatively more stable. Phosphodiesterases have been employed for the convenient preparation of specific nucleoside 2 - or 3 -phosphates by selective cleavage of a particular 0-P linkage in nucleoside 2 3 -cyclic phosphates. ... 

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