Phosphorothioate monoester

A/-[3-(2-[ F]fluoropyridin-3-yloxy)-propyl]-2-bromoacetamide (p F]FPyBrA) was recently prepared by nucleophilic / eferoaromatic radiofluorination using a three-step radiochemical pathway and obtained in 20% overall non-decay-corrected yield in less than 85 min. In this reagent, the pyridinyl moiety carries the radioactive fluorine and the 2-bromoacetamide function ensures the alkylation of phosphorothioate monoester groups at the 3 - or 5 -end of a single-stranded oligonucleotide [18],... 

The hydrolysis rates of the dianions of phosphate and phosphorothioate monoesters are substantially accelerated by the addition of polar aprotic solvents such as DMSO and MeCN because the activation barrier A becomes smaller due to a lowering of the enthalpy of activation. The enthalpy transfer of the transition states in the... 

A number of chiral [180]phosphorothioate monoesters (compound 5) have been synthesized, and these syntheses have been described in detail in several reviews (102, 103, 108). In this section only the most commonly used compounds, chiral [a-180]AMPS (28), chiral [0-18O]ADP/3S (29), and chiral [7-180] ATP7S (30) are discussed. 

Lowe, Cullis, and co-workers have described general methods for the synthesis of oxygen chiral phosphorothioate monoesters (see Figs. 3 and 4). The synthesis by Cullis is strictly analogous to the synthesis of chiral phosphate monoesters by Knowles except that (- )-ephedrine is thiophosphorylated with PSCI3... 

The mechanism of an actual hydrolysis reaction catalyzed by this prototype phosphomonoesterase has never been studied stereochemically. This apparent omission is presumably explained by the very low catalytic efficiency of the enzyme toward phosphorothioate monoesters as compared to phosphate monoesters (75) certainly, chiral [ O, 0]phosphorothioate 0-ester substrates already exist, and methodology is available for the configurational analysis of the chiral [ 0, 0, 0]thiophosphate that would be produced if the chiral substrate were hydrolyzed in H2. In fact, the low catalytic reactivity of phosphorothioate O-esters and the high reactivity of phosphorothioate S-esters has been explained by the enzyme utilizing nucleophilic catalysis (an associate mechanism) to achieve hydrolysis of the phosphate ester bond 40). 

Alkyl monoesters of thiophosphoric acid have not hitherto been readily accessible compounds owing to indifferent yields and lengthy and difficult isolation procedures. A simple preparative route involves reaction of OO-di-t-butyl hydrogen phosphorothioate with the appropriate alkyl halides followed by elimination of the t-butyl groups with dry hydrogen chloride in dichloromethane ... 

Phosphate diester Phosphorothioate diester Phosphonate monoester Phosphonamidate... 

Hydrolysis Products of Various 0- and S-Substituted Monoesters of Phosphorothioic Acid by Alkaline and Acid Phosphatases ... 

A new one-pot method has been developed by Kraszewski for the synthesis of aryl nucleoside phosphate (3a-p) and phosphorothioate (4a-p) diesters. This method, based on H-phosphonate chemistry, employed diphenyl phosphoroch-loridate and a series of phenols. Depending on the substituents present on the phenols, oxidation conditions were optimized to avoid competing hydrolysis. A versatile procedure that permits easy access to H-phosphonoselenoate monoesters (5) has been developed by Stawinski. These monoesters, obtained by selenisation of a phosphinate using triphenylphosphine selenide in combination with trimethylsilyl chloride, reacted with a suitable nucleoside in pyridine/acetonitrile in the presence of diphenyl phosphorochloridate to yield... 

Full details of the synthesis of unsymmetrical diesters of pyrophosphoric acid by the reaction of the disilver salt of a monoester of phosphorothioic acid and a phosphate monoester have been published. In view of the good yields, the mild conditions, and the absence of symmetrical pyrophosphate byproducts it appears to be superior to previous routes to the nucleotide pyrophosphate coenzymes. Further, the findings that the procedure is insensitive to... 

An additional reason for the inferior performance of the H-phosphonate method compared to the phosphoramidite lies in its mechanism, which makes the synthesis very sensitive to pre-activation of the H-phosphonate monoesters with the conventional coupling agents, which must be avoided [138], However, the main appeal of the H-phosphonate approach lies in the ease it offers for the synthesis of backbone analogues modified at the phosphorus atom phosphorothioates [139], phos-photriesters [126] and especially phosphoramidates [126, 140, 141]. Now it is rarely used for routine oligonucleotide synthesis but very often for the preparation of variously modified analogues. Further developments in the H-phosphonate method have been made in the last decade by Polish [142] and Japanese researchers [143]. 

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). 

Nucleoside H-phosphonothioate monoesters can be converted into the corresponding diesters with an efficiency similar to that of H-phosphonate derivatives. H-Phosphonothioate diesters seem to be promising for the preparation of other phosphate analogues— phosphorothioamidates, alkyl phosphorothioates, and phosphorothioates [202],... 

Methodology. Filippov has reported a one-pot procedure to prepare phosphate, phosphorothioate and phosphorofluoridate monoesters as well as pyrophosphate monoesters of nucleosides. This versatile approach made use of di(p-methoxybenzyl)-A, A -diisopropylphosphoramidite. While little information was provided on the preparation and stability of the phosphoramidite reagent, its use in the reaction with benzoate-protected thymidine in the presence of dicyanoimidazole as an activator yielded the di(p-methoxybenzyl)phosphite of thymidine [46]. This phosphite could subsequently be oxidised (Scheme 3) to the phenylthioate ester [47a], the phosphate monoesters [47b], the phosphoramidate [47c, d], the phosphorofluoridate [47e], the nitrophenolate diester [47f] and to the fully protected dinucleotide [47g]." ... 

Catrina IE, Hengge AC. Comparisons of phosphorothioate with phosphate transfer reactions for a monoester, diester, and triester isotope effect studies. J Am Chem Soc. 2003 125 7546-7552. 

Catrina IE, Hengge AC. Comparisons of phosphorothioate and phosphate monoester transfer reactions activation parameters, solvent effects, and the effect of metal ions. JAm Chem Soc. 1999 121 2156-2163. 

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