Uridine 2 ,3 -phosphorothioate

C9HioN20tPS CsHibN+ Uridine 2, 3 -phosphorothioate, triethylam-monium salt, m.p. 204-205°C... 

Nucleoside 2, 3 -cyclic phosphorothioates are prepared by reacting the 5 -acetylnucleoside with triimidazole phosphinsulfide followed by aqueous work-up and deblocking [17]. This procedure is illustrated in Fig. 5 for the exo- and endo-isomers of 2, 3 -cyclic uridine phosphorothioate, 2, 3 -cyclic UMPS, which were first synthesized by Eckstein and associates. The two could be separated because the endo- isomer is crystalline while the other is an oil. After repeated crystallization the pure endo- isomer was obtained and its crystal structure determined, giving its absolute configuration [18]. 

C9H10N2O7PS-C9H16N+ Uridine 2, 3 -(triethylammonium phosphorothioate) URIDPS10 30 456... 

An alternative approach for the synthesis of 2, 3 -0,0-cyclic //-phosphonate 20a was based on the condensation of a mixture of uridine 3 - and 2 -//-phosphonates (23 and 24 respectively) induced by pivaloyl chloride (Scheme 9) [24], Its reaction with elemental sulfur in carbon disulfide gave 5 -0-DMT-uridine 2, 3 -cyclic phosphorothioate (21a) which after final deprotection afforded the desired 2, 3 -cyclic phosphorothioate 22a (Scheme 9). Its Sp and Rp diastereomers were separated by HPLC [24],... 

In this context, it is interesting to note that the first synthesis of 2, 3 -0,0-cyclic phosphorothioate 22a was reported by Eckstein in 1968 [25], He also isolated pure Rp diastereomer by fractional crystallization of the triethylammonium salts [26] and used it as reference to determine the absolute configurations of the other phosphorothioate analogues [27], 2, 3 -0,0-Cyclic H-phosphonate 20a was used as a key substrate for the synthesis of uridine 2, 3 -0,0-cyclic boranophosphate 27. Silylation of H-phosphate 20a gave the phosphite triester 25 (two diastereomers). Its boronation, with simultaneous removal of the trimethylsilyl group, was achieved by its reaction with borane-A.A-diisopropylethylamine complex (DIPEA-BH3). 

Stereochemical studies support in-line mechanisms for both the transesterification and hydrolysis steps of ribonuclease catalysis. For example, chiral uridine 2, 3 -cyclic phosphorothioates are hydrolyzed with inversion of configuration, with the diastereoisomer shown yielding a 2 -monophosphothioate of the R configuration at phosphorus. 

A quantum mechanical method has been used to study the TSs of the uridine phosphorylation reaction and an acid-catalysed Sn2 is the main mode of reaction. The ribonucleotide sulfur analogue 2 -deoxy-2 -thiouridine 3 -(p-nitrophenyl phosphate) (295) undergoes transphosphorylation to give 2, 3 -cychc phosphorothioate (296) followed by hydrolysis to give 2 -deoxy-2 -thiouridine 2 -phosphorothioate (297)... 

In 1970, Eckstein and co-workers reported the first stereochemical study of an enzyme-catalyzed hydrolysis of a phosphate ester, the hydrolysis of the endo isomer of uridine 2, 3 -cyclic phosphorothioate (enrfo-cyclic UMPS) (72) by ribonuclease A (RNase A) 13). The hydrolysis of RNA catalyzed either by base or by RNase A proceeds by a two-step mechanism in which the 2 -hydroxyl group of a nucleotide unit within an RNA molecule acts as a nucleophile on the 3 -phosphodiester bond to displace the 5 -hydroxyl group of the neighboring nucleoside to form a 2, 3 -cyciic phosphate intermediate. RNase A then catalyzes the hydrolysis of this cyclic phosphate, mimicked by Eckstein s endo-cyclic UMPS, to yield the ultimate 3 -mononucleotide product. 

A number of aryl 3 -uridylyl phosphorothioates have been prepared, using a new method involving the 3 -H-phosphonate as an intermediate the kinetics of base catalysis and leaving group dependence in the intramolecular alcoholysis of the phosphorothioates was studied. The 3 -phenylphosphonates of adenosine and uridine have been made and evaluated as substrates of 3 -nucleotidases. Reaction of thymidine with an oxyphosphorane was used to make thymidin-3 -yl benzoin phosphate. ... 

Diethyl pyrocarbonate has been used to convert uridine 2 - or 3 -phosphate into the 2, 3 -cyclic phosphate in high yield, and an adamantyl 2, 3 -cyclic phosphonate (421) was obtained when uridine reacted with I-adamantylphos-phonyl chloride. Phosphorylation of ribonucleosides with pyrophosphoryl chloride followed by hydrolysis in neutral solution afforded a simple synthesis of ribonucleoside 2, 3 -cyclic phosphate 5 -phosphates. Two phosphorylating agents mentioned earlier in this section can also yield 3, 5 -cyclic phosphates either by treatment of nucleoside 5 -(2-iV7V-dimethylamino-4-nitrophenyl phosphates) with acetic acid in pyridine (Scheme I4i) i, 83 qj. treatment of nucleoside 5 -(5 -methyl phosphorothioates) with iodine in pyridine. Another route to 3, 5 -cyclic phosphates involved cyclization of the nucleoside 5 -trichIoro-methylphosphonates (422) (obtained by the action of trichloromethylphosphonyl... 

Key to the solution is the isolation of two diastereoisomers of uridine 2, 3 -cyclic phosphorothioate. Both isomers were used for hydrolysis in... 

This chapter summarizes the techniques that have been developed for the syntheses and configurational analyses of phosphate mono- and diesters that are chiral only by virtue of substitution with the stable isotopes of oxygen O, 99.759% natural abundance O, 0.037% natural abundance and a nuclear spin of and K), 0.204% natural abundance. In addition, a few enzyme systems in which these techniques have been used are described. This approach, which dates back only to 1978, was not the first method to ascertain the stereochemical consequences of enzyme-catalyzed reactions at phosphorus. In 1970, Usher and Eckstein reported the seminal experiment in this field (Usher et al., 1970) the stereochemical course of the hydrolysis of the endo isomer of uridine 2, 3 -cyclic phosphorothioate catalyzed by... 

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