Thymidine 3 ,5 -cyclic phosphate, hydrolysis

Since it is well established that the P-chiral phosphorothio-ates serve as effective probes in mechanistic studies for the phos-phoryl group transfer enzymes /16/, we turned our attention to the application of diastereomeric 8 (B=Thy, Ar=pN02C6Hi -,/17f) to elucidate the mode of action of spleen phosphodiesterase (SPDE, EC 3.1.1. 18). This enzyme splits the phosphodiester bonds to yield nucleoside 3 -phosphates. In the case of it was expected that its SPDE-catalyzed hydrolysis in 180 H 2O medium leads to P-chiral thymidine 3 - 180 phosphorothioate. On the contrary to our expectation the main product of this reaction was thymidine cyclic 3 ,5 - Rp phosphorothioate (10) /6/. By treatment of 8 under the same conditions, but in the absence of the enzyme, no trace of J 0 was detected. ... 

A detailed investigation has been reported into the cleavage of 3 - 5 -uridyluridine to form the 2, 3 -cyclic phosphate, and its isomerization to 2 5 -uridyluridine. The hydrolysis of uridine 2 -, 3 - and 5 -phosphoromonothio-ates under acidic and neutral conditions has been investigated in mild acid only hydrolysis to uridine occurs, whilst at low pH desulfurization occurs in the cases of the 2 - and 3 -thioates. The same workers have also studied the kinetics of hydrolysis and desulfurization of the diastereomeric monothio-analogues of uridine 2, 3 -cyclic phosphate under neutral or acidic conditions desulfurization competes with phosphoester hydrolysis. The hydrolysis of the 2 -thionucleoside 3 -phosphate 267 (X=SH) has been studied the predominant reaction pathway at pH 13 is the formation of the 5-phosphate whilst at pH 7-10 mostly the 2, 3 -cyclic monothiophosphate was produced. The 2 -fluorocompound 267 (X=F), which has a C-3 -endo- conformation, underwent hydrolysis ten times faster than did the deoxycompound 267 PC=H). The kinetics of hydrolysis of thymidine 5 -boranomonophosphate (269) have been studied by NMR. It was found that 269 hydrolyses slowly to thymidine and [03P-BH3 ], with the latter hydrolysing even more slowly to phosphonate and boric acid. ... 

In connection with mechanisms for the alkaline hydrolysis of DNA, the kinetics of hydrolysis of thymidine 3 -phosphodiesters with alcohols such as 2,2,2-trichloroethanol, and also of thymidinyl-(3 -5 )-thymidine, have been studied. With the trifluoroethyl phosphate, the 3, 5 -cyclic phosphate is an intermediate in alkaline hydrolysis, but this was not the case with the dinucleotide. Studies using density functional theory calculations were also reported. ... 

The thymidine oxyphosphorane 135 has been prepared by ester exchange, and underwent hydrolysis to give primarily the 5 -dialkyl phosphate. The cyclic analogue 136 of UMP has been synthesized for incorporation into antisense sequences to impart nuclease resistance. Its conformation was found to be similar to that of a nucleotide unit in A-type DNA duplexes. ... 

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