Phosphorothioates nucleoside 3 ,5 -cyclic

Stereospecific Synthesis and Assignment of Absolute Configuration at Phosphorus in Nucleoside 3 - and 5 -0-Arylphosphorothioates and Nucleoside Cyclic 3, 5 -Phosphorothioates... 

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. 

The 2, 3 - (9,0-cyclic //-phosphonates 20a-d were formed, as ca 1 1 mixture of diastereomers (as monitored by 31P-NMR ), in the reaction of 5 -protected ribonu-cleosides 16a-d with diphenyl //-phosphonate in pyridine. Their sulfurization readily afforded the expected cyclic phosphorothioates 21a-d which upon subsequent removal of the 5 -protecting group afforded the respective nucleoside 2, 3 -0,0-cyclophosphorothioates 22a-d in excellent yields (70-90%) (Scheme 8) [23],... 

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. ... 

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]. 

Two groups have reported the synthesis of compounds of type (139) as potential models for ring-opening reactions of cyclic AMP. These studies included cases where the dioxaphosphorinane ring was both apical-equatorial and diequatorial, and conformations were studied by n.m.r.i98,i99 xhe predominant formation of 3 -monophosphates in the base-catalysed hydrolysis of nucleoside 3, 5 -cyclic phosphates has been interpreted in terms of the lone pair orientation effect, which may decrease the energy of the transition state for P-O bond-breaking.200 Conformational studies have been carried out on the diastereomers of adenosine cyclic 3 ,5 -phosphorothioate, where chair conformations predominate, and for the / p-isomer of deoxyadenosine cyclic phosphoranilidate, where a chair-twist equilibrium... 

Reaction of a nucleoside with thiophosphoryl chloride, followed by base-promoted cyclization, provides a direct synthesis of nucleoside-3, 5 -cycllc phosphorothioates (both epimers at phosphorus). 125 Treatment of cyclic AMP with dlphenylphosphoiyl chloride produces the mixed anhydride, predominantly of Rp configuration (62), due to the greater basicity of the axial oxygen in the cAMP. The anhydride reacted with dimethylamine with inversion to give the cyclic phosphoramidate.i26 Activation of cAMP with POCI3 in (MeOlaPO, followed by treatment with an amine, also gave predominantly the Sp-phosphoramidate (63),127 and in the case of a protected cAMP, oxalyl chloride activation achieved a similar result. 128 The hydrolysis of... 

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... 

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