Nucleoside phosphorothioates synthesis

Detailed studies on the stereocontrolled synthesis of oligo(nucleoside phosphorothioate by the oxathiaphospholane approach were performed with monomers 15 [20].The optimization ofthe coupling step was performed [20,23] involving the amount of the monomer (20 mg for 1 pmol synthesis), the concentration of DBU (1 mol/1) and the coupling time (450 s). To complete the pro-... 

Kraszewski et al. [208] have developed a new, efficient method for the synthesis of phosphorothioate diester, based on the H-phosphonate chemistry. The reaction of aryl nucleoside H-phosphonate with elemental sulfur furnished the corresponding aryl nucleoside phosphorothioate. The synthesis of phosphorothioates can be carried out as a four-components-one-pot reaction, by allowing nucleoside H-phosphonate to react with phenols in the presence of diphenyl phosphorochloridate to furnish aryl nucleoside H-phosphonates, which react with elemental sulfur. 

As regards the modification of intemucleosidic links, bis(deoxynucleosidyl)-trimethylsilyl phosphites 190 can be converted to phosphorofluoridates 191 by the use of S02C1F,230 and dibenzoyltetrasulfide has been advocated as a rapid sulfur transfer agent in the synthesis of nucleoside phosphorothioates, being used to prepare a phosphorothioate after each cycle of a phosphoramidite synthesis.231 Oxidation of intemucleosidic H-phosphonothioates (2 -deoxy series) with iodine in aqueous acetonitrile in the presence of trimethylamine gives... 

These otherwise promising results have been overwhelmed by a new strategy recently developed for the synthesis of oligo(nucleoside phosphorothioate)s (33). It has been proven that reaction of 5 -0-... 

Fig. 4 Synthesis of individual homochiral oligo(nucleoside phosphorothioates). 1 = DBU/acetonitrile ii = Ac20/2,6-lutidine, yV-methyl imidazole Hi=dichloroacetic acid/methylene chloride iv = 25% ammonium hydroxide.

Stereocontrolled Synthesis of Oligo(Nucleoside Phosphorothioates) (OligoS)... 

Stec, W. J. Wilk, A. Stereocontrolled Synthesis of 01igo(nucleoside phosphorothioate)s. Angew. Chem. Int. Ed. Engl. 1994, 33, 709-722... 

Nucleoside 5 -phosphorothioates have also been employed as activated nucleotide derivatives for synthesis of pyrophosphates.321 The interaction of tributylammonium 2, 3 -di-0-benzoyluridine 5 -phosphorothioate (73) with silver a-D-glucopyranosyl and a-D-galac-topyranosyl phosphates in pyridine solution, with subsequent de-benzoylation, gave the corresponding glycosyl esters in 60-70% yield. This procedure can probably be classified as a variant of the mixed-anhydride method, the driving force of the reaction being the formation of insoluble silver sulfide. 

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

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... 

Phosphorothioate and boranophosphate linkages introduced into DNA or RNA using nucleoside 5 -[a-thio]triphosphates and nucleoside 5 -[a-borano]tri-phosphates are more resistant to exo- and endonucleases than normal 3, 5 phosphodiester linkages. Combination of the two modifications yielded a novel non-bridging-disubstituted chiral a-triphosphate nucleoside, namely the thymidine 5 -[a-P-borano, a-P-thio] triphosphate (119). The synthesis was the modification of a procedure developed for the synthesis of nucleoside triphosphates and previously reported by the group. 

The early attempts to use relatively easily available diastereomerically pure nucleoside 3 -0-(2-cyanoethyl-AT,AT-diisopropylphosphoramidite) monomers for the stereospecific synthesis of PS-Oligos failed because of inevitable racemiza-tion of Pm intermediate caused by an excess of lff-tetrazole necessary for efficient elongation of oligonucleotide chain [13]. An idea to use for that purpose appropriately protected nucleosides functionalized at 3 -0 position with 2-thio-1,3,2-oxathiaphospholane moiety arose from the studies on the reactions of di-substituted phosphorothioates with oxiranes [14,15], and in particular from the observation that PS-PO exchange in 0,0-diphenyl phosphorothioate (8) upon treatment with ethylene oxide in methanol solution resulted in formation of... 

Monomers [180]-15a-d were successfully used for the synthesis of several stereodefined oligo(nucleoside [180]phosphorothioate)s. Their stereochemistry and isotopic enrichment were confirmed by a combined enzymatic-mass spectrometry method employing snake venom phosphodiesterase or calf spleen nuclease, and MALDI TOF mass spectrometry. 

The 2-oxo analogues of dithiaphospholanes 81, namely appropriately protected nucleoside 5 -0- (83a) or 3 -0-(2-oxo-l,3,2-dithiaphospholanes) (83b) have also been used as P-prochiral substrates for the potentially asymmetric synthesis of dinucleotides with P-chiral phosphorothioate internucleotide linkage (85, X=0) (Scheme 21, path b). For example, reaction of 5 -0-DMT-thymi-dine-3 -0-(2-oxo-l,3,2-dithiaphospholane) (83b) with NMsobutyryl-3 -0-acetyl deoxyguanosine in the presence of DBU provided corresponding dinucleoside 3, 5 -phosphorothioate of isomeric composition RP/SP=28/72 [110]. 

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