Nucleosides phosphoramidites

The hydroxy groups of the pyrimido[l,6-c][l,3]oxazine 316 (R1 = R2 = H) were mono-tritylated with 4,4 -(MeO)2-trityl chloride in pyridine/NEt3. The mixture of the two products 316 (R1 =4,4 -(MeO)2-trityl R2 = H) and 316 (R1 = H R2 = 4,4 -(MeO)2-trityl) was coupled with nucleoside phosphoramidites, oxidized to protected dinucleosides and the isomers were separated <1999NN2031>. 

Acid salts of imidazole- and benzimidazole-related compounds have been evaluated as alternative promoters to the various activators developed for the condensation of a nucleoside phosphoramidite and a nucleoside. The acid/azole complexes were developed to circumvent some of the disadvantages most commonly encountered in both solution- and solid-phases. Azolium promoters were shown to achieve high yielding coupling reactions even with nucleosides of low reactivity. Hayakawa has also reviewed and broadened the recent phosphoramidite methodologies by describing the versatility of allyl and allyloxycar-... 

Another type of convertible nucleoside phosphoramidite, a derivative of (5 S)-5 -C-(5-bromo-2-penten-l-yl)-2 -deoxyribosylfuranosyl thymidine (49), has been reported. The synthesis of this phosphoramidite was stereoselective and involved a Sakurai reaction between 5 -C-thymidine aldehyde and allyltrimethylsilane. Seela has reported the synthesis of the ribosyl-phosphoramidite derivatives of 7-bromo- and 7-iodo-8-aza-7-deazapurine-2,6-diamine (50a,b) from advanced synthetic precursors and of the bromo- and iodo-derivatives at the 5-position of uracyl phosphoramidite (51a,b). He further described the effect on base-pair stability due to their incorporation into oligonucleotide duplexes. ... 

Tor has reported a versatile method for the site-specific incorporation of polypyridine Ru and Os complexes into DNA oligonucleotides using solid-phase phosphoramidite chemistry. Nucleoside phosphoramidites containing a [(bpy)2M(3-ethynyl-l,10-phenanthroline)] " metal center covalently attached to... 

Monaharan has developed a versatile synthetic route for the synthesis of 2 -0-[(N, iV-dimethylamino)-oxyethyl] modified purine and pyrimidine nucleoside phosphoramidites (63a-d) to be used as antisense oligonucleotide building blocks. In the syntheses of the purine-based analogues, the (iV, N-dimethylamino)-oxyethyl group was introduced via a 2 -allyloxy nucleoside intermediate, while the pyrimidine-based nucleosides were obtained from the TBDMS-protected 2,2 -anhydro-5-methyluridine via ring opening reaction in the presence of borane and ethylene glycol. The aminoxy derivatives were... 

A selective method which involves the selective pivaloyloxymethyl protection of the N1 of pseudouridine followed by methylation at N3 was developed to prepare the 5-benzhydryloxybis(trimethylsilyloxy)silyl, bis(2-acetoxy-ethoxy)me-thyl- protected phosphoramidite derivative (139) of the nucleoside 3-methylpseu-douridine. The methylated pseudouridine phosphoramidite was successfully used in oligonucleotide synthesis for the NMR study of helix 69 of E. coli 23S rRNA. 2-Thiouridines incorporating 2 -modified nucleoside phosphoramidites... 

A series of chloro-, fluoro- and nitro-protected nucleoside phosphoramidite derivatives of quinazoline-2,4-dione (201) has been prepared and their ability to form DNA triplexes has been assessed. 

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