- Tritylation of alcohols under mild conditions without using silver salts
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Secondary alcohols were conveniently tritylated under mild conditions within a short running time with tritylium trifluoroacetate generated in situ from trityl alcohols and trifluoroacetic anhydride. No expensive silver salts were needed for the reactions. Four secondary alcohols were tritylated with both mono- and dimethoxy trityl alcohols giving good to excellent isolated yields. The reaction was also tested on four nucleoside derivatives that have primary alcohols. Satisfactory results were also obtained.
- Shahsavari, Shahien,Chen, Jinsen,Wigstrom, Travis,Gooding, James,Gauronskas, Alexander,Fang, Shiyue
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p. 3877 - 3880
(2016/08/02)
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- Ultrafast cleavage and deprotection of oligonucleotides synthesis and use of C(Ac) derivatives
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We have investigated the use of alkylamines as fast cleavage and deprotection reagents for the solid phase synthesis of oligonucleotides and found methylamine/ammonium hydroxide (or methylamine) as an efficient reagent. The transamination side product formed with the commonly used dC(b2) has been eliminated by the use of dC(Ac) phosphoramidite. This system has successfully been used in the synthesis of oligonucleotides and oligonucleoside phosphorothioates. DMT dC(Ac) hydrogen phosphonate and DMT ribo C(Ac)-2'-OMe phosphoramidite also have been prepared and used in the synthesis of oligonucleotides.
- Reddy,Hanna, Naeem B.,Farooqui, Firdous
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p. 1589 - 1598
(2007/10/03)
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- Differential reactivity of carbohydrate hydroxyls in glycosylations. II. The likely role of intramolecular hydrogen bonding on glycosylation reactions. Galactosylation of nucleoside 5'-hydroxyls for the syntheses of novel potential anticancer agents
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Contrary to expectations, many primary hydroxy groups are completely unreactive in glycosylation reactions, or give the desired glycosides in very low yields accompanied by products of many side reactions. Hydrogens of such primary hydroxyls are shown to be intramolecularly hydrogen bonded. Intermediates formed by nucleophilic attack by these hydroxyls on activated glycosylating agents may resist hydrogen abstraction. This resistance to proton loss is postulated to be the origin of the observed unreactivity. It is shown that successful glycosylations take place under acidic conditions under which such hydrogen bonds cease to exist. Accordingly, direct galactosylations of the normally unreactive 5'-hydroxyls of nucleosides were accomplished for the first time with a galactose trichloroacetimidate donor in chloroform under silver triflate promotion. It is noted that such galactosylated anticancer nucleosides may have improved biological specificity. Contrary to expectations, many primary hydroxy groups are completely unreactive in glycosylation reactions, or give the desired glycosides in very low yields accompanied by products of many side reactions. Hydrogens of such primary hydroxyls are shown to be intramolecularly hydrogen bonded. Intermediates formed by nucleophilic attack by these hydroxyls on activated glycosylating agents may resist hydrogen abstraction. This resistance to proton loss is postulated to be the origin of the observed unreactivity. It is shown that successful glycosylations take place under acidic conditions under which such hydrogen bonds cease to exist. Accordingly, direct galactosylations of the normally unreactive 5′-hydroxyls of nucleosides were accomplished for the first time with a galactose trichloroacetimidate donor in chloroform under silver triflate promotion. It is noted that such galactosylated anticancer nucleosides may have improved biological specificity.
- Whitfield,Douglas,Tang,Csizmadia,Pang,Moolten,Krepinsky
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p. 2225 - 2238
(2007/10/02)
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- Fast Cleavage and Deprotection of Oligonucleotides
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We have developed methylamine/ammonia as a fast cleavage and deprotection reagent which effects complete cleavage of oligonucleotides from the solid support in 5 min at room temperature and complete deprotection in 5 min at 65 deg C.The problem of transamination side products formation, faced with the commonly used dCbz (10percent side product) upon treatment with methylamine/ammonia, has been sucessfully solved by the use of dCac (0.0percent side product).DMT dCac phosphoramidite-methylamine/ammonia system furnished oligonucleotides in equal or superior quality as compared to the other systems.
- Reddy, M. P.,Hanna, N. B.,Farooqui, Firdous
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p. 4311 - 4314
(2007/10/02)
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