- Stable Benzylic (1-Ethynylcyclohexanyl)carbonates Protect Hydroxyl Moieties by the Synergistic Action of [Au]/[Ag] Catalytic System
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Chemical syntheses of oligosaccharides and glycosides call utilization of many protecting groups that can be installed or deprotected without affecting other functional groups present. Benzyl ethers are routinely used in the synthesis of glycans as they can be subjected to hydrogenolysis under neutral conditions. However, installation of benzyl ethers is often carried out under strong basic conditions using benzyl halides. Many a times, strongly basic conditions will be detrimental for some of the other sensitive functionalities (e.g., esters). Later introduced reagents such as benzyl trichloroacetimidate and BnOTf are not shelf-stable, and hence, a new method is highly desirable. Taking a cue from the [Au]/[Ag]-catalyzed glycosidations, we have identified a method that enables protection of hydroxyl groups as benzyl, p-methoxybenzyl, or naphthylenemethyl ethers using easily accessible and stable carbonate reagent. A number of saccharide-derived alcohols were subjected to the benzylation successfully using a catalytic amount of gold phosphite and silver triflate. Furthermore, the protocol is suitable for even protecting menthol, cholesterol, serine, disaccharide OH, and furanosyl-derived alcohol easily. The often-utilized olefins and benzoates, as well as benzylidene-, silyl-, Troc-, and Fmoc-protecting groups do not get affected during the newly identified protocol. Regioselective protection and one-pot installation of benzyl and p-methoxybenzyl ethers are demonstrated.
- Chakraborty, Saptashwa,Mishra, Bijoyananda,Neralkar, Mahesh,Hotha, Srinivas
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p. 6604 - 6611
(2019/06/14)
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- Some observations on the reductive ring opening of 4,6-O-benzylidene acetals of hexopyranosides with the borane trimethylamine-aluminium chloride reagent
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Reductive ring openings of 3-O-benzoyl-4,6-O-benzylidene-d-glucopyranosides with BH3·NMe3-AlCl3 are accompanied by side reactions, such as debenzoylation and reduction of the benzoate to benzyl ether. This phenomenon was r
- Daragics, Katalin,Szabó, Pál,Fügedi, Péter
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experimental part
p. 1633 - 1637
(2011/09/14)
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- METHOD FOR PREPARING HEXOSE DERIVATIVES
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A method for preparing hexose derivatives comprises the steps of providing a silylated hexose, treating the silylated hexose with a first carbonyl compound in the presence of a catalyst to form an ketalized hexose, treating the ketalized hexose with a second carbonyl compound followed by treating with a first reductant to form an etherized hexose, and converting the etherized hexose into a target hexose derivative, which can be 2-alcohol hexose, 3-alcohol hexose, 4-alcohol hexose, or a 6-alcohol hexose. In particular, the present invention can prepare the hexose derivatives with highly regioselective scheme to protect individual hydroxyls of monosaccharide units and install an orthogonal protecting group pattern in a one-pot manner
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Page/Page column 2; 4; 6-7; Sheet 6/9
(2009/05/29)
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- Targeting the delivery of glycan-based paclitaxel prodrugs to cancer cells via glucose transporters
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This report describes the synthesis of four novel paclitaxel based prodrugs with glycan conjugation (1-4). Glycans were conjugated using an ester or ether bond as the linker between 2′-paclitaxel and the 2′-glucose or glucuronic acid moiety. These prodrug
- Lin, Yih-Shyan,Tungpradit, Rudeewan,Sinchaikul, Supachok,An, Feng-Ming,Liu, Der-Zen,Phutrakul, Suree,Chen, Shui-Tein
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scheme or table
p. 7428 - 7441
(2009/12/23)
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- Tandem catalysis for a one-pot regioselective protection of carbohydrates: The example of glucose
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(Chemical Equation Presented) Fine-tuning the conditions for a tandem reaction using a single catalyst in a single reaction vessel leads to carbohydrate building blocks displaying different patterns of protecting groups (see picture). This process greatly simplifies the access to oligomers, as illustrated by the rapid assembly of a trisaccharide.
- Francais, Antoine,Urban, Dominique,Beau, Jean-Marie
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p. 8662 - 8665
(2008/09/18)
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- A convenient method for the synthesis of dialkyl ethers by alkylation of alcohols using phosphinimidates in the presence of a catalytic amount of trimethylsilyl triflate
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An alkylation reaction of alcohols with alkyl N-(methylsulfonyl) diphenylphosphinimidates proceeded smoothly in the presence of a catalytic amount of trimethylsilyl triflate (Me3SiOTf) in DME at room temperature and the corresponding ethers were afforded in good to high yields. An alkyl N-(methylsulfonyl)diphenylphosphinimidate can be prepared easily from an alkyl diphenylphosphinite and methanesulfonyl azide, and is isolated without tedious operation. Moreover, it is easy to handle and can be stored for several months at room temperature because of its air- and moisture-resistant character. Also, one-pot tertiary alkylations of alcohols by using t-alkyl diphenylphosphinites and diphenoxyphosphoryl azide proceeded efficiently in the presence of a catalytic amount of Me3SiOTf in cyclohexane/CH 2Cl2 at 0°C or -10°C, and gave the corresponding tertiary alkyl ethers in good yields. By following these methods, various ethers having alkali-sensitive functional groups can be prepared easily.
- Aoki, Hidenori,Mukaiyama, Teruaki
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p. 1255 - 1264
(2007/10/03)
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- An efficient method for alkylation of alcohols with alkyl P,P-diphenyl-N-(methanesulfonyl)phosphinimidates
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Alkyl P,P-diphenyl-N-(methanesulfonyl)phosphinimidates, easily prepared from alkyl diphenylphosphinites and methanesulfonyl azide, are used as a useful reagent for O-alkylation of alcohols in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate (Me3SiOTf). Copyright
- Aoki, Hidenori,Mukaiyama, Teruaki
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p. 1016 - 1017
(2007/10/03)
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- Synthesis and nmr characterisation of methyl mono- and DI-0-α-L-rhamnopyranosyl-α-d-glucopyranosiduronic acids
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The synthesis and NMR characterisation of methyl mono- and di-O-α-L-rhamnopyranosyl-α-D-glucopyranosiduronic acids 1-6 are described. Two commercial starting products were used: methyl α-D-glucopyranoside 7 for the preparation of 1 and 2, and methyl (R)-4,6-O-benzylidene-α-D-glucopyranoside 8 for 3-6. Oxidation reaction of the hydroxymethyl group of glucose to a carboxylic acid group was performed by sodium hypochlorite 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-mediated procedure after the coupling reaction. Glycosylation was carried out using the trichloroacetimidate approach with trimethylsilyl trifluoromethanesulfonate (TMSOTf) as promoter, resulting in a completely stereoselective formation of the a glycosyl linkage.
- Battistelli, Chiara Laura,De Castro, Cristina,Iadonisi, Alfonso,Lanzetta, Rosa,Mangoni, Lorenzo,Parrilli, Michelangelo
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