- Hafnium Triflate as a Highly Potent Catalyst for Regio- and Chemoselective Deprotection of Silyl Ethers
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As a Group IVB transition metal Lewis acid, hafnium triflate [Hf(OTf) 4 ] exhibited exceptionally high potency in desilylations. Since the amounts of Hf(OTf) 4 required for the deprotection of 1°, 2°, 3° alkyl and aryl tert -butyldimethylsilyl (TBS) ethers are significantly different, ranging from 0.05 mol% to 3 mol%, regioselective deprotection of TBS could be easily implemented. Moreover, chemoselective cleavage of different silyl ethers or removal of TBS in the presence of most hydroxyl protecting groups was also accomplished. NMR analyses of silyl products from TBS deprotection indicated that Hf(OTf) 4 -catalyzed desilylation may proceed via different mechanisms, depending on the solvent used.
- Zheng, Xiu-An,Kong, Rui,Huang, Hua-Shan,Wei, Jing-Ying,Chen, Ji-Zong,Gong, Shan-Shan,Sun, Qi
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p. 944 - 953
(2019/02/10)
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- Hafnium trifluoromethanesulfonate catalyzed silyl ether protecting group removing method
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The invention provides a hafnium trifluoromethanesulfonate catalyzed silyl ether protecting group removing method. Various silyl ether protecting groups of nearly 50 kinds of substrates can be efficiently removed in 0.5-16 hours at room temperature by taking 0.02mol%-0.3mol% hafnium trifluoromethanesulfonate as a catalyst, a silyl ether protected hydroxyl compound as a substrate and conventional AR methanol as a solvent. 42 kinds of silyl ether protecting group removing products can be obtained at high yield by performing conventional slica column chromatography purification on a crude product. By regulating the use amount of the catalyst, the Hf(OTf)4 catalyst can realize regioselective removal of 1-degree, 2-degree and 3-degree alkyl TBS and aryl TBS protective groups. Moreover, in a proper equivalent scope, the Hf(OTf)4 catalyst can also realize 1) chemoselective removal of different kinds of silica-based protective groups; and 2) chemoselective removal of 1-degree TBS protective groups under the condition of not affecting a majority of common hydroxyl protective groups.
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Paragraph 0009; 0013; 0014
(2019/01/21)
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- A Green and Sustainable Route to Carbohydrate Vinyl Ethers for Accessing Bioinspired Materials with a Unique Microspherical Morphology
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Synthesizing chemicals and materials from renewable sources is one of the main aims of modern science. Carbohydrates represent excellent renewable natural raw materials that are ecofriendly, inexpensive, and biologically compatible. A green procedure has been developed for the vinylation of carbohydrates by using readily available calcium carbide. Various carbohydrates were utilized as starting materials, resulting in mono-, di-, and tetravinyl ethers in high to excellent yields (81–92 %). The synthesized biobased vinyl ethers were utilized as monomers in free radical and cationic polymerizations. A unique combination of a smooth surface and intrinsic microcompartments was achieved in the synthesized materials. Two types of biobased materials were prepared involving microspheres and intrinsic hollow compartments in polymers. Scanning electron microscopy with built-in ion beam cutting was applied to reveal the spatial hierarchical structures in 3D space.
- Rodygin, Konstantin S.,Werner, Irina,Ananikov, Valentine P.
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p. 292 - 298
(2017/12/26)
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- Improved and practical synthesis of 2-deoxy-l-ribose by hypophosphite-mediated deoxygenation
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An improved and practical route for a large-scale synthesis of 2-deoxy-L-ribose starting from L-arabinose has been developed. This is the first reported synthesis of 2-deoxy-L-ribose in which deoxygenation has been mediated by hypophosphite reagents instead of by organotin reagents.
- Chen, Li-Li,Ming, Xun,Cen, Jun-Da
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experimental part
p. 1 - 7
(2011/10/31)
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- Catalytic asymmetric epoxidation of alkenes with arabinose-derived uloses
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Four L-erythro-2-uloses were readily prepared from L-arabinose via a reaction sequence involving Fischer glycosidation, acetalization and oxidation. Bulky steric sensors at the anomeric center could enhance the stereoselectivity of the dioxirane epoxidation and one of the uloses performed with good enantioselectivity towards trans-stilbene (up to 90% ee). However, the catalysts decomposed during the epoxidation and the maximum chemical yield was only 13% under the basic conditions. Three L-threo-3-uloses could overcome the decomposition problem based on the electron withdrawing effect of the ester group(s) α to the ketone functionality. The best chemical yield was up to 93% using a ketone with two flanking ester groups. One of the improved uloses displayed moderate enantioselectivity towards trans-disubstituted and trisubstituted alkenes (40-68% ee).
- Shing, Tony K. M.,Leung, Yiu C.,Yeung, Kwan W.
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p. 2159 - 2168
(2007/10/03)
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- A practical synthesis of L-ribose
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L-Ribose was synthesized by a simple four-step method with overall yield of 76.3% from a protected L-arabinose derivative, which is a compatible intermediate for the synthesis of L-deoxyribose. The key step of this strategy is the Swern oxidation and subsequent stereoselective reduction accompanied by inversion of the 2-hydroxy group of protected L-arabinose.
- Akagi, Masao,Omae, Daichi,Tamura, Yoshinori,Ueda, Tetsujiro,Kumashiro, Tetsuya,Urata, Hidehito
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p. 866 - 868
(2007/10/03)
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- Monocyclic L-Nucleosides, analogs and uses thereof
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Novel monocyclic L-Nucleoside compounds have the general formula STR1 Embodiments of these compounds are contemplated to be useful in treating a wide variety of diseases including infections, infestations, neoplasms, and autoimmune diseases. Viewed in terms of mechanism, embodiments of the novel compounds show immunomodulatory activity, and are expected to be useful in modulating the cytokine pattern, including modulation of Th1 and Th2 response.
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- Improved synthesis of 2-deoxy-L-ribose
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Improved synthesis of 2-deoxy-L-ribose and the corresponding 2-deoxy- 3,5-di-O-p-toluoyl-α-L-erythro-pentofuranosyl chloride are described from L- arabinose.
- Zhang, Weijian,Ramasamy, Kanda S.,Averett, Devron R.
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p. 2357 - 2365
(2007/10/03)
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- Medicinal foodstuffs. XVI. Sugar beet. (3): Absolute stereostructures of betavulgarosides II and IV, hypoglycemic saponins having a unique substituent, from the roots of Beta vulgaris L.
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The absolute stereostructures of betavulgaroside II having a dioxolane- type substituent and betavulgaroside IV having an acetal-type substituent, which were isolated from the roots of Beta vulgaris L. (sugar beet, Chenopodiaceae) and exhibited hypoglycemic activity on glucose-loaded rats, were determined by the chemical correlations of betavulgarosides II and IV with a known saponin, momordin I. In these chemical correlations, the α-L- arabinopyranosyl moiety of momordin I was converted to a dioxolane-type substituent of betavulgaroside II or to an acetal-type substituent of betavulgaroside IV. Additionally, the 2'-diastereoisomer of betavulgaroside IV was synthesized from momordin I, and four acetal-type substituent analogues were also synthesized from L- and D-arabinose.
- Murakami, Toshiyuki,Matsuda, Hisashi,Inadzuki, Masahiro,Hirano, Kazuhiro,Yoshikawa, Masayuki
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p. 1717 - 1724
(2007/10/03)
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- Synthesis of 13C-Labeled Patulin [4-Hydroxy-4H-furo[3,2-c]pyran-2(6H)-one] to Be Used as Internal Standard in a Stable Isotope Dilution Assay
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A synthetic route was established for the preparation of [13C2]-4-hydroxy-4H-furo[3,2-c]pyran-2(6H)-one (patulin) to be used in a stable isotope dilution assay. Mass spectral analyses were performed using electron impact ionization (EI), negative electrospray ionization (ESI), collision-induced dissociation (CID), and atmospheric pressure ionization. Fragmentation routes in the EI mode and in CID were concluded and compared with each other.
- Rychlik,Schieberle
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p. 5163 - 5169
(2007/10/03)
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- Absolute stereostructures of betavulgarosides III and IV, inhibitors of glucose absorption, from the roots of Beta vulgaris L. (sugar beet)
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The absolute stereostructures of betavulgarosides III and IV, which were isolated from the roots of Beta vulgaris L. (sugar beet) and exhibited inhibitory activity on glucose absorption, were determined by the chemical correlation of betavulgaroside IV with a known saponin momordin I, which included the conversion from the α-L-arabinopyranosyl moiety of momordin I to the acidic acetal-type substituent of betavulgarosides III and IV via the α-L-ribopyranosyl derivative. Furthermore, four acidic acetal-type substituent analogues were synthesized from L- and D-arabinose.
- Yoshikawa, Masayuki,Murakami, Toshiyuki,Inaduki, Masahiro,Hirano, Kazuhiro,Yamahara, Johji,Matsuda, Hisashi
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p. 561 - 563
(2007/10/03)
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- Ylidenebutenolide Mycotoxins. Concise Syntheses of Patulin and Neopatulin from Carbohydrate Precursors
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Conversion of arabinose 10 to the protected ketone 13 followed by Wittig condensation to 14, acidcatalysed cyclisation (to lactone 16), dehydration and deprotection provides a brief synthesis of the mycotoxic substance patulin 1, which is produced by Penicillium and Aspergillus spp.In a similar manner, the biogenetic precursor to patulin, neopatulin 8, is synthesized from lyxose 25 via the key intermediates 24, 28 and 30.
- Bennett, Mandy,Gill, G. Byron,Pattenden, Gerald,Shuker, Anthony J.,Stapleton, Alan
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p. 929 - 937
(2007/10/02)
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- Lithium aluminium hydride reduction of glycopyranoside-monosulfonates: Formation of branched furanosides
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Lithium aluminum hydride reduction of glycopyranoside-monotosylates caused three reactions: (1) stereospecific 1,2-shift, producing branched furanosides (path A), (2) reductive O-S bond cleavage, producing the original glycosides (path B), and (3) reductive removal of the tosyloxy group, producing deoxyglycosides (path C). The path A reaction was particularly evident for the monotosylates at 2-O, 3-O, and 4-O: for example, methyl 2-O-tosyl-α-D-xylopyranoside gave methyl 2-deoxy-2-C-(hydroxymethyl)-α-D-α-erythrofuranoside in 60% yield. This reaction opens a new and efficient route to branched glycofuranosides of natural and unnatural type. Stereo-electronic requirements of this reaction in relation to the balance of the other two reactions are discussed.
- Tsuda,Nishimura,Ito
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p. 1983 - 1989
(2007/10/02)
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