- Total Synthesis of the Naturally Occurring Glycosylflavone Aciculatin
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The new flavone-glycoside aciculatin (1), from Chrysopogon aciculatus, has been shown to have cytotoxic, anti-inflammatory, and antiarthritis activity. Further biological studies have been limited because of the limited availability of 1 from natural sources. Herein the first total synthesis of 1 in an overall yield of 8.3% is described. The synthesis involved the regio- and stereoselective glycosylation-Fries-type O-to-C rearrangement to construct the C-aryl glycosidic linkage, followed by a Baker-Venkataraman rearrangement and cyclodehydration to form the flavone scaffold.
- Yao, Chun-Hsu,Tsai, Chi-Hui,Lee, Jinq-Chyi
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Read Online
- Reactivity–Stereoselectivity Mapping for the Assembly of Mycobacterium marinum Lipooligosaccharides
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The assembly of complex bacterial glycans presenting rare structural motifs and cis-glycosidic linkages is significantly obstructed by the lack of knowledge of the reactivity of the constituting building blocks and the stereoselectivity of the reactions i
- Hansen, Thomas,Ofman, Tim P.,Vlaming, Joey G. C.,Gagarinov, Ivan A.,van Beek, Jessey,Goté, Tessa A.,Tichem, Jacoba M.,Ruijgrok, Gijs,Overkleeft, Herman S.,Filippov, Dmitri V.,van der Marel, Gijsbert A.,Codée, Jeroen D. C.
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p. 937 - 945
(2020/12/09)
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- Total syntheses of the non-peptide bradykinin B1 receptor antagonist velutinol a and its analogs, seco-pregnanes with a cage-like moiety
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We describe here the syntheses of velutinol A (1) and the structurally similar compounds 24 sharing a highly oxygenated seco-pregnane cage-like structure. The synthesis of velutinol A (1, 15,16-seco-pregnane) features the highly regioselective construction of |14 silyl enol ether from 15-keto-21,22-diol, followed by stereoselective introduction of a sterically hindered β-hydroxy group at the C14 position by Rubottom oxidation. Prolonged reaction time and the use of an excess amount of mCPBA at this step allowed double Rubottom oxidation, enabling us to introduce the requisite hydroxy groups at the C14 and C16 positions in one pot. Subsequent oxidative cleavage of the C1516 bond, deprotection, and intramolecular acetalization allowed the concise total synthesis of velutinol A (1). Utilization of α,α-dihydroxy-ketone, the double Rubottom oxidation product, for formation of the ether F-ring by 5-exo-cyclization, and subsequent C1421 oxidative cleavage, effectively achieved the synthesis of pentalinonside-aglycon (2). Construction of the 14,15-seco-structures of two other analogs, argeloside aglycon (3) and illustrol (4), was achieved by BaeyerVilliger oxidation of 15(21)-keto derivatives. Introduction of the 20-oxo group potentially embedded in argeloside aglycon was accomplished by Wacker oxidation of |20, which was constructed by GriecoNishizawa syn-β-elimination of the C21-primary alcohol obtained by reduction of the BaeyerVilliger product. Intra-molecular double acetalization of the 15,16-dihydroxy-14,20-oxo derivative to form the cage-like structure of the DEF-rings required a moderately weak acid. This step was the key to accessing argeloside aglycon (3), as otherwise the easily aromatized β,γ-dihydroxyketone moiety was transformed to furan. Sharpless asymmetric dihydroxylation of |20 to set the C20 stereocenter, followed by intramolecular double acetalization, achieved the stereoselective synthesis of illustrol With all synthesized compounds, structural requirements of steroidal bradykinine B1 receptor antagonist would be revealed.
- Tamiya, Minoru,Isaka, Nobuhisa,Kitazawa, Takaaki,Hasegawa, Atsushi,Ishizawa, Kazuya,Ikeda, Mayu,Kawada, Saki,Ishiguro, Masaji
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supporting information
p. 1474 - 1494
(2019/09/30)
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- Synthesis of MeON-neoglycosides of digoxigenin with 6-deoxy- and 2,6-dideoxy-D-glucose derivatives and their anticancer activity
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Cardiac glycosides show anticancer activities and their deoxy-sugar chains are vital for their anticancer effects. In order to study the structure-activity relationship (SAR) of cardiac glycosides toward cancers and get more potent anticancer agents, a series of MeON-neoglycosides of digoxigenin was synthesized and evaluated. First, ten 6-deoxy- and 2,6-dideoxy-D-glucopyranosyl donors were synthesized starting from methyl α-D-glucopyranoside and 2-deoxy-D-glucose. Meanwhile, the digoxigenin was obtained by acidic hydrolysis of commercially available digoxin as glycosyl acceptor. Then, a 22-member MeON-neoglycoside library of digoxigenin was successfully synthesized by neoglycosylation method. Finally, the induction of Nur77 expression and its translocation from the nucleus to cytoplasm together with cytotoxicity of these MeON-neoglycosides were evaluated. The SAR analysis revealed that C3 glycosylation is required for their induction of Nur77 expression. Moreover, some MeON-neoglycosides (2b and 8b) could significant induce the expression of Nur77 and its translocation from the nucleus to cytoplasm. However, these compounds showed no inhibitory effects on the proliferation of cancer cells, suggesting that they may not induce apoptosis of NIH-H460 cancer cells and their underlying potential and application toward cancer cells deserves future study.
- Wang, Dong-dong,Li, Xiao-san,Bao, Yu-zhou,Liu, Jie,Zhang, Xiao-kun,Yao, Xin-sheng,Sun, Xue-Long,Tang, Jin-Shan
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supporting information
p. 3359 - 3364
(2017/07/07)
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- Stereoselective synthesis of α-linked 2-deoxy glycosides enabled by visible-light-mediated reductive deiodination
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2-Deoxy sugars and their derivatives occur abundantly in many pharmaceutically important natural products. However, the construction of specific 2-deoxy-glycosidic bonds remains as a challenge. Herein, we report an efficient way to prepare 2-deoxy-a-glycosides by glycosylation of 2-iodo-glycosyl acetate and subsequent visible-light-mediated tin-free reductive deiodination. We have successfully applied the postglycosylational-deiodination strategy in the synthesis of more than 30 mono-, di-, tri-, tetra- and pentadeoxysaccharides with excellent stereoselectivity and efficiency. This method has also been applied to the synthesis of a 2-deoxy-tetrasac-charide containing four a-linkages.
- Wang, Hao,Tao, Jinyi,Cai, Xinpei,Chen, Wei,Zhao, Yueqi,Xu, Yang,Yao, Wang,Zeng, Jing,Wan, Qian
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p. 17319 - 17323
(2015/02/19)
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- Synthesis of ribo-hexopyranoside- and altrose-based azacrown ethers and their application in an asymmetric Michael addition
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The synthesis of four new ribo-hexopyranoside-based chiral lariat ethers of monoaza-15-crown-5 type and two altropyranoside-based crown ethers were elaborated. Our syntheses utilized the regioselective ring opening of the oxiran moiety of the 2,3-anhydro sugars by nucleophilic reagents to afford the key intermediates. The reaction of methyl-2,3-anhydro-4,6-O-benzylidene-α-d- mannopyranoside with ethanolamine is especially of interest to afford a 3-substituted altropyranoside. One of the ribo-hexopyranoside-based lariat ethers with a 4-methoxyphenyl substituent induced an enantioselectivity of 80% when used as catalyst in the Michael addition of diethyl acetamidomalonate to trans-β-nitrostyrene under phase transfer catalytic conditions.
- Rapi, Zsolt,Bakó, Péter,Keglevich, Gy?rgy,Sz?llsy, áron,Drahos, László,Hegeds, László
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- Assembly of digitoxin by gold(I)-catalyzed glycosidation of glycosyl o-alkynylbenzoates
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Digitoxin, a clinically important cardiac trisaccharide, was assembled efficiently from digitoxigenin and 3,4-di-O-tert-butyldiphenylsilyl-d- digitoxosyl o-cyclopropylethynylbenzoate in 9 steps and 52% overall yield via alternate glycosylation and protecting group manipulation. The present synthesis showcases the advantage of the gold(I)-catalyzed glycosylation protocol in the synthesis of glycoconjugates containing acid-labile 2-deoxysugar linkages.
- Ma, Yuyong,Li, Zhongzhen,Shi, Hefang,Zhang, Jian,Yu, Biao
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p. 9748 - 9756
(2012/01/04)
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- Chiral pool synthesis of calystegine A3 from 2-deoxyglucose via a Brown allylation
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Calystegine A3 is a naturally occurring nortropane iminosugar of which there previously have been three total syntheses. Inspired by our previous work we here report on a fourth approach using 17 steps from 2-deoxy-d-glucose applying a diastereoselective allylation protocol.
- Rasmussen, Tina Secher,Jensen, Henrik Helligs?
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scheme or table
p. 2855 - 2861
(2012/01/04)
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- Substrate flexibility of vicenisaminyltransferase VinC involved in the biosynthesis of vicenistatin
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A glycosyltransferase VinC is involved in the biosynthesis of antitumor β-glycoside antibiotic vicenistatin. It catalyzes a glycosyl transfer reaction between dTDP-α-D-vicenisamine and vicenilactam. Previous identification of its broad substrate specifici
- Minami, Atsushi,Eguchi, Tadashi
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p. 5102 - 5107
(2008/02/04)
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- Synthesis of D-rubranitrose by using a novel method for constructing functionalized branched-chain structures
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Convenient synthesis of D-rubranitrose from D-glucose was achieved by using simple and novel methods for deoxygenation and construction of functionalized branched-chain structures. The total yield of D-rubranitrose from methyl 4,6-O-benzylidene-α-D-glucop
- Sato, Ken-Ichi,Miyama, Daisuke,Akai, Shoji
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p. 1523 - 1525
(2007/10/03)
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- Synthesis of a-ring synthon of 19-nor-1alpha,25-dihydroxyvitamin D3 from (D)-glucose
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The present invention provides a method for the synthesis of an A-ring synthon phosphine oxide used in the preparation of 19-nor vitamin D compounds, and to novel synthetic intermediates formed during the synthesis. The new method prepares the phosphine oxide from (D)-glucose.
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- Novel synthesis of 2-substituted 19-norvitamin D A-ring phosphine oxide from D-glucose as a building block
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19-Norvitamin D A-ring phosphine oxide 5 was synthesized by a new sequence mode starting from D-glucose as a chiral template. Transformation of the pyranoside ring into the A-ring carbocycle was achieved by the Pd-catalyzed Ferrier rearrangement. The phosphine oxide 5 was obtained in an 18% overall yield by this novel cost-effective method.
- Shimizu, Masato,Iwasaki, Yukiko,Shibamoto, Yoshinori,Sato, Miki,DeLuca,Yamada, Sachiko
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p. 809 - 812
(2007/10/03)
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- Studies of the stereoselective reduction of ketosugar (hexosulose)
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The results from the studies of the stereoselective reduction of ketosugar (hexosulose) were reported. Combining our results and those reported in the literature, we summarize the factors in controlling the stereoselective reduction of ketosugars. These findings are valuable in the synthesis of various carbohydrate derivatives.
- Chang, Cheng-Wei Tom,Hui, Yu,Elchert, Bryan
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p. 7019 - 7023
(2007/10/03)
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- Insights into the branched-chain formation of mycarose: Methylation catalyzed by an (S)-adenosylmethionine-dependent methyltransferase
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A C-methyltransferase involved in methyl-branch formation in sugars has been characterized for the first time. TylC3, an (S)-adenosylmethylthionine(AdoMet)dependent enzyme, catalyzes the attachment of a methyl branch [Eq. (1)] in the biosynthesis of L-myc
- Chen, Huawei,Zhao, Zongbao,Hallis, Tina M.,Guo, Zhihong,Liu, Hung-Wen
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p. 607 - 610
(2007/10/03)
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- Novel and convenient method for the syntheses of 2,6-dideoxypyranoses, 3,6-dideoxypyranoses, and azido (amino) analogs of 3,6-dideoxypyranoses
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A novel method of regioselective deoxygenation of methyl 4,6-O-benzylidene-2,3-di-O-tosyl-α-D-glucopyranoside, and its application for the syntheses of 2,6-dideoxypyranoses, 3,6-dideoxypyranoses, and azido (amino) analogs of 3,6-dideoxypyranoses were reported.
- Chang, Cheng-Wei Tom,Clark, Terri,Ngaara, Mumbi
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p. 6797 - 6801
(2007/10/03)
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- Total synthesis of soraphen A(1α)
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The convergent synthesis of macrolide soraphen A(1α) is described starting from glucose (western part) and mannose (eastern part). Mannose was converted into a 2-deoxyribohexopyranoside that could be methylated and reduced stereoselectively. Chain elongation at C-6 was carried out by stereoselective addition of a magnesium acctylide. The two fragments (western and eastern) were assembled by a Julia olefination followed by macrolactonization. The introduction of the methyl group at C-2 of norsoraphen occurred stereoselectively for thermodynamic reasons.
- Abel, Stephan,Faber, Dominik,Hueter, Ottmar,Giese, Bernd
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p. 188 - 197
(2007/10/03)
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- Thio-sugars III. Radical catalyzed thione-thiol rearrangement of cyclic thionocarbonates on a pyranose ring: Formation of cis-arranged cyclic thiolcarbonates
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Pyranoside 3,4-cis-thionocarbonates, under radical-promoted reaction conditions (method A, B, or C, described in the text), gave O-S rearrangement products, 3,4-thiolcarbonates of cis-stereochemistry, in acceptable yields. 2,3-Thionocarbonates of trans-stereochemistry also gave the rearrangement products of cis-stereochemistry preferentially in method B (photolysis with hexabutyldistannane). Although regio-control of the product was not satisfactory in most cases, some of the results suggested that the regioselectivity of the reaction is markedly influenced by the stereochemistry of the anomeric position of the substrates. The products were converted to thioglycosides (peracetate forms) by conventional means.
- Tsuda, Yoshisuke,Noguchi, Shinsuke,Kanemitsu, Kimihiro,Sato, Yoshiyuki,Kakimoto, Kyoko,Iwakura, Yumiko,Hosoi, Shinzo
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p. 971 - 980
(2007/10/03)
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- Selective generation of free radicals from epoxides using a transition-metal radical. A powerful new tool for organic synthesis
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Bis(cyclopentadienyl)titanium(III) chloride reacts with epoxides by initial C-O homolysis. The regiochemistry of the opening is determined by the relative stabilities of the radicals. Depending on the reaction partners, these radicals undergo intramolecular (hex-5-enyl cyclization) or intermolecular additions to olefins. The resultant radicals are efficiently scavenged by a second equivalent of Ti(III) to afford the corresponding Ti(IV) derivative. Treatment of this intermediate with electrophiles such as H+ or halogens provides a route to functionalized cyclopentanes and other useful products. The radical initially formed from an epoxide can also be trapped by H-atom donors such as 1,4-cyclohexadiene or tert-butyl thiol, resulting in an overall reduction of the epoxide. In the absence of a H-atom donor or an olefin, this radical is trapped by Ti(III), resulting in a β-oxido-Ti organometallic species which undergoes facile elimination to give an olefin. The reaction conditions are remarkably mild and are applicable to very sensitive substrates.
- RajanBabu,Nugent, William A.
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p. 986 - 997
(2007/10/02)
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- The Synthesis of Some Pyrrolidines as Potential Precursors to Retronecine
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Methyl β-D-galactopyranoside was converted into methyl 4-azido-3-O-benzyl-6-O-t-butyldiphenylsilyl-2,4-dideoxy-β-D-arabino-hexoside, but subsequent transformation of the anomeric centre into a dithioacetal was unsatisfactory. Alternatively, methyl β-D-galactopyranoside easily gave methyl 4-azido-3,6-di-O-benzyl-2,4-dideoxy-β-D-arabino-hexoside, and this could be transformed by a reductive amination into two pyrrolidines as potential precursors to retronecine. Related chemistry gave (4S,5S,6R)-6-benzyloxy-4-benzyloxymethyl-3-oxa-1-azabicyclooctan-2-one, the structure of which was confirmed by a single-crystal X-ray structure determination. Finally, the synthesis of a potential precursor to heliotridine (an epimer of retronecine), namely methyl 4-azido-3-O-benzyl-6-O-t-butyldiphenylsilyl-2,4-dideoxy-α-D-ribo-hexoside, from methyl α-D-mannopyranoside is reported.
- Ferro, Vito,Skelton, Brian W.,Stick, Robert V.,White, Allan H.
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p. 787 - 803
(2007/10/02)
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- General Synthesis of Homochiral Trisubstituted γ-Butyrolactones
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The synthetically useful keto ester methyl 2-deoxy-2-(2-ethoxy-2-oxoethyl)-4,6-O-(phenylmethylene)-α-D-ribo-hexopyranosid-3-ulose can be prepared exclusively by reaction of the potassium enolate of methyl 2-deoxy-4,5-O-(phenylmethylene)-α-D-erythro-hexopy
- Alker, David,Jones, D. Neville,Taylor, G. Mark,Wood, William W.
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p. 1119 - 1126
(2007/10/02)
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- An Efficient Deoxysugar Synthesis using Bu4NBH4 via an SN2 Reduction
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Deoxysugar derivatives were prepared from the corresponding triflate, tosylate, halogen, and epoxide derivatives.Employing the tetrabutylammonium tetrahydroborate reagent, the deoxygenation proceeds via an SN2 type displacement in good yield.
- Sato, Ken-ichi,Hoshi, Toshio,Kajihara, Yasuhiro
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p. 1469 - 1472
(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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- Studies of the Mechanistic Diversity of Sodium Cyanoborohydride Reduction of Tosylhydrazones
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Reduction of tosylhydrazone derivatives of ketones and aldehydes with sodium cyanoborohydride in acidic medium is a mild, albeit versatile, deoxygenation reaction.The reaction mechanism has been proposed to proceed via either a direct hydride attack route or a tautomerization-then-reduction route.By using a mild reduction procedure (NaBH3CN, THF-MeOH, 0 deg C), it has been possible to stop the deoxygenation halfway and isolate the nascent tosylhydrazine product.Characterization of the resulting hydrazine to define the origin of the hydrogen being delivered to theformer carbonyl carbon has allowed us to unambiguously distinguish between these two possible mechanisms.Studies of reduction of tosylhydrazones derived from conjugated and saturated ketones confirmed earlier speculation that these reductions occur through a direct hydride attack mechanism.The reduction of para-substituted methyl phenyl ketone tosylhydrazones revealed a competition between these two mechanisms.Substrates bearing electron-donating substituents prefer to direct hydride attack pathway, while those with electron-withdrawing substituents favor an initial tautomerization prior to reduction.Sugar and hydroxyl ketone tosylhydrazones are also reduced by competing mechanisms.The mechanistic diversity in those cases may be attributed to the inductive effects compelled by the α substituents and the conformational constraints imposed by the ring structure.The mechanistic insights gained from these studies indicate that the direct hydride attack mechanism is the main reaction pathway due to the propensity of NaBH3CN to selectively attack the iminium ion.The tautomerization-then-reduction mechanism prevails only when the tautomerization of hydrazon to azohydrazine is facilitated.
- Miller, Vaughn P.,Yang, Ding-yah,Weigel, Theresa M.,Han, Oksoo,Liu, Hung-wen
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p. 4175 - 4188
(2007/10/02)
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- A Synthesis of (2S,6S)-2-Hydroxymethyl-6-methoxytetrahydropyran; a Useful Chiral Intermediate
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(2S,6S)-2-Hydroxymethyl-6-methoxytetrahydropyran (2) has been prepared in enantiomerically pure form in 13percent yield from D-glucose.
- Jones, Keith,Wood, William W.
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p. 999 - 1002
(2007/10/02)
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- The Deoxygenation of Some Carbohydrate Diols via Derived Cyclic Thiocarbonate
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The treatment of methyl 2,6-di-O-methyl-3,4-O-thiocarbonyl-β-D-galactoside with methyl iodide gives mainly the 3-deoxy-3-iodo-D-guloside, whereas the α-anomer of the above and methyl 2-O-methyl-3,4-O-thiocarbonyl-β-L-arabinoside give mainly the 4-deoxy-4-
- Patroni, Joseph J.,Stick, Robert V.,Engelhardt, Lutz M.,White, Allan H.
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p. 699 - 711
(2007/10/02)
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- Stereochemical dependence of the mechanism of deoxygenation, with lithium triethylborohydride, in 4,6-O-benzylidenehexopyranoside p-toluenesulfonates
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Lithium triethylborohydride was shown to react with methyl 4,6-O-benzylidene-α-D-hexopyranoside 2- and 3-tosylates, and 2,3-ditosylates, in the manno, allo, and altro configurational series both by O-S fission (O-desulfonylation) and by C-O fission (C-desulfonyloxylation), to produce carbinol and deoxy functions, respectively.The results were compared with those previously obtained with the corresponding gluco and galacto isomers, and the degree of facility of the cleavage reactions was seen to depend on the position of the sulfonic ester groups and the overall configuration of the molecules.The mechanism of reductive desulfonyloxylation also depended on configuration and was demonstrated to involve intermediary epoxide formation or displacement by internal hydride shift as the principal paths; competing elimination and direct nucleophilic displacement were found to occur in the allo series, whereas reduction accompanied by ring contraction has thus far been encountered only in the conformationally less constrained, cis-fused acetal system of the galacto series.Like the borohydride reagent, lithium aluminum hydride was found to react (though much more slowly) with the altro 2,3-ditosylate by the epoxide-mediated mechanism, although the latter hydride is known to desulfonyloxylate the α-D-gluco-isomer by a different, intramolecular reduction mechanism.
- Baer, Hans H.,Mekarska-Falicki, Miroslawa
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p. 3043 - 3052
(2007/10/02)
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- Synthesis of L-Daunosamine
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A convenient and inexpensive preparation of methyl 4,6-O-benzylidene-2-deoxy-α-D-erythrohexopyranosid-3-ulose (2), an important intermediate for the synthesis of L-daunosamine (1) is described.
- Gurjar, M. K.,Yadav, J. S.,Rama Rao, A. V.
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p. 1139 - 1140
(2007/10/02)
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- A CONVENIENT METHOD FOR THE PREPARATION OF 4,6-O-BENZYLIDENEGLYCALS FROM METHYL 2,3-ANHYDRO-4,6-O-BENZYLIDENE-α-D-HEXAPYRANOSIDES
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The reaction of methyl 2,3-anhydro-4,6-O-benzylidene-α-D-allopyranoside (1) with ethylmagnesium bromide in the presence of CuI afforded 4,6-O-benzylidene-1,2-dideoxy-D-ribo-hex-1-enopyranoside (2).Similarly, methyl 2,3-anhydro-4,6-O-benzylidene-α-D-gulopy
- Tsuda, Nobuo,Yokota, Sumio,Kudo, Takashi,Mitsunobu, Oyo
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p. 289 - 292
(2007/10/02)
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- A Convenient Synthesis of Methyl 4,6-O-Benzylidene-2-deoxy-α-D-erythro-hexopyranosid-3-ulose
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Methyl 4,6-O-benzylidene-2-deoxy-α-D-erythro-hexopyranosid-3-ulose, a key intermediate in the synthesis of L-daunosamine, has been prepared in 100 g lots starting from D-glucose.
- Ingle, T. R.,Dhekne, Vijay V.,Kulkarni, V. R.,Rao, A. V. Rama
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- DESULFONYLOXYLATION OF SOME SECONDARY p-TOLUENESULFONATES OF GLYCOSIDES BY LITHIUM TRIETHYLBOROHYDRIDE; A HIGH-YIELDING ROUTE TO 2- AND 3-DEOXY SUGARS
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Lithium triethylborohydride (LTBH) reacts readily with p-toluenesulfonates of methyl 4,6-O-benzylidene-α-D-glucopyranoside (4) to give deoxyglycosides in >90percent yield.Thus, the 2,3-ditosylate (1) and the 3-monotosylate (2) thereof afford methyl 4,6-O-benzylidene-2-deoxy-α-D-ribo-hexopyranoside (7) in highly regio- and stereo-selective reactions that proceed via methyl 2,3-anhydro-4,6-O-benzylidene-α-D-allopyranoside (6), and the 2-monotosylate (8) of 4 gives the 3-deoxy-α-D-arabino isomer (12) of 7 via the corresponding 2,3-anhydro-α-D-mannopyranoside 11.In the series of the corresponding β anomers, the 3-monotosylate 14 and the 2-monotosylate 16 are similarly desulfonyloxylated, with equal ease, but furnish mixtures of regioisomeric deoxyglycosides, namely, the 3- and 2-deoxy-β-D-ribo derivatives 20 and 21, and the 2- and 3-deoxy-β-D-arabino derivatives 22 and 23, respectively.It could be shown that this difference is due to the failure of the intermediary, β-glycosidic epoxides 18 and 19 (the anomers of 6 and 11) to obey the Fuerst-Plattner rule in their reductive ring-opening with LTBH.The β-glycosidic 2,3-ditosylate 15 reacts less readily, and gives 20-23, with 20 preponderating.The 2-O-methyl-3-O-tosyl-β-D-glucopyranoside 24 is partly desulfonylated and partly desulfonyloxylated, whereas its 3-O-methyl-2-O-tosyl isomer 27 undergoes desulfonylation exclusively.The reductions of 1, 2, and 8 by LTBH are compared with those previously effected by lithium aluminum hydride, which are slower, involve considerable desulfonylation, and afford lower yields of deoxyglycosides, with the main products differing from those obtained by the action of LTBH.Mechanistic differences associated with the two reductants are discussed.
- Baer, Hans H.,Hanna, Hanna R.
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- Reactions of Relevance to the Chemistry of Aminoglycoside Antibiotics. Part 14. A Useful Radical-deamination Reaction
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Primary, secondary, and tertiary aliphatic or alicyclic isocyanides are smoothly reduced under radical conditions using tri-n-butylstannane to the corresponding hydrocarbons.The relative ease of reduction is tertiary > secondary > primary.Aromatic isocyanides are not reduced under these conditions.The reduction of isothiocyanates (or isoselenocyanates) by tri-n-butylstannanae also affords hydrocarbons, but here the isocyanides have been shown to be intermediates.The reduction of a compound with isocyanide and xanthate functions in a 1,2-relationship gives a smooth radical fragmentation to furnish an olefin.An efficient synthesis of 2-deoxy-D-glucose starting with glucosamine is described.
- Barton, Derek H. R.,Bringmann, Gerhard,Lamotte, Genevieve,Motherwell, William B.,Motherwell, Robyn S. Hay,Porter, Alexander E. A.
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p. 2657 - 2664
(2007/10/02)
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