- Synthetic routes toward pentasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O181
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An efficient synthetic strategy has been developed for the synthesis of the pentasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O181. A one-pot, two step iterative glycosylation and [2 + 3] block glycosylation strategy have been adopted for the construction of the pentasaccharide derivative 2, which was then transformed into target compound 1 after a series of functional group transformations. Here H2SO4-silica has been used successfully as a promoter for all glycosylation reaction. The stereoselective outcomes of all glycosylation reactions were very good. The 2-acetamido-2,6-dideoxy-L-glucose (L-QuipNAc) building block was obtained from known carbohydrate L-rhamnose precursors.
- Kumar, Harikesh,Mandal, Pintu Kumar
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Read Online
- An expeditious stereoselective synthesis of natural (-)-Cassine via cascade HWE [3 + 2]-cycloaddition process
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l-Rhamnose is transformed to (-)-Cassine via a remarkable four step one pot reaction. The Horner-Wadsworth-Emmons [3 + 2]-1,3-dipolar cycloaddition reaction cascade is the pivotal step in this reaction sequence and makes the synthesis highly efficient. The Royal Society of Chemistry 2006.
- Herdeis, Claus,Kuepper, Patrick,Ple, Sophie
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Read Online
- Expeditious Synthesis of a Tetrasaccharide Repeating Unit of the O-Antigen of Escherichia coli O163
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The synthesis of the tetrasaccharide repeating unit of the O-antigen of Escherichia coli O163 as its p-methoxyphenyl (PMP) glycoside was achieved followed by sequential glycosylation strategy through thioglycoside activation using sulfuric acid immobilized on silica (H2SO4-silica) in conjunction with N-iodosuccinimide as a Bronsted acid catalyst. The application of one-pot reaction conditions for two glycosylations and in situ PMB-group removal reduced the number of reaction steps significantly. The l-QuipNAc building block was obtained from known carbohydrate l-rhamnose precursors. The stereoselective outcomes of all glycosylation reactions were found to be very good. A late-stage TEMPO-mediated oxidation was performed for the formation of required uronic acid moiety. An analogue of the target tetrasaccharide was also prepared by using one-pot glycosylation approach. Such synthetic oligosaccharides could later be effectively conjugated with an appropriate protein to furnish glycoconjugate derivatives for their use in immunochemical studies.
- Karki, Geeta,Kumar, Harikesh,Rajan, Remya,Mandal, Pintu Kumar
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Read Online
- Chaunopyran A: Co-Cultivation of Marine Mollusk-Derived Fungi Activates a Rare Class of 2-Alkenyl-Tetrahydropyran
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Co-cultivation of Chaunopycnis sp. (CMB-MF028) and Trichoderma hamatum (CMB-MF030), fungal strains co-isolated from the inner tissue of an intertidal rock platform mollusc (Siphonaria sp), resulted in transcriptional activation of a rare class of 2-alkenyl-tetrahydropyran, chaunopyran A (7), and biotransformation and deactivation of the antifungal pyridoxatin (1), to methyl-pyridoxatin (8). This study illustrates the complexity of offensive and counter-offensive molecular defenses encountered during fungal co-cultivation, and the opportunities for activating new, otherwise transcriptionally silent secondary metabolites.
- Shang, Zhuo,Salim, Angela A.,Capon, Robert J.
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Read Online
- Automated, Multistep Continuous-Flow Synthesis of 2,6-Dideoxy and 3-Amino-2,3,6-trideoxy Monosaccharide Building Blocks
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An automated continuous flow system capable of producing protected deoxy-sugar donors from commercial material is described. Four 2,6-dideoxy and two 3-amino-2,3,6-trideoxy sugars with orthogonal protecting groups were synthesized in 11–32 % overall yields in 74–131.5 minutes of total reaction time. Several of the reactions were able to be concatenated into a continuous process, avoiding the need for chromatographic purification of intermediates. The modular nature of the experimental setup allowed for reaction streams to be split into different lines for the parallel synthesis of multiple donors. Further, the continuous flow processes were fully automated and described through the design of an open-source Python-controlled automation platform.
- Bennett, Clay S.,DeYong, Ashley E.,Florek, John,Nguyen, Tu-Anh,Pohl, Nicola L. B.,Stamper, Gavin,Vasquez, Olivea,Yalamanchili, Subbarao,Zsikla, Alexander
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supporting information
p. 23171 - 23175
(2021/09/25)
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- Diastereoselective Synthesis of Thioglycosides via Pd-Catalyzed Allylic Rearrangement
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Stereoselective glycosylation is challenging in carbohydrate chemistry. Herein, stereoselective thioglycosylation of glycals via palladium-catalyzed allylic rearrangement yields various substituents on α-isomer thioglycosides. Two comprehensive series of aryl and benzyl thioglycosides were obtained via a combination of thiosulfates with glycals derived from glucose, arabinose, galactose, and rhamnose. Furthermore, diosgenyl α-l-rhamnoside and isoquercitrin achieved selectivity via stereospecific [2,3]-sigma rearrangements of α-sulfoxide-rhamnoside and α-sulfoxide-glucoside, respectively.
- Jiang, Xuefeng,Li, Jiagen,Wang, Ming
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p. 9053 - 9057
(2021/11/30)
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- Preparation method and application of first-class rhamnose C-glycoside
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The invention provides a rhamnose C-glycoside drug. The structural formula is shown as below, wherein R1 comprises a phenyl group, a substituted phenyl group, and various alkyl groups of C1 to C10, R2comprises a phenyl group and a substituted phenyl group, and the substituted phenyl groups of the R1 and the R2 comprise alkyl groups, halogen atoms, alkoxy groups and alkylthio-substituted phenyl groups. A preparation method of the rhamnose C-glycoside drug includes acetylating and brominating rhamnose in sequence to obtain the rhamnose C-glycoside drug. The prepared product is applied to preparation of drugs resistant to gastric cancer, breast cancer and liver cancer.
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Paragraph 0030; 0035-0036
(2020/03/11)
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- Tuning the Chemoselectivity of Silyl Protected Rhamnals by Temperature and Br?nsted Acidity: Kinetically Controlled 1,2-Addition vs Thermodynamically Controlled Ferrier Rearrangement
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An acidity- and temperature-dependent chemoselective glycosylation of silyl-protected rhamnals with alcohols has been revealed. The reaction undergoes a 1,2-addition pathway with (±)-CSA as the catalyst at rt, affording kinetically controlled 2-deoxyl rhamnosides. In contrast, only thermodynamically controlled 2,3-unsaturated rhamnosides are formed via Ferrier rearrangement when elevating reaction temperature to 85 °C or using CF3SO3H instead. This tunable glycosylation allows facile and practical access to both 2-deoxyl and 2,3-unsaturated rhamnosides with excellent yields and high α-stereoselectivity.
- Wang, Jincai,Deng, Chuqiao,Zhang, Qi,Chai, Yonghai
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supporting information
p. 1103 - 1107
(2019/02/14)
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- Stereocontrolled Synthesis of Highly Substituted trans α,β-Unsaturated Ketones with Potent Anticancer Properties from Glycals
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A novel synthetic route for highly substituted conjugated ketones has been developed utilizing glycals as starting materials. The two-step process combined the Heck reaction/Lewis acid promoted ring opening to afford the products in 33–80 % overall yields and with a high level of trans stereoselectivity. Since the products are essentially the aldols, this methodology may be employed in some cases as an alternative synthetic route to the typical aldol condensation. Densely substituted, selectively protected conjugated ketones are synthetically attractive structures which, in our case, proved to be biologically equally appealing. Namely, they showed activity against several cancer cell lines, such as HeLa, K562, MDA-MB-453, in some instances overperforming cisplatin used as a standard.
- Jovanovic, Predrag,Petkovic, Milos,Simic, Milena,Jovanovic, Milos,Tasic, Gordana,Crnogorac, Marija Djordjic,Zizak, Zeljko,Savic, Vladimir
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p. 4701 - 4709
(2019/07/31)
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- Palladium catalyzed stereocontrolled synthesis of C-aryl glycosides using glycals and arenediazonium salts at room temperature
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A stereocontrolled synthesis of aryl-C-glycosides was achieved using glycals and aryldiazonium salts in the presence of palladium acetate. A wide range of glycals including d-glucal, d-galactal, l-rhamnal, d-xylal and d-ribal underwent C-arylation at the anomeric carbon in the presence of different aryldiazonium tetrafluoroborates and gave synthetically useful 2,3-deoxy-3-keto-α-aryl-C-glycosides in good to excellent yields. Broad substrate scope, simple operation and room temperature reactions make this protocol very attractive in organic synthesis.
- Singh, Adesh Kumar,Kandasamy, Jeyakumar
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supporting information
p. 5107 - 5112
(2018/07/29)
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- General Approach to Five-Membered Nitrogen Heteroaryl C-Glycosides Using a Palladium/Copper Cocatalyzed C-H Functionalization Strategy
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A general approach to the synthesis of diverse heteroaryl-C-Δ1,2-glycosides has been developed by employing the Pd(OAc)2/CuI cocatalyzed direct cross-coupling of five-membered nitrogen heterocycles with 1-iodoglycals in a C-H activation manner. Using this method, 27 examples of heteroaryl-C-Δ1,2-glycosides, containing indoles, thiazoles, benzothiazoles, imidazoles, benzimidazoles, and benzoxazoles as aglycones were obtained in 43-99% yield.
- Zhang, Shuo,Niu, You-Hong,Ye, Xin-Shan
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supporting information
p. 3608 - 3611
(2017/07/15)
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- 3-Aminodeoxypyranoses in Glycosylation: Diversity-Oriented Synthesis and Assembly in Oligosaccharides
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A concise, diversity-oriented approach for the synthesis of naturally occurring 3-amino- and 3-nitro-2,3,6-trideoxypyranose derivatives and analogues thereof from simple sugars has been developed. In addition, we investigated the synthesis of various 3-aminoglycosyl donors and their application in glycosylation reactions. These studies led to the successful synthesis of a tetrasaccharide containing four different 3-aminosugar components using ortho-alkynylbenzoate donors.
- Zeng, Jing,Sun, Guangfei,Yao, Wang,Zhu, Yangbin,Wang, Ruobin,Cai, Lei,Liu, Ke,Zhang, Qian,Liu, Xue-Wei,Wan, Qian
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supporting information
p. 5227 - 5231
(2017/04/27)
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- An efficient method for the synthesis of pyranoid glycals
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A simple and efficient procedure was designed for the preparation of pyranoid glycals. In a novel fashion, a series of protected glycopyranosyl bromides underwent reductive elimination in the presence of zinc dust and ammonium chloride in CH3CN at 30-60 °C. The corresponding glycals were obtained with excellent isolated yields (72-96%) in a short time (20-50 min). Furthermore, the transformation was compatible with different protection patterns and conveniently scalable (86% for 45 g acetobromoglucose) which made it very applicable in organic synthesis.
- Chen, Heshan,Xian, Ting,Zhang, Wan,Si, Wenshuai,Luo, Xiaosheng,Zhang, Bo,Zhang, Meiyu,Wang, Zhongfu,Zhang, Jianbo
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supporting information
p. 42 - 46
(2016/07/06)
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- TMSBr-mediated solvent- and work-up-free synthesis of α-2-deoxyglycosides from glycals
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The thio-additions of glycals were efficiently promoted by a stoichiometric amount of trimethylsilyl bromide (TMSBr) to produce S-2-deoxyglycosides under solvent-free conditions in good to excellent yields. In addition, with triphenylphosphine oxide as an additive, the TMSBr-mediated direct glycosylations of glycals with a large range of alcohols were highly α-selective.
- Hsu, Mei-Yuan,Liu, Yi-Pei,Lam, Sarah,Lin, Su-Ching,Wang, Cheng-Chung
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supporting information
p. 1758 - 1764
(2016/10/05)
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- Pseudo enantiomeric carbohydrate olefin ligands - Case study and application in kinetic resolution in rhodium(I)-catalysed 1,4-addition
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In order to investigate significant differences in asymmetric induction for pseudo enantiomeric carbohydrate olefin ligands in rhodium(I)-catalysed 1,4-addition reactions, we designed a set of new olefin ligands differing in relative configuration and pyranoside conformation. With these, we have successfully elucidated structural requirements for metal binding and also identified an improved alternative for one pseudo enantiomer. Furthermore, we report the efficient kinetic resolution of a racemic 4-hydroxycyclopentenone derivative by 1,4-addition.
- Grugel, Holger,Albrecht, Fabian,Boysena, Mike M. K.
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supporting information
p. 3289 - 3294
(2015/02/05)
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- A convenient and efficient synthesis of glycals by zinc nanoparticles
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A simple and efficient method for the synthesis of pyranoid glycals utilizing the reductive elimination of glycopyranosyl bromides by zinc nanoparticles in an acetate buffer is described. A variety of pyranoid glycals derivatives were obtained, especially for the synthesis of 6-deoxy-4,6-O-benzylidene and disaccharide glycals with good yields.
- Xu, Yun,Wang, Wenjun,Cai, Yu,Yang, Xia,Wang, Peng George,Zhao, Wei
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p. 46662 - 46665
(2014/12/10)
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- Highly diastereoselective 1,2-dichlorination of glycals using NCS/PPh 3: Study of substituent and solvent effects
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Highly diastereoselective 1,2-dichlorination of glycals has been achieved at room temperature conditions in good to excellent yields using a milder, more convenient, less hazardous reagent combination NCS/PPh3 giving only one major product out of four possible diastereomers [either α-gluco (2) or α-manno (4)] depending upon the substituents. The diastereoselectivity is maximum (100% α/β-selectivity as well as cis/trans selectivity) for d-galactal and l-rhamnal derivatives. Detailed studies showed that solvent and substituent effects play a significant role in determining the product distribution.
- Hussain, Altaf,Mukherjee, Debaraj
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p. 1133 - 1139
(2014/02/14)
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- A rapid synthesis of pyranoid glycals promoted by β-cyclodextrin and ultrasound
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A convenient and environmentally benign procedure for the synthesis of glycals from glycosyl bromides with very low zinc dust loading (1.5 equiv.) is described. The process is activated by β-cyclodextrin and ultrasound. Based on 19 samples, this method has been demonstrated to be highly effective for a broad range of glycosyl bromides, including acid- or base-sensitive and disaccharide glycosyl bromides. A yield of 85%-96% of glycals was obtained. Copyright
- Zhao, Jinzhong,Shao, Huawu,Wu, Xin,Shi, Shaojing
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experimental part
p. 1434 - 1440
(2011/11/05)
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- Noteworthy observations accompanying synthesis of the apoptolidin disaccharide
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A stereoselective synthesis of the apoptolidin disaccharide is reported. The key chemistry features a new transformation utilizing a highly selective tetramethylalkoxyalanate[v]-directed syn-methylation of a vinylogous ester, isolation of a hydrate of a 2-keto sugar, an eco-friendly radical cleavage of a bromomethyl group, and an efficient preparation of a fluorodisaccharide via the use of XtalFluor-E.
- Srinivasarao, Madduri,Park, Taesik,Chen, Yuzhong,Fuchs, Philip L.
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supporting information; experimental part
p. 5858 - 5860
(2011/07/08)
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- A simple and convenient method for the synthesis of pyranoid glycals
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A simple, mild, and environmentally benign synthesis procedure of pyranoid glycals is described. In a novel fashion, protected glycopyranosyl bromides undergo the reductive elimination in the presence of zinc in phosphate buffer at room temperature. The pyranoid glycals were obtained in good-to-excellent yields (18 examples).
- Zhao, Jinzhong,Wei, Shanqiao,Ma, Xiaofeng,Shao, Huawu
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experimental part
p. 168 - 171
(2011/02/26)
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- On the synthesis of the 2,6-dideoxysugar l-digitoxose
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As deoxysugars are integral components of many natural products, the development of efficient chemical and enzymatic routes to prepare these compounds is of particular interest. Herein, we report a comparison of several synthetic methodologies used to prepare protected derivatives of the 2,6-dideoxysugar l-digitoxose. A novel, stereoselective synthetic route to efficiently access methyl 4-O-tert-butyldimethylsilyl-2,6-dideoxy-3-O-trimethylsilyl-α-l-ribo-hexopyranoside in 35% yield over nine facile steps is described.
- Timmons, Shannon C.,Jakeman, David L.
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p. 2695 - 2704
(2008/03/14)
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- Preparation of an analogue of orbicuside A, an unusual cardiac glycoside
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A steroid containing a multi-linked glycoside, analogous to the bufadienolide orbicuside A, has been prepared. The key steps were (i) the preparation of a 2α-allyloxycarbonyloxy-3β-hydroxy steroid, (ii) a Ferrier reaction between the steroid and a rhamnal derivative, (iii) removal of protecting group and oxidation of the 2-hydroxy group, (iv) dihydroxylation of the pseudoglycal from the sterically more hindered side and finally (v) ring closure by acetal formation under acidic conditions.
- Dixon, John T.,Van Heerden, Fanie R.,Holzapfel, Cedric W.
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p. 393 - 401
(2007/10/03)
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- The design and synthesis of novel anomeric hydroperoxides: Influence of the carbohydrate residue in the enantioselective epoxidation of quinones
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We present a study of the base (DBU)-catalysed epoxidation of a number of important naturally occurring quinones using a series of pyranose-derived anomeric hydroperoxides. The absolute (viz. d or l) stereochemistry of the carbohydrate, electronic nature of the 6-substituent and ring substitution are all important variables, both for the formation of the hydroperoxide and its reactivity. Reactions studied were the epoxidation of a precursor of the natural antibiotic, alisamycin and a series of naphthoquinones related to Vitamin K. In the best case, an ee of 82% was obtained; either product enantiomer is accessible according to the absolute stereochemistry of the carbohydrate. Finally, a molecular modelling study of the reaction is reported, concluding that the reactions are under kinetic control and that the observed ees cannot be explained by considering transition states that involve only the quinone and peroxide anion. It seems likely that the DBU molecule may play a key role in the transition state.
- Bundu, Abass,Berry, Neil G.,Gill, Christopher D.,Dwyer, Catherine L.,Stachulski, Andrew V.,Taylor, Richard J.K.,Whittall, John
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p. 283 - 293
(2007/10/03)
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- A new catalyst for the reductive elimination of acylated glycosyl bromides to form glycals
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Ethylene-N,N′-bis(salicylideneiminato(IV)) {VO(salen)} was developed as a catalyst for the reductive elimination of acylated glycosyl bromides to form glycals. VO(salen) to be an effective catalyst for the preparation of glycals on a multi-gram scale. The catalyst was green in colour and changed to brown as the reaction progress.
- Stick, Robert V.,Stubbs, Keith A.,Tilbrook, D. Matthew G.,Watts, Andrew G.
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- A short and efficient transformation of rhamnose into activated daunosamine, acosamine, ristosamine and epi-daunosamine derivatives, and synthesis of an anthracycline antibiotic acosaminyl-ε-iso-rhodomycinone
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3-Amino-2,3,6-trideoxyhexopyranoses are essential constituents of most anthracycline antitumour antibiotics. For an investigation of structure-activity relationships, the four diastereomeric amino sugars daunosamine, acosamine, ristosamine, and epidaunosamine were synthesised in short and efficient routes starting from commercially available rhamnose. Several glycosyl donors were provided and their use was exemplified in the synthesis of acosaminyl-ε-iso-rhodomycinone.
- Renneberg, Bernd,Li, Yue-Ming,Laatsch, Hartmut,Fiebig, Heinz-Herbert
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p. 861 - 872
(2007/10/03)
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- Development of a catalytic cycle for the generation of C1-glycosyl carbanions with Cp2TiCl2: Application to glycal synthesis
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A catalytic cycle has been developed for the conversion of glycosyl halides to their corresponding glycals using Cp2TiCl2. This process can be effectively used with only 30% of the in situ generated single electron reducing agent in contrast to the 2 equivalents normally employed. (C) 2000 Published by Elsevier Science Ltd.
- Hansen,Daasbjerg,Skrydstrup
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p. 8645 - 8649
(2007/10/03)
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- Preparation of acylated pyranoid glycals in neutral aqueous medium by using chromium(II) complexes as reagents
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Reactions of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (3) with chromium(II)L complexes (L = EDTA, NTA, IDA, GLY, MAL) in neutral (5 95% purity. Complexes of Cr(II) with L = EDTA, NTA were similarly efficient with 2,3,4,6-tetra-O-acetyl-α-D- glucopyranosyl chloride (2) in furnishing glucal 13, while with L = IDA, GLY, MAL hydrolysis of 2 could not be suppressed. Under the same conditions [Cr(II)(EDTA)]2- also efficiently gave the corresponding glycals 14-19 from 2,3,4,6-tetra-O-benzoyl- (4) and 2,3,4,6-tetra-O-pivaloyl-α-D-glucopyranosyl bromide (5), per-O-acetylated α-D-galactopyranosyl chloride (6) and bromide (7), α-D-mannopyranosyl chloride (8), α-D-xylopyranosyl chloride (9), and bromide (10), β-D-arabinopyranosyl bromide (11), and α-L-rhamnopyranosyl chloride (12).
- Kovacs, Gyoengyver,Toth, Krisztina,Dinya, Zoltan,Somsak, Laszlo,Micskei, Karoly
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p. 5253 - 5264
(2007/10/03)
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- A convenient synthesis of glycals employing in-situ generated Cp2TiCl
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Reductive elimination of acetylated glycosyl bromides to the corresponding glycal is easily achieved by mixing the bromide with Cp2TiCl2 and Mn in THF, and hence does not require the separate preparation of Cp2TiCl using glove-box techniques.
- Hansen, Thomas,Krintel, Sussie L.,Daasbjerg, Kim,Skrydstrup, Troels
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p. 6087 - 6090
(2007/10/03)
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- Carbohydrate based IMDA/aldol strategy towards the densely functionalized trans-decalin subunit of azadirachtin
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L-Rhamnal is converted into an hex-2-en-4-ulo C-glycopyranoside in which properly configured diastereomeric centers, asymmetric as well as geometric, are developed in the pendant anomeric substitutent via a Claisen aldol addition, and the resulting product proceeds via an IMDA reaction to provide a highly functionalised terpene AB ring system.
- Haag, Dieter,Chen, Xiao-Tao,Fraser-Reid, Bert
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p. 2577 - 2578
(2007/10/03)
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- A convenient, highly efficient one-pot preparation of peracetylated glycals from reducing sugars
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A convenient, highly efficient, one-pot, three-step procedure has been developed for the synthesis of peracetylated glycal derivatives from various reducing sugars including D-glucose, D-galactose, L-rhamnose, L-arabinose, D-maltose, D-lactose, and maltotriose. This procedure involves peracetylation of the reducing sugars with acetic anhydride and HBr/acetic acid followed by the transformation of the anomeric acetates to the corresponding bromides with additional HBr/acetic acid and finally reductive elimination of the 1-bromo and 2-acetoxy groups with Zn/CuSC4·5H2O in acetic acid/water containing sodium acetate. The overall yields of purified peracetylated glycals from the corresponding sugars range from 50 - 98%.
- Shull, Brian K.,Wu, Zhijun,Koreeda, Masato
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p. 955 - 964
(2007/10/03)
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- Antibody-oligosaccharide interactions: the synthesis of 2-deoxy-&α-L-rhamnose containing oligosaccharide haptens related to Shigella flexneri variant Y antigen
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A series of di-and trisaccharide glycosides based on the α-L-Rha(1->3)β-D-GlcNAc and α-L-Rha(1->3)α-L-Rha(1->3)β-D-GlcNAc elements have been synthesized to locate the minimal oligosaccharide determinant of the Shigella flexneri O-polysaccharide, which is built from a tetrasaccharide repeating unit, 2) α-L-Rhap(1->2)α-L-Rhap(1->3)α-L-Rhap(1->3)β-D-GlcNAcp(1->n.These compounds are also serve to identify the carbohydrate surface of the Shigella antigen that interacts with a monoclonal antibody, currently the subject of crystallographic studies.Two strategies utilizing suitably protected glycals 1 and 19 were employed to obtain analogs bearing either terminal od glycosylated 2,6-dideoxy-α-L-arabino-hexopyranosyl (2-deoxy-α-L-rhamnopyranosyl) residues.N-Iodosuccinimide activation of the glycals in the presence of selectively protected mono- and disaccharide alcohols afforded 2-deoxy-2-iodo-α-L-rhamnopyranosides and these were ultimately reduced during deprotection stages to afford the desired functionality.Di-O-acetyl L-rhamnal 1 reacted with monosaccharides 2 and 7, and with disaccharide 11, to yield disaccharides 4 and 8, and trisaccharide 12, each bearing a terminal 2-deoxy-α-L-rhamnopyranosyl residue.The selectively protected 3-O-benzoyl-4-O-benzyl-L-rhamnal 19 was synthesized from L-rhamnal and used to prepared trisaccharide 22, which contained an internal 2-deoxy-2-iodo-α-L-rhamnopyranosyl unit.Removal of protecting groups gave the oligosaccharides 6, 10, 14, and 23.Oligosaccharides that contained a 2-deoxy-α-L-rhamnopyranosyl residue showed enhanced inhibitory power: in the case of trisaccharide 23 a 1.8 kcal mol-1 relative increase in free energy of binding compared to a larger pentasaccharide epitope, α-L-Rhap(1->2)α-L-Rhap(1->3)α-L-Rhap(1->3)β-GlcAcp(1->2)α-L-Rhap-1->OMe.These data suggest that the rhamnose O-2 hydroxyl of residue C points toward and has important interactions with bindinbg site amino acids.
- Hanna, H. Rizk,Bundle, David R.
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p. 125 - 134
(2007/10/02)
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- Stereoselective synthesis of α-linked 2-deoxysaccharides and furanosaccharides by the use of 2-deoxy 2-pyridyl-1-thio pyrano- and furanosides as donors and methyl iodide as an activator
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A practical and highly stereoselective glycosidation methodology is described, where anomeric mixture of 2-deoxy 2-pyridyl-1-thiopyranoside donors (1-3,27) have been coupled with several sugar alcohols (4-8,29,31) on activation by methyl iodide to obtain axially linked 2-deoxysaccharides (9-17,30,32,33). Application of this method for the synthesis of disaccharide fragment 28 of avermectin is also described. Utility of this method is also shown by use of 2-pyridyl-1-thiofuranosides (34-36) as donors to prepare α-linked furanosides (42-51).
- Mereyala,Kulkarni,Ravi,Sharma,Rao,Reddy
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p. 545 - 562
(2007/10/02)
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- Alternative syntheses of L-(-)-oleandrose from L-rhamnose. Preparation of glycals
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L-Rhamnal (2) is prepared from L-rhamnose (3) by use of an improved generalized Fischer-Zach reaction. L-Rhamnal (2) is then converted to L-(-)-oleandrose (1) by stannylene mediated selective methylation and effective hydration. Benzyl α-L-oleandrose (12) is prepared by selective methylation and deoxygenation of L-rhamnose (3).
- Bredenkamp,Holzapfel,Toerien
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p. 2459 - 2477
(2007/10/02)
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- A MILD GENERAL METHOD FOR THE SYNTHESIS OF α-2-DEOXY-DISACCHARIDES: SYNTHESIS OF L-OLEANDROSYL-L-OLEANDROSE FROM D-GLUCOSE
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A mild, general method for the stereoselective synthesis of α-2-deoxy disaccharides is described using 2-deoxy-2-pyridyl 1-thioglycosides 4, 7, 8 as glycosyl donors and methyl iodide as an activator.Thus, a disaccharide 6 component of avermectin family is synthesized starting from D-glucose.
- Ravi, D.,Kulkarni, Vinayak R.,Mereyala, Hari Babu
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p. 4287 - 4290
(2007/10/02)
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- Stereoselective C-Glycosidation of Glycals with Organoaluminum Reagents
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A new approach to the stereoselective synthesis of C-glycosides from glycals with various organoaluminum reagents has been demonstrated.
- Maruoka, Keiji,Nonoshita, Katsumasa,Itoh, Takayuki,Yamamoto, Hisashi
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p. 2215 - 2216
(2007/10/02)
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- Aluminium Amalgam, a New Reagent in Glycal Synthesis
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The glycals (8-14) have been synthesized by reduction of the corresponding glycosyl bromides (1-7) by aluminium amalgam.Glycals carrying acid-sensitive substituents can also be synthesized by the use of this reagent.
- Jain, Sudha,Suryawanshi, S. N.,Bhakuni, D. S.
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p. 866 - 867
(2007/10/02)
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- Selective acylation of 6-deoxyglycals.
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L-Rhamnal was acylated under a variety of conditions with various acylating reagents. Substitution of the hydroxyl group in the allylic position was favored when acetyl chloride, N-acetylimidazole, benzoyl chloride, and N-benzoylimidazole were used (40-60% net yields), whereas the homoallylic group of L-rhamnal was selectively protected when acetic anhydride-pyridine was employed for the acylation. The monoacetates of L-fucal underwent O-3----O-4 migration of the acetyl group, and selective acylation of this glycal could not be achieved.
- Horton,Priebe,Varela
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p. 317 - 324
(2007/10/02)
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- On the acetoxylation of 2,3-dihydro-4-pyrones: a concise, fully synthetic route to the glucal stereochemical series
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The acetoxylation of the title compounds at C3 with Mn(OAc)3 is described.
- Danishefsky, Samuel,Bednarski, Mark
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p. 3411 - 3412
(2007/10/02)
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- Acid-catalyzed and Enzymatic Hydrolysis of trans- and cis-2-Methyl-3,4-epoxytetrahydropyran
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Whereas the acid-catalyzed hydrolysis of trans- and cis-3,4-epoxy-2-methyltetrahydropyran gives the corresponding diols by opening both at C-4 and C-3 (64percent attack at C-4 in the trans-epoxide, 86percent in the cis-epoxide), the hydrolysis of the same substrates catalyzed by rabbit liver microsomal epoxide hydrolase is entirely regiospecific and involves in both cases exclusive attack at C-4.The racemic cis-epoxide reacts at a faster rate than the trans.The 2R,3R,4S-enantiomer of the latter epoxide reacts at a much faster rate than its antipode to yield the (-)-(2R,3R,4R)-diol which is isolated at least 98 percent optically pure up to almost 50 percent conversion when starting from the racemic substrate.A reference sample of optically pure (+)-(2S,3S,4S)-diol was prepared from L-rhamnose.The enantiomeric excess of the (-)-(2R,3R,4R)-diol was also determined more precisely through g.l.c. analysis of diastereoisomeric MTPA esters.The present results confirm previous hypotheses on the topology of the hydrolase active site and emphasize the overriding importance of the orientation of a lipophilic substituent near the oxirane ring.
- Catelani, Giorgio,Mastrorilli, Ettore
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p. 2717 - 2721
(2007/10/02)
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