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1.
Stereoselective Synthesis of α‐3‐Deoxy‐D‐manno‐oct‐2‐ulosonic Acid (α‐Kdo) Glycosides Using 5,7‐O‐Di‐tert‐butylsilylene‐Protected Kdo Ethyl Thioglycoside Donors 下载免费PDF全文
Jia‐Sheng Huang Wei Huang Xue Meng Xin Wang Peng‐Cheng Gao Prof. Dr. Jin‐Song Yang 《Angewandte Chemie (International ed. in English)》2015,54(37):10894-10898
An efficient methodology for the synthesis of α‐Kdo glycosidic bonds has been developed with 5,7‐O‐di‐tert‐butylsilylene (DTBS) protected Kdo ethyl thioglycosides as glycosyl donors. The approach permits a wide scope of acceptors to be used, thus affording biologically significant Kdo glycosides in good to excellent chemical yields with complete α‐selectivity. The synthetic utility of an orthogonally protected Kdo donor has been demonstrated by concise preparation of two α‐Kdo‐containing oligosaccharides. 相似文献
2.
Kazuaki Ishihara Kazuki Nishimura Katsuya Yamakawa 《Angewandte Chemie (International ed. in English)》2020,59(40):17641-17647
Catalytic enantioselective α‐fluorination reactions of carbonyl compounds are among the most powerful and efficient synthetic methods for constructing optically active α‐fluorinated carbonyl compounds. Nevertheless, α‐fluorination of α‐nonbranched carboxylic acid derivatives is still a big challenge because of relatively high pKa values of their α‐hydrogen atoms and difficulty of subsequent synthetic transformation without epimerization. Herein we show that chiral copper(II) complexes of 3‐(2‐naphthyl)‐l ‐alanine‐derived amides are highly effective catalysts for the enantio‐ and site‐selective α‐fluorination of N‐(α‐arylacetyl) and N‐(α‐alkylacetyl) 3,5‐dimethylpyrazoles. The substrate scope of the transformation is very broad (25 examples including a quaternary α‐fluorinated α‐amino acid derivative). α‐Fluorinated products were converted into the corresponding esters, secondary amides, tertiary amides, ketones, and alcohols with almost no epimerization in high yield. 相似文献
3.
N. Chary Mamillapalli Prof. Govindasamy Sekar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(51):18584-18588
Synthesis of enantiomerically enriched α‐hydroxy amides and β‐amino alcohols has been accomplished by enantioselective reduction of α‐keto amides with hydrosilanes. A series of α‐keto amides were reduced in the presence of chiral CuII/(S)‐DTBM‐SEGPHOS catalyst to give the corresponding optically active α‐hydroxy amides with excellent enantioselectivities by using (EtO)3SiH as a reducing agent. Furthermore, a one‐pot complete reduction of both ketone and amide groups of α‐keto amides has been achieved using the same chiral copper catalyst followed by tetra‐n‐butylammonium fluoride (TBAF) catalyst in presence of (EtO)3SiH to afford the corresponding chiral β‐amino alcohol derivatives. 相似文献
4.
Joanna Borowiecka 《Heteroatom Chemistry》1999,10(6):465-470
The first examples of S‐thiophosphate derivatives of 2‐bromo‐2‐deoxy sugars 7–12 were synthesized by reacting alkyl ammonium salts 1–4 of thiophosphoric acids with α‐1,2‐cis (5) or α‐1,2‐trans dibromo sugars (6) and addition of free thiophosphoric acids 1a or 2a to 2‐bromo‐D‐glucal (13). It was observed that the solvent determines formation of either the O‐ or S‐glycosyl compound. β‐Thiophosphates can be transformed to the α‐configuration in the presence of acid in quantitative yield. The structures of the synthesized derivatives of 7–12 were confirmed by spectroscopic methods. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 465–470, 1999 相似文献
5.
Two types of reactions, namely the Pudovik reaction of benzaldehyde and acetophenone with diethyl phosphite as well as the substitution of the α‐hydroxyphosphonates so‐formed by primary amines to afford α‐aminophosphonates, were evaluated by quantum chemical calculations at the B3LYP/6‐31G(d,p) level. An unexpected neighboring group effect was found to enhance the substitution. A series of new α‐aminophosphonates was synthesized by the microwave‐assisted substitution of α‐hydroxyphosphonates by alkylamines. 相似文献
6.
α‐Peptide–Oligourea Chimeras: Stabilization of Short α‐Helices by Non‐Peptide Helical Foldamers 下载免费PDF全文
Dr. Juliette Fremaux Laura Mauran Dr. Karolina Pulka‐Ziach Dr. Brice Kauffmann Dr. Benoit Odaert Dr. Gilles Guichard 《Angewandte Chemie (International ed. in English)》2015,54(34):9816-9820
Short α‐peptides with less than 10 residues generally display a low propensity to nucleate stable helical conformations. While various strategies to stabilize peptide helices have been previously reported, the ability of non‐peptide helical foldamers to stabilize α‐helices when fused to short α‐peptide segments has not been investigated. Towards this end, structural investigations into a series of chimeric oligomers obtained by joining aliphatic oligoureas to the C‐ or N‐termini of α‐peptides are described. All chimeras were found to be fully helical, with as few as 2 (or 3) urea units sufficient to propagate an α‐helical conformation in the fused peptide segment. The remarkable compatibility of α‐peptides with oligoureas described here, along with the simplicity of the approach, highlights the potential of interfacing natural and non‐peptide backbones as a means to further control the behavior of α‐peptides. 相似文献
7.
Charge‐Induced Secondary Structure Transformation of Amyloid‐Derived Dipeptide Assemblies from β‐Sheet to α‐Helix 下载免费PDF全文
Dr. Ruirui Xing Dr. Chengqian Yuan Dr. Shukun Li Dr. Jingwen Song Prof. Dr. Junbai Li Prof. Xuehai Yan 《Angewandte Chemie (International ed. in English)》2018,57(6):1537-1542
Secondary structures such as α‐helix and β‐sheet are the major structural motifs within the three‐dimensional geometry of proteins. Therefore, structure transitions from β‐sheet to α‐helix not only can serve as an effective strategy for the therapy of neurological diseases through the inhibition of β‐sheet aggregation but also extend the application of α‐helix fibrils in biomedicine. Herein, we present a charge‐induced secondary structure transition of amyloid‐derived dipeptide assemblies from β‐sheet to α‐helix. We unravel that the electrostatic (charge) repulsion between the C‐terminal charges of the dipeptide molecules are responsible for the conversion of the secondary structure. This finding provides a new perspective to understanding the secondary structure formation and transformation in the supramolecular organization and life activity. 相似文献
8.
Francesco Paolo Invidiata Stefania Aiello Giancarlo Furno' Enrico Aiello Daniele Simoni Riccardo Rondanin 《Journal of heterocyclic chemistry》2000,37(2):355-361
Thermal rearrangement of 3‐acylisoxazole arylhydrazones allowed facile preparation of 2H‐1,2,3‐triazoles which were firstly reacted with isoamyl nitrite and then with an opportune arylhydrazine to produce the corresponding α‐hydroxyiminohydrazones 8a‐h . The reaction of compounds 8a‐h with phosphorus pentachloride afforded the desired 4,4′‐bitriazoles 1a‐h . The α‐hydroxyiminoketone derivative 7 or the α‐diketone 14 reacted easily with 1,2‐phenylenediamine to afford 1,2,3‐triazoles 2a‐c bearing the quinoxaline moiety at position 4. Improved yields of the quinoxalines 2a‐c were obtained when 1,2‐phenylenediamine was reacted with the dioxime 15. 相似文献
9.
Benito Alcaide Prof. Dr. Pedro Almendros Dr. Teresa Martínez del Campo Rocío Carrascosa 《化学:亚洲杂志》2008,3(7):1140-1145
A mild, palladium(II)‐catalyzed reaction of α‐allenols with α‐allenic esters in a heterocyclization/cross‐coupling sequence, applicable to a wide range of substitution patterns, has been developed for the preparation of 2,3,4‐trifunctionalized 2,5‐dihydrofurans. Our studies indicate high levels of chemo‐ and regiocontrol. The possibility of using optically active substrates as well as substrates of increased steric demand, such as tertiary α‐allenols, makes this novel sequence of heterocyclization/cross‐coupling an attractive method in organic synthesis. The current mechanistic hypothesis invokes a regiocontrolled palladium(II)‐mediated intramolecular oxypalladation of the free allenol component, that then undergoes a cross‐coupling reaction with the allenic ester partner, followed by a trans‐β‐deacyloxypalladation with concomitant regeneration of the PdII species. 相似文献
10.
Heteroannulation of Arynes with α‐Amino Imides: Synthesis of 2,2‐Disubstituted Indolin‐3‐ones and Application to the Enantioselective Total Synthesis of (+)‐Hinckdentine A 下载免费PDF全文
Dr. Rubén O. Torres‐Ochoa Dr. Thomas Buyck Dr. Qian Wang Prof. Dr. Jieping Zhu 《Angewandte Chemie (International ed. in English)》2018,57(20):5679-5683
A novel heteroannulation reaction between α‐amino imides and in situ generated arynes has been developed for the synthesis of 2,2‐disubstituted indolin‐3‐ones. An enantioselective total synthesis of the marine alkaloid (+)‐hinckdentine A was subsequently accomplished using this reaction as a key step. A catalytic enantioselective Michael addition of an α‐aryl‐α‐isocyanoacetate to phenyl vinyl selenone was employed for the construction of the enantioenriched α‐quaternary α‐amino ester. 相似文献
11.
Symmetrical and unsymmetrical α‐diazo‐β‐diketones undergo thermal Wolff rearrangements to generate α‐carbonylketenes to participate as dienes in Diels–Alder reactions with 4‐aryl‐2‐methyl‐2,3‐dihydro‐1,5‐benzothia/diazepines to give, whereapplicable, regiospecific cycloadducts, 4a,5,6,12‐tetrahydro‐1H/1H,7H‐1,3‐oxazino[3,2‐d][1,5]benzo‐thia/diazepin‐1‐ones. A mechanism of formation of the regiospecific cycloadducts is suggested. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 35–40, 1999 相似文献
12.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(45):14420-14424
A general catalytic hydrogen transfer‐mediated α‐functionalization of 1,8‐naphthyridines is reported for the first time that benefits from a hydrogen transfer‐mediated activation mode for non‐activated pyridyl cores. The pyridyl α‐site selectively couples with the C8‐site of various tetrahydroquinolines (THQs) to afford novel α‐functionalized tetrahydro 1,8‐naphthyridines, a class of synthetically useful building blocks and potential candidates for the discovery of therapeutic and bio‐active products. The utilization of THQs as inactive hydrogen donors (HDs) appears to be a key strategy to overcome the over‐hydrogenation barrier and address the chemoselectivity issue. The developed chemistry features operational simplicity, readily available catalyst and good functional group tolerance, and offers a significant basis for further development of new protocols to directly transform or functionalize inert N‐heterocycles. 相似文献
13.
Jie Cheng Liang Xu Edwin D. Stevens Mark L. Trudell Sari Izenwasser Dean Wade 《Journal of heterocyclic chemistry》2004,41(4):569-574
Two conformationally constrained tropane derivatives were prepared as rigid nicotinic acetylcholine receptor ligands. A palladium catalyzed intramolecular α‐arylation reaction was employed to generate the tricyclic compounds in good yields from N‐(bromo‐chloropyridylmethyl)‐8‐azabicyclo[3.2.1]octan‐3‐ones. 相似文献
14.
Lu Wang Jing‐Liang Wang Chang‐Ming Dong 《Journal of polymer science. Part A, Polymer chemistry》2005,43(20):4721-4730
Both star‐shaped poly(ε‐caprolactone) (PCL) having 4 arms (4sPCL) and 6 arms (6sPCL) and linear PCL having 1 arm (LPCL) and 2 arms (2LPCL) were synthesized and then investigated for inclusion complexation with α‐cyclodextrin (α‐CD). The supramolecular inclusion complexes (ICs) were in detail characterized by 1H NMR, differential scanning calorimetry, thermogravimetric analysis, wide angle X‐ray diffraction, solid‐state carbon nuclear magnetic resonance spectroscopy using cross‐polarization and magic‐angle spinning, and Fourier transform infrared, respectively. The stoichiometry (CL:CD, mol:mol) of all ICs increased with the increasing branch arm of PCL polymers, and it was in the order of α‐CD‐6sPCL1 ICs > α‐CD‐4sPCL ICs > α‐CD‐2LPCL ICs > α‐CD‐LPCL ICs. All analyses indicated that the branch arms of star‐shaped PCL polymers were included into the hydrophobic α‐CD cavities and their original crystalline properties were completely suppressed. Moreover, the ICs of star‐shaped PCL with α‐CD had a channel‐type crystalline structure similar to that formed between the linear PCL and α‐CD. Furthermore, the thermal stability of the free PCL polymers probably controlled that of the guest polymers included in the ICs. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4721–4730, 2005 相似文献
15.
Debromination of N‐benzyl 4‐ or 5‐substituted α‐bromo‐α‐p‐toluenesulfonylglutarimides is achieved with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) to give the N‐benzyl 4‐ or 5‐substituted α‐p‐toluenesulfonylglutarimides. The DBU/THF system is applied to a new methodology for the synthesis of bicyclic glutarimide skeleton in moderate yields. 相似文献
16.
Self‐Assembled Cyclic d,l‐α‐Peptides as Generic Conformational Inhibitors of the α‐Synuclein Aggregation and Toxicity: In Vitro and Mechanistic Studies 下载免费PDF全文
Dr. Marina Chemerovski‐Glikman Eva Rozentur‐Shkop Dr. Michal Richman Dr. Asaf Grupi Asaf Getler Prof. Haim Y. Cohen Dr. Hadassa Shaked Cecilia Wallin Dr. Sebastian K. T. S. Wärmländer Prof. Elisha Haas Prof. Astrid Gräslund Prof. Jordan H. Chill Prof. Shai Rahimipour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14236-14246
Many peptides and proteins with large sequences and structural differences self‐assemble into disease‐causing amyloids that share very similar biochemical and biophysical characteristics, which may contribute to their cross‐interaction. Here, we demonstrate how the self‐assembled, cyclic d,l ‐α‐peptide CP‐2 , which has similar structural and functional properties to those of amyloids, acts as a generic inhibitor of the Parkinson′s disease associated α‐synuclein (α‐syn) aggregation to toxic oligomers by an ?off‐pathway“ mechanism. We show that CP‐2 interacts with the N‐terminal and the non‐amyloid‐β component region of α‐syn, which are responsible for α‐syn′s membrane intercalation and self‐assembly, thus changing the overall conformation of α‐syn. CP‐2 also remodels α‐syn fibrils to nontoxic amorphous species and permeates cells through endosomes/lysosomes to reduce the accumulation and toxicity of intracellular α‐syn in neuronal cells overexpressing α‐syn. Our studies suggest that targeting the common structural conformation of amyloids may be a promising approach for developing new therapeutics for amyloidogenic diseases. 相似文献
17.
Gabriel J. Summers Rejoice B. Maseko B. M. Parveen Beebeejaun Carol A. Summers 《Journal of polymer science. Part A, Polymer chemistry》2011,49(12):2601-2614
The synthesis of a new compound, 2‐[(4‐bromomethyl)phenyl]‐4,5‐dihydro‐4,4‐dimethyloxazole ( 1 ), and its utility in the synthesis of oxazoline‐functionalized polystyrene by atom transfer radical polymerization (ATRP) methods are described. Aromatic oxazolyl‐functionalized polymers were prepared by the ATRP of styrene, initiated by ( 1 ) in the presence of copper(I) bromide/2,2′‐bipyridyl catalyst system, to afford the corresponding α‐oxazolyl‐functionalized polystyrene ( 2 ). The polymerization proceeded via a controlled free radical polymerization process to produce the corresponding α‐oxazolyl‐functionalized polymers with predictable number‐average molecular weights, narrow molecular weight distributions in high‐initiator efficiency reactions. Post‐ATRP chain end modification of α‐oxazolyl‐functionalized polystyrene ( 2 ) to form the corresponding α‐carboxyl‐functionalized polystyrene ( 3 ) was achieved by successive acid‐catalyzed hydrolysis and saponification reactions. The polymerization processes were monitored by gas chromatography analyses. The unimolecular‐functionalized initiator and functionalized polymers were characterized by thin layer chromatography, spectroscopy, size exclusion chromatography, and nonaqueous titration analysis. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011. 相似文献
18.
Transition‐Metal‐Free Formal Decarboxylative Coupling of α‐Oxocarboxylates with α‐Bromoketones under Neutral Conditions: A Simple Access to 1,3‐Diketones 下载免费PDF全文
Zhen He Xiaotian Qi Shiqing Li Yinsong Zhao Prof. Dr. Ge Gao Prof. Dr. Yu Lan Yiwei Wu Prof. Dr. Jingbo Lan Prof. Dr. Jingsong You 《Angewandte Chemie (International ed. in English)》2015,54(3):855-859
A transition‐metal‐free formal decarboxylative coupling reaction between α‐oxocarboxylates and α‐bromoketones to synthesize 1,3‐diketone derivatives is presented. In this reaction, a broad scope of substrates can be employed, and neither a metal‐based reagent nor an additional base is required. DFT calculations reveal that this reaction proceeds through a coupling followed by decarboxylation mechanism and the α‐bromoketone unprecedentedly serves as a nucleophile under neutral conditions. The rate‐determining step is an unusual hydrogen‐bond‐assisted enolate formation by thermolysis. 相似文献
19.
Wenhui Zhang Qingquan Wu Allen G. Oliver Anthony S. Serianni 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(6):610-615
The crystal structure of methyl α‐d ‐mannopyranosyl‐(1→3)‐2‐O‐acetyl‐β‐d ‐mannopyranoside monohydrate, C15H26O12·H2O, ( II ), has been determined and the structural parameters for its constituent α‐d ‐mannopyranosyl residue compared with those for methyl α‐d ‐mannopyranoside. Mono‐O‐acetylation appears to promote the crystallization of ( II ), inferred from the difficulty in crystallizing methyl α‐d ‐mannopyranosyl‐(1→3)‐β‐d ‐mannopyranoside despite repeated attempts. The conformational properties of the O‐acetyl side chain in ( II ) are similar to those observed in recent studies of peracetylated mannose‐containing oligosaccharides, having a preferred geometry in which the C2—H2 bond eclipses the C=O bond of the acetyl group. The C2—O2 bond in ( II ) elongates by ~0.02 Å upon O‐acetylation. The phi (?) and psi (ψ) torsion angles that dictate the conformation of the internal O‐glycosidic linkage in ( II ) are similar to those determined recently in aqueous solution by NMR spectroscopy for unacetylated ( II ) using the statistical program MA′AT, with a greater disparity found for ψ (Δ = ~16°) than for ? (Δ = ~6°). 相似文献
20.
Daniel E. Lynch Gillian E. Spicer Ian Mcclenaghan 《Journal of heterocyclic chemistry》2005,42(7):1363-1368
Three α‐phenylmalonamides have been prepared by the selective nucleophilic cleavage of 5,7‐dimethyl‐2‐phenyl‐1‐oxo‐1H‐pyrazolo[1,2‐a]pyrazol‐4‐ylium‐3‐olate in solventless microwave syntheses. The three weak nucleophiles employed were aniline, p‐chloroaniline and m‐toluidine. The α‐phenylmalonamides of these three aniline derivatives could not be prepared using the previously reported solvent syntheses via 3‐oxopyrazolo[1,2‐a]pyrazol‐8‐ylium‐1‐olates. All products were characterised using, infrared spectroscopy, 1H nmr and electrospray mass spectrometry. The single crystal X‐ray structures of the starting pyrazolo‐[1,2‐a]pyrazole and α‐phenylmalon‐m‐toluidide are also reported. 相似文献