共查询到20条相似文献,搜索用时 46 毫秒
1.
Chemical Synthesis of Rare Natural Bile Acids: 11α‐Hydroxy Derivatives of Lithocholic and Chenodeoxycholic Acids 下载免费PDF全文
Kazunari Namegawa Kyoko Iida Kaoru Omura Shoujiro Ogawa Alan F. Hofmann Takashi Iida 《Lipids》2018,53(4):403-411
A method for the preparation of 11α‐hydroxy derivatives of lithocholic and chenodeoxycholic acids, recently discovered to be natural bile acids, is described. The principal reactions involved were (1) elimination of the 12α‐mesyloxy group of the methyl esters of 3α‐acetate‐12α‐mesylate and 3α,7α‐diacetate‐12α‐mesylate derivatives of deoxycholic acid and cholic acid with potassium acetate/hexamethylphosphoramide; (2) simultaneous reduction/hydrolysis of the resulting △11‐3α‐acetoxy and △11‐3α,7α‐diacetoxy methyl esters with lithium aluminum hydride; (3) stereoselective 11α‐hydroxylation of the △11‐3α,24‐diol and △11‐3α,7α,24‐triol intermediates with B2H6/tetrahydrofuran (THF); and (4) selective oxidation at C‐24 of the resulting 3α,11α,24‐triol and 3α,7α,11α,24‐tetrol to the corresponding C‐24 carboxylic acids with NaClO2 catalyzed by 2,2,6,6‐tetramethylpiperidine 1‐oxyl free radical (TEMPO) and NaClO. In summary, 3α,11α‐dihydroxy‐5β‐cholan‐24‐oic acid and 3α,7α,11α‐trihydroxy‐5β‐cholan‐24‐oic acid have been synthesized and their nuclear magnetic resonance (NMR) spectra characterized. These compounds are now available as reference standards to be used in biliary bile acid analysis. 相似文献
2.
Xiang Li Siyu Li Suyan Sun Fan Yang Weiguo Zhu Yu Zhu Yusheng Wu Yangjie Wu 《Advanced Synthesis \u0026amp; Catalysis》2016,358(10):1699-1704
An efficient and generally applicable protocol for decarboxylative coupling of α,α‐difluoroarylacetic acids with ethynylbenziodoxolone (EBX) reagents has been developed, affording α,α‐difluoromethylated alkynes bearing various functional groups in moderate to excellent yields. Remarkably, this potassium persulfate (K2S2O8)‐promoted reaction employs water as solvent under transition metal‐free conditions, thus providing a green synthetic approach to α,α‐difluoromethylated alkynes.
3.
BoyapatiM. Choudary Koosam Mahendar M. Lakshmi Kantam Kalluri V.S. Ranganath Taimur Athar 《Advanced Synthesis \u0026amp; Catalysis》2006,348(14):1977-1985
Nanocrystalline magnesium oxide was found to be an effective heterogeneous, solid base catalyst for the one‐pot Wittig reaction to afford α,β‐unsaturated esters and nitriles in excellent yields with high E‐stereoselectivity in the presence of triphenylphosphine under mild conditions. 相似文献
4.
Gaetano Giammona Gennara Cavallaro Giovanna Pitarresi Elisa Pedone 《Polymer International》2000,49(1):93-98
In the present study the derivatization of two water‐soluble synthetic polymers, α,β‐poly(N‐2‐hydroxyethyl)‐DL ‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy), with glycidyltrimethylammonium chloride (GTA) is described. This reaction permits the introduction of positive charges in the macromolecular chains of PHEA and PAHy in order to make easier the electrostatic interaction with DNA. Different parameters affect the reaction of derivatization, such as GTA concentration and reaction time. PHEA reacts partially and slowly with GTA; on the contrary the reaction of PAHy with GTA is more rapid and extensive. The derivatization of PHEA and PAHy with GTA is a convenient method to introduce positive groups in their chains and it permits the preparation of interpolyelectrolyte complexes with DNA. © 2000 Society of Chemical Industry 相似文献
5.
Yohan Park Young Ju Lee Suckchang Hong Mi‐hyun Kim Myungmo Lee Taek‐Soo Kim Jae Kyun Lee Sang‐sup Jew Hyeung‐geun Park 《Advanced Synthesis \u0026amp; Catalysis》2011,353(18):3313-3318
A new enantioselective α‐alkylation of α‐tert‐butoxycarbonyllactams for the construction of β‐quaternary chiral pyrrolidine and piperidine core systems is reported. α‐Alkylations of N‐methyl‐α‐tert‐butoxycarbonylbutyrolactam and N‐diphenylmethyl‐α‐tert‐butoxycarbonylvalerolactam under phase‐transfer catalytic conditions (solid potassium hydroxide, toluene, −40 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐3,3′,5,5′‐tetrahydro‐2,6‐bis(3,4,5‐trifluorophenyl)‐4,4′‐spirobi[4H‐dinaphth[2,1‐c:1′,2′‐e]azepinium] bromide [(S,S)‐NAS Br] (5 mol%) afforded the corresponding α‐alkyl‐α‐tert‐butoxycarbonyllactams in very high chemical (up to 99%) and optical yields (up to 98% ee). Our new catalytic systems provide attractive synthetic methods for pyrrolidine‐ and piperidine‐based alkaloids and chiral intermediates with β‐quaternary carbon centers. 相似文献
6.
NataliyaS. Goulioukina GrigoriiN. Bondarenko SergeyE. Lyubimov VadimA. Davankov KonstantinN. Gavrilov IrinaP. Beletskaya 《Advanced Synthesis \u0026amp; Catalysis》2008,350(3):482-492
It was shown that the catalytic hydrogenation of α‐iminophosphonates by molecular hydrogen can serve as a convenient method for the synthesis of racemic and optically active α‐aminophosphonates. Up to 94% ee was achieved in the rhodium‐catalyzed enantioselective hydrogenation using chiral ligand (R)‐BINAP. 相似文献
7.
Susana Marmesat Leonardo Velasco Maria Victoria Ruiz‐Méndez José María Fernández‐Martínez Carmen Dobarganes 《European Journal of Lipid Science and Technology》2008,110(8):776-782
The objective of the study was to investigate the performance at frying temperature of a new sunflower oil with high content of oleic and palmitic acid (HOHPSO) and containing γ‐tocopherol as the most abundant natural antioxidant. HOHPSO either containing α‐ or γ‐tocopherol (HOHPSO‐α and HOHPSO‐γ, respectively) were obtained from genetically modified sunflower seeds and refined under identical conditions. The oil stability against oxidation, as measured by Rancimat at 120 °C, was much higher for the oil containing γ‐tocopherol, suggesting the higher effectiveness of γ‐tocopherol as compared to α‐tocopherol to delay oxidation. Experiments at high temperature (180 °C) simulating the conditions applied in the frying process clearly demonstrated that, for the same periods of heating, the oil degradation and the loss of natural tocopherol were significantly lower for the oil containing γ‐tocopherol. Comparison of different genetically modified sunflower oils with different fatty acid compositions confirmed that oil degradation depended on the fatty acid composition, being higher at a higher degree of unsaturation. However, the loss of tocopherol for a similar level of oil degradation was higher as the degree of unsaturation decreased. Overall, the results showed that HOHPSO‐γ had a very high stability at frying temperatures and that mixtures of HOHPSO‐α and HOHPSO‐γ would be an excellent alternative to fulfill the frying performance required by the processors and the vitamin E content claimed by the consumers. 相似文献
8.
Yi‐Ning Wang Bukuo Ni AllanD. Headley Guigen Li 《Advanced Synthesis \u0026amp; Catalysis》2007,349(3):319-322
The 2‐Ns‐based aminohalogenation of α,β‐unsaturated ketones has been achieved in an ionic liquid, 1‐n‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide {[bmim][N(SO2CF3)2]}. [Bmim][N(SO2CF3)2] was found to be superior not only to classical organic solvents but also to its counterpart, [bmim][BF4], which was proven to be successful in the TsNCl2‐based aminohalogenation but failed to give any product for this reaction. The present process takes the advantage of 2‐NsNCl2 as the stable nitrogen/halogen source in a one‐pot operation without the use of any metal catalysts, it is convenient to perform without special protection of inert gases. Eight examples were examined with good to excellent stereoselectivity (1:5 to one isomer) and modest to good chemical yields (53–72 %). 相似文献
9.
Romain Blanc Laurent Commeiras Jean‐Luc Parrain 《Advanced Synthesis \u0026amp; Catalysis》2010,352(4):661-666
A new, highly efficient and mild N‐heterocyclic carbene (NHC)‐mediated organocatalytic procedure for the transfer of tin from tributyl(trimethylsilyl)stannane (Bu3SnSiMe3) onto aldehydes for the preparation of α‐silyloxyalkylstannanes and γ‐silyloxyallylstannanes has been developed. 相似文献
10.
11.
Yanmei Liu Hua Lai Bo Rong Tie Zhou Jia Hong Chao Yuan Shujing Zhao Xiaolong Zhao Biao Jiang Qiang Fang 《Advanced Synthesis \u0026amp; Catalysis》2011,353(17):3161-3165
An efficient strategy for a high‐yielding and stereoselective synthesis of α‐trifluoromethyl unsaturated carboxylic acids directly from the reactions of 3,3,3‐trifluoropropanoic acid (CF3CH2COOH) with various aryl aldehydes in the presence of titanium tetrachloride (TiCl4) is reported here for the first time, which is a valuable expansion for the classical Knoevenagel reaction. Because these compounds may have potential applications in organic electronics and can be easily converted to the corresponding fluorinated alcohols and amino acids with excellent bioactivity, this route should be a good choice for the preparation of α‐trifluoromethyl‐containing derivatives. 相似文献
12.
Krishna Bahadur SomaiMagar Yong Rok Lee 《Advanced Synthesis \u0026amp; Catalysis》2014,356(16):3422-3432
Efficient one‐step syntheses of α,β‐ and β,β‐dihaloenones were achieved by ruthenium(II)‐catalyzed reactions between cyclic or acyclic diazodicarbonyl compounds and oxalyl chloride or oxalyl bromide in moderate to good yields. This methodology offers several significant advantages, which include ease of handling, mild reaction conditions, one‐step reaction, and the use of an effective and non‐toxic catalyst. The synthesized compounds were further transformed into highly functionalized novel molecules bearing aromatic rings on the enone moiety using the Suzuki reaction.
13.
14.
Luca Deiana Gui‐Ling Zhao Shuangzheng Lin Pawel Dziedzic Qiong Zhang Hans Leijonmarck Armando Crdova 《Advanced Synthesis \u0026amp; Catalysis》2010,352(18):3201-3207
The first example of a highly enantioselective organocatalytic aziridination of α‐substituted α,β‐unsaturated aldehydes is presented. The reaction is catalyzed by simple chiral amines and gives access to highly functional terminal azirdines containing an α‐tertiary amine stereocenter in high yields and enantiomeric ratios (95.5:4.5–98:2). 相似文献
15.
Xing‐Kuan Chen Chang‐Wu Zheng Sheng‐Li Zhao Zhuo Chai Ying‐Quan Yang Gang Zhao Wei‐Guo Cao 《Advanced Synthesis \u0026amp; Catalysis》2010,352(10):1648-1652
A highly enantioselective Michael addition of cyclic 1,3‐dicarbonyl compounds to β,γ‐unsaturated α‐keto esters catalyzed by amino acid‐derived thiourea‐tertiary‐amine catalysts is presented. Using 5 mol% of a novel tyrosine‐derived thiourea catalyst, a series of chiral coumarin derivatives were obtained in excellent yields (up to 99%) and with up to 96% ee under very mild conditions within a short reaction time. 相似文献
16.
Fushun Liang Jiqing Zhang Jing Tan Qun Liu 《Advanced Synthesis \u0026amp; Catalysis》2006,348(14):1986-1990
A series of unusual fused tetraheterocyclic compounds 3 , consisting of a thiopyran (ring A), a thiophene (ring B), a pyridine (ring C), and an imidazole or a pyrimidine (ring D) core, with a bridgehead nitrogen and an angular methyl group, were successfully synthesized by a catalyst‐free, one‐pot, two‐component domino reaction of 4‐(4‐methyl‐1,3‐dithiol‐2‐ylidene)‐1,7‐bis(aryl/heteroaryl)hepta‐1,6‐diene‐3,5‐dione 2 and diamines. In this reaction, up to five new bonds were formed accompanied by the C S bond cleavage of the 1,3‐dithiole ring of 2 , with water as the only by‐product. 相似文献
17.
Tang‐Lin Liu Zhao‐Lin He Qing‐Hua Li Hai‐Yan Tao Chun‐Jiang Wang 《Advanced Synthesis \u0026amp; Catalysis》2011,353(10):1713-1719
The first catalytic asymmetric 1,3‐dipolar cycloaddition of azomethine ylides with various sterically hindered α,α,β‐trisubstituted 2‐alkylidene‐cycloketones has been developed successfully with silver acetate/TF‐BiphamPhos complex for the construction of spiro heterocyclic compounds containing pyrrolidine motifs and a spiro quaternary stereogenic carbon center. The highly efficient catalytic system exhibited high reactivity, excellent diastereoselectivity, good enantioselectivity and broad substrate scope under mild conditions. Subsequent transformations led to the expedient preparation of synthetically useful spiro[pyrrolidine‐tetrahydropyranone] and spiro[pyrrolidine‐isochroman‐1‐one] without loss of the diastereo‐ and enantiomeric excesses. 相似文献
18.
Koji Yonehara Yasuyuki Miyoshi Aki Tsukajima Takeo Akatsuka Makoto Saito 《Advanced Synthesis \u0026amp; Catalysis》2011,353(7):1071-1075
The methodology in this article is a palladium(II)/copper(II)‐ or palladium(II)‐catalyzed intermolecular cyclization of acrylic acid with alkenes to produce α‐methylene‐γ‐butyrolactone derivatives using molecular oxygen as an environmentally benign oxidant. In this system, the carboxylato, especially trifluoroacetato, or trimethylacetato ligand, plays a quite important role to afford a high catalytic activity by suppressing the deposition of palladium(0) black. 相似文献
19.
Wenjing Xia Hong Yao Dan Liu Linxiang Zhao Yu Zhou Hong Liu 《Advanced Synthesis \u0026amp; Catalysis》2016,358(11):1864-1869
Herein, we disclose the N‐heterocyclic carbene (NHC)‐catalyzed [3+3] annulation of challenging esters with methyl ketoimines for the highly enantioselective synthesis of intriguing δ‐lactams featuring various substituent patterns. The annulation occurs under mild conditions and offers good tolerance, good yields and excellent enantioselectivities. The six‐membered heterocyclic products are valuable for the synthesis of bioactive molecules.
20.
P. Selvam S.U. Sonavane S.K. Mohapatra R.V. Jayaram 《Advanced Synthesis \u0026amp; Catalysis》2004,346(5):542-544
Chemoselective reduction of α,β‐unsaturated carbonyls to the corresponding alcohols was achieved by a catalytic transfer hydrogenation (CTH) method using cobalt(II)‐substituted hexagonal mesoporous aluminophosphate (CoHMA) molecular sieve catalyst. Further, the catalyst was found to be promising as a heterogeneous catalyst as the yield was practically unchanged after up to six cycles. 相似文献