共查询到20条相似文献,搜索用时 31 毫秒
1.
Jong Hwa Jeong Young Hun An Youn K. Kang Quang Trung Nguyen Hyosun Lee Bruce M. Novak 《Polyhedron》2008
The reaction between ZnCl2 and (S)-N-ethyl-N-phenyl-2-pyrrolidinemethanamine (S-EPP) as a chiral ligand affords [ZnCl2(S-EPP)], whose structure has been determined by X-ray crystallography. [ZnEt2(S-EPP)] has demonstrated high activity toward the polymerization of rac-lactide with a maximum turnover frequency (TOF) of 121. Despite the intended stereocontrol by employing a chiral ligand, however, the observed heterotacticity was limited to under 0.6. The MWDs of the PLAs were found to be modulated by changing the solvent or controlling the concentration of the monomer in the solution. The glass transition temperature (Tg) was critically dependent on the MW within the narrow MWD regime, but the dependence became significantly shallow when the MWD was broadened. 相似文献
2.
《Tetrahedron: Asymmetry》2007,18(14):1682-1687
Racemic ethyl 3-hydroxybutanoate rac-1 was transformed into ethyl (R)-acetoxybutanoate (ee = 92%) with 85–90% chemical yields using enantioselective acylation with isopropenyl acetate in the presence of Candida antarctica lipase B (CAL-B, Novozym 435) under solvent-free conditions, followed by mesylation of the unreacted (S)-alcohol in the reaction mixture and inversion of configuration with cesium acetate in DMF in one pot. When the (R)-acetoxybutanoate was subjected to alcoholysis with ethanol and CAL-B, enantiopure (R)-1 (ee >99%) was produced. 相似文献
3.
A total synthesis of (R,S)S-glucoraphanin (GRP) has been completed by a novel, simple and convenient method in high overall yield (17% over seven steps). The study describes a method for the synthesis of natural and unnatural (methylsulfinyl)alkyl glucosinolates (GLs) and also opens useful pathways to synthesize GRP as well as other sulfinyl GLs. 相似文献
4.
Madeleine Delamare Sébastien Belot Frédéric Martinet Henri B. Kagan 《Tetrahedron letters》2009,50(15):1702-5466
Tenatoprazole, a substituted imidazopyridinyl derivative, is an irreversible proton pump inhibitor (PPI), which is used for the prevention and treatment of gastric acid-related diseases. A new highly efficient asymmetric oxidation using cumene hydroperoxide (CHP) as the oxidant in the presence of titanium tetraisopropoxide (Ti(OiPr)4) and (+)-(1R,2S)-cis-1-amino-2-indanol, in a polar aprotic solvent at 0-20 °C, has been developed to prepare tenatoprazole with an enantiomeric excess of >99%, a chemoselectivity of >90% and a chemical yield of >90% from the corresponding sulfide. This procedure was successfully implemented on scales ranging from 100 mg to multiple kilograms. Detailed studies of the parameters controlling purity and yield for this reaction are presented. 相似文献
5.
Stephen G. Davies James A. LeePaul M. Roberts Jeffrey P. StonehouseJames E. Thomson 《Tetrahedron letters》2012,53(9):1119-1121
The asymmetric synthesis of (−)-(S,S)-homaline was achieved in 8 steps from commercially available starting materials using the diastereoselective conjugate addition of the novel lithium amide reagent lithium (R)-N-(3-chloropropyl)-N-(α-methyl-p-methoxybenzyl)amide to methyl cinnamate to install the correct stereochemistry. Subsequent functional group manipulation of the resultant β-amino ester and Sb(OEt)3-mediated macrolactamisation was followed by homodimerisation to give (−)-(S,S)-homaline in 18% overall yield, representing the first asymmetric, and by far the most efficient synthesis of this natural product reported to date. 相似文献
6.
Biotransformation of (+)-(1R,2S)-fenchol by the larvae of Spodoptera litura was carried out. Substrate was converted to three new terpenoids, (+)-(1R,2S)-10-hydroxyfenchol, (+)-(1R,2R,3S)-8-hydroxyfenchol and (−)-(1S,2S,6S)-6-exo-hydroxyfenchol, and one known terpenoid, (−)-(1R,2R,3R)-9-hydroxyfenchol. These structures were established by NMR, IR, specific rotation and mass spectral studies. 相似文献
7.
A convergent synthesis of (4R,15R,16R,21S)-rollicosin (1) and (4R,15S,16S,21S)-rollicosin (2) was accomplished. Hydroxy lactone 6a and/or 6b were synthesized from 4-pentyn-1-ol, and α,β-unsaturated lactone 7 was synthesized from γ-lactone 8 and 5-hexen-1-ol. Inhibitory activity of these compounds was examined with bovine heart mitochondrial complex I. 相似文献
8.
Abhishek KalerVachan Singh Meena Manpreet SinghBrahmam Pujala Asit K. ChakrabortiUttam Chand Banerjee 《Tetrahedron letters》2011,52(41):5355-5358
A novel biocatalytic method for the enantioselective synthesis of (R)-bromo-3-[4-(2-methoxy-ethyl) phenoxy]-2-propanol [(R)-BMEPP], a precursor for the synthesis of (S)-metoprolol, an anti hypertensive drug is described. We have developed kinetic resolution of rac-BMEPP by transesterification using Candida rugosa lipase and vinyl acetate as the acyl donor affording the product with excellent conversion (49%) and ee (>99%). Various reaction parameters (source of enzyme, reaction media, and concentration of substrate and acylating agent) for the enzymatic kinetic resolution have been reported. 相似文献
9.
A convergent enantioselective total synthesis of (−)-(S)-stepholidine, a drug candidate for the treatment of schizophrenia and/or drug abuse, was described, which represented the first example of successful auxiliary-assisted Bischler–Napieralski cyclization of amide bearing bromine atom at 2-position of the C ring, followed by an introduction of the aryl methyl ester via Br–Li exchange. (−)-(S)-Stepholidine was synthesized in 6 steps, with 52% overall yield and >99% ee. The reported synthesis is practically free from chromatographic separation. 相似文献
10.
Sousuke Hara 《Tetrahedron》2004,60(37):8031-8035
The stereocontrolled synthesis of the protected (2S,3S)-N-methyl-5-hydroxyisoleucine, a component of halipeptins A and B with potent anti-inflammatory activity, has been achieved. The key steps include (i) installation of a double bond to bicyclic lactam 4 using N-tert-butyl phenylsulfinimidoyl chloride, (ii) highly exo-selective Michael reaction with lithium dimethylcuprate in the presence of chlorotrimethylsilane, and (iii) Ru-catalyzed oxidative deprotection of N,O-benzylidene acetal to the acid anhydride. 相似文献
11.
Anna GliszczyńskaRados?aw Bonikowski Józef Kula Czes?aw WawrzeńczykKornelia Cio?ak 《Tetrahedron letters》2011,52(34):4461-4463
(R)- and (S)-Lavandulol are important compounds in the cosmetics industry and in pheromone research. We have developed syntheses of (R)- and (S)-lavandulol from (S)- and (R)-limonene, respectively, by microbial Baeyer-Villiger oxidation of the intermediate unsaturated hydroxy ketone. It has been found that the same strain of Acremonium roseum can be successfully used in the key step of the synthesis of both enantiomers of lavandulol. 相似文献
12.
Pauline W. Ondachi 《Tetrahedron letters》2008,49(3):569-572
Enantiopure (S)-6-alkoxynicotine derivatives have been synthesized in two steps from (S)-nicotine via (S)-6-iodonicotine. Deprotonation and substitution at the C-5 position of the pyridine ring of (S)-6-methoxynicotine were achieved using mesityllithium as the base at 0 °C. Conditions for the C-4 lithiation/substitution of (S)-6-isopropoxynicotine and (S)-5-chloro-6-methoxynicotine were also developed. 相似文献
13.
Wen Zhang 《Tetrahedron letters》2004,45(48):8921-8924
Axially dissymmetric P,S-heterodonor ligand L3 synthesized from BINOL is an effective promoter in the palladium(0)-catalyzed Suzuki cross-coupling reaction of phenylboronic acid with aryl bromides and iodide at 60-80 °C. On the basis of 13C and 31P NMR spectroscopic investigation and X-ray diffraction, it was revealed that N,N-dimethylthiocarbamate-phosphine ligand L3 might be a P,S-heterodonor bidentate ligand to palladium(0) center. 相似文献
14.
A novel dichloro zinc complex (L1)ZnCl2, where L1 is N,N′-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocyclohexane, has been synthesized and characterized. The dimethyl derivatives, generated in situ from the well characterized dichloro zinc complexes (L1)ZnCl2 and (L2)ZnCl2, where L2 is N,N′-bis-(benzyl)-(R,R)-1,2-diaminocyclohexane, were employed as initiators for the ring opening polymerization (ROP) of rac-lactide (rac-LA). The complexes were found to be highly efficient initiators yielding the polylactide (PLA) with a narrow molecular weight distribution. The catalytic activity and heterotactic selectivity of the Zn(II) complexes were affected by the substituents on the phenyl groups of benzyl moieties in (R,R)-1,2-diaminocyclohexane. The dimethyl derivative of (L2)ZnCl2 produced highly stereocontrolled PLA with Pr = 0.75 at −25 °C. 相似文献
15.
N-alkyl 1,2-amino alcohols were rearranged stereospecifically by using TFAA/Et3N. This rearrangement has been used to synthesize N-isopropyl-3-(aryloxy)-2-hydroxypropylamines, β-adrenergic blocking agents such as (S)-toliprolol and (S)-propanolol. 相似文献
16.
A convenient five step synthesis of (S)-homolysine, incorporating a key olefin cross-metathesis step in the chain extension methodology, has been developed, together with a six step related synthesis of a new homologue of arginine, (S)-bishomoarginine. 相似文献
17.
A concise asymmetric total synthesis of (12S)-12-hydroxymonocerin (1) and (12R)-12-hydroxymonocerin (2) were efficiently achieved from the known 4-bromo-2,6-dimethoxyphenol. The synthetic approach was inspired by our biomimetic synthesis of (+)-monocerin (3) and 7-O-demethylmonocerin (4). The cis-fused furobenzopyranones of 1 and 2 was efficiently constructed via an intramolecular nucleophilic trapping of a quinonemethide intermediate, which was obtained by benzylic oxidation of compound 10 using 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). 相似文献
18.
Ivanna Rivera Juan Carlos Mateos Alain Marty Georgina Sandoval Sophie Duquesne 《Tetrahedron letters》2013
Besides the well-known papain, lipolytic activity is another interesting enzymatic activity present in latex from Carica papaya. This lipolytic activity is strongly attached to the latex solid phase, resulting in a naturally immobilized biocatalyst. In this work we describe the kinetic resolution of (R,S)-2-bromophenylacetic acid octyl ester by Carica papaya crude latex and two partially purified latex fractions. Several parameters, such as substrate concentration and solvent effects were studied. The best results were obtained using decane as solvent with 50 mM of substrate and 50 mg/mL enzyme/reaction medium; under these conditions, a high enantioselectivity (E >200) was obtained with crude latex. A twofold increase of the initial rate maintaining E >200 was obtained using purified fractions without protease and without esterase. Lipase from Carica papaya latex is the most enantioselective wild-type enzyme ever described for the studied reaction. 相似文献
19.
Guanghui Deng Yuanyuan Li Yu Zhou Jiang Wang Hualiang Jiang Hong Liu 《Tetrahedron》2008,64(46):10512-10516
The non-proteinogenic amino acid (2S)-2-amino-3,3-bis(4-fluorophenyl)propanoic acid [(S)-1] is a key intermediate required for the synthesis of Denagliptin (2a). Denagliptin is a dipeptidyl peptidase IV (DPP IV) inhibitor that is being developed for the treatment of type-2 diabetes mellitus. A diastereoselective, cost-efficient synthetic procedure for (S)-1 was developed by alkylating a Ni(II) glycine equivalent derived from (S)-2-[(N-benzylprolyl) amino] benzophenone [(S)-BPB]. The alkylated product was then decomposed to isolate the target amino acid (S)-1 (ee >99%) and ligand (S)-BPB, which can be reused in subsequent reactions. The enantiomer (R)-1 and racemate (rac)-1 were synthesized from their corresponding Ni(II) glycine equivalents. Denagliptin diastereomers (2), derived from the key intermediates (S)-1, (R)-1, and (rac)-1 were synthesized, and their dipeptidyl peptidase IV inhibitory activities were investigated. These findings are important in the design and synthesis of DPP IV inhibitors. 相似文献
20.
Harald Gröger Werner Hummel Claudia Rollmann Hendrik Hüsken Christine Wunderlich Karlheinz Drauz 《Tetrahedron》2004,60(3):633-640
The substrate range of a novel recombinant (S)-alcohol dehydrogenase from Rhodococcus erythropolis is described. In addition, an enzyme-compatible biphasic reaction medium for the asymmetric biocatalytic reduction of ketones with in situ-cofactor regeneration has been developed. Thus, reductions of poorly water soluble ketones in the presence of the alcohol dehydrogenase from R. erythropolis and a formate dehydrogenase from Candida boidinii can be carried out at higher substrate concentrations of 10-200 mM. The resulting (S)-alcohols were formed with moderate to good conversion rates, and with up to >99% ee. 相似文献