New chiral catalysts: synthesis and fragmentation pattern of C9-o-silanized cinchonidines

Summary We synthesized C9-O-silyl ethers of cinchonidine and dihydrocinchonidine (1-8), seven of which have not been known before. The structures of the compounds were verified by ESI-ion-trap MS and ¹H-NMR. Fragmentation of silyl ethers containing Si-phenyl bonds was studied for the first time. The compounds obtained will be utilized as chiral catalysts of certain asymmetric syntheses.</o:p>     

Separation of Cinchona alkaloids on a novel strong cation-exchange-type chiral stationary phase—comparison with commercially available strong cation exchanger and reversed-phase packing materials

A recently reported chiral strong cation exchanger (cSCX) type stationary phase was investigated for the LC separation of a series of Cinchona alkaloids and synthetic derivatives thereof to test its usefulness as alternative methodology for the separation of those important pharmaceuticals. The cSCX column-packing material was qualitatively compared on the one hand against a commercially available non-enantioselective SCX-material, PolySulfoethyl-A, and, on the other hand, against a modern C18 reversed-phase stationary phase which is commonly employed for Cinchona alkaloid analysis. Both SCX columns showed no pronounced peak-tailing phenomena which typically hamper Cinchona alkaloid RP analysis and require specific optimization. Thus, the cSCX-based assay provided new feasibilities for the separation of the Cinchona alkaloids in polar organic mode as opposed to conventional reversed-phase methodologies. In particular, a method for the simultaneous determination of eight Cinchona alkaloids (quinine, quinidine, cinchonine, cinchonidine, and their corresponding dihydro analogs) using the cSCX column in HPLC has been developed and exemplarily applied to impurity profiling of a commercial alkaloid sample. Furthermore, both SCX materials allowed successful separation of C9-epi and 10,11-didehydro derivatives from their respective educts in an application in synthetic Cinchona alkaloid chemistry. Figure An alternative separation principle - HPLC separation of strongly basic natural Cinchona alkaloids and synthetic derivatives thereof by means of a strong cation-exchanger type chiral stationary phase     

Surface Raman characterization of cinchonidine-modified polycrystalline platinum in ethanol: effects of temperature and comparison with 10,11-dihydrocinchonidine

The adsorption of the chiral modifier cinchonidine on platinum in ethanol as a function of temperature has been studied with surface-enhanced Raman spectroscopy (SERS). The temperature range chosen was from 30 to 70 °C, within which both the activity and selectivity of cinchonidine-modified Pt catalysts have been shown to change dramatically. Platinum surfaces were modified with 260 μM cinchonidine in ethanol, and examined both in pure ethanol and in the modifying solution itself. Adsorbed cinchonidine under pure ethanol was found to partially desorb as the temperature was raised, accompanied by an increase in the average tilt of the quinoline group with respect to the surface. In contrast, the presence of solution-phase cinchonidine resulted in an increase in the cinchonidine surface coverage and average tilt as temperature was raised. In a previous study [J. Mol. Catal. A 212 (2004) 277] we showed that hydrogen causes a dramatic enhancement in the SERS response of adsorbed cinchonidine. This was attributed to a conversion of cinchonidine to 10,11-dihydrocinchonidine on the Pt surface and a more flat orientation of the quinoline group. In both pure ethanol and in 260 μM cinchonidine, the presence of hydrogen causes a significant decrease in the alkaloid SERS bands at temperatures above 40 °C. In addition, the average tilt of the quinoline group increases significantly at these elevated temperatures. The temperature-dependence of 10,11-dihydrocinchonidine adsorption was also investigated, and is almost identical to that observed for cinchonidine in the presence of hydrogen. This lends further support to the conclusion that cinchonidine is being hydrogenated on the Pt surface in the presence of hydrogen. The significant changes observed on the cinchonidine-modified Pt surface above 40 °C correlate well with reported decreases in enantioselectivity and turn-over frequency at similar temperatures during ethyl pyruvate hydrogenation.     

Effect of the substituent position on the enantioselective hydrogenation of methoxy-substituted 2,3-diphenylpropenoic acids over palladium catalyst

The enantioselective hydrogenation of mono and dimethoxy-substituted 2,3-diphenylpropenoic acids has been studied over cinchonidine modified supported Pd catalyst. The hydrogenation of the six monosubstituted methoxy derivatives of (E)-2,3-diphenylpropenoic acid showed that the position of the substituent has a decisive influence on the initial reaction rate and the enantioselectivity. High enantioselectivities, 86–90%, were obtained in the hydrogenation of mono-substituted derivatives with a favourable substituent position. The results were rationalized in terms of either the electronic or the steric effects of the methoxy substituent determined by its position. These suggestions were also applicable in interpreting the results obtained in the hydrogenation of substituted (Z)-2,3-diphenylpropenoic acids and selected dimethoxy (E)-2,3-diphenylpropenoic acids. The combined steric and electronic effects of the substituents on the α- and β-phenyl rings ensured the highest enantioselectivities, up to 92% ee, in the hydrogenation of (E)-2-(2-methoxyphenyl)-3-(4-methoxyphenyl)propenoic acid.     

金鸡纳生物碱电喷雾质谱裂解规律研究

利用电喷雾离子阱质谱（ES-ITMS）技术进行了金鸡纳中4种喹啉类生物碱（奎宁、奎尼定、辛可宁和辛可尼定）的电喷雾质谱研究。在优化的质谱条件下,正离子全扫描时,4种生物碱都易形成带一个质子的分子离子;进一步碰撞诱导解离四种母离子,二级质谱表明羟基丢失、奎宁环断裂及重排为其主要裂解方式。     

Asymmetric Hydrogenation of Ethyl Pyruvate using Layered Double Hydroxides–Supported Nano Noble Metal Catalysts

Layered double hydroxide (LDH)–supported nano noble metal heterogeneous catalysts are synthesized by ion exchange of K₂PtCl₆, Na₂PdCl₄ and impregnation of RhCl₃ ^.3H₂O followed by reduction with H₂. The LDH–Rh, Pt, and Pd catalysts are tested in the enantioselective hydrogenation of ethyl pyruvate to ethyl lactate with very good yields and enantiomeric excess's (e.e.'s) of up to 72% were obtained with Pt. The catalyst was recovered and reused for several cycles with consistent activity.     

Efficient asymmetric Michael reaction of 2-oxindole-3-carboxylate esters with maleimides catalyzed by cinchonidine

A highly efficient enantioselective Michael reaction of 2-oxindole-3-carboxylate esters with N-maleimides catalyzed by commercially available cinchonidine was described. The desired adducts, containing a quaternary center at the C3-position and a vicinal tertiary center, were obtained in excellent yields (up to 99%), good enantioselectivities (up to 85% ee), and diastereoselectivities (dr>90:10) in the presence of 0.05–5 mol % catalyst loading.     

Catalytic asymmetric synthesis of α-(trifluoromethyl)benzylamine via cinchonidine derived base-catalyzed biomimetic 1,3-proton shift reaction

Here we describe catalytic asymmetric synthesis of α-(trifluoromethyl)benzylamine (1) via biomimetic transamination using chiral base. Imine 4 was isomerized to Schiff base 5 using 50 mol.% of cinchonidine derivatives as a catalyst in chloroform, methanol or acetonitrile. In the case of cinchonidine 6 as a catalyst, the reaction conducted in chloroform allowed for 79% conversion of the starting imine 4 in 52 days. The product imine 5 was obtained of (R) absolute configuration in 35% ee as individual compound without any byproducts. The catalyst 6 can be recovered (>95%) by adding n-hexane to the reaction mixture followed by a simple filtration.     

辛可尼丁的催化氢波

在浓度为０．２ｍｏｌ／Ｌ ＮＨ３·Ｈ２Ｏ－０．２ｍｏｌ／Ｌ ＮＨ４Ｃｌ（ｐＨ＝９．２０）的底液中,辛可尼丁在单扫示波极谱上有一灵敏的催化氢波。导数波峰电位于－１．４２Ｖ（ｖｓ,ＳＣＥ）附近。该峰具有一定吸附性。     

亲水性高分子稳定的纳米铂催化丙酮酸乙酯不对称氢化

贵金属纳米粒子因其优异的催化性能而在近年得到人们的重视．纳米粒子因表面积大而需要加入稳定剂以防止其团聚或次级粒子的产生．贵金属Pt纳米粒子经过生物碱辛可尼丁或合成不对称诱导剂的修饰后作为多相不对称催化剂，催化丙酮酸酯不对称加氢已经成为一种模型反应，检验催化