Activation of a ring methyl substituent in pentamethylcyclopentadienyl rhenium(V) compounds: Synthesis and characterization of the 1,2,3,4-tetramethyl-5,6-dihydrofulvene-5,6-dithiolato complex [ReO{(S)(SCH2)C(5)Me(4)}(C(5)Me(5))]

Reaction of the half-sandwich rhenium(v) complexes [Re-Cl-4(C(5)Me(5))] or [Re(O)Cl-2(C(5)Me(5))] with H2S in chloroform in the presence of pyridine leads to the chiral dithiolato complex [ReO((S)(SCH2)C(5)Me(4))(C(5)Me(5))] 1.

SYNTHESIS OF 2 NEW HYDROGEN-BOND INDUCED LIQUID-CRYSTALS

Two new hydrogen bond induced liquid crystals with 4-butoxy benzoic acid as the proton donor and two chiral substituted stilbazole as the proton acceptor have been synthesized. Their liquid crystal transitions were studied by DSC and optical polarized microscope, the IR spectra of the complexes show the existence of the intermolecular hydrogen bond. The results of DSC and optical polarized microscope show that one of them (4BA-VSZ) has a chiral smectic C phase.

SYNTHESIS AND PROPELLER-PROPELLER TRANSITION OF OPTICALLY-ACTIVE POLY(DIPHENYL-O-TOLYLMETHYL METHACRYLATE)

Diphenyl-o-tolylmethyl methacrylate (DPTMA) was synthesized and polymerized using initiators of organolithium complexes with (+) - (2S,3S) -dimethoxy-1,4-bis(dimethylamino) butane (DDB) and (-) -sparteine (Sp) as the chiral ligands. DDB was suitable for its complex effective to prepare optically active poly(diphenyl-o-tolylmethyl methacrylate) (PDPTMA) with one-handed helical conformation, whereas only low-molecular weight polymer was formed when Sp was used as ligand due to the repulsive hindrance between the triarylmethyl group and the ligand. A new mutarotation, propeller-propeller transition, was observed for PDPTMA from the optical rotation curves and CD spectra in THF solution. The equivalent period of PDPTMA was estimated to be 14 angstrom based on the x-ray diffraction. (C) 1993 John Wiley & Sons, Inc.

SYNTHESIS AND PROPELLER PROPELLER TRANSITION OF OPTICALLY-ACTIVE POLY(DIPHENYL-O-METHOXYPHENYLMETHYL METHACRYLATE)

Diphenyl-o-methoxyphenylmethyl methacrylate was polymerized with several organolithium complexes of chiral ligand such as (-)-sparteine (Sp) and (S,S)-(+)-2,3-dimethoxy-1,4-bis(dimethylamino)butane (DDB). (+)-DDB was effective in preparing a polymer of high optical rotation, whereas (-)-Sp only gave oligomers with low optical rotation for the repulsive hindrance between the bulky ester group and the rigid ligand. The optical rotation of the polymer decreased rapidly to a constant value due to the propeller-propeller transition, which has been demonstrated by H-1 n.m.r. and circular dichroic spectra.

DIELS-ALDER REACTIONS CATALYZED BY LANTHANIDE CHLORIDES

Lanthanide chlorides have been found to catalyze the Diels-Alder synthesis of 2-butoxy-3, 4-dihydro-2H-pyran and several norbornene derivatives under mild conditions. In particular, the heavier lanthanide chlorides are very active catalysts for some (4 + 2) cycloaddition reactions. The catalyst activities and selectivities generally increase with increasing atomic number of the rare earth elements.

DIELS-ALDER REACTION CATALYZED BY RARE-EARTH CHLORIDES

Rare earth chlorides were used to catalyze the synthesis of 2-butoxy-3, 4-dihydro-2H-pyran using equimolar acrolein and vinyl butyl either. The cycloadduct is unstable which undergoes catalytic ring opening oligomerization. The way to stabilize the cyclo adduct has been studied, thus high yields of 90-95% were obtained.

Heterogeneous asymmetric hydrogenation of ethyl pyruvate on chirally modified Pt/Al2O3 catalyst with fixed-bed reactor

The enantioselective hydrogenation of ethyl pyruvate on the cinchonidine modified Pt/Al2O3 catalyst was investigated using a high-pressure reaction system with a fixed-bed reactor for the purpose to produce the,chiral product without separating the catalyst from the reaction system. The reaction was also investigated in a batch reactor for comparison. About 60% e. e. and 90% e. e. were obtained with the fixed-bed reactor and the batch reactor respectively, demonstrating the possibility for the heterogeneous asymmetric hydrogenation in the fixed-bed reactor. Some adsorbed chiral modifier, cinchonidine, can be slowly removed from the surface of Pt/Al2O3 under the continuous flow reaction, as a result, the e, e, values drops with the reaction time in the fixed-bed reactor. The enantio-selectivity is higher in the fixed-bed reactor, but lower in the batch reactor when ethanol was used as solvent than that when acetic acid as solvent. CO was used as molecular probe to characterize the adsorption of cinchonidine an the catalyst surface by IR spectroscopy, A red shift observed in IR spectra of coadsorbed CO with cinchonidine suggests that the cinchonidine adsorption is mainly through the pi -interaction with platinum surface and donating electron to the platinum surface.

Study of interaction between drug enantiomers and serum albumin by capillary electrophoresis

The interaction between drugs and human serum albumin (HSA) was investigated by capillary electrophoresis (CE). It involves stereoselectivity, drug displacement and synergism effects. Under protein-drug binding equilibrium, the unbound concentrations of drug enantiomers were measured by frontal analysis (FA). The stereoselectivity of verapamil (VER) binding to HSA was proved by the different free fractions of two enantiomers. In physiological pH (7.4, ionic strength 0.17 phosphate buffer) when 300 mu M (+/-) VER were equilibrated with 500 mu M HSA, the concentration of unbound S-VER was about 1.7 times its antipode. The binding constants of two enantiomers, KR-VER and KS-VER, were 2670 and 850 M-1, respectively. However, no obvious stereoselective binding of propranolol (PRO) to HSA was observed. Trimethyl-beta-cyclodextrin (45 mM) was used as a chiral selector in pH 2.5 phosphate buffer. Several drug systems were studied by the method. When ibuprofen (IBU) was added into VER-HSA solution. R-VER was partially displaced while S-VER was not displaced at all. A binding synergism effect between bupivacaine (BUP) and verapamil was observed and further study suggested that verapamil and bupivacaine occupy different binding site of HSA (site II and site III, respectively).

Application of liquid pre-column capillary electrophoresis technique to the study of interaction between drug enantiomers and human serum albumin

Based on the chiral separation of several basic drugs, dimetindene, tetryzoline, theodrenaline and verapamil, the liquid pre-column capillary electrophoresis (LPC-CE) technique was established. It was used to determine free concentrations of drug enantiomers in mixed solutions with human serum albumin (HSA). To prevent HSA entering the CE chiral separation zone, the mobility differences between HSA and drugs under a specific pH condition were employed in the LPC. Thus, the detection confusion caused by protein was totally avoided. Further study of binding constants determination and protein binding competitions was carried out. The study proves that the LPC technique could be used for complex media, particularly the matrix of protein coexisting with a variety of drugs.

High performance cocktail functional monomer for making molecule imprinting polymer

In order to make a molecule imprinting polymer (MIP) with highly chiral selectivity against N-t-Boc-L-Trp, a new kind of "cocktail" functional monomer: acrylamide+2-vinylpyridine was investigated. The MIP showed impressive chiral selectivity (alpha=3.23). With the increasing of water content in the mobile phase, ionic and hydrophobic interaction were found to be responsible for the chiral recognition process instead of the hydrogen bond. Tailing and peak asymmetry problems were overcome by using linear gradient elution. Physical properties such as thermal stability and pore structure for the MIP were also investigated.

A study of a molecular mechanics field used in simulating enantiorecognition

A molecular mechanics field, Alchemy II, was utilized to model the chiral recognition between S-N-acetyl-alpha-methyl-alpha-naphthylamine and (R, S)-N-(3, 5-dinitrophrnyl)-alpha-methyl-benzeneacetamide and between beta-cyclodextrin and (R, S)-fenoprofen. Some preliminary results have: been obtained to sustain the three-point action models and the induce-fit action in enantiorecognition.

Direct enantiomer separation of 2-phenylcyclopropanecarboxylate esters on cyclodextrin derivatives stationary phases in GC

Direct enantiomeric separation of all four optical isomers of 2-phenylcyclopropane carboxylate ester was first achieved on each of the three different beta-cyciodextrin chiral stationary phases (CSPs) in GC. Using these CSPs, enantiomeric excess of the products of enantioselective cyclopropanation can be determined directly, conveniently and fast.

Sulfamide-amine alcohol catalyzed enantioselective alkynylation of aromatic ketones

The new readily available sulfamide-amine alcohol 11 was found to be effective in catalyzing enantioselective phenylacetylene addition to aromatic ketones without using another central metal, providing the chiral tertiary propargylic alcohols in good yields (up to 83%) and enantioselectivities (up to 83% e.e.). The conditions of this catalytic process are both mild and Simple, (c) 2005 Elsevier B.V. All rights reserved.

Heterogeneous enantioselective epoxidation catalyzed by Mn(salen) complexes grafted onto mesoporous materials by phenoxy group

Three chiral Mn(salen) complexes were immobilized into different mesoporous material via phenoxy group by a simplified method and they show high activity and enantioselectivity for asymmetric epoxidation of various substituted unfunctional olefins. The heterogeneous Mn(salen) catalysts show comparable ee values for asymmetric epoxidation of styrene and 6-cyano-2,2-dimethylchromene and much higher ee values for epoxidation of a-methylstyrene (heterogeneous 79.7% ee versus homogeneous 26.4% ee) and cis-beta-methylstyrene (heterogeneous 94.9% ee versus homogeneous 25.3% ee for cis-epoxide) than the homogeneous catalysts. These heterogeneous catalysts also remarkably alter the cis/trans ratio of epoxides for asymmetric epoxidation of cis-beta-methylstyrene (heterogeneous 21 versus homogeneous 0.38). The axial tether group does not make a big effect on ee values and the increase in ee value and change in cis/trans ratio are mainly attributed to the axial immobilization mode and the support effect of heterogeneous catalysts. The catalysts keep constant ee values for the recycle tests of eight times for asymmetric epoxidation of a-methylstyrene. And several possibilities were proposed to elucidate the difference in ee values of heterogeneous catalysts from homogeneous catalysts. (c) 2005 Elsevier B.V. All rights reserved.

Stereoselektywna addycja pochodnych orto-toluiloamidów do imin jako metoda syntezy alkaloidów protoberberynowych

Wydział Chemii: Pracownia Spektrochemii Organicznej