Theoretical investigation of the stereoselectivity of some Diels-Alder reactions involving cyclopentadiene

The stereoselectivity of some Diels-Alder reactions was investigated by means of ABEEM-oTr model. Combined with local hard-soft and acid-base （HSAB） principle, we made reasonable explanation by calculating local softness of atom and bond regions for the stereoselectivity of four Diels-Alder reactions involving cyclopentadiene.

On QSAR Study of Stereoselectivity for Wittig Reaction

Molecular structures of reactants were characterized by molecular electronegativity distance vector （VHMED） considering hydrogen association. A reasonable molecular modeling equation with 4-parameters was achieved for quantitative structure-property/activity relationship （QSPR/QSAR） by stepwise multiple regression （SMR） that the variable was introduced item by item in significant level order. A high correlation coefficient （R = 0.980） demonstrates that the model is able to well express a quantitative relation between stereoselectivity and the reactant structures as quantitative structure-reactivity/stereoselectivity relationship （QSRR/QSSR）. The multiple correlation coefficient （Rcv= 0.964） was tested through cross-validation with the leave-one-out （LOO） procedure. The above results show that the model possesses high estimation stability and good prediction ability between the amount of both cis and trans isomers in products and reactants.

Highly efficient synthesis of(R)-1,3-butanediol via anti-Prelog reduction of 4-hydroxy-2-butanone with absolute stereoselectivity by a newly isolated Pichia kudriavzevii

(R)-1,3-butanediol is an important pharmaceutical intermediate, and the synthesis of(R)-1,3-butanediol using green biological methods has recently been of interest for industrial application. Here, a novel strain QC-1 that efficiently transforms 4-hydroxy-2-butanone to(R)-1,3-butanediol was isolated from soil samples. Based on morphological, physiological, and biochemical tests and 5.8 S-internal transcribed spacer sequencing, the strain was identified as Pichia kudriavzevii QC-1. The reaction conditions were optimized to 35 ℃, pH 8.0, rotation speed 200 rpm, and 6:5 mass ratio of glucose to 4-hydroxy-2-butanone. Evaluation of the effects of 4-hydroxy-2-butanone concentrations on yield and cell survival rate showed that 85.60 g·L^-1 product accumulated, with an enantiomeric excess of more than 99%, when 30 g·L^-14-hydroxy-2-butanone was added at 0, 10, and 30 h in a 3-L bioreactor. Thus, strain QC-1 showed excellent catalytic activity and stereoselectivity for the synthesis of(R)-1,3-butanediol from 4-hydroxy-2-butanone.

STEREOSELECTIVITY IN THE SYNTHESIS OF DIADENYLYL METHYLPHOSPHONATE

Stereoselectivity was found during the coupling reaction to form 2',5'-and 3', 5'-linked diadenylyl methylphosphonate.

From Reactivity and Regioselectivity to Stereoselectivity: An Odyssey of Designing PIP Amine and Related Directing Groups for C-H Activation

What is the most favorite and original chemistry developed in your research group? Developing PIP amine for regio-and enantioselective methylene C-H activation. How do you get into this specific field? Could you please share some experiences with our readers?

Tris(bipyridine) Chromium (Ⅲ): Stereoselectivity in Binding to DNA

Recently, there has been considerable attention focused on the binding of metal complexes to DNA. Since the middle 1980s, Barton et al. have found that the chirl octahedral complexes that contain planar aromatic ligands can bind to double-helical DNA stereoselectively, and the chirl intercalator [Ru（phen）3]3+ has been used as the probe to recognize B and Z-form DNA. The photophysical studies indicated that the complexes containing 1, 10-phenanthroline or larger planar aromatic ligands can be intercalated into DNA stereoselectively and the complexes containing smaller ligands such as 2, 2’-

Promotion Mechanism of H2O for Stereoselectivity in Pd(Ⅱ)-catalyzed C—H Aryiation of Diarylphosphinamides with Arylboronic Acids

On the basis of a series of control experiments and nuclear magnetic resonance analyses,it is discovered that Boc-protected amino acid ligand coordinated to Pd center is partly replaced by N,N-dimethylformamide,and H2O can inhibit coordination of N,N-dimethylformamide to Pd center.The novel action mechanism perfectly explains H2O promotion for stereoselectivity in Pd(II)-catalyzed C—H aryiation of diarylphosphinamides with arylboronic acids.

STUDIES ON THE STEREOSELECTIVITY AND SUBSTITUTED GROUPS OF (+)-CAMPHOR DERIVATIVES

From (+)- camphor, six new (+)-camphor derivatives were synthesized. According tothe structure and chemical properties of the derivatives, the relation between the substitutedgroups and the stereoselectivity of alkylations and reduction was examined. It is found thatthe chemical shift of protons of C(8), C(9) methyl groups and chemical properties of carbonylO(2) are associated with the substituted groups.

Stereoselectivity of Acetalization and Ketalization Reactions of Glycerol and Its Modified Derivatives

Twenty one 1,3 dioxolanes with varieties of substituents at 2,4 positions were synthesized by acid catalyzed acetalization and ketalization reactions of glycerol and its modified derivatives. The assignment and quantitative analyses of thermodynamically equilibrated cis and trans 1,3 dioxolanes were completed by 1H NMR. The stereoselective regularity was found in acetalization and ketalization reactions of glycerol and its modified derivatives. The stereoselective regularity of the condensation reactions was reasonably explained by anomeric effect and 2,4 nonbonded interaction.

Analysis of chiral non-steroidal anti-inflammatory drugs flurbiprofen,ketoprofen and etodolac binding with HSA

The protein binding of non-steroidal anti-inflammatory drugs flurbiprofen, ketoprofen and etodolac with human serum albumin （HSA） was investigated using indirect chiral high performance liquid chromatography （HPLC） and ultrafiltration techniques. S-（-）-1-（1-naphthyl）- ethylamine （S-NEA） was utilized as chiral derivatization reagent and pre-column derivatization RP-HPLC method was established for the separation and assay of the three pairs of enantiomer. The method had good linear relationship over the investigated concentration range without interference. The average extraction efficiency was higher than 85% in different systems, and the intra-day and inter-day precisions were less than 15%. In serum albumin, the protein binding of etodolac enantiomers showed significant stereoselectivity that the affinity of S-enantiomer was stronger than R-enantiomer, and the stereoselectivity ratio reached 6.06; Flurbiprofen had only weak stereoselectivity in HSA, and ketoprofen had no stereoselectivity at all. Scatchard curves showed that all the three chiral drugs had two types of binding sites in HSA.

Functional characterization of a novel microbial esterase identified from the Indian Ocean and its use in the stereoselective preparation of(R)-methyl mandelate

Genomic mining has identifi ed a novel microbial alkaline esterase from the Indian Ocean. This esterase was overexpressed in E. coli BL21(DE3) and further functionally characterized. Under optimal conditions(10 mmol/L substrate, p H 6.0, 2 h at 40 °C), this esterase can hydrolyze racemic methyl mandelate to( R)-methyl mandelate with very high optical purity(e. e. >99%) and yield(nearly 90%). Interestingly, the stereoselectivity of this esterase is opposite to that of two previously reported lipases that can generate( S)-methyl mandelate through the hydrolysis of racemic methyl mandelate. No organic solvents or other additives were required to optimize the optical purity and production of the fi nal chiral product(R)-methyl mandelate, which can potentially simplify the production procedure of( R)-methyl mandelate catalyzed by esterase.

Stereoselective glucuronidation of carvedilol by Chinese liver microsomes

Objective: To study the stereoselective glucuronidation of carvedilol (CARV) by three Chinese liver microsomes. Methods: The metabolites of CARV were identified by a hydrolysis reaction with β-glucuronidase and HPLC-MS/MS. The enzyme kinetics for CARV enantiomers glucuronidation was determined by a reversed phase-high pressure liquid chromatogra-phy (RP-HPLC) assay using (S)-propafenone as internal standard after precolumn derivatization with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosylisothiocyanate. Results: Two CARV glucuronides were found in three Chinese liver microsomes incubated with CARV. The non-linear regression analysis showed that the values of Km and Vmax for (S)-CARV and (R)-CARV enantiomers were (118±44) μmol/L, (2 500±833) pmol/(min·mg protein) and (24±7) μmol/L, (953±399) pmol/(min·mg protein), respectively. Conclusion: These results suggested that there was a significant (P<0.05) stereoselective glucuronidation of CARV enantiomers in three Chinese liver microsomes, which might partly explain the enantioselective pharmacokinetics of CARV.

Enantioselective Aldol Reactions of Aliphatic Aldehydes with Singh’s Catalyst

Aldols from aliphatic aldehydes had been synthesized enantioselectively using Singh’s catalyst. Self and crossed aldol reactions with several linear aldehydes were performed.

Catalytic Characteristics of Lipase Immobilized in CTAB/TX-100 MBG

CTAB/TX-100 microemtdsion-based gel（MBG）, which could be soaked in aqueous solution for a long time without mechanical strength and shape changes, was successfully prepared. Lipase immobilized in this gel had a higher activity than that in CTAB MBG when catalyzed the esterification reaction between n-hexanoic acid and n-octanol and its enantioselectivity was slightly higher when catalyzed the stereoselective esterification reaction between racemic ibuprofen and n-octanol. In aqueous solution, lipase in CTAB/TX-100 MBG could catalyze smoothly the hydrolysis reaction of olive oil and could be reused many times without the evident change of MBG mechanical strength although its activity decreased 41.8% after nine-time recycles.

A Stereoselective Synthesis of Substituted Allyl Alcohol by Threecomponent Rection of Acetylenic Sulfone,Phenylselenomagnesium Bromide and Ketones

Phenylseleno and sulfonyl substituted allyl alcohols were synthesized stereoselectively by the three-component reaction of acetylenic sulfone, phenylselenomagnesium bromide and ketones in one-pot.

Stereoselective Addition of N-Alkylhydroxylamines to α,β-Unsaturated Nitro Compounds

N-Alkylhydroxylamines have been shown to undergo a stereospecific cis addition to 1-phenyl-2 -nitropropene compounds, whereas the corresponding O-alkylhydroxylamines give no diastereoselectivity. The concerted addition mechanism was provided to explain the difference.

Stereoselectivities in α- and β-Amino Acids Catalyzed Mannich Reactions Involving Cyclohexanone

The effects of two different amino acid catalysts on the stereoselectivities in the direct Mannich reactions of cyclohexanone,p-anisidine and p-nitrobenzaldehyde were studied with the aid of density functional theory.Transition states of the stereo-determining C ＂C bond-forming step with the addition of enamine intermediate to the imine for the L-proline（·-amino acid） and （R）-3-pyrrolidinecarboxylic acid（·-amino acid）-catalyzed processes were reported.B3LYP/6-31G calculations provide a good explanation for the opposite syn vs.anti diastereoselectivities of these two different kinds of catalysts（syn-selectivity for the ·-amino acid catalysts,anti-selectivity for the ·-amino acid catalysts）.Calculated and observed diastereomeric ratio and enantiomeric excess values are in reasonable agreement.

A Facile Synthsis of ω-Bromo-Diene Via Solid/LiquidTransferred Wittig Reactions of ω-Bromobutyltriphenylphosphonium Salts With α.β -Unsaturated Aldehydes

A new approach to the synthesis of co -bromo-dienes was carried out by usingsolid/liquid transferred Wittig reactions between in -bromobutyltriphenylphosphoniumsalt and Q. 6 -unsaturated aldehydes.

Highly Stereoselective Synthesis of trans-3-Chloro-β-lactams from Imines and Mixed Chloroacetyl and Nitroacetyl Chlorides

A series of trans-3-chloro-β-lactams was synthesized stereospecifically from imines and chloroacetyl chloride or a mixture of chloroacetyl chloride and nitroacetyl chloride, prepared from vinylidene chloride and a mixture of concentrated nitric acid and sulfuric acid, in the presence of triethylamine. The reaction of vinylidene chloride and the mixed acid was investigated. The formation mechanism of chloroacetyl chloride and nitroacetyl chloride and their reaction process with imines were proposed.