- Highly enantioselective insertion of carbenoids into O-H bonds of phenols: An efficient approach to chiral α-aryloxycarboxylic esters
-
A highly efficient copper-catalyzed asymmetric carbenoid insertion into O-H bonds of phenols has been realized by using chiral spiro bisoxazoline ligands, affording α-aryloxypropionates and the related propionic acids in high yields with excellent enantiomeric excesses. Copyright
- Chen, Chao,Zhu, Shou-Fei,Liu, Bin,Wang, Li-Xin,Zhou, Qi-Lin
-
p. 12616 - 12617
(2008/03/14)
-
- Microbial deracemization of α-substituted carboxylic acids: Substrate specificity and mechanistic investigation
-
A new enzymatic method for the preparation of optically active α-substituted carboxylic acids is reported. This technique is called deracemization reaction, which provides us with a route to obtain the enantiomerically pure compounds, theoretically in 100% yield starting from the racemic mixture. This means that the synthesis of a racemate is almost equal to the synthesis of the optically active compound, and this concept is entirely different from the commonly accepted one in the asymmetric synthesis. Using the growing cell system of Nocardia diaphanozonaria JCM3208, racemates of 2-aryl- and 2-aryloxypropanoic acid are deracemized smoothly and (R)-form-enriched products are recovered in high chemical yield (>50%). In addition, using optically active starting compounds and deuterated derivatives as well as inhibitors, we have disclosed the fact that a new type of enzyme takes part in this biotransformation, and that the reaction proceeds probably via the same mechanism as that in rat liver.
- Kato, Dai-Ichiro,Mitsuda, Satoshi,Ohta, Hiromichi
-
p. 7234 - 7242
(2007/10/03)
-
- Microbial deracemization of alpha-substituted carboxylic acids.
-
An enzyme system of Nocardia diaphanozonaria JCM 3208 catalyzes the inversion of the chirality of various alpha-substituted carboxylic acids, such as 2-phenylpropanoic acid and 2-phenoxypropanoic acid derivatives, via a novel deracemization reaction.
- Kato, Dai-ichiro,Mitsuda, Satoshi,Ohta, Hiromichi
-
p. 371 - 373
(2007/10/03)
-
- Asymmetric dearomatization of η2-arene complexes: Synthesis of stereodefined functionalized cyclohexenones and cyclohexenes
-
A nonracemic η2-arene complex (2) was prepared from (R)-(+)-methyl-2- phenoxypropionate and pentaammineosmium(II) with high coordination diastereoselectivity (>9:1). Complex 2 was then treated with HOTf, an acetal, or a Michael acceptor to gene
- Chordia, Mahendra D.,Harman, W. Dean
-
p. 2725 - 2736
(2007/10/03)
-
- Preparation of mixtures of (R)- and (S)-2-(4-alkanoylphenoxy)- or (R)- and (S)-2-(4-aroylphenoxy)propionic esters
-
A mixture of (R)- and (S)-2-(4-alkanoylphenoxy)- or (R)- and (S)-2-(4-aroylphenoxy)propionic esters I STR1 with an enantiomeric excess of at least 90% is prepared by reacting a mixture of (R) and (S) enantiomer of a 2-phenoxypropionic ester II STR2 in which the appropriate (R) or (S) isomer is present in excess, with a carboxylic acid derivative of the formula III (X=OH, halogen, R1 COO or sulfonyloxy) in the presence of a Friedel-Crafts catalyst. The (R)- or (S)-2-(4-alkanoylphenoxy)propionic esters and (R)- or (S)-2-(4-hydroxyphenoxy)propionic esters are used for preparing crop protection agents and drugs.
- -
-
-
- Optical resolution of aryloxypropionic acids and their esters by HPLC on cellulose tris-3,5-dimethyl-triphenylcarbamate derivative
-
Chiral chromatographic resolution of a series of antiphlogistic 2- aryloxypropionic acids and their methyl and ethyl esters was performed using a Chiralcel OD column. The CSP selected resolved most of the acids and esters efficiently, the enantiomers being well separated without requiring time consuming analysis. Chromatographic separation of R enriched samples was performed to determine the correct elution order. Using eluting systems such as hexane and 2-propanol, or hexane, 2-propanol and formic acid, the S enantiomer of all acids and esters was always found to elute first. We also considered the role of electron-donating or electron-withdrawing substituents (at the aryloxylic moiety) on the chiral resolution. It was shown that the electronic features of the substituents have more influence on the chiral interactions between the solutes and the CSP than their steric hindrance. Finally we determined, by molecular models, the interaction between CSP and solutes. In this way were able to determine all the potential sites for interactions, which are compatible with the conformations of the compounds and the structure of the stationary phase, and point out those interactions which enable chiral resolution.
- Azzolina,Collina,Ghislandi
-
p. 1401 - 1416
(2007/10/02)
-
- A NEW CHIRAL HOST COMPOUND 10,10'-DIHYDROXY-9,9'-BIPHENANTHRYL. OPTICAL RESOLUTION OF PROPIONIC ACID DERIVATIVES, BUTYRIC ACID DERIVATIVES, AND 4-HYDROXYCYCLOPENT-2-EN-1-ONE DERIVATIVES BY COMPLEXATION
-
Optically active 10,10'-dihydroxy-9,9'-biphenanthryl was designed as a new chiral host compound for optical resolution of guest compounds, and was found to be wery effective for resolution of the title guest compounds.
- Toda, Fumio,Tanaka, Koichi
-
p. 1807 - 1810
(2007/10/02)
-
- Enzyme catalysed hydrolysis of chlorophenoxypropionates
-
We report on the enzymatic hydrolysis of methyl 2-phenoxypropionate and of the following chlorinated derivatives: methyl o-chloro-, m-chloro-, p-chloro-, and o,p-dichloro-2-phenoxypropionates. α-Chymotripsyn, lipase, and pig liver esterase have an R enantioselectivity whereas subtilisin has an S enantioselectivity.Enantiomeric excess (e.e.) cover a wide range (from 5 to 100percent).
- Chenevert, Robert,D'Astous, Linda
-
p. 1219 - 1222
(2007/10/02)
-