Aryloxypropionate

A number of herbicides are 2-aryloxypropionic acids (see Chapter 31). These herbicides were originally used as racemates, but in the agrochemical field, as in the pharmaceutical field, there... 

Reagent for the Resolution of Carboxylic Acids. Reagent (1) and its enantiomer have been used, although not as extensively as the more common (S)-a-Methylbenzylamine, as resolving agents for carboxylic acids via fractional crystallization of the corresponding diastereomeric salts. Examples of acids resolved this way include (2)-(6). Additional examples, such as man-delic, hydratopic, and a-aryloxypropionic acids, can be found in the literature. ... 

In addition to aryl carboxylic acids, including profens (2-aryl propionic acid NS AIDs) (see Fig. 9.36) [393,398], the terguride-based CSP has shown the potential to re.solve the enantiomers of 2-aryloxypropionic acids [394] and of A-dansyl, A-3,5-dinitrobenzoyl, A-benzoyl, A-P-naphthoyl amino acid derivatives [395]. 

Aiylcaiboxylic acids, A-dan.syl amino acids 2-Arylcarboxylic acids Halogen-substituted 2-aryloxypropionic acids Amino acid derivatives... 

Similarly, enantiomeric mixtures of carboxylic acid esters can be separated using transesterification (Fig. 22). An n-butanol/water biphasic medium aryloxypropionic acid methyl ester vras transesterified stereoselec-tively, yielding the butylester of the R enantiomer (69). 

Figure 22 Stereoselective tnins-esterification of aryloxypropionic acid methyl ester.

Azzolina, O., Collina, S., Ghislandi,V., Optical resolution of aryloxypropionic acids and their esters by HPLC on cellulose tris-3,5-dimethyl-triphenyl carbamate... 

The catalyst Cu/(S S,S)-23a was also efficient for the insertion of O—H bonds of phenols (Scheme 44) [109], Under similar conditions as that for N—H insertion reactions, a wide range of phenol derivatives underwent O—H bond insertion with a-diazopropionates, providing a-aryloxypropionates with excellent enantioselectivities (95-99.6% ee). The Pd/(S, S,5 )-23a-catalyzed asymmetric O—H bond insertion reaction between a-aryl-a-diazoacetates and phenols provided the first enantioselective method for the preparation of chiral a-aryloxy-a-arylacetates, which are ubiquitous in biologically active molecules (Scheme 45) [110]. 

Other nucleophiles react with equal facility with 189 [72] (Scheme 28). Phenols furnish (/ )-2-aryloxypropionates (199) in high yield. Even protected sugar derivatives displace the triflate group to afford muramic acid analogs [73]. Potassium salts of alkyl or aryl carboxylic acids produce (i )-lactates (200) and mercaptans give (i )-thiolactates (201) [72]. 

B.Blessington et al.. Proposed primary reference methods for the determination of some commercially important chiral aryloxypropionate herbicides in both free acid and ester forms, J. Chromatogr., 483(1989)349. 

Enantioselective Inhibition of Lipases. The addition of weak chiral bases such as amines or aminoalcohols has been found to have a strong influence on the selectivity of Candida rugosa [288] and Pseudomonas sp. lipase [494]. The principle of this selectivity enhancement was elaborated as early as 1930 [495]. As shown in Scheme 2.72, the resolution of 2-aryloxypropionates by CRL proceeds with low to moderate selectivity in aqueous buffer alone. The addition of chiral bases of the morphinan-type to the medium led to a significant improvement of about one order of magnitude. 

For organisms which express both pathways for nitrile hydrolysis, the stereochemical pathways can be very complex. The latter is illustrated by the microbial resolution of cx-aryl-substituted propionitriles using a Rhodococcus butanica strain (Scheme 2.109) [697]. Formation of the natural L-acid and the o-amide indicates the presence of an L-specific amidase and a nonspecific nitrile hydratase. However, the occurrence of the (5)-nitrile in case of Ibuprofen (R = i-Bu, e.e. 73%) proves the enantioselectivity of the nitrile hydratase [694]. In a related approach, Brevibacter-ium imperiale was used for the resolution of structurally related a-aryloxypropionic nitriles [698]. 

Padiglioni, P., Polcaro, C.M., Marchese, S., Sinibaldi, M. and Flieger, M. (1996) Enantiomeric separation of halogen-substituted 2-aryloxypropionic acids by high-performance liquid chromatography on a terguride-based chiral stationary phase. /. Chromatogr. A, 756, 119-127. 

Fenoxaprop Aryloxypropionate Acetyl CoA carbox-ylase (ACCase) Inhibition of acetyl CoA carbox-ylase in fatty acid synthesis pathway 1984 Post- em gence Cereals Grasses, 200-500... 

Figure 30 Synthesis of (R)-2-aryloxypropionic acids from the corresponding racemic nitriles by an (R)-specific amidase from Brevibacterium imperiale B222.

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