A-phenoxypropionic acids

The range of action of a-phenoxypropionic acids differs from that of phenoxyacetic acids, as was established by Luckwill and Lloyd-Jones (1960). They assumed that decarboxylation causing the detoxication of the molecule is inhibited in certain plant species because of the a-methyl substitution, and that this kills the weeds resistant to phenoxyacetic acids (Fawcett et al., 1953 Lush and Leafe, 1956). Leafe (1962) found that Galium aparine (cleavers), resistant to MCPA, is killed by... 

Dichlorprop is prepared by the condensation of 2,4 dichlorophenol and a-chloropropionic acid, or by the chlorination of a-phenoxypropionic acid. The technical product is a 1 1 mixture of the biologically active dextrorotatory ( +) isomer and the biologically inactive levorotatory (-) isomer. Its biological action was first reported by Zimmermann and Hitchcock (1944), but it was only introduced in 1961. 

With regard to the resolution of enantiomers, some applications can be found with modified silica gel supports. Thus, a Pirkle-type CSP was used for the separation of 200 mg of a racemic benzodiazepinone [75]. Also tris-(3,5-dimethylphenyl)carba-mate of cellulose coated on silica [91, 92] was applied successfully to the resolution of the enantiomers of 2-phenoxypropionic acid and to oxprenolol, alprenolol, propranolol among other basic drugs. However, the low efficiency of this technique and the relative high price of the CSPs limits its use to the resolution of milligram range of sample. 

Another example of the use of the MTD and MTD approaches can be found in a series of optically active o-phenoxypropionic acids with auxin-like activity, partly published in ( ). The R-stereo isomers are much more active than the S-analoges. Both series were analyzed by Lien et al. (10) and a correlation with ir, a and the Van der Waals volume was found. The Pfeiffer rule is explained in terms of different structural requirements for the substituents as measured by and van der Waals volume. Analysing the series using STERIMOL delivered equations containing too many parameters. In Table III the equations are given as a result of... 

Figure 6. Standards used in Equation 13 (left) and in Equation 17 (right) to obtain MTD values in a series of stereo isomers of phenoxypropionic acids.

Fluazifop-butyl (26) (78BEP865137) is a promising heterocyclic representative of a new group of phenoxypropionic acids that are not auxin mimics. 

Phenoxypropionic acid (249.0 g, 1.50 mol) is dissolved in four equivalents of thionyl chloride (438.0 ml, 6.0 mol) and heated to reflux until the HCI evolution has ceased. The solution is then cooled to room temperature and concentrated under reduced pressure to give 281.0 g (100% yield) of phenoxypropionyl chloride as a brown oil which solidifies on cooling. 

Phenoxypropionic acid herbicides contain a stereogenic center that can be derived from 2-chloro-propionic acid and include fluazifop-butyl (29) and flamprop (30).245... 

The fragmentation pathways for the methyl esters are strongly dependent on the type of acid, i.e. whether a derivative of phenoxyacetic acid, phen-oxypropionic acid, or phenoxybutyric acid, and on the nature of the substitution of the aromatic ring. The methyl esters of chlorinated phenoxyacetic and phenoxypropionic acids show reasonably abundant molecular ions (about 20% relative to the base peak) which, together with the chlorine isotope patterns, permit easy identification of these compounds. In contrast, the spectra of the methyl esters of chlorinated phenoxybutyric acids are dominated by the fragment ion at m/z 101, with only low abundance of molecular ions. However, the spectra also show... 

Two groups of chiral aromatic carboxylic acids are important commercial intermediates for the agricultural and pharmaceutical industries. The R enantiomer of a-phenoxypropionic adds confers biological activity for a number of herbiddes. The S enantiomer of a variety of arylpropionic adds is the biologically active form of the nonsteroidal antiinflammatory products labeled profens. Racemic mixtures of the alkyl esters of these propionic add derivatives have been effectiwly resolved to yield the desired optically active carboxylic acids (64-66). Figure 20 shows examples of the resolution of aromatic propionic acid esters. 

Stereoselective dehalogenation of 2-haloaIkanoic acids has been demonstrated for a number of halidohydrolases (80-82). Figure 77 details the production of an L-haloacid intermediate used in the production of phen-oxypropionic acid herbicides. The R enantiomer of chloropropionic acid is selectively hydrolyzed to (S)-lactic acid due to an inversion of configuration that occurs during the hydrolysis (83). (S)-2-chloroproprionic acid is used as a chiral synthon to produce a number of (R)-phenoxypropionic acid herbicides, for example, Fusilade 2000 (ICI). 

Hermansson, J. Erikson, M. Direct liquid chromatographic resolution of acidic drugs using a chiral al-acid glycoprotein column (Enantiopac). J.Liq.Chromatogr., 1986, 9, 621-639 [chiral also bendroflu-methiazide, disopyramide, ethotoin, hexobarbital, ketoprofen, naproxen, 2-phenoxypropionic acid, RAC 109]... 

An example of the effect of pH on the separation of the enantiomers of 2-phenoxypropionic acid is shown by the chromatograms in figure 8.2. It is seen that both the absolute retention and the chiral selectivity increases as the pH is reduced and that a pH change of only 2 units, results in a switch from the enantiomers being coincidentally eluted, to their being eluted with a very large separation factor. This indicates that the... 

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