Phenoxypropionate herbicides

The synthesis of phenoxypropionate herbicides form 2-halopropionic acids, based on the specific esterification of S-isomers with butanol catalyzed by porcine pancreatic lipase (Hasan et al. 2006)... 

Phenoxyalkanoics. The phenoxyalkanoic herbicide grouping is composed of two subgroups, the phenoxyacetic acids and the phenoxypropionic acids. The phenoxyacetic acid herbicides include some of the first commercially successhil herbicides, eg, 2,4-D. They continue to be widely used for foUar control of broadleaf weeds. The more heavily functionalized phenoxypropionic acid herbicides are relatively new herbicides compared to the phenoxyacetic acids and are used primarily for selective control of grassy weeds in broadleaf crops (2,296,297). 

Phenoxyalkanoates. There has been considerable interest in the persistence of chlorinated phenoxyalkanoates—and particularly of phenoxyacetates and phenoxypropionates, which have been used as herbicides. This has therefore stimulated studies on the degradation of these aryl-alkyl ethers. Considerable effort has been directed to elucidating the subsequent... 

Phenoxy herbicides, 10 520 Phenoxypropionic acid herbicides, 13 314 Phenoxy resins, 10 6, 364-365 Phentermine, 3 91... 

Guillaume, Y.C. et al.. Chiral discrimination of phenoxypropionic acid herbicides on teicoplanin phase effect of mobile phase modifier, Chromatographia, 55, 143, 2002. 

MTD and MTD approaches will be discussed and compared using QSAR of insecticidal benzoylphenyl-ureas, DDT-type analogs and benzylchrysanthemates, herbicidal benzonitriles and nitrophenols, and plant-growth regulating phenoxypropionic acids. 

Other herbicidal phenoxyacetic and phenoxypropionic acids have some properties similar to those of (2,4-dichlorophenoxy)acetic acid, but often have quite different species selectivity. Some of the differences can be explained on the basis of molecular stability, persistence, or mobility in the toxic form, as well as on the basis of differences in solubility and in absorption through leaves or roots. 

BASF (Ludwigshafen, Germany) produces isomerically pure (i )-2-(4-hydroxy-phenoxy)-propionic acid (HPOPS) from (P)-2-phenoxypropionic add (POPS) on a 100 m3 fermenter scale for use as a herbicide intermediate (Figure 7.30) (Cooper, 1990). 

The phenoxypropionic acid herbicides (Chapter 31) rely on an SN2 reaction to convert the S-2-chloropropionic acid (1) to the ff-2-aryloxy derivative 2.3 These compounds are also available from lactic acid by substitution reactions -lactic acid (3) requires two inversions, whereas S-lactate (4) only requires one (Schemes 22.2 and 22.3).4... 

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... 

Miiller, M.D. Buser, H.-R., Conversion reactions of various phenoxyalkanoic acid herbicides in soil. 1. Enantiomerization and enantioselective degradation of the chiral 2-phenoxypropionic acid herbicides Environ. Sci. Technol 1997, 31, 1953-1959. 

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). 

Guillaume et al. [30] studied the effect of pH on the chiral resolution of phenoxypropionic acid herbicides. 

The oxidation of phenols to catechols or hydroquinones by tyrosinase enzymes has been developed for biocatalysis. For example, the ortho-hydroxylation of L-tyrosine 162 (and also substituted variants) to give l-DOPA 163 has been extensively studied due to the importance of l-DOPA in the treatment of Parkinson s disease [92, 93]. An arene hydroxy lating enzyme having a broad substrate scope is 2-hydroxybiphenyl 3-monooxygenase from Pseudomonas azelaica, which is able to oxidize many ortho-substituted phenols 68 to the corresponding catechols 127 [94], as shown in Scheme 32.19. A notable example of an industrial biocatalytic arene hydroxylation that has been employed on very large scale (lOOm fermentation) is the pora-hydroxylation of R)-2-phenoxypropionic acid 164 by whole cells of Beauveria bassiana Lu 700 to give (R)-2-(4-hydroxyphenoxy)propionic acid 165, an important intermediate in herbicide manufacture [95]. 

To explain the inhibition of the incorporation of malonic acid into fatty acid in intact plants by the cyclohexane-1,3-diones (Burgstahler 1985) and aryloxy-phenoxypropionic acid-herbicides (Hoppe and Zacher 1982), we suggest the action of a malonate and/or malony1-CoA decarboxylase, able to catalyze the formation of acetate/acetyl-CoA, substrates the incorporation of which into fatty acids can then be blocked by these herbicides. Our model is summarized in Figure 4. 

Hoppe, H.H. and Zacher, H., 1985. Inhibition of fatty acid biosynthesis in isolated bean and maize chloroplasts by herbicidal phenoxy-phenoxypropionic acid derivatives and structurally related compounds. Pestic. Biochem. Physiol. 298-305. 

The selective grass herbicides of the phenoxypropionic acid type and the cyclohexanedione type, which were developed to kill Gramineae weeds in dicotyledonous crop plants, inhibit de novo fatty-acid synthesis [7]. Plastidic ACCase has been identified as the target of these herbicides [7], but it is not known whether the prokaryote form of the enzyme is inhibited in vitro by the herbicides... 

Nonspecific disruption of membrane permeability was proposed for difenopenten-ethyl ethyl 4-[(4-trifluoromethyl)phenoxyl-2-pentanoate, which uncoupled and inhibited respiration in corn and soybean mitochondria. This was considered to be a secondary effect of this aryloxy-phenoxypropionate analogue (see Chapter 3) due to the relatively high in vitro concentration. A similar conclusion was made for another aryl-oxyphenoxypropionate, diclofop, which uncoupled state 4 respiration, inhibited state 3 respiration, and caused swelling of isolated wheat and wild oat mitochondria. The inhibition of respiration was proposed to be due to an effect prior to the electron transport chain, that is, an effect on succinate or malate dehydrogenase. A potent inhibition of state 3 respiration was also reported for the herbicide UK J72J (2-ethylamino-4-amino-5-thiomethyl-6-chloropyrimidine), with succinate as substrate.Difenzoquat also inhibits state 3 respiration in isolated wheat and wild oat mitochondria however, this was not thought to be a significant contribution to the chlorotic contact symptoms observed with this translocated herbicide. Difenzoquat also possesses a weak bipyridinium-type PSI electron acceptor activity which causes chlorosis. ... 

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