Fluopicolide | Fungicides | Anti-oomycetes | Cellular Delocalization of Spectrin-like Protein(s)

Fluopicolide [2,6-Dichloro-N-{[3-chloro-5-(trifluoromethyl)-2- pyridinyl]methyl}benzamide] is an oomycete-specific fungicide with a novel mode of action. Fluopicolide has both systemic and translaminar activities. Chemically it is a member of acylpicolides chemical class of fungicides, and blessed with a high antifungal activity against a broad spectrum of Oomycetes, such as Phytophthora infestans, Plasmopora viticola, and various Pythium species [1, 2].

Fluopicolide: 2D and 3D Structure

It shows no cross-resistance to other commercially anti-Oomycete fungicides, and can inhibit the development of strains that are resistant to phenylamides, strobilurins, or dimethomorph, and iprovalicarb. Fluopicolide exhibits excellent activity against oomycetes in vivo as well as antifungal activity in vitro; indeed, the ability is related to its translocation toward the stem tips via the xylem.

The activity of Fluopicolide is expected to be via a mechanism of cellular delocalization of spectrin-like protein(s) in oomycetes, from the plasma membrane to the cytoplasm.

Mechanism for Activity

Oomycota or oomycetes form a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms. Even if oomycetes seem to share some morphological, physiological and biochemical features with fungi, they are phylogenetically distant. They are filamentous, microscopic, absorptive organisms that reproduce both sexually and asexually. Oomycetes occupy both saprophytic and pathogenic lifestyles, and include some of the most notorious pathogens of plants, causing devastating diseases such as late blight of potato and sudden oak death.

Fluopicolide affects several stages of the life cycle of the different Oomycetes studied, such as the release and the motility of zoospores, the germination of cysts, the growth of the mycelium, and sporulation.

The rapidly induced effects of fluopicolide led to the investigation in greater detail of proteins known to be associated with the cytoskeleton. Fluopicolide does not inhibit respiration, has no direct effect on membrane composition, and does not significantly alter tubulin polymerization or the tubulin and actin contents of the cell.

One such candidate here was spectrin, which is known to play a crucial role in membrane stability by anchoring to other cytoskeletal proteins in animal cells. Upon Fluopicolide treatment, a complete loss of plasma membrane localization of these spectrin-like protein(s) was observed, such that they became distributed as spherical spots in the cytoplasm of the hyphae cells. The kinetics of this effect revealed that such spectrin-like protein delocalization occurred very rapidly, within 3 min of Fluopicolide treatment. Notably, such delocalization was maintained with longer treatment times. Clearly, the action of Fluopicolide was to induce a cellular delocalization of spectrin-like protein(s), from the plasma membrane to the cytoplasm.

Developer

Flucopicolide was discovered by Aventis Cropscience, which later became Bayer Cropscience. Bayer launched this unique fungicide in 2006, and as of 2007, Flucopicolide was only available commercially as a co-formulation with Fosetyl-Al for use in vines (as Profiler) and as a co-formulation with propamocarb for use on potatoes and vegetables (as Infinito).

Reported Activities for Fluopicolide

Fluopicolide, when applied to the zoospores of P. infestan at a concentration of only 1 µg/ml, caused the zoospores to stop swimming within 1 min; the zoospores subsequently swelled and burst within a few minutes.

In vitro, Fluopicolide strongly inhibited the mycelial growth of P. infestans, with an 80% inhibition being observed at a concentration as low as 0.1 µg/ml over four to seven days.

A publication in 2012 [1], quoted the following crops and pathogens on which Fluopicolide has been tested successfully:

Potato (Phytophthora infestans)  

Tomato (Phytophthora infestans)

Peppers (Phytophthora capsici)  

Leek (Phytophthora porri)   

Vines (Plasmopara viticola)

Brassicas (Peronospora parasitica)      

Tobacco (Peronospora tabacina)

Cucurbits (Pseudoperonospora cubensis)    

Lettuce (Bremia lactucae)   

Roses (Peronospora sparsa)       

Activities for Fluopicolide

%Inhibition (mycelial growth of P. infestans @ 0.1 ug/ml Fluopicolide) = 80%

Summary

Common name: Fluopicolide; AE C638206; AEC638206; AE-C638206

Trademarks: Profiler; Infinito

Molecular Formula: C14H8Cl3F3N2O

CAS Registry Number: 330459-31-9

CAS Name: 2,6-Dichloro-N-{[3-chloro-5-(trifluoromethyl)- 2-pyridinyl]methyl}benzamide

Molecular Weight: 383.58

SMILES: O=C(NCC1=NC=C(C(F)(F)F)C=C1Cl)C2=C(Cl)C=CC=C2Cl

InChI Key: GBOYJIHYACSLGN-UHFFFAOYSA-N

InChI: InChI=1S/C14H8Cl3F3N2O/c15-8-2-1-3-9(16)12(8)13(23)22-6-11-10(17)4-7(5-21-11)14(18,19)20/h1-5H,6H2,(H,22,23)

Mechanism of Action: Cellular Delocalization of Spectrin-like Protein(s)

Activity: Anti-oomycetes; Fungicides

Status: Launched 2006

Chemical Class: Amides; Small-molecules; Benzene containing; Pyridines; Acylpicolides; Fluoro containing; Chloro containing; Trifluoro molecules

Originator: Aventis Cropscience/Bayer Cropscience

Fluopicolide Synthesis

US6828441B2: The patent reports synthesis for Fluopicolide and derivatives. The process appears to be an industrial one. Yields are not disclosed.

Ethyl 2-(3-chloro-5-trifluoromethyl-2-pyridyl)glycinate: To a stirred solution of sodium hydride (0.445 g) in dry dimethylformamide (4 ml) at 0° C. was added ethyl N-(diphenylmethylene)glycinate (1.485 g) in dry dimethylformamide (3 ml) and stirring was continued for 20 minutes. 2,3-Dichloro-5-(trifluoromethyl)pyridine (1.58 g) in dry dimethylformamide (4 ml) was then added dropwise over 10 mins at 5° C. and the reaction mixture was stirred for 2 hours at room temperature. 2M hydrochloric acid (25 ml) was added and stirring continued for 2 hours. The solution was washed with diethyl ether and the layers were separated. The aqueous phase was neutralised with saturated aqueous sodium bicarbonate and extracted with ethyl acetate. The combined ethyl acetate layers were washed with brine (×2), dried (MgSO₄), filtered and the solvent removed to leave a residue which was purified by silica gel chromatography eluting with ethyl acetate/light petroleum (40-60° C.) to give the title product.

(3-chloro-5-(trifluoromethyl)pyridin-2-yl)methanamine: A mixture of the product from stage a) (0.24 g) and 3M hydrochloric acid (20 ml) was heated under reflux for 4 hours. On cooling the mixture was washed with diethyl ether and the layers separated. Water was removed from the aqueous phase by azeotropic evaporation with toluene (×3) to give the title product.

A solution of (3-chloro-5-trifluoromethyl-2-pyridyl)methylamine (0.35 g) in dry ether (2 ml) was added to a solution of 2,6-Dichlorobenzoyl chloride (0.39 g) and triethylamine (0.27 ml) in dry ether (5 ml) and the mixture stirred overnight. Water (20 ml) and ethyl acetate (10 ml) were added and the organic phase was separated and washed with aqueous sodium hydrogen carbonate, dried and evaporated under reduced pressure. The residue was purified by silica gel chromatography to give Fluopicolide [2,6-Dichloro-N-{[3-chloro-5-(trifluoromethyl)- 2-pyridinyl]methyl}benzamide], m.p. 127-30° C.

Identifications:

1H NMR (Estimated) for Fluopicolide

Adverse Reports:

Available data suggest that Fluopicolide is free from issues related to carcinogenicity, mutagenicity and sensitization. Moreover, it has no embryotoxic and/or teratogenic potential.

Others:

Acute oral toxicity (rat) LD₅₀ = greater than 5000 mg/kg

Acute dermal toxicity (rat) LD₅₀ = greater than 5000 mg/kg

Bird (quail), acute oral, LD₅₀, = greater than 2250 mg/kg

Honeybee, contact, LD₅₀ = greater than100 ug per bee

The readers are welcome to share their views.

References:

1. Toquin, V.; et. al. Fluopicolide: A New Anti-Oomycetes Fungicide? Chap. 21: Modern Crop Protection Compounds, Second Edition. Wiley-VCH Verlag GmbH & Co. KGaA. 2012 (FMO only)

2. Moloney, B. A.; et. al. 2-pyridylmethylamine derivatives useful as fungicides. US6828441B2

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