Drug – bio-affecting and body treating compositions – Designated organic active ingredient containing – Ester doai
Reexamination Certificate
1998-10-19
2001-05-08
Kumar, Shailendra (Department: 1621)
Drug, bio-affecting and body treating compositions
Designated organic active ingredient containing
Ester doai
C514S535000, C514S536000, C560S043000
Reexamination Certificate
active
06228884
ABSTRACT:
The present invention relates to a novel method of controlling and preventing Oomycete infection of plants by using metalaxyl, furalaxyl or benalaxyl, hereinbelow termed active ingredient I, in each case with an R-enantiomer content of over 70% by weight, and to suitable fungicidal compositions for this purpose.
Metalaxyl was the first commercially available preparation from the series of the class of active ingredients originally termed acylalanines, later phenylamides, which are outstandingly active against Oomycetes. The Oomycetes include all downy mildews, which attack mainly potatoes, tomatoes, vines, hops, maize, sugar beet, tobacco, vegetables, lettuce, but also bananas, rubber, as well as lawns and ornamentals.
The preferred application of the acylalanine fungicides is foliar application, the foliage and the growing plant being treated with the active ingredient. Some of the active ingredient is taken up by the plant, but some remains on the plant and is washed off by the rain or otherwise taken up by the soil due to leaf drop or time of maturation. In the case of soil application, the active ingredient is incorporated into the soil directly by applying it in liquid form, or, for example, by means of granules.
A disadvantage in this context is the slow degradation rate of the representatives of this substance class in the soil, which depends largely on whether the soils are humous soils, mixed sandy/loamy soils or strongly adsorptive soils (loam/clay). In the case of prolonged treatment periods, on the one hand in perennial crops, such as grapevines, on the other in typical soil crops, such as potatoes, sugar beet or lawns, the soils may be subjected to cumulative loading with acylalanine fungicides, which, in turn, are an environmental hazard, but in particular a groundwater hazard.
Metalaxyl is N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-DL-alanine methyl ester.
Benalaxyl is N-(2,6-dimethylphenyl)-N-(phenylacetyl)-DL-alanine methyl ester.
Furalaxyl is N-(2,6dimethylphenyl)-N-(2-furanylcarbonyl)-DL-alanine methyl ester.
The compounds are known from the literature. The degradation data given vary. The reference book “The Pesticide Manual”, 10th Edition 1994, edited by the British Crop Protection Council, gives the following information on the hydrolytic half-lives of these products. (DT=disappearance time).
Metalaxyl:
DT-50 (20° C.)
pH1:
>200 d
pH9:
115 d
Benalaxyl:
DT-50
pH9.25:
86 d
Furalaxyl:
DT-50 (20° C.)
pH1:
>200 d
pH9:
>200 d
These data show an undesirably high stability in the aqueous medium.
Attempts were made to accelerate the degradation behaviour by means of suitable formulations, for example by means of hydrophobic additives which prevent deeper penetration of the active ingredient into the soil and expose it on the surface to the incidence of sunlight and to elevated temperatures. It was attempted to exploit a further disadvantageous property of the acylalanine fungicides, namely their high volatility, which is a nuisance under the effect of sun and high temperatures. It would have been expected that the volatility of the active ingredient on the soil surface would be equally high, a fact which has not been observed in practice.
All these attempts have not resulted in convincing solutions. Once the active ingredient is adsorbed by the soil surface, even only within the uppermost 2 cm, degradation is reduced drastically, which entails all the adverse consequences of sparingly degradable active ingredients which the expert is familiar with.
Entirely surprisingly, it has now been found that the solution of this problem is found in the acylalanine active ingredient itself, in which the R-enantiomer is, unexpectedly, degraded more rapidly than the S-enantiomer or than the commercially available active ingredients which are based on the racemates in question. Since 1975, which is when this substance class became known, one has been familiar with the fact that it is the R-enantiomer anyway which is the more fungicidally active ingredient (cf e.g. GB-1 500 581).
As a solution for practical use, the literature has never seriously proposed, in 19 years, the allegedly adjacent solution of using, from the start, the respective R-enantiomer of an acylalanine fungicide. On the one hand, one must not underestimate the technological difficulties of preparing an R-enantiomer in pure form or an active substance enriched with R-enantiomer (for example fractional crystallization of the racemate or stereospecific synthesis), on the other hand there was no incentive and no technological necessity for the practitioner for acting in such a way. However, the decisive factor is this. It could not have been assumed that a reduction or complete elimination of the proportion of S-enantiomer in the racemate would solve the problem of the unduly long residence time of the active ingredient in the soil. As yet, no R-enantiomers, or R-enantiomer-enriched racemates, of acylalanine fungicides have been put on the market. With respect to the overall ecological situation of the otherwise effective control of downy mildews (Oomycetes) with acylalanine fungicides, in particular with metalaxyl, the solution of the degradation problem proposed herein is of decisive technological importance in agricultural practice worldwide. It is a standard demand in crop protection to achieve an optimal effect with an active ingredient at the lowest dosage rate required while simultaneously keeping the pollution of the environment as low as possible.
In the field of the acylalanine fungicides, in particular in the case of its main representative, metalaxyl, this problem can be considered as solved. An evidently better biodegradability in the soil is achieved if the content of R-enantiomer in the active ingredient is over 70% by weight.
REFERENCES:
patent: 4151299 (1979-04-01), Hubele
patent: 5723491 (1998-03-01), Nuninger et al.
patent: 1448810 (1976-09-01), None
Fisher and Hayes, Crop Protection, 1985, 4 (4), pp. 501-510.
Gozzo et al., Pesticide Science, vol. 16, No. 3, Jun. 1985.
Schwinn et al., Abhandlungen dder Akademie der Wissenschaft der DDR, vol. 1982, No. 1, 123-133, (1983).
Moser, H.; Vogel, C; (1978). Preparation and Biological Activity of the Enantiomers of CGA48988, a New Systemic Fungicide. Fourth International Congress of Pesticide Chemistry (IUPAC), Zurich, Jul. 24-28, 1978. Abstract vol. II, p. 310.
Ellgehausen Holm
Goggin John Edward Nicholas
Nuninger Cosima
Sozzi Dino
Kumar Shailendra
Syngenta Investment Corporation
Teoli, Jr. William A.
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