Metalaxyl Explained

Metalaxyl is an acylalanine fungicide with systemic function.[1] Its chemical name is methyl N-(methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate. It can be used to control Pythium in a number of vegetable crops, and Phytophthora in peas. Metalaxyl-M is the ISO common name[2] and Ridomil Gold is the trade name for the optically pure (-) / D / R active stereoisomer, which is also known as mefenoxam.[3]

It is the active ingredient in the seed treatment agent Apron XL LS.[4]

The fungicide has suffered severe problems. The fungicide was marketed for use against Phytophthora infestans. However, in the summer of 1980, in the Republic of Ireland, the crop was devastated by a potato blight epidemic after a resistant race of the oomycete appeared.[5] Irish farmers later successfully sued the company for their losses.Maximum pesticide residue limits for the EU/UK are set at 0.5 mg/kg for oranges and 1.0 mg/kg for apples. As early as 1998 Pythium was known to be widely developing resistance to metalaxyl[6] which was the most effective control at the time. Various Pythium populations have been known to have resistance to mefenoxam since the 1980s and metalaxyl since 1984.[7] There is wide variability in resistance/sensitivity between Pythium species, with some populations showing complete ineffectiveness.

Synthesis

The first synthesis of metalaxyl was disclosed in patents filed by Ciba Geigy.[8]

2,6-Xylidine is alkylated with methyl 2-bromopropionate to give an alanine derivative. This is further reacted with the acid chloride of methoxyacetic acid to yield racemic metalaxyl.[8] [9] The homochiral, single-isomer version of the chemical, which retains all its fungicidal activity, has been manufactured.[10]

Notes and References

  1. Sukul. P. Spiteller. M. Metalaxyl: persistence, degradation, metabolism, and analytical methods.. Reviews of Environmental Contamination and Toxicology. 2000. 164. 1–26. 12587832.
  2. Web site: Compendium of Pesticide Common Names: metalaxyl . BCPC.
  3. Monkiedje. Adolphe. Spiteller. Michael. Effects of the phenylamide fungicides, mefenoxam and metalaxyl, on the microbiological properties of a sandy loam and a sandy clay soil. Biology and Fertility of Soils. 2002. 35. 6. 393–398. 10.1007/s00374-002-0485-1. 22642870.
  4. Web site: dead. bmz10s02.pdf. Government of Manitoba. https://web.archive.org/web/20070930171045/http://www.gov.mb.ca/agriculture/crops/vegetablecrops/pdf/bmz10s02.pdf. 2007-09-30.
  5. http://www.bspp.org.uk/bsppnews/bsppnews32/bsppnews32-3.htm Working on potato blight in Northern Ireland
  6. Web site: Survey of Pythium Isolates for Resistance to Subdue (metalaxyl) . . 2020-11-23.
  7. Sanders . P. L. . Failure of Metalaxyl to Control Pythium Blight on Turfgrass in Pennsylvania . . . 68 . 1 . 1984 . 0191-2917 . 10.1094/pd-68-776 . 776.
  8. GB . 1500581 . Substituted amides and their use as fungicides . patent . 1978-02-08 . 1974-04-09 . Ciba-Geigy AG.
  9. 10.1002/adsc.202100898 . Two-Step Continuous-Flow Synthesis of Fungicide Metalaxyl through Catalytic C−N Bond-Formation Processes . 2022 . Ishitani . Haruro . Yu . Zhibo . Ichitsuka . Tomohiro . Koumura . Nagatoshi . Onozawa . Shun-ya . Sato . Kazuhiko . Kobayashi . Shū . Advanced Synthesis & Catalysis . 364 . 18–23 .
  10. 10.1023/A:1019164928084 . 1997 . Blaser . Hans-Ulrich . Spindler . Felix . Enantioselective catalysis for agrochemicals. The case histories of (S)–metolachlor, (R)–metalaxyl and clozylacon . Topics in Catalysis . 4 . 3/4 . 275–282 .

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