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| Names | |
|---|---|
| IUPAC name 2,2,4,4-Tetramethyl-6-(3-methylbutanoyl)cyclohexane-1,3,5-trione | |
| Other names Isovaleroylsyncarpic acid; 6-Isovaleroyl-2,2,4,4-tetramethyl-1,3,5-cyclohexanetrione | |
| Identifiers | |
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3D model (JSmol) | |
| ChemSpider |
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| UNII | |
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| Properties | |
| C15H22O4 | |
| Molar mass | 266.337 g·mol−1 |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Leptospermone is achemical compound (a β-triketone) produced by some members of the myrtle family (Myrtaceae), such asCallistemon citrinus (Lemon Bottlebrush), a shrub native to Australia, andLeptospermum scoparium (Manuka), a New Zealand tree from which it gets its name.[1] Modification of thisallelopathic chemical to producemesotrione led to the commercialization of derivative compounds asHPPD inhibitorherbicides.
Leptospermone was first identified in 1927 and was extracted from a variety of plants in 1965, 1966 and 1968. It was first identified as a chemical inCallistemon citrinus in California in 1977. A biologist at the Western Research Centre of Stauffer Chemical Company noticed that very few plants grew underCallistemon citrinus bushes. After taking soil samples and creating an array of extracts, one was identified as an herbicide. While it did have herbicidal effects, the rate required for sufficient coverage was too high to be of practical use.[2]
Leptospermone was optimized into thousands of compounds. Several were extremely effective but were too toxic, environmentally persistent or not selective enough. There are now several members of the triketone class ofHPPD inhibitor herbicides on the market.[3][4]
Leptospermone can be synthesized fromphloroglucinol by a reaction with 3-methylbutanenitrile (isovaleronitrile) in the presence of azinc chloride catalyst. Phloroisovalerone imine is produced which is thenalkylated withiodomethane after initial treatment withsodium ethoxide and methanol to produce an intermediate which is treated withaqueous hydrochloric acid resulting in isovaleroylsyncarpic acid (leptospermone).[5]
Biochemically, the plants take a different approach. Despite the fact that the biochemical synthesis has not been specifically investigated, it is clear that leptospermone is not an oxidizedterpene (or specifically asesquiterpene,ei. C15) as the cyclisation offarnesyl pyrophosphate cannot produce two dimethylate carbons that are separated by a single carbon nor would this be consistent with the natural occurrence of similar compounds with different keto-aryl side-chains in the members of theMyrtaceae (eg. flavesone, papuanone, isoleptospermone and grandiflorone[1]). Phloroglucinol is biosynthesized in a single step from malonyl-CoA[6] and could be the intermediate, but other routes of biosynthesis may be possible, such as viaisobutyryl-CoA, the result of the decarboxylative condensation of ketoisovalerate (ketone form ofvaline) (cf.polyketides).
Leptospermone was the blueprint for the compoundmesotrione which has the trade nameCallisto, aSyngenta herbicide.[4]
