Synthesis And Insecticidal Activity Of Pogostone

ObjectivesPogostemonis Herba is the dried aerial part of Pogostemon cablin (Blanco) Benth.(Labiatae), commonly known as’Guang-Huo-Xiang’ in Chinese. It has been traditionally used in Chinese medicine to resolve dampness, whet appetite, arrest vomiting, release the exterior and expel summer-dampness. Pogostemonis Herba is a common Chinese herbal medicine frequently used to treat for common cold, nausea, diarrhea, rhinitis, headaches and fever.Moreover, patchouli oil, the essential oil of Pogostemonis Herba, is also used in cosmetics, deodorants and insecticides. Pogostone is one of the main effective components of Pogostemon cablin (Blanco) Benth.. In vitro experiments indicated that pogostone significantly inhibited Candida albicans, Cryptococcus neoformans, Rhizopus fungi. The literature search discovered that the analogues and hydrolysates had effective insecticidal activities.Essential oil of Pogostemon cablin (Blanco) Benth. has been reported to exhibit strong insecticidal activities, but few studies have focused on the insecticidal activity of its main individual constituent, pogostone. In addition, we have explored two synthesis methods of pogostone without optimized synthesis process. The goal of this research was to optimize the synthesis of pogostone and investigate the insecticidal activity of pogostone against two harmful noctuid insects, Spodoptera litura (Fabricius) and Spodoptera exigua (Hubner).Method1This study was to improve a novel synthetic method (Route three) of pogostone base on the previous method.Synthetic route one:DHA was applied to react with isobutyraldehyde in the dry THF solution added with diethylamine for the intermediate. Then catalytic hydrogenated the intermediate to prepare pogostone.Synthetic route two:In the presence of DMAP and DCC,4-hydroxy-6-methyl-2-pyrone was applied to react with Isobutylacetic acid in the toluene.Synthetic route three:The reaction principle was the same as route two. Isobutylacetic acid was applied to react with thionyl chloride for the preparation of the acyl chloride of isobutylacetic acid. Then take4-hydroxy-6-methyl-2-pyrone as reactants to react with the acyl chloride in the trifluoroacetic acid to prepare pogostone.2The optimum synthesis technology was explored by controlling the different material ratio as well as temperature and time, with the perpendicular experimental method.3The activities of pogostone against lepidopterous insect pests was preliminary investigated in laboratory, and the determined activities were as follow:antifeedant, larvicidal (oral toxicity and contact toxicity), growth-inhibition (larvae-pupae-adults) and ovicidal activity.ResultsThis study improved a novel synthetic method of pogotone with the following advantages:simple steps, low cost, targets easy to get and high conversion rate. The optimum synthesis conditions were:(1) The mole ratio of4-hydroxy-6-methyl-2-pyrone and Isobutylacetic acid was1:1.5;(2) The second step reaction temperatue was about70℃;(3) The second step reaction time was about4h. The product purity measured by HPLC and yield were97.87%and71.54%respectively.In a no-choice assay, PO exhibited strong antifeedant activity against S. litura and S. exigua. PO showed pronounced larvicidal activities, including oral toxicity (LC50986.88mg L-1and545.61mg L-1respectively) and contact toxicity (LC501041.42mg L-1and519.48mg L-1respectively) against these two noctuid insects. Additionally, PO treatment significantly increased the larval and pupal developmental period. Furthermore, PO showed moderate ovicidal activities and influenced the emergence and deformity of the moth. However, PO failed to exert a potent effect on adult development. These tested parameters proved to be dose dependent for both insect species.ConclusionNovel synthetic route3has the following advantages, such as simple steps,low cost,targets easy to get and high conversion rate. And the process was further optimized, thus it can be used as the industrial production of pogostone. Pogostone possesses strong insecticidal activities, especially antifeedant, larvicidal, growth inhibitory and pupicidal activities, against S. litura and S. exigua. Pogostone may partly account for the insecticidal activity of patchouli oil and may be a promising candidate for the control of agricultural insects.