Synthesis Of Curcumin Benzenesulfonate Analogues And Their Acaricidal Activity Against Tetranychus Cinnabarinus (Acari:Tetranychidae)

Curcumin is a natural polyphenol product that can be obtained from the rhizome of turmeric (Curcuma longa). Recent studies have shown that curcumin and its derivatives not only possessed anti-inflammatory, antioxidant and anticancer activities in pharmacological field, but also have good acaricidal activities against a wide range of agricultural pest mites. Therefore, we used curcumin as the leading compound for the synthesis of some novel curcumin benzenesulfonate analogues based on the preliminary studies of the pesticide research laboratory of natural products in southwest university, then choose the compound which has higher acaricidal activity as the original drug to prepare its microemulsion with a view to enhance its activity and develop a new highly effective acaricides of curcumin.1 The synthesis of curcumin-benzenesulfonate analoguesBased on the characters of the symmetric phenolic hydroxyl groups in curcumin molecular structure, seven curcumin-benzenesulfonate analogues have been synthesized with different benzenesulfonyl chloride analogues by the use of triethylamine and cupric oxide (CuO) as catalysts. The structure of the target products have been identified by the infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), elemental analysis (EA). Through the structural retrieval of Chemfinder and Chemical Abstracts, the synthetical derivatives of this research is belong to the new type of curcumin derivatives, and have not been reported previously.2 The acaricidal activity assessment of curcumin-benzenesulfonate analoguesThe acaricidal activity of curcumin-benzenesulfonate analogues against the nymphs, female adult mites and eggs of Tetranychus cinnabarinus was evaluated by slide dip method and leaf dip method with curcumin and 95% pyridaben as control. The results showed that the acaricidal activity of the synthetical derivatives against the nymphs, female adult mites of T. cinnabarinus was higher than that of curcumin 48 h after treatment with the benzenesulfonate analogues of fluorine substituted with an LC50 of 0.13624 mg/mL and 0.91611 mg/mL and benzene substituted with an LC50 of 0.12731 mg/mL and 0.77509 mg/mL as best. Although the acaricidal activity of the synthetic derivatives was lower compared with the 95% pyridaben (The LC50 values of 48 h after treatment against the nymphs and female adults of T. cinnabarinus were 0.02138 mg/mL and 0.03519 mg/mL, respectively.). Thus, we conclude that the biological activity of curcumin can be enhanced by the addition of benzenesulfonate groups into the curcumin molecule structure, and the phenolic hydroxyl structure is an important active site for curcumin. Meanwhile, it provides a new idea for the structural modification of curcumin by coupling the sulfonate groups into the curcumin molecule.3 The preparation of curcumin-4-Fluorobenzensulfonate microemulsion and its acaricidal activityTaking all factors into consideration, curcumin-4-fluorobenzensulfonate was selected as the original drug for the preparing of curcumin-4-fluorobenzensulfonate microemulsion by the method of pseudo-ternary phase diagrams combined with an orthogonal test analysis. The optimal prescription was listed as follows:The curcumin-4-fluorobenzensulfonate is 1.35 wt.%, DMF is 3.15 wt.%, glycerol is 6 wt.%, Termul-200 is 11.2 wt.%, SDBS is 2.8 wt.%, distilled water is 75.5 wt.%. Quality test results show that all the indicators of the prepared microemulsion reach the relevant stability criteria, and its stability pH range is 6.4 and 7.6. The acaricidal activity against the nymphs and female adults of T. cinnabarinus showes the LC50 value of 48h after treatment is 0.07627 mg/mL and 0.23191 mg/mL, and apparently improve the acaricidal activity of curcumin-4-fluorobenzensulfonate by 44.0% and 74.7%, respectively. Although the acaricidal activity of the prepared microemulsion is still lower compared with that of the 95% pyridaben, the fact that microemulsion formulation can significantly enhance the acaricidal activity of curcumin-4-fluorobenzensulfonate is a good result it provides a valuable idea for the development of curcumim and its derivatives in the future research.4 The greenhouse efficacy test of curcumin-4-Fluorobenzensulfonate microemulsionIn order to evaluate the practical effects of curcumin-4-Fluorobenzensulfonate microemulsion against T. cinnabarinus, the greenhouse efficacy test was used to determine the indoor control efficacy of curcumin-4-Fluorobenzensulfonate microemulsion against T. cinnabarinus, with a view to determine the optimal concentration for mite control and lay the foundation for the further field promotion. The results show that the prepared curcumin-4-Fluorobenzensulfonate microemulsion has a better control efficacy against T. cinnabarinus at the concentration of 54 mg/mL under the greenhouse condition, the dropping rate of insect will reach 70.55% 7 days after treatment, but the efficacy has shown a significant decline 15 days after treatment. Although this result was less satisfactory than Envidor at the concentration of 80 mg/mL with the dropping rate of insect of 93.89%, the adopted concentrations of the prepared microemulsion (54 mg/mL) is lower compared to Envidor (80 mg/mL). Therefore, we can enhance the effective content of curcumin-4-Fluorobenzensulfonate in the microemulsions through the improvement of the technological process, and the screening of some relavant pesticide adjuvants is expected to further enhance the control efficacy of microemulsions against T. cinnabarinus and extend the residual period of our prepared microemulsions.