Study On The Isolation, Identification And Inseeticidal Activity Of Alkaloids From Cynanchum Komarovii

Cynanchum komarovii belongs to the family of Asclepiadaceae. It is mainly distributed in Ningxia, Gansu, Shanxi, Inner Mongolia and Qinghai provinces of China. In recent years, the researches on. the chemical constituents and biological activity of Cynanchum komarovii have been reported, however, the studies on the insecticidal activities of Cynanchum komarovii have been mainly focused on the crude extract or total alkaloid. There is no information about the insecticidal activities of monomeric alkaloids. The present study was to isolate the active alkaloid constituents responsible for the insecticidal activity of Cynanchum komarovii. We selected the high insecticidal part of tatal alkaloids in Cynanchum komarovii for the screening of active substance with bioassay-guided fractionation approach. The insecticidal activities of the isolated monomeric alkaloid against Plutella xylostella and Wolfberry aphis were examined and compared with that of total alkaloid. In addition, the relationship between structures and insecticidal activity of alkaloids from Cynanchum komarovii were analyzed. The obtained main conclusions were as follows:1. Extraction of alkaloids from Cynanchum komaroviiOn the basis of single factor experiment, the technological parameters of ultrasound-assisted extraction of total alkaloid from Cynanchum komarovii were optimized by the orthogonal test program. The optimal conditions of ultrasound-assisted extraction were determined as follows: ethanol concentration was70%(v), ratio of material to liquid was1:25(g/mL), ultrasound-assisted extraction time was50min and extraction temperature was60℃. Under these conditions, the yield of crude alkaloid was0.3741%. The sequence of the effect of different factors on extraction yield was: ethanol concentration>ratio of material to liquid> extraction temperature> ultrasonic time.2. Insecticidal activity of alkaloids from the aerial and underground parts of Cynanchum komaroviiThe insecticidal activity of alkaloids from the aerial and underground parts of Cynanchum komarovii against Plutella xylostella and Wolfberry aphis was compared. The results indicated that the alkaloids from the different parts of Cynanchum komarovii displayed pronounced contact toxicity activity against Plutella xylostella and Wolfberry aphis. The alkaloids from the underground parts was little weak than it from the aerial parts of Cynanchum komarovii in insecticidal activity.3. Isolation and identification of the insecticidal constituents of alkaloids from Cynanchum komaroviiBased on column chromatography separation and bioassay-guided trace, three insecticidal constituents were obtained (named alkaloid1, alkaloid2and alkaloid3), and their structures were determined by the analysis of ESI-MS, IR,1H-NMR,13C-NMR and DEPT spectra and comparison with the available published data which were identified to be antofine,6-O-desmethylantofine and6-O-desmethylsecoantofine, respectively.4. Insecticidal activities of alkaloids from Cynanchum komarovii and analysis of structure-activity relationshipThe insecticidal activities and action mode of the isolated monomeric alkaloid against Plutella xylostella and Wolfbery aphis were tested by different methods and compared with that of total alkaloid. The results indicated that these three alkaloids exhibited obvious antifeedant, contact toxicity and growth inhibition activity against Plutella xylostella. Compared to the antifeedant, contact toxicity and growth inhibition activity, the alkaloids1,2and3revealed weak feeding toxicity. Comparing the insecticidal activities of these compounds with that of the total alkaloids of Cynanchum komarovii revealed that the isolated alkaloids were less toxic than the total alkaloids. This suggests that maybe there are other insecticidal components in the total alkaloid fractions, which were not isolated in this study. The insecticidal activity of total alkaloids should be attributed to the synergistic effect of alkaloid1,2and other components present in the mixture.The analysis on the structure-activity relationships of alkaloids have concluded that the phenanthrene ring is important for keeping excellent insecticidal activity and the substituent at the C-6position of phenanthroindolizidine alkaloids is important in determining activity.