A New Insecticidal Sesquiterpene Ester from Celastrus Angulatus

A new sesquiterpene polyol ester with a β-dihydroagarofuran skeleton, NW37 (1), and three known compounds NW13 (2), NW16 (3) and NW35 (4) were isolated by bioassay-guided fractionation from the highly polar MeOH extracts of the root bark of Celastrus angulatus. Their chemical structures were elucidated mainly by analyses of MS and NMR spectral data. The insecticidal activity of compound 1 against 4th instar Mythimna separata larvae with a KD50 value of 252.3 μg·g-1 was demonstrated.

Celastrus angulatus, a plant of the this family, is widely distributed in China and used for the treatment of rheumatism in traditional Chinese medicine and as an insecticide [11,12].In our previous studies, some antifeedant, narcotic, and insecticidal ingredients were isolated from the toluene extracts of the root bark of C. angulatus.To obtain a sufficient number of compounds for QSAR research on their insecticidal activity against Mythimna separata, the chemical constituents from the root bark of C. angulatus were re-investigated guided by activity-guided fractionation.These studies have led to the isolation of a novel sesquiterpene polyol ester NW37 (1).In this paper, the isolation, structure elucidation and insecticidal activity of compound 1 were presented.

Plant material
The root bark of C. angulatus was collected in Qinling mountain, Taibai County, Shaanxi Province, People's Republic of China, in October 2007, authenticated by Dr. Hua Yi of the College of Life Sciences, Northwest Agricultural & Forestry University, and dried in the shade (at room temperature).Voucher specimens (samples no.NWAU2007-A18) were deposited at the College of Plant Protection, Northwest Agricultural & Forestry University.

Insecticidal activity
Toxic leaf discs of known area were treated with known amounts of the test samples dissolved in acetone (acetone and celangulin V were used as negative and positive control).The 4 th instar larvae of M. separata were fed with the discs for 12 h (repeated 10 times for each sample).After 24 h, the numbers of knocked-down larvae (symptoms: the larvae were narcotized and could not move; the bodies were immobilized and very soft; and the response disappeared completely) were recorded, and the toxicity was ascertained by estimating the median knock-down dose (KD 50 value) of the test sample [14].

Figure 3 .
Figure 3.The structures of celangulatin C, celangulatin F and angulatin A.

Table 1 .
The NMR data of compound 1.

Table 2 .
The KD 50 data of 1~4 and other compounds.