Bioactive Constituents of Conyza Albida

Abstract

Alkynes and spathulenol were isolated from Conyza albida (Asteraceae); some of the compounds were lethal against Artemia sp. and cytotoxic against KB cells.

Introduction

Conyza albida Willd. ex Sprengel (Compositae) is a species growing in Argentina. Formerly, it was included as a synonym of C. bonariensis var. microcephala Cabr., but, there is enough evidence to consider it a valid entity at species level [1].

Conyza albida is reported to have expectorant, antitussive, and antiinflamatory activities [2,3]. Since C. albida usually grows together with C. bonariensis populations, it is believed that both species are useful in the treatment of urinary affections, liver diseases, stomach ulcers, and to wash sores [4] as well as an antihelmintic, digestive and diuretic [5,6,7].

There are no phytochemical studies, nor information on the active constituents of C. albida. We now present the results on the bioactivity-guided fractionation of an active extract of the leaves of C. albida and the evaluation of the activity of the pure compounds against Artemia sp., KB cells and as topoisomerase I inhibitors.

Experimental Procedures

Dry leaves of Conyza albida were extracted with CH₂Cl₂. The total extract MeOH-H₂O 20% was partitioned between hexane, Et₂O, EtOAc and H₂O. All the extracts, including the water extract, were concentrated to dryness and tested in the brine shrimp toxicity test (BSTT). The hexane and Et₂O extracts gave positive results with LC₅₀ = 99 μg/ml and LC₅₀ = 96 μg/ml, respectively. They were fractionated, guided by the BSTT, by vacuum liquid, centrifugal planar and preparative thin layer chromatographies. The isolates were identified by a combination of the following spectroscopic methods:

GC-MS, IR, UV, ¹H NMR and ¹³C NMR.

Results and Discussion

The ethyl ether extract afforded two bioactive fractions with similar chemical composition. After further purification the following compounds were identified: alkenynes 1, 2 [8,9], 3 [8,9], and spathulenol 4 [10]. The hexane fraction contained alkenynes 1-3 and 1-dodecen-7,11-dimethyl-3-methylene [11] which was inactive. This is the first report on compound 1, although the trans isomer was obtained by synthesis [12].

Compound	BSTT (μg/ml)	KB (μg/ml)	DNA Topoisomerase I (%)
	1.3	7.3	-
	1.2	9.2	-
	5.2	19.1	21
	4.2	9	39

Positive controls: BSTT, berberine LC₅₀ = 8.4 μg/ml; against KB cells, colchicine IC₅₀ = 0.02 μg/ml.