Analysis of kaurenic acids methyl esters by gas chromatography

Abstract

GeneralKaurenic acids (Figure 1) are secondary metabolites found in Compositae. Espeletiinae [ 11 is a subtribe of this family which comprises plants that grow above 2500 m in the Andes of northern South America. Kaurenic acids, as well as other diterpenoids, seem to play a role in the protection of these plants against low temperatures [2]. On the other hand, some kaurenic acids have been found to be useful as starting materials for the synthesis of some substances of potential pharmacological interest [3].There are more than 100 species of Espeletiinae in Venezuela, Colombia, and Ecuador, and all species studied thus far contain mixtures of different kaurenic acids. It was therefore considered appropriate to develop a method of analysis for rapid screening. Since most kaurenic acids do not absorb above 220 nm, which is a drawback for HPLC analysis, gas-liquid chromatography was considered the method of choice. The free acids can be separated on non-polar capillary columns but tail. Their methyl esters, which are easily prepared by reaction with diazomethane, give better resolution. The kaurenic acids present in the leaves of young plants of Espeletia schultzii and Coespeletia moritziana collected at Pic0 del Aguila were analyzed to test the method. Experimental f MaterialsKaurenic acids were obtained at our laboratory from different species of Espeletiina [4-71. Preparation of Methyl Esters10 mg of each acid was dissolved in diethyl ether and left overnight to react with a solution of diazomethane. The methyl estersPresented at Colacro Vl, Caracas, Venezuela, January 1996 were purified over silica gel on an open column and eluted with C6Hi2 and C6H12/(C2H5)20 mixtures. 1 mg of each purified methyl ester was dissolved in 0.1 mL of CH2Cl2 for analysis. Extraction of Kaurenic Acids from Leaves of Espeletia schultzii and Coespeletia moritzianaLeaves from E. schultzii were dried and ground; 10 g of dry leaveswere extracted with n-C6Hi2:(C2H5)20 (4:1) in a Soxhlet apparatus. The acidic fraction was obtained by shaking the extract three times with 0.1 N NaOH solution. The aqueous solution was acidified, shaken with (C2H5)20, and treated with ethereal diazomethane. The methyl ester mixture was taken to dryness and dissolved in 5 mL of CH2Cl2. . The acid fraction obtained from 10 g of dry and ground leaves of C. moritziana was treated in the same way. Internal Standard(-)-Kaur-15-en-19-oic acid methyl ester (2b) was used as internal standard. This acid does not occur as a natural constituent in E. schultzii or C. moritziana. It has a retention time of 4.1 minutes and elutes between l b and 3b. Gas ChromatographyGLC analyses were carried out on a Perkin-Elmer Autosystem apparatus. Experiments were performed on a 12 m long capillary column (0.2 mm diam.) coated with methylpolysiloxane (25 pm). The oven temperature was programed from 250 "C (5 min) to 300 "C (5"/min). Helium was used as carrier gas at 0.6 mL /min.The injector and detector temperatures were maintained at 300 "C. 1 .O FL samples were injected with a sp...

iso-Kaurenoic acid from Wedelia paludosa D.C.

“…It has been found in a few number of Annonaceae and Asteraceae species, including Annona glabra (Hsieh et al 2004), Smallanthus maculatus (Rios and Leon 2006), Wedelia biflora (Miles et al 1990, Li et al 2007) and some species belonging to the subtribe Espeletiinae (Asteraceae, tribe Heliantheae), such as Espeletia semiglobulata, Coespeletia spicata and Libanothamus humbertii (Viloria et al 1997, Usubillaga et al 2003. This is the first report on the occurrence of isokaurenoic acid (3) in W. paludosa D.C.…”

Kaurenic acid: An in vivo experimental study of its anti-inflammatory and antipyretic effects

“…This study was performed using the egg albumin model. [ 10 ] Sprague-Dawley rats ( n = 10) were randomly allocated in three groups: an experimental group received KA (20, 40, 80, and 160 mg/kg i.p. ), a standard treatment group was treated with acetylsalicylic acid (ASA: 50, 100, 200, and 250 mg/kg), and a control group received 0.9% saline solution (1 mL).…”