Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2002
Publication Date: 4/1/2002
Citation: Smith, D.J. and Shappell, N.W. 2002. Technical note: eperimerization of ergopeptine alkaloids in organic and aqueous solvents. Journal of Animal Science 80:1616-1622.
Interpretive Summary: Alkaloids are nitrogen-containing compounds of complex chemical structure that have pharmacological or toxicological activities. Ergot alkaloids present in tall fescue are believed to be the causative agent of fescue foot, a toxicity syndrome sometimes expressed in cattle grazing tall fescue. One of the most prevalent ergot alkaloids present in tall fescue is ergovaline. In aqueous solution, ergovaline can "epimerize" (change it 3-dimensional shape) rapidly to form "epimers" that are biologically incactive. These studies were initiated in order to determine under what conditions ergovaline and ergocryptine epimerize most rapidly and under what conditions they remain relatively stable. It was found that eperimization rates of ergopeptines are very slow when stored in aprotic solvents at less than zero degrees Celsius. Isomerization rates were temperature, pH, and solvent composition dependent. Data from this study can be used select storage conditions for solvated ergopeptine alkaloids and provide evidence that ergovaline may rapidly epimerize to biologically inactive compounds.
Technical Abstract: Purified ergopeptine alkaloids are often used in studies related to tall fescue toxicosis without regard to epimerization that occurs when ergopeptines are solvated. The objectives of this study were to measure the rates of alpha-ergocryptine epimerization to ergocryptinine at room temperature and at 40 degrees C, and to measure the rate of ergovaline epimerization to ergovalinine at 37 degrees C. Ergocryptine tartrate was stable (< 0.5 % epimerization) in protic or aprotic solvents when stored at 40 degrees C for 20 to 52 days. At room temperature, ergocryptine epimerization in chloroform did not occur; epimerization was modest in acetone and acetonitrile (< 5%), but was great in methanol (78% by 38 d) and in a 70:30 water methanol mix (47% by 42 d). Ergovaline epimerization to ergovalinine occurred at 37 degrees C in 0.1 M phosphate buffers (pH 3, 7.5, and 9) in 10% aqueous solutions of fetal bovine serum (FBS), and in water, methanol, and acetonitrile. The degree of epimerization at 37 degrees C was solvent dependent. Epimerization rates with respect to time were roughly linear in phosphate buffer (pH 3 only), water, methanol, and acetonitrile; epimerization rates resembled first order kinetics in phosphate buffers (pH 7.5 and 9) and in the presence of FBS (pH 3, 7.5 and in Dulbecco's culture media). Epimerization equilibria (48 to 63% ergovaline) were reached within approximately 1 to 19 h. Results from this study indicate that researchers conducting studies with purified ergopeptines should carefully control the storage conditions of solvated ergopeptines and measure isomeric composition under the actual experimental conditions used in experiments.