ARS | Publication request: Isolation and Identification of the First C-17 Limonin Epimer, Epilimonin

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 27, 2008
Publication Date: June 20, 2008
Citation: Breksa III, A.P., Dragull, K.D., Wong, R.Y. 2008. Isolation and Identification of the First C-17 Limonin Epimer, Epilimonin. Journal of Agricultural and Food Chemistry. 56:5595-5598.

Interpretive Summary: This is the first known report of the isolation and characterization of an epimer of limonin. The epimer, named epilimonin, was isolated by fractional crystallization from a mixture consisting mainly of limonin and epilimonin obtained as a byproduct from our efforts to isolate limonin glucoside. Side-by-side comparison of the MS, IR and 1H and 13C NMR data of epilimonin and limonin lead to the assignment of C-17 as the site of epimerization.

Technical Abstract: Limonoids are a family of highly oxygenated triterpenoid secondary metabolites found in significant quantities in Citrus and reported to possess multiple health-promoting properties. This is the first known report of the isolation and characterization of an epimer of limonin. The epimer, named epilimonin, was isolated by fractional crystallization from a mixture consisting mainly of limonin and epilimonin obtained as a byproduct from our efforts to isolate limonin glucoside. Side-by-side comparison of the MS, IR and 1H and 13C NMR data of epilimonin and limonin lead to the assignment of C-17 as the site of epimerization. An earlier study on the bioavailability of limonin glucoside in humans had indicated that limonin glucoside was metabolized to give limonin and a second limonin metabolite. Results from analyzing epilimonin by the same chromatographic conditions used for the bioavailability study suggest that the second limonin metabolite was epilimonin.