Investigation into the presence of Monatin in related plant species

Abstract

Monatin, comprising the 4 isomers of (indol-3-yl)-2-amino-4-carboxy-4-hydroxypentanoic acid, is a high intensity sweetener isolated from the bark of the roots of Schlerochiton ilicifolius, a spiny-leafed hardwood shrub growing in the rocky hills of the Limpopo Province in South Africa. The original isolation of natural monatin from the plant involved the extensive fractionation of an aqueous extract of the root bark of S. ilicifolius using AG50WX8 strong acid cation exchange resin followed by successive gel filtration procedures using Biogel P2 and Sephadex G10 [1]. Recent work conducted by the CSIR analyzed aqueous extract of minimally processed plant material. Using an an HPLC-mass spectrometry method with Marfey's Reagent as a chiral derivitizing agent, both the (2S,4S) and (2R,4R) monatin enantiomers were found to be present in the root and root bark of plant samples collected from several locations. These data confirmed the natural occurrence of the 2R,4R isomer in S ilicifolius, in addition to the 2S,4S configuration that was reported in the original work. The latter determination was based on comparison of the specific optical rotation of the purified monatin with those of related 4-hydroxy-4-methylglutamic acids.