Terpenoid composition of Lippia dulcis

Abstract

The composition of Lippia dulcis, an intensely sweet herb endemic to tropical America, was investigated using plants collected in Puerto Rico. Contrary to previous reports, it is characterized by the presence of a high percentage of sesquiterpenoids (79%). Isolation experiments and gas chromatographic characterization using direct injection, show that the intensely sweet sesquiterpenoid (+)-hernandulcin (36%) and its epimer (-)- epi-hernandulcin (22%) are the main constituents of these herbs. The oil contains, if any, undetectable amounts of camphor (<< 0.01%). These findings are in sharp contrast with the composition reported earlier for 'Hierba dulce', a pungent Mexican plant identified as L. dulcis. Only trace amounts of hernandulcin (40 ppm wt/wt, dry weight) were reported in the plants from Mexico. The volatile oil isolated from these plants by steam distillation consisted mainly of monoterpenoids (86%). A bitter monoterpenoid, camphor, made up as much as 53% of the essential oil of the Mexican plants. If the identity of the Mexican plants is confirmed, these results may reveal the existence of two chemotypes of this herb, i.e. an hernandulcin type and a camphor type.