Marrubium vulgare L. (Horehound, Lamiaceae) is a widespread Mediterranean plant used in folk medicine to cure a variety of diseases. Chemically, this genus is best known for its furanic labdane diterpene marrubiin, which has potent antinociceptive [1] and expectorant [2] effects. Other furanic labdane diterpenes including premarrubenol, marrubenol and premarrubiin have been repeatedly reported to occur in this plant [3], [4] but pharmacological information about these components is lacking. In a previous report, we have demonstrated that treatment with an aqueous extract of the aerial parts of M. vulgare significantly lowered the systolic blood pressure in spontaneously hypertensive rats (SHR), related to a vasodilatory effect exhibited by the extract ex vivo as well as in vitro [5]. The present study deals mainly with the isolation and structural elucidation of the compounds responsible for the vasorelaxant activity ascribed to this plant.Preincubation of rat aorta with the cyclohexane fraction of M. vulgare water extract evoked a dose-dependent inhibition of KCl-induced contraction while the aqueous fraction showed no effect ( Table 1). Bio-guided fractionation of this cyclohexane extract by column chromatography gave several fractions, two of which showed a high activity. The first one was further purified using preparative TLC on silica gel (Si 60 F 254 Merck) with hexane-diethyl ether (4 : 6) as mobile phase, yielding 10. C, COSY, HMQC, HMBC) allowed us to identify it as marrubenol, previously isolated from M. vulgare [7]. Table 2 gives, for the first time, the complete NMR assignments of marrubenol. Its structure was further confirmed by comparison with marrubenol obtained by reduction of marrubiin (Fig. 1).The effects of marrubiin and marrubenol on the contractions evoked by high-KCl depolarizing solution in aortic segments were compared to the effect of the calcium channel blocker verapamil, a well known antihypertensive drug which inhibits the contraction evoked by high-KCl solution in arteries [8]. Marrubenol and marrubiin inhibited the aortic contraction in a concentration-dependent manner (Fig. 2)
AbstractCrude extracts of the aerial parts of Marrubium vulgare show a potent in vitro inhibition of KCl-induced contraction of rat aorta. Bio-guided fractionations, spectroscopic analysis and chemical derivatization revealed the furanic labdane diterpenes marrubenol and marrubiin as the most active compounds.