Bioactive Steroids and Triterpenes from Melilotus messanensis and Their Allelopathic Potential

Abstract

The aerial parts of Melilotus messanensis (sweet clover) afforded, from moderately and polar bioactive fractions, 11 triterpenes and five steroids. A series of aqueous solutions at 10−4–10−9 M of five steroids and nine triterpenes was monitored to test their effects on germination and growth of the monocots Hordeum vulgare and Allium cepa, and the dicots Lactuca sativa (var. nigra and var. romana) and Lycopersicon esculentum. An important stimulatory effect on H. vulgare germination (between 40% and 80% for almost all tested compounds) was observed. Some considerations about the ecological role of triterpenes on M. messanensis are made. In addition to known lupane triterpenes (platanic acid and 3β,28,30-lup-20(29)-enetriol), oleanane triterpenes (soyasapogenol B, soyasapogenol G, and messagenolide), a gammacerane triterpene (gammacer-16-en-3-one), five new lupane triterpenes (messagenic acids A–E: (27-cis-4-hydroxycinnamoyloxy)-betulinic acid; 27-(trans-4-hydroxycinnamoyloxy)betulinic acid; 20(S)-3β-hydroxy-29-oxolupan-28-oic acid; 3β,30-dihydroxylup-20(29)-en-28-oic acid; and 3β,20-dihydroxylup-18(19)-en-28-oic acid, respectively), and sterols (β-sitosterol, ergosterol peroxide, 7α-hydroxysitosterol, 7β-hydroxysitosterol, and 7-oxositosterol) were isolated and chemically characterized. Their structures and stereochemistry were elucidated by spectroscopic methods (one- and two-dimensional 1H and 13C NMR, IR, MS).