Chemotaxonomic value of sterols and steroidal sapogenins in the genus Trigonella

Abstract

The composition in sterols and steroidal sapogenins was investigated in seven species of the genus Trigonella. Fenugreek ( Trigonella foenum-graecum L.), considered as representative of this genus, was used as a reference species. Its sterolic composition is characterized by a quasi absence of stigmasterol and by the presence of Δ7-sterols and of pollinastanol (14α-methyl-9β,19-cyclo-5α-cholestan-3β-ol), an unusual sterol. The composition in steroidal sapogenins (11 different compounds representing 1.5% DW) is also taken into consideration. The results of the analysis of these substances in the seven species studied are presented and their taxonomic contribution is discussed. First, our results support the unchanged assignment of T. corniculata (L.) L., T. caerulea (L.) Ser. and T. melilotus caeruleus (L.) Ascherson et Graebner to the genus Trigonella. They confirm the regroup of the two last species under the name of T. caerulea (L.) Ser. The transfer of T. monspeliaca L. to the genus Medicago is also confirmed, this species presenting a sterolic composition different from the other species but similar to that of Medicago sativa L. However, our results do not support completely the unchanged assignment of T. calliceras Fisch. in M. Bieb. to the genus Trigonella, nor the reassignment of T. cretica (L.) Boiss. to Melitotus cretica (L.) Desr., the composition of this species being close to that of Trigonella foenumgraecum L. for the compounds investigated. In conclusion, we propose the use of pollinastanol and steroidal sapogenins as chemotaxonomic markers to investigate the generic separation between Trigonella, Medicago and Melilotus.