HPLC and NMR analysis of the phenyl-ethanoid glycosides pattern of Verbascum thapsus L. cultivated in the Etnean area

Verbascum thapsus L., commonly known as great mullein or common mullein, is a biennial herbaceous plant belonging to the Scrophulariaceae family [1]. It has a long tradition of use in ethnopharmacology since it is well know to posses several medicinal properties going from the expectorant and demulcent to the diuretic, anti-inflammatory, sedative, astringent, antiviral, antibacterial and antifungal ones and for these it has been long used in several parts of the world to treat respiratory problems as well as earache, eczema, hemorrhoids, diarrhea, fever, tumor and allergies [2]. Several phytochemical constituents have been evidenced in this species such as volatile oils, saponins, flavonoids, phenyl-ethanoid glycosides and iridoids [2]. Nevertheless, no study has ever been performed on a cultivated exemplar of this species coming from the Etnean area and, in particular, the attention was focused on phenyl-ethanoid glycosides which can be very useful additive compounds for food products especially due to their high antioxidant and antimicrobial effects [3]. This phytochemical analysis was carried out by means of HPLC-UV, HPLC-MSn and NMR and evidenced the presence of seven phenyl-ethanoid glycosides i.e. verbascoside (1), iso-verbascoside (2), leucosceptoside A (3), martynoside (4), samioside (5), alyssonoside (6) and leucosceptoside B (7). These results were extremely peculiar since leucosceptoside A (3) represents a new constituent for the genus, samioside (5) is a new strict constituent for the species and martynoside (4) is a new real constituent for the species. Moreover, this huge accumulation of specific PhGs in a cultivated exemplar of V. thapsus has never been seen before and this is probably due to the specific environmental conditions adopted for the plant growth. In conclusion, this analysis showed how this specimen derived from such particular method of cultivation may be a possible perfect source for these compounds and also of potential use in the ethnopharmacological field like other wild V. thapsus exemplars.