REASSESSMENT OF MELITTIS MELISSOPHYLLIM L. SUBSP. MELISSOPHYLLUM IRIDOIDIC FRACTION

Melittis melissophyllum L. subsp. melissophyllum (Lamiaceae family) is a perennial herb characterized by big scented flowers and occurring in central and southern Europe along tracks and roads covered in half shadow till the altitude of 1400 m a.s.l.. In Italy it is present everywhere on the territory. In the traditional medicine it is used as antispasmodic and digestive as well as against insomnia and eyes inflammations. In this work we report on the iridoidic fraction of Melittis melissophyllum subsp. melissophyllum collected at flowering in May 2012 in Piedilapiaggia, near the town of Camerino (central Italy), at 600 m above sea level.The study of the ethanolic extract of this plant allowed the isolation and the identification of a total of six iridoids which were monomelittoside (1), melittoside (2), harpagide (3), acetyl-harpagide (4), ajugoside (5) and allobetonicoside (6). Compounds (1), (2), (3), (4) and (5) have been already evidenced in plants belonging to the genus Melittis and, in particular, harpagide (3) and its acetyl-derivative (4) are considered chemotaxonomic markers for this genus and also for other correlated genera in the Lamiaceae family such as Ajuga, Stachys and Galeopsis. In addition, it is very important to underline the presence of compound (6), recognized for the first time in this species. This compound is not new in absolute in the family of Lamiaceae and especially in members of the subfamily Lamioideae such as Stachys macrantha, S. glutinosa and Betonica officinalis. However, the relevance of allobetonicoside consists in the occurrence of an allose residue, a no common sugar. Actually, allose has been often found in species of the subfamily Lamioideae even if it mostly regarded flavonoids which are considered of chemotaxonomical relevance for some correlated genera of Lamiaceae. Alike as for allosyl-glycosidic flavonoids, the presence of allosyl-glycosidic iridoids may also be an additional chemosystematic evidence of botanical relationships among Lamiaceae species and genera