MONOTERPENE GLYCOSIDES PATTERN AND VOLATILE FRACTION ANALYSIS OF AJUGA CHAMAEPITYS (L.) SCHREB. SUBSP. CHAMAEPITYS.

Ajuga chamaepitys (L.) Schreb. subsp. chamaepitys (Lamiaceae, subfamily Ajugoideae), also known as Ground Pine or Camaepitium, is an Euri-mediterrranean species which is distributed in almost all Italian regions. Among the secondary metabolites isolated from A. chamaepitys neo-clerodane diterpenoids, steroidal glucosides, triterpenes, phenylethanoid, flavonoids and anthocyanins were the most important. Instead, nothing has ever been done about the iridoid glycosides content. The analysis of the iridoidic fraction of A. chamaepitys flowering aerial parts led to the identification of several compounds: ajugoside (1), reptoside (2), 8-O-acetyl-harpagide (3), harpagide (4), an harpagide-derivative under study (5), asperulosidic acid (6) and deacetyl asperulosidic acid (7). Compounds (1), (2), (3) and (4) are considered chemotaxonomical markers for several genera of Lamiaceae and already evidenced in species belonging to this genus such as A. reptans L., A. decumbens Thunb, A. remota Benth. (synonym of Ajuga integrifolia Buch.-Ham.), A. chamaecistus subsp. tomentella (Boiss.) Rech.f., Ajuga postii Briq. and A. turkestanica. On the other hand, the presence of asperulosidic acid (6) and deacetyl asperulosidic acid (7) is worthy of mention and, at the same time, unusual. In fact, asperuloside and its derivatives are considered characteristics and distinctive of the Rubiaceae family, since they have been largely isolated from species belonging to this family. This is the first time that these kind of compounds were isolated from species belonging to Lamiaceae and may suggest a reconsideration of chemotaxonomy of Ajugoideae subfamily. The composition of the hydrodistilled essential oil from the aerial parts showed the presence of sesquiterpene hydrocarbons (30.8%), followed by diterpenes (15.0%), esters (13.7%) and monoterpene hydrocarbons (11.1%). Main representatives of these classes were germacrene D (13.4%), kaurene (8.3%) and (E)-phytol (5.3%), ethyl linoleate (13.7%), and β-pinene (6.8%), respectively. This species resulted to be a typical essential oil poor species which produce less monoterpenoids (oil yield 0.1%). The reported composition showed some quantitative differences with respect to that reported for different subspecies of A. chamaepitys and of various geographic origin but appeared to have little value for chemotaxonomic purposes.