## 4 Secondary Metabolites Identified in the _Leontopodium_ Taxa  
Considering the traditional use of the _Leontopodium_ herbs in the traditional medicine in Europe and Asia, several studies were conducted to identify the secondary metabolites responsible for the curative effects of these folk remedies. Many scientific articles investigated the content of secondary metabolites in _Leontopodium_ species, the first papers indicating the presence of the main compounds from the phenylpropanoids' class, such as chlorogenic and 3,4-di-O-caffeoylquinic acids [17; 56; 64] and flavonoid derivatives from luteolin [55; 64; 80], in the methanolic extracts from leaves and infloresances. In the roots, the analysis of essential oils revealed, for the first time, the presence of terpenoids [56] and a chroman [18]. Other studies identified sitosterol [17] and different sesquiterpenes, such as isocomene and its derivatives, modhephene and an acetoxy derivative, along with a derivative of carophyllene [19] in a root extract. Subsequently, many phytochemical studies on _L. alpinum_ succeeded in determining almost 50 different secondary metabolites, very well described in the review paper presented by [PERSON] and [PERSON] [53]. Roots and hairy roots cultures represent a valuable source of secondary metabolites, including sesquiterpenes, such as \(\beta\)-isocompene, silpinhene, silpinberfolene acetate [9; 11; 49; 81] and bisabolene derivatives [4; 54], diterpenes derivates from the _ent_-kaurenoic acid [4], coumarins such as obliquin, its derivatives and one benzofuran [11], lignans such as leoligin and its methoxy-derivatives [4; 10; 11; 20] and two polyacetylenes [4]. The aerial parts are a rich source of phenolic compounds, mainly caffeoyl-D-glucaric acid derivatives, such as leontopodic acid A [5], leontopodic acid B and 3,5-di-O-caffeoylquinic acid [82] and tetracaffeyol-D-glucaric acid derivative [37; 83]. Flavonoids like apigenin, luteolin and their \(O\)-glycosylated derivatives but also chrysoeriol and quercetin glycosylated derivatives, were described in aerial parts [82; 84], while some papers highlighted the presence of fatty acids, such as linoleic and linolenic acid [8; 81]. In several Asian species, the presence of flavones derived from luteolin and apigenin was also described in aerial plant extracts [80; 82]. Further phytochemical investigations have shown that flavones and flavonoid glycosides are the main components of _L. leontopop_dioides_ whole plant extracts [22; 28]. Among these, in addition to the previously identified compounds, a series of methoxylated \(O\)-glycoslated and/or acyl flavone derivatives from kaempfer [22; 28] or luteolin [85], coinferin and its derivatives, as well as tetrahydro-3-methoxyflavone [23], dihydroxy flavanone, di/tetrahydrodrox flavonol or dihydroxy flavanol derivatives were also isolated [15]. Additionally, new secondary metabolites were discovered in aerial parts of the species _L. leontopodioides_: two new compounds, a neolignan and a benzofuran [15]; two new _ent_-kaurene diterpenoids, leontocin A and leontocin B; a new lignan, leontolignan [78]; nine isobenzofuranones, including six new ones, together with three known isobenzofuranones [79]. Other researchers isolated isotrichocarpin, leontopodioside D and E, along with nebredonside A, pungenin, betulbuside A and two glucopyranoside derivates in extracts from the _L. leontopodioides_ whole plants [86] and five new isobenzofuranones named leontoaerialosides A, B, C, D and E [87]. The first discovered coumarins named leontonanin, together with six known compounds, umbelliferone, 3, 4', 7-trihydroxyflavone, oleanolic acid, \(\beta\)-sitosterol, daucosterol and stearic acid, were described in _Leontopodiumanum_ Hand.-[PERSON] [88]. In another Asian species, _Leontopodium longifolium_ [PERSON], an obliquin derivative, a coumarin, and three new bisabolenes were identified in a root extract [38]. Further, a norsesquiterpene called longifolactone and other three _ent_-kaureneoic acid derivates were isolated from roots [35].