high a-thujone, low (3-thujone frans-chrysanthenyl ac.
camphoi oc- + p-pinene
1,8-cineole high trans nerolidol and carvacrol
Figure 2 Tree diagram of the Cluster Analysis calculated on the data matrix of Table 4. Two main clusters are evident: one consisting of high a-thujone species and the other made of several minor subclusters. See comments on text. From Mucciarelli et al. 1995.
However, the most important group of sesquiterpenes found in the tribe Anthemideae is represented by the sesquiterpene lactones. These molecules have been extensively investigated in the genus Artemisia in chemotaxonomic and other studies. While germacranolides and guaianolides are the dominant compounds of the tribe, santanolides have been reported particularly in Artemisia (e.g. A. cina). However, a particular feature of A. annua is its biosynthetic capacity for the cyclization of a germacradiene precursor to a cadinanolide (Herz 1977), while several other germacranolides have also been found to occur in the genus (e.g. costunolide).
Dimeric guaianolides, such as absinthin and anabsinthin, are responsible for the bitter taste of extracts from A. absinthium and all these compounds are proazulenes or proazulenogenous. Azulenes are compounds of some pharmaceutical importance owing to their antiseptic and antibacterial properties and certain lactones are known to form azulenes (Herout and Sorm 1954; Novotny et al., 1960). Among santanolides, douglanin and arglanin are present in A. douglasia, whereas artecalin and balchanin are found in A. californica and A. balchanorum, respectively. Several reports on new sesquiterpene lactones appear frequently in the bibliographic browsers. Here we will illustrate the wide variability of compounds present in the genus. Matricarin and hanphyllin were found in A. argvi, parishin B and C in A. absinthium (Ovezdurdyev et al, 1987), six new eudesmanolides closely related to taurin were extracted from A. santonicum (Mericli et al, 1988), two new eudesmanolides were obtained from A. herba-alba (Ahmed et al., 1990), a new germacrano-lide and a novel germacranolide dimer were found in A. barrelieri (Marco et al., 1991), whereas frigins A, B and C were isolated from A. frigida (Konovalova and Sheichenko 1991).
The aerial parts of A. glabella, a perennial plant widespread on the Kazakh dry steppe hills, contain the sesquiterpene lactones arglabin (Fig. 3), argolide and dihydroargolide (Adekenov et al., 1995). New germacrane lactones have been isolated from A. feddei (Fig. 3), A. herba-alba, A. ludoviciana (Fig. 3) and A. rutifolia, whereas some new eudesmanolides were isolated from A. gracilescens (gracilin; Fig. 3), A. argyi, A. nitrosa (nitrosin; Fig. 3), A. rutifolia, A. coerulescens, A. tournefortiana, A. fragrans, A. herba-alba, A. santolinifolia, A. splendens and A. xerophytica, and new guaianolides were extracted from A. feddei, A. frigida, A. argentea, A. argyi, A. douglasiana (leucodin derivative; Fig. 3), A. ludoviciana, A. mesatlantica (mesantilantin A; Fig. 3), A. rutifolia and A. xerophytica (ligustrin derivative; Fig. 3) (Fraga 1992; 1993; 1994).
Quite recently two new eudesmanolides and two new guaianolides have been obtained from A. lerchiana (Todorova and Krasteva 1996), while a new eudesmenoic acid has been isolated from A. phaeolepis (Tan et al., 1995). The extraction of air dried aerial parts of A. eriopoda afforded a sesquiterpene mixture containing three new eudesmane diols: lj6,6j6-dihydroxy-4(14)-eudesmene, 5a-hydroxyisoptero-carpolone and 1-oxo-cryptomeridiol (Fig. 3) (Hu et al., 1996a), whereas A. pontica was found to contain seven new 5-hydroxyeudesmanolides in addition to artemin (Fig. 3), 5-epi-artemin and 8-a-hydroxytaurin (Trendafilova et al., 1996). In A. herba-alba a new eudesmanolide has been named herbalbin (1 a-hydroxy-3a,4a-epoxyeudesm-5a,6/3,7a,llj8H-12,6-olide; Fig. 3) (Boriky et al., 1996), whereas in A. mongolica the new eudesmane 6a,8 a-dihydroxyisocostic acid methyl ester has been isolated along with the eudesmane derivative ludovicin B (Hu et al., 1996b). A new germacranolide: 4,5/3-epoxy-10a-hydroxy-l-en-3-one-iraws-germacran-6,al2-olide has been isolated from aerial parts of A. pallens (Rojatkar et al., 1996), whereas six sesquiterpene lactones with the uncommon rotundane skeleton have been extracted from the aerial parts of A. pontica (Fig. 3) (Todorova et al., 1996).
Sesquiterpene lactones of the cadinanolide, germacranolide, guaianolide, eudesmanolide, secoeudesmanolide and helenanolide groups have been investigated by Bicchi and Rubiolo, (1996) in A. umbelliformis by HPLC-MS coupled through a particle beam interface. Several new germacranolides and guaianolides have been extracted from A. reptans, A. turcomanica and A. deserti (Marco et al., 1993; Marco et al., 1994a), whereas thirteen eudesmanolides and a 1,10-secoeudesmano-lide have been obtained from the North African A. hugueti and A. ifranensis (Fig. 3) (Marco et al, 1994b).
Artemisinin (Fig. 3), a sesquiterpene lactone that will be treated in more detail later in this book, is a typical santanolide of A. annua. A rapid, sensitive and specific method has been developed for the simultaneous determination of artemisinin and its bioprecursors by means of reversed-phase HPLC using electrochemical and UV detection in A. annua (Van den Berghe et al., 1995).
Among diterpenes, phytene-l,2diol has been isolated from A. annua and the presumed biogenetic precursor of the diol is thought to be phytol (Brown 1994a). The triterpene fernerol was obtained from A. vulgaris (Hegnauer 1977), whereas a lanostane-type triterpenoid (9jS-lanosta-5-ene-3a,27-diol 3a-palmitoleate) and two 13,14-seco-steroids (13,14-seco-cholest-7-ene~3,6a,27-triol 3,27-diocta-8',6'-dienoate and 13,14-seco-cholest-5-ene-3j8,27-methanoate 3/3-hexadeca-ll',13',15'-trien-l'-onate) have been isolated from the roots of A. scoparia (Sharma et al., 1996).
Flavonoids are widespread in the Anthemideae and their evaluation has proved to be a valuable tool for chemotaxonomic studies. However, according to Seeligmann, (1996) when considered at the familial level the distribution of the basic structures of flavonoids does not always reflect phylogenetic relationships between genera and is not in accordance with the degree of evolution.
In the Anthemideae, luteolin, apigenin and quercetin are the most common compounds (Fig. 4). More than 160 individual flavonoid components have been isolated in the genus Artemisia and about one third of them are derivatives of the flavones luteolin and apigenin (Belenovskaja 1996). Some derivatives of these compounds have also been isolated from A. sacrorum, like the isomeric compound genkwanin (Chandrashekar et al., 1965) and from A. pygmaea, like rhamnazin (Fig. 4), the 7,3'-dimethyl ether of quercetin (Rodriguez et al., 1972).
The rare compound 3,5-dihydroxy-6,7,8-trimethoxyflavone has been isolated from A. klotzchiana (Dominguez and Cardenas 1975). A. pontica at the flowering stage accumulated apigenin and luteolin methyl esters, whereas before flowering the plants produced mainly apigenin derivatives (Wollenweber and Valant-Vetschera 1996). Two new flavones were isolated from A. giraldii and their structures were identified as 4',6,7-trihydroxy-3',5'-dimethoxyflavone and 5',-5-dihydroxy-3',4',8~ trimethoxyflavone. These two compounds showed antibiotic activity against Staphylococcus aureus, Sarcina lutea, Escherichia coli, Pseudomonas aeruginosa, Proteus spp., Aspergillus flavus and Trichoderma viride (Zheng et al., 1996).
The aerial parts of A. stolonifera afforded a new phenolic glycoside from natural sources, 2,4,6-trihydroxy acetophenone 2-0-/3-D~glucopyranoside, coniferin and the acetophenone glycoside 2,4-dihydroxy~6-methoxy acetophenone 4-0-/3-D-glucopy-ranoside. The latter compound was cytostatic to macrophages (Lee et al., 1996). Artemisia annua leaf and stem extract contain apigenin, luteolin, kaempferol, quercetin, isorhamnetin, luteolin-7-methyl ether, isokampferide, quercetagetin 3-methyl ether, quercetagetin 4'-methyl ether, tomentin, astragalin, isoquercitrin, quercimeritrin and two chromenes (Fig. 4).
Some flavones extracted from A. annua, e.g. casticin, chrysoplenetin and cirsineol were found to enhance the antimalarial activity of artemisinin. In particular, casticin arglabin leucodin derivative ligustrin derivative
arglabin leucodin derivative ligustrin derivative mesantilantin A
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