Other Asteraceae Groups

The therapeutic efficacies of other members of the Asteraceae containing SQLs are summarized in the following text. 

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The other major group of irregular monoterpenes is formed by non-head-to-tail fusion of isoprene units. Important members include artemisia ketone 64, santolinatriene 65, chrysanthemol 66, yomogi alcohol 67 and lavandulol 68 (Structure 4.15). Lavandulane-type compounds occur in the families Lamiaceae (Labiatae) and Apiaceae (Umbelliferae), while chrysanthemane, artemisane and santolinane types occur in the family Asteraceae (Compositae) [47,48]. 

Most of the new source reports concern species from the Asteraceae, with many of the flavonols being isolated from aerial parts, where they are accumulated externally. They range from simple to more complex structures. There appears to be a tendency towards 6-methox-ylation rather than towards 8-methoxylation, in addition to possible OMe-substitution of other positions of the flavonol molecule. Flavonols with 6,8-di-O-methylation and additional OMe-groups are also found in several genera such as Senecio, Psiadia, or Inula, to cite but a few examples. 

The lignans are a large group of plant phenolics, biosynthesized from the union of two phenylpropane molecules e.g., both matairesinol (Centaurea species, family Asteraceae) and podophyllotoxin Podophyllum peltatum, family Berberidaceae) are formed from the phenylpropane coniferyl alcohol. Lignans are essentially cinnamoyl alcohol dimers, though further cyclization and other structural modifications result in various structural types, e.g. dibenzylbutyrolactone and epoxy lignan. 

Chemicals that are potentially capable of phototoxic action have been Isolated from more than 30 flowering plant families. Their occurrence among Important monocot and dlcot families is shown in Table 1. Most of the taxa represented in this table synthesize several types of photosensitizers. Members of the Asteraceae (sunflower family) and the Rutaceae (citrus family) for example synthesize the widest range of phototoxic compounds. Other families (e.g., Hypericaceae, Llliaceae, Moraceae and Orchidaceae) either lack or fail to express such biosynthetic diversity. Plants from these latter groups contain phototoxins derived from a single metabolic pathway. 

Considering that only a small fraction of the 20000 Asteraceae species as the major pool of STL structures have been subject to phytochemical studies, and that many plants of other families may contain such compounds, the knowledge on their structural diversity as described in the first section will increase further in the future. At the same time, their biological activity and potential use is a field of very active research in many groups and it appears that a lot of interesting findings in this respect are yet to be made. 

Flavanones, by virtue of their role as biosynthetic intermediates, occur in most plants, but they are also accumulated widely (Grayer, 1989). Most of the approximately 320 known flavanones possess the ( — )-(25)-configuration. Flavanones are common in the Asteraceae and Fabaceae, and the genus Citrus of the Rutaceae, but they have been reported in at least 60 other families (Bohm, 1988). However, compounds of this type are overlooked frequently in surveys of flavonoid composition of plants, and representatives of this group of compounds may occur more widely in nature. 

The pyrethrins represent a group of six closely-related monoterpene esters and are invaluable insecticidal substances isolated from pyre-thrum flowers, such as Chrysanthemum cinerariaefolium, and several other species in the Asteraceae family. Pyrethrins are indicated for treatment of skin parasites, such as head lice. They block sodium channel repolarization of the arthropod neurons, which leads to parasite paralysis and death. Permethrin is also used to treat head lice infestation. However, the growing resistance of head lice to pyrethrin and permethrin is becoming a serious concern [88]. 

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