Sesquiterpenoids sesquiterpene lactones

The primary active chemical constituent in feverfew is parthenolide, a sesquiterpenoid lactone (figure 8.8) (Robbers et al. 1996). Levels of sesquiterpene lactones vary across different types of extracts ethanol extracts contain about 0.5%, whereas aqueous ones contain 0.3% (Gromek et al. 1991). The sesquiterpene lactones in feverfew inhibit the... 

The Chinese Eupatorium chinense has afforded ten new sesquiterpenoids, three of which are chlorinated, eupachinilides C (263), E (264), and F (265) (518). The Chinese medicinal plant Eupatorium lindleyanum contains the chlorinated guaianes eupalinilides A (266), D (267), E (268), and H (269), amongst other non-chlori-nated eupalinilides and nine known sesquiterpenoids (579). The Oregon coastal perennial plant Artemisia suksdorfii contains four novel chlorinated sesquiterpene lactones 270-273 520). 

Tanacetum species contain mainly sesquiterpenoids and flavonoids, whereas the other terpenoids and phenolic compounds are rarely found. Since the importance of sesquiterpenes, sesquiterpene lactones and flavonoids from the chemosystematic point of view, especially the... 

This review aims to present the most relevant aspects of the synthesis of bioactive sesquiterpenoids and sesquiterpene lactones starting from a-santonin (1), as well as from artemisin (2), that have appeared in the literature from 1987 to the present [9]. Other relevant work prior to this period, or work contained in previous reviews, will be briefly described or referred to where appropriate for the sake of clarity or comparison. 

The Ci5 terpenoids known as sesquiterpenoids are the most chemically diverse group of terpenoids known in nature. Like monoterpenoids, many sesquiterpenoids contribute to the flavor and fragrances of a variety of plant products. To date about 10,000 sesquiterpenoids are known (32), and in the plant kingdom they commonly occur as hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, lactones, and oxiranes. The acyclic sesquiterpene hydrocarbons a- and p-farnesenes (HI and H2, respectively) (Fig. 8) are constituents of the oils... 

Furantriol (18.27), isolated from L. mitissimus (84), is one of the few lactarane sesquiterpenes in which one of the gem-methyl groups at C-11 is oxidized and it was chemically correlated (82) with lactarorufin B (11.71), another example of this kind. The Polish authors suggested that lactone 11.71 was enzymatically formed from furan 18.27, and that a C-15 oxidized sesquiterpene of the velutinal type was the common precursor of both compounds in the mushroom (84). Actually, the possibility for the C-15 methyl group to be oxidized at an early stage of the lactarane biosynthesis seems to be confirmed by the recent finding of C-15 hydroxylated protoilludane sesquiterpenoids (5.1 and 5.2) in L. violascens (23) (Table 5). 

The occurrence of a,P-unsaturated carbonyl structures in comparison with other terpenoid classes, is rather high. A very high percentage, 63 % of all sesquiterpenes in the DNP and 81 % of all sesquiterpenoid lactones, contain at least one a,P-unsaturated carbonyl structure element, while these numbers are lower in case of the mono-, di- and triterpenes (10/75%, 14/59% and 7/51%, respectively (numbers based on DNP [4]). However, it becomes evident from these figures that lactone groups tend to be associated with a,P-unsaturated carbonyls throughout all classes of terpenoids. 

Sesquiterpenes are aliphatic or cyclic, isoprenoid Cl5 -compounds encompassing an almost bewildering array of structural types (cf. Figs. 106-108). They may be saturated or contain isolated double bonds. Often hydroxy, oxo, aldehyde, carboxylic acid, and lactone groups are present. Most compounds are volatile and lipophilic. Nitrogen-containing sesquiterpenes (sesquiterpenoid alkaloids) occur in some families of higher plants. 

There have been several analyses of sesquiterpenes whose structures are based on the azulene skeleton. To define completely the stmeture and absolute stereochemistry of the cytotoxic sesquiterpenoid lactone gaillaidin... 

Apart from the diversity presented by their core structures, sesquiterpenes are commonly decorated with lactone moieties and hydroxyls throughout the basic core. Thus, usually isolated biologically active natural sesquiterpenes are highly oxidized, referred in the literature as sesquiterpe-noids. The a,p-unsaturated lactone functionality is a common feature of many cytotoxic sesquiterpenoids accounting as a powerful alkylating side through a Michael-type addition to suitable biomolecules as the cysteine residues on proteins and enzymes. Thus, several biological active sesquiterpenoids have been isolated and used in traditional and modem... 

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