Germacrone

FIGURE 11.5 Terpenoids, (a) The basic five-carbon units isopentane and isoprene. (b) The monoterpenes borneol and a-pinene. (c) A monoterpene lactone, nepetalactone. (d) A sesquiterpene, germacrone. (e) A triterpene, papyriferic acid, from paper birch. 

Snowshoe hare Labrador ten Ledum Germacrone (sesquiterpene)... 

Some defenses are so effective that herbivores do not consume any amount of a plant. Snowshoe hares are deterred from feeding on Labrador tea. Ledum groenlandicum, by germacrone, a sesquiterpene, the major compound of its essential oil. Leaves and fresh growth internodes contain large amounts of germacrone (Reichardt etal, 1990a). Yet beaver, C. canadensis, in Saskatchewan,... 

Reichardt, P. B., Bryant, J. P., Anderson, B. J., etal. (1990a). Germacrone defends Labrador tea from browsing by snowshoe hares. Journal of Chemical Ecology 16,1961-1970. 

Elemenone (359), a compound which co-occurs with germacrone (358) in Bulgarian zdravetz oil and which can be formed from germacrone (358) by thermal rearrangement, has recently been synthesized by a route (Scheme 34) in which the... 

While a dynamic NMR study38 was carried out to reveal rather complicated patterns of conformational interconversion in some eleven-membered sesquiterpenes including humulene (40) and zermbone, an interesting controversy concerning conformational stability in the germacrone family of sesquiterpenes is worth mentioning here. 

Rhododendron dauricum DC Man Shan Hong (Daurian rhododendron) (leaf) Germacrone, flavonoid, farreol, feriol, quercetin, myricetin, anromedotoxin, rhodotoxin.33 Antitussive, antiasthmatic. 

Rhododendron mucronatum G. Don Bai Du Juan Hua (white azalea) (flower) Essential oil, germacrone, farreol, grayanotoxin, gossypetin, azaleatin, 5-methyl kaempferol, 5-methyl myricetin, syringic acid, dihydroquercetin, coumarins, phenolic acid, p-hydroxybenzoic acid, protocatechuic acid, vanillic acid.48 Treat cough, asthma, headache, respiratory infection. 

Hikino et al. [153] have investigated by enzymatic means the stereospecific epoxidation reactions of olefinic double bonds in the plant Curcuma zedoaria Roscoe. They studied the bioconversion of germacrone (207), a constituent of C. zedoaria, by microorganisms in the hope of obtaining stereoselective epoxidation as in the case of the plant. Cuminghamella blakesleeana yielded three major products (208 - 210) from germacrone, Fig. (42). 

More recently, Asakawa et al. [154] described the biotransformation of germacrone by Aspergillus niger. A very unstable allylic alcohol (211) was obtained from the metabolite of germacrone along with (213), Fig. (42). 

Fig. (42). Biotransformation of germacrone by Cunninghamella blakesleeana (after [153]) and by Aspergillus niger (after [154])...

Two new sesquiterpene ketoalcohols -turmeronol A and turmeronol B - have also been reported from the dried rhizome (Imai et al., 1990). Five sesquiterpenes, e.g. germacrone-13-al, 4-hydroxybisabola-2, 10-diene-9-one, 4-methoxy-5-hydroxybisabola-2,10-diene-9-one, 2,5 -dihydroxybisabola-3,10-diene and pro-curcumadiol, have been isolated and identified... 

Ginsenoside-Rhl (triterpene glycoside saponin) Ginsenoside-Rh2 (triterpene glycoside saponin) Germacrone (sesquiterpene)... 

A further examination of the essential oil of Asarum caulescens Maxim, has resulted in the isolation and identification of caulolactone A (338) and B (339). Interestingly both these compounds co-occur with germacrone 4,5-epoxide (337), and in fact treatment of this epoxide With anhydrous aluminium chloride gives both these lactones in 10% and 8% yields respectively. Mechanistically this has been rationalized in terms of two conformations of the epoxide as depicted in... 

Scheme 53. Molecular models do not make this mechanism seem very likely and further work on the structures of caulolcatone A and B may be required. A further study of the photochemistry of germacrone (340) has shown that direct irradiation causes isomerization only of the A °-double bond whereas acetophenone-sensitized irradiation induces isomerization of both the and...

A plethora of products is obtained when either elemol (273), in the presence of p-nitrobenzoic acid (or benzoic acid), or elemyl-p-nitrobenzoate is pyrolysed at about 200 °C. These include the elemenes (274)—(276) together with the selinenes (277)—(281). The sequence of formation and the factors affecting the thermolyses are discussed in depth, together with the data for the thermolysis of dihydro-geijerene (282). This latter compound has been synthesized from germacrone (227) by a Cope rearrangement to j3-elemenone (283) followed by a retro-aldoliza-tion to (284) and subsequent Wolff-Kishner reduction. 

AlCb in ether has been used to explore intramolecular cyclization of some germacrones, and gives a [5.3.0] bicyclic derivative in one instance, illustrated in equation (137). ... 

---