Germacrene structure

It should be noted that the stereochemical aspects of the Cope rearrangement are widely used for synthesis of various natural products, e.g. of the elemene-type derivatives 493-496 starting from germacrene-type sesquiterpenes 492 having cyclodeca-1,5-diene structure with stable conformations (equation 186)244. 

STRANDEN, M., LIBLIKAS, I KONIG, W. A., ALMAAS, T. J., BORG-KARLSON, A.-K., MUSTAPARTA, H., (-)-Germacrene D receptor neurones in three species of heliothine moths structure-activity relationships, J. Comp. Physiol. A, 2003, 189, 563-577. 

Following is the structure of Germacrene A, a hydrocarbon synthesized in plants and studied for its insecticidal properties. Classify each of the sp hybridized carbons on Germacrene A as 1°, 2°, 3°, or 4°. (See Example 3.4)... 

The composition of the root oil seems to be varying with the age, too. Although there are hardly any reports on this issue, it seems that this variability may be the result of structural transformations. Stahl-Biskup and Wichtmann (1991) detected a decrease of germacrene B, the characteristic compound (in 51%) of the seedlings parallel with secondary thickening of the roots and formation of secondary oil cavities. The roots of adult plants contained mainly aliphatic aldehydes up to 68% of the oil. In the contrary, the herb oil of seedling and adult plants did not differ signi candy from each other. 

Petunia. During petal Umb expansion germacrene D and cadina-3,9-diene were emitted by the flowers of the garden petunia, P. x hybrida (Hook.) Vilm., a hybrid between P. integrifolia (Hook.) Schinz Thell. and P. axillaris (Lam.) Britton, Stern Poggenburg (Verdonk et al. 2003). Structures of closely related derivatives of both sesquiterpenes are shown in Fig. 7.4. 

The number of sesquiterpenes is high (over 150 compounds). There are compounds with aliphatic (farnesenes), monocyclic (humulenes, bisabolenes, elem-enes), bicyclic (cadinenes, muurolenes, selinenes, caryophyllenes, germacrenes), tricyclic (copaenes, ylangenes, longifolenes.longicyclenes), and tetracyclic (sati-vene) structures. 

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