Germacrenes synthesis

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. 

Composition The European Pharmacopoeia lists linalyl acetate (56-78%), linalool (6.5-24%) and germacrene D (1.0-12%). a-Terpineol is limited to 5.0%, a- and P-thujone to 0.2%. Sclareol (0.4-2.6%) is found mainly in the concrete and is used for the synthesis of ambra fragrance materials. Further constituents are linalool oxide, geraniol, nerol, neryl and terpinyl acetate, citronellol, 1,8-cineole, benzaldehyde and n-nonanal. For further literature see [64, 65]. 

The anionic oxy-Cope rearrangement of substrate 2 is used as the key step in a synthesis of ( + )-germacrene D (an ubiquitous plant product thaL serves as a biogenetic precursor to a number of the sesquiterpene families) and (+)-periplanone [(+)-periplanone B, the sex pheromone of the American cockroach Perip/aneta amerkana]950 9 5 2... 

C15H20O2, Mr 232.32, colorless cryst., mp. 110-111 °C, [a]p +145.8° (CHCI3) soluble in chloroform, ethanol, and THE. An a,j3-unsaturated sesquiterpene lactone with the germacrene skeleton (see ger-macrenes) from Aristolochia reticulata and A. serpen-taria. The absolute configuration has been determined both by X-ray diffraction and enantiospecific synthesis. ... 

Synthetic routes to germacrenes are always of interest. This year, McMurry has applied his low-valent titanium based method to bicyclogermacrene (45), from (44), and Schreiber et al. have summarized a short synthesis of germacrene D (48) which relies heavily on the site- and stereo-selective enolization of (46) to (47) using the conformational bias in the ten-membered ring intermediate (46). In a first example of the oxy-Cope (6 - 14 membered)... 

The four membrane fractions are incubated with [ 1- C] IPP and assayed for 5 enzymic activities. Figure 1 shows that the membranes sedimenting in the upper band A exhibit the greatest activity in the synthesis of sesquiterpene hydrocarbons particularly p-selinene and germacrene D. Lower amounts of radioactivity are also present in B and C whereas only traces of synthesis of hydrocarbons are found in D. 

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