Germacrane sesquiterpenes

Raucher et al. used a tandem Cope-Claisen rearrangement during total synthesis of the germacrane sesquiterpene (+)-dihydrocostunolide (3)2 (Scheme 1.4c). 

Kikkanol D monoacetate (germacrane sesquiterpene) Kikkanol E (germacrane sesquiterpene)... 

Dauben et al. [153] successfully applied this procedure to the total synthesis of the cembranoid crassin acetate methyl ether (258). As shown in Scheme 86, the keto aldehyde 256 was treated with TiClj/Zn-Cu in refluxing DME to give the cyclic olefin 257 in 65% yield (E Z = 4 3). The germacrane sesquiterpenes have also been synthesized using this method [154],... 

Finally, mention should be made of the increasing application of the intramolecular Nuclear Overhauser Effect (NOE) which has played an important role not only as an aid to structural elucidation but also in the conformational determination of some of the germacrane sesquiterpenes. These results have a significant bearing on the understanding of transannular effects and chemical reactivity. 

This reductive alkylation was used in a synthesis of 8, which contains the 10-membered ring system of germacrane sesquiterpenes. Thus the tetralonc 5 was converted by way of 6 into the tosylate 7. On treatment with LDA in THF at 24°, 7 underwent a Grob-type fragmentation to give 8. 

Periplanone B is the most active sex pheromone found in the alimentary tract and excreta of the American cockroach Periplaneta americana. An elegant total synthesis of this germacrane sesquiterpene was achieved by SCHREIBER and SANTINI Cyclodecatrienone 1 is an obvious precursor. One of the oxirane rings arises from epoxidation of the enone CC double bond, the other from [2-1-1]-cycloaddition of a carbene to the carbonyl bond of the enone. Oxidation of the methylene group introduces the additional carbonyl double bond. The CC double bond of the enone results from an elimination of HX in the a-X-substituted cyclodecadienone 2, which, on its part, is feasible by substitution of cyclodecadienone 3. An electrocyclic opening of the cyclobutene ring in 4 provides the 1,3-diene substructure in 3. 

Mtagawa, I., Cui, Z., Son, B.W., Kobayashi, M., and Myoboku, Y. (1987) Nephtheoxydiol, a new cytotoxic hydroperoxy-germacrane sesquiterpene, and related sesquiterpenoids from an Okinawan soft coral of Nephthea species (Nephtheidae). Chem. Phann. Bull, 35, 124-135. 

Martins, D.L. and Epifanio, R.D. (1998) A new germacrane sesquiterpene from the Brazilian endemic gorgonian Phyllr otgia dilatata Esper. J. Brazil. Chem. Soc.,9, 586-590. 

The trans-cis isomerization process observed in the eudesmane/germacrane ring system has been utilized for the synthesis of the c/s-fused sesquiterpene occidentalol, 48a, and its 7-epi isomer, 48b (Scheme ll)22. Photolysis of the traws-fused diene 45 at —78°C afforded triene 46, which upon warming underwent disrotatory electrocyclization to give 47a and 47b as a 1 2 mixture of diastereomers. Apparently, the carboalkoxy group imparts... 

A quite detailed review of transannular cyclizations was published201 wherein their important role in biomimetic syntheses of sesquiterpenes as well as explanation of the biogenetic formation of the polycyclic natural compounds from their monocyclic precursors is discussed. The great significance of these transformations for the synthesis of natural products is also emphasized in a series of reviews which describe the cyclizations to form terpene derivatives, e.g., of the germacrane and humulene systems202-206. 

Recently, germacrene-A (III) has been identified as the alarm pheromone of the sweet clover aphid Therioaphis trifolii (38). This alarm releaser, which has often been proposed as the progenitor of cyclic sesquiterpenes, constitutes the second compound with a germacrane-type skeleton to be identified as an insect pheromone. 

Epoxy-5,10-dihydoxy-6a-angeloyloxy-9 (3-isobutyloxy germacran-8a, 12-olide (germacranolide sesquiterpene lactone) Carpesium divaricatum (Asteraceae) l iNOS expression [per inhibiting NFkB activation]... 

For other examples of stereospecific Cope rearrangements of germacrane-type sesquiterpenes see refs 1039-1041. 

Reports on the sesquiterpene composition of Baccharis genus are recorded in the literature. From some representatives of this genus growing in Texas and Mexico, sesquiterpene hydrocarbons, such as germacrane D and caryophyllenepoxide were isolated [34], From Baccharis dracunculifolia D. C. sesquiterpene hydrocarbons like germacrane D, 8-cadinene,... 

Cardui benedicti herba Cnici herba Blessed thistle Cnicus beiiedictus L. Asteraceae DAC 86. GAB 90, MD Sesquiterpene lactons (-0.25%), (germacran type) cnicin, salonitenolid and artemisiifoliii lit of the drug, 800-1800 Essential oil (0.03%-0.1%) citral, cilronellal cinnamic acid, acetylene derivatives Pig. 8... 

---