Calamenenes

Figure 10.24 Total ion current chromatograms obtained after headspace SPME for (a) the archaeological incense and (b) B. carteri olibanum. Peak labels correspond to compound identification given in Table 10.3. Peaks labelled by letters correspond to the following compounds a, pinocamphone b, borneol c, calamenene d, cadalene. Among other finger prints, the occurrence of dimer 2 (111), cembrene A (120) and isoincensole acetate (128) confirm that this sampleis olibanum and attributes its botanical source to B. carteri or B. sacra. Reproduced from S. Hamm, J. Bleton, J. Connan, A. Tchapla, Phytochemistry, 66, 1499 1514. Copyright 2005 Elsevier Limited...

The reduction of simple trisubstituted olefins derived from 25d has found use in the enantioselective total synthesis of pseudopteroxazole 31c, demethyl methoxy-calamenene 32c, and both enantiomers of mutisianthol 33c (Scheme 4) [41,46,47]. 

Tetralins indanes. P205 can be used for cyclodehydration for substrates such as 1-aryl-l-pentanols or 2-aryl-2-hexanols. In the case of secondary alcohols, yields are sometimes improved by dehydration with TsOH to a styrene followed by cyclization with P2O5.1 The product of the second example is a known sesquiterpene, calamenene. 

An enantioselective approach to cytotoxic nor-calamenenes via electron-transfer-driven benzylic umpolung of an arene tricarbonyl chromium complex. Synthesis 2003, 1851-1855. 

The absolute configurations of ( + )-calamene (268) and ( + )-7-hydroxy-calamenene (269), metabolites of Eremophila drummondii, have been established by AT-ray crystallographic analysis. These compounds are therefore enantiomeric to calamenenes previously found in other plants. Laevigatin (270), a constituent of the essential oil of Eupatorium laevigatum, has been assigned structure (270) on the basis of spectroscopic evidence and oxidation to-furano-cadalene (271). ... 

Apart from the n-alkanes discussed above, epicuticular wax hydrocarbons contain sesqui- and diterpenoids. These compounds are based on the structural skeletons of cadinane and abietane, respectively, which are shown in Fig. 7-24. The sesquiterpenoids recovered by Simoneit and Mazurek (1982) in the rural aerosol were calamenene, tetrahydrocadalane, and cadalene. These compounds presumably are degradation products of cadinane derivatives (various isomers of cadinenes and cadinols), which are ubiquitous in essential oils of many higher plants (Simonsen and Barton, 1961). The major diterpenoid hydrocarbons observed in the aerosol samples were dehy-droabietane, dehydroabietin, and retene. The main source of abietane derivatives are coniferous resins. The parent compounds dehydrate fairly rapidly to yield the more stable hydrocarbons found in the aerosols. These may then serve as markers for hydrocarbons arising from vegetation, in addition to the odd-to-even carbon number preference in the n-alkanes. 

Another sesquiterpene class represented in the Eremophila genus is that of the bicyclic calamenenes. Two sesquiterpenes, (-r)-calamenene (76) and its 7-hydroxy derivative (77), were isolated from E. drummondii (69). At that time, contradictory claims regarding the absolute configuration of the known (-)-calamenene had been made. This confusion was resolved by an... 

The calamenene skeleton contains only two asymmetric carbon atoms 1,4-disposed on a tetralin system. Until recently, the synthesis of this skeleton had only been achieved starting from chiral pool agents with the two asymmetric carbon atoms of interest of predetermined configuration (71,72). Recent developments in synthetic methodology now allow the elaboration of the 1,4-P-aiw-or 1,4-ci j- disubstituted system starting from 5-methoxytetralone or its equivalent (73-75). 

The second pathway involves the intermediacy of a carbocation derived from 2Z,6 -famesyl pyrophosphate. Following a 1,3-hydride shift, the resulting allylic carbocation can cyclize to the decalin ring system which characterises the calamenenes (76,77) and the cadinenes (79-82,85). The derivation of oplopanone (88) by ring contraction of the cadinene system seems likely. 

Serrulatanes The most common diterpene skeleton found in Eremophila is that represented hy the hicarbocyclic serrulatane group of compounds (101-104). Essentially, these are isoprenologues of the calamenene sesquiterpenes in which the dimethylallyl derived unit of the acyclic precursor does not participate in cyclisation. The first example of this skeleton was found in dihydroxyserrulatic acid (120) which was isolated from E. serrulata (101). As observed for the calamenenes, the presence of the serrulatane skeleton can be inferred from nmr spectroscopic data. 

All serrulatanes so far described contain the l/ ,4S-stereochemistry in contrast to the calamenenes ( R,AR) from Eremophila species with which, in at least two cases, they co-occur. 

Confirmation of the structure proposed, the location of the primary hydroxyl group and the relative stereochemistry of 131 was provided by an X-ray diffraction study which showed that the viscidane skeleton was isoprenologous with a-acorene (ent-133). For the determination of the absolute configuration, a correlation with this sesquiterpene ring system seemed convenient using the method developed for the serrulatane-calamenene correlation. To this end, the methyl ester was... 

---