3 -Cembrene

Propose a structure for cembrene that is consistent with its formation from geranylgeranyl diphosphate. 

Boswellia carterii Verticilla-4(20),7,11-Triene (Compound 1) and the Other Cembrenes... 

The separation and collection of the violet zone (Rj 0.98) of fraction 1 led to the isolation of m- and p-camphorene (compound 4 and compound 5) and cembrane A as well. Thongh m- and p-camphorene are taxonomic marker substances of the species B. serrata, it is pointless to use them in TLC, because the corresponding violet spot on the chromatogram of B. carterii stands for verticilla-4(20),7,l 1-triene, the taxonomic marker substance of B. carterii and cembrene A, too. These violet snbstances shonld be reserved for GC investigations. 

The GC-MS data (Figure 16.11) of the violet zone of B. carterii revealed that the unchanged diterpenes (verticillatriene, cembrene A, and cembrene C) and the nortriterpenes with carbohydrate structure originated from the pyrolyzed triterpenes (Figure 16.12) of the a- and (3-boswellic acids, named 24-norursa-3,12-diene (compound 7), 24-norursa-3,9(ll),12-triene (compound 8), 24-noroleana-3,12-diene (compound 9), and 24-noroleana-3,9(ll),12-triene (compound 10). 

For olibanum, six characteristic diterpenes were observed cembrene A (94), cembrene C (98), isoincensole acetate (104), a dimer of a-phellandrene (86) and two unidentified compounds (92) and (103). 

Frankincense, also called olibanum, is a natural oleo gum resin that exudes from incisions in the bark of Boswellia trees [46, 47]. Diterpenes like incensole or isoincensole and their oxide or acetate derivatives (see Figure 10.3) are characteristic biomarkers of olibanum [48]. Although diterpenoid hydrocarbons possessing the cembrane skeleton have been isolated from a variety of terrestrial and marine organisms, their occurrence and particularly that of cembrenes A and C (see Figure 10.3) is supplementary proof of the presence of olibanum in a sample. Optimisation of the SPME conditions was done with the aim of trapping these low volatile diterpenes. 

Figure 10.3 Structure of cembrene A, cembrene C and isoincensole acetate. Reproduced from S. Hamm, E. Lesellier, J. Bleton, A. Tchapla, J. Chromatogr., A, 1018, 73 83. Copyright 2003 Elsevier Limited...

Sampling time 60 min extraction temperature 80°C. Monoterpenes a-pinene, p-myrcene, a-phellandreneand limonene sesquiterpenes a-cubebene, a-copaene, p-elemene, p-caryophyllene, a-humulene, y-muurolene, p-eudesmene and caryophyllene oxide diterpenes cembrene A and isoincensole acetate. 

The first observation is the similarity between the chemical compositions of both the Boswellia carteri and Boswellia sacra. For these three olibanum samples, a-pinene (2), (3-myrcene (8) and limonene (14) are the predominant monoterpenes. p-Caryophyllene (73) is the major sesquiterpene besides a-copaene (65), a-humulene (also called a-caryophyllene) (78) and caryophyllene oxide (95). The characteristic olibanum compounds isoincensole and isoincensole acetate (128) together with cembrene A (120) are the main diterpenes. 

Boswellia serrata olibanum has a chemical composition close to that of both the B. carteri and of B. sacra, but contains compounds that are absent in those from other Boswellia and could be used as markers methylchavicol (38), p-anisaldehyde (47), methyleugenol (70), isocaryophyllene (82), sesquiterpene 91, elemicin (92) and an unidentified diterpene (124) eluting between cembrene C (123) and verticilla-4(20),7,ll-triene (125). It is devoid of (5-caryophyllene (73), a-humulene (78), caryophyllene oxide (95) and bornyl acetate (50). 

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...

Fig. 5a. Part of the spectra obtained with the ID multiple selective INADEQUATE experiment III applied to cembrene 3 dissolved in CDCI3. The spectra were obtained after appropriate processing, showing the responses in the olefinic and the aliphatic regions after selective inversion of carbons...

NT541 Takagi, Y., T. Fujimori, H. Kaneko, and K. Kato. Cembrene, from Japanese domestic tobacco Nicotiana tabacum. Agr Biol Chem 1980 44 467-468. 

Synthetic endeavours have continued in the diterpenoid series. The cyclization of geranylgeranic acid chloride to derivatives of cembrene, and their conversion into cembrene itself, have been described. Some further extensions of the route to macrocyclic diterpenoids based on the intramolecular cyclization of epoxysulphides and the subsequent modification of the macrocylic product have been described. ... 

Commiphora myrrha Engler Mo Yao (Myrrh) (stem) From gum resin, essential oils including myrcene, alpha-camphorene, Z-guggulsterol, guggulsterol, makulor, cembrene 33 Stimulate blood flow, relieve pain, promote tissue regeneration. 

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