Incensole

Another striking difference relates to the diterpenes (Figure 16.3) B. carterii reveals strong peaks that have been assigned to verticilla-4 (20),7,ll-triene (compound 1), incensole acetate (compound 2), and incensole (compound 3) and, on the other hand, Boswellia serrata shows peaks of m- and / -camphorene (compoimd 4 and compound 5) as well of cembrenol (= serratol) (compound 6). 

The brownish colored zone (Rj 0.28) of incensole (compound 3), which occurs in both the resin and the volatile fractions of B. carterii, draws the hue between the volatile diterpenes and the nonvolatile triterpenes. B. carterii reveals two further colored prominent spots, a yellowish-ochre (Rf 0.65) of incensole acetate (compound 2) and a violet-colored spot (Rj 0.98) of verticilla-4(20),7,ll-triene (compound 1). Lane 2 and lane 3 reveal a light blue area (Rj 0.60) of 1,8-cineol that is only visible in freshly distilled oils. 

FIGURE 16.6 Purification steps of fraction 2 and 3 from B. carterii. (A) GC and TLC data of fractions 2 and 3. (B) GC data of incensole acetate after separation and purification of the zone Rf 0.50. (C) Mass spectrum of incensole acetate (compound 2). 

To isolate the brownish spot of incensole in fraction 4, the mobile phase, dichlo-romethane-diisopropylether (95 -r 5 v/v) was favored. The marked zones were scraped off in a larger scale. After collection and extraction of the zones, the roughly separated substance was pnrified several times until the collected extracts revealed one brownish spot, which matched the incensole (compound 3) peak on GC. Figure 16.7 illustrates the purification steps. 

FIGURE 16.9 An overview of the marker substances of (A) B. carterii and (B) B. serrata. (A) Lane 1 incensole (compound 3), lane 2 and 3 hexane extract of B. carterii, lane 4 incensole acetate (compound 2), lane 5 verticilla-4(20),7,ll-triene (compound 1). (B) Lane 1 m-camphorene (compound 4) and p-camphorene (compound 5), lane 2 cembrenol (compound 6), lane 3 Hexane extract of B. serrata. 

The isolation of the second violet zone (Rf 0.55) succeeded more easily with B. serrata resins because there was no interference with incensol acetate. 

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. 

The chemical composition of B. papyrifera olibanum is markedly different from that of other Boswellia, with small amounts of monoterpenes and sesquiterpenes, large amounts of w-octanol (18) and -octy I acetate (40), with the latter being the major compound, and the presence of particular diterpenes [incensole (127), incen-sole acetate (129), incensole oxide (130) and incensole oxide acetate (131)] and the absence of both isoincensole and isoincensole acetate (128). Linear carboxylic acids from hexanoic acid (10) to lauric acid (93) were also identified in B. papyrifera olibanum exclusively. 

The samples coming from Eritrea, Jerusalem and Liban could be undoubtedly attributed to B. papyrifera, because of their characteristic constituents octanol (18), octyl acetate (40), linear caboxylic acids (10, 20, 36, 49, 63), incensole (127) and its acetate and oxide derivatives (129-131). 

Samples purchased on markets in Sa da and San a in Yemen comprise no diterpenes from the incensole family but large amounts of dimers of ot-phellan-drene, in particular dimer 3 (113), and of both compounds 55 and 56. This pattern identifies them as B. frereana olibanum. 

Figure 10.7 Total ion current chromatograms obtained after headspace SPME for (a) incense from Mount Athos and (b) B. papyrifera olibanum. Peak labels correspond to compound identification given in Table 10.3. The occurrence of the following biomarkers of B. papyrifera olibanum in the incense from Mount Athos are a clear indication of its botanical origin n octanol (18), n octylacetate (40), incensole (127), incensole acetate (129), incensole oxide (130) and incensole oxide acetate (131). Artefacts. Reproduced from S. Hamm, J. Bleton,). Connan, A. Tchapla, Phytochemistry, 66, 1499 1514. Copyright 2005 Elsevier Limited...

Incensole (113) and isoincensole oxide (114) have been synthesized from muku-lol by methods which allow the determination of their stereochemistry. The X-ray analysis of a thunbergadienediol (115), obtained from Greek tobacco, has been described. ... 

A small amount of isoincensole oxide (116) has been isolated from frankincense, the resin of Boswellia carteri. It is also a minor product of the epoxidation of incensole. The epoxide ring is very inert in this compound. 

Ibogamines, 358 Ibogane alkaloids, 389 Imidazoles, 245, 246 Iminium salts, 292-293 l,6-lmino[10]annulene, 266 Iminoaziridines, 76 Iminophosphoranes, 106 2-lminotetrahydrofuranes, 202 Incensole, 351 Indanones, 327 Indene, 100 Indenes, 262 Indenones, 430 Indoles, 21-22, 135 Indoline, 277, 314 lodination, 359-360 Iodine, 179-181... 

Reaction with unsaturateti alcohols and ketones. This brominating reagent reacts with some iinsalurated alcohols, for example (2), to form bromo ethers (3) and (4)." This reaction was used in a synthesis of t//-incensole (8) from dl-mukulol (5) as formulated. ... 

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