Amyrins

Fig. 27. Total synthesis of P-amyrin [559-70-6] (256) via a carbocationic cyclization, where TMS = trimethylsilyl.

Partial Synthesis of a-Amyrin Acetate Proof of the Structure and Stereochemistry... 

The first synthesis of a P-amyrin derivative was accomplished by a convergent route which depended on cation-olefin cyclization to form the critical central ring. The plan of synthesis was largely guided by the selection of SM goals for the A/B and E ring portions of the target. 

Rhodamine 6G long-chain hydrocarbons [169] squalene, a-amyrin [170] methyl esters of fatty acids [171] glycerides [91] sterols [172, 173] isoprenoids, quinones [HI] lipoproteins [174] glycosphingolipids [175] phenolic lipids [176] phosphonolipids [177] increasing the sensitivity after exposure to iodine vapor [178,179]... 

Amylene, stabilizer for solvents 120 Amylose reagent 173 a-Amyrin 44,69 jS-Amyrin 69 a-Amyrin benzoate 63 Anabolics 303, 411, 430,432 Anacardol 288... 

Amyl nitrite reagent lb 115 Amylose la 173 a-Amyrin la 44,63,69 P-Amyiin la 69... 

Knob (southern Canterbury Administrative Region see Fig. 2.11) and cycloartenol methyl ether [58] was found in plants from Clarke River, whereas four other collections failed to yield any TMEs. Similarly, populations of C. rigida (Raoul) Zotov from eastern South Island do not synthesize TMEs, whereas those from western South Island were shown to accumulate p-amyrin methyl ether [59]. An additional difference between populations from these two sites lies in the capacity of the former to produce short-chain wax components, as opposed to long-chain compounds from the latter (Cowlishaw et al., 1983). Different chemodemes were also described for C. cheesemanii (Hackel ex Cheesem.) Zotov plants from North Island exhibited lupeol methyl ether as the dominant compound along with lesser amounts of arun-doin and two unidentified compounds, whereas populations from the South Island had arundoin as the major compound with lesser amounts of lupeol methyl ether. 

Tenerife and La Palma, revealed the existence of luteolin and an array of simple phenolic derivatives as well as three known phytosterols, B-amyrin, sitosterol, and stigmasterol. The phenols identified comprised a set of phenylpropanoids myristicin [566] (see Fig. 6.16 for structures 566-573), methyleugenol [567], todadiol [568], todatriol [569], crocatone [570], elemicin [571], apiole [572], and the coumarin scopoletin [573]. The occurrence of these compounds is recorded in Table 6.5. The differences between the two profiles were taken by Gonzalez and his co-workers... 

The plant is known to produce norbisabolane diterpenes, including phyllanthusols A and B, which are both cytotoxic (36). From the bark, pentacyclic triterpenoids, phyl-lanthol, and olean-12en-3[3-ol (p-amyrin) have been isolated (37). Note lupane- and oleanane-type triterpenoids isolated from the bark of Phyllanthus flexuosus, such as olean-12-en-3 (3,15 a-diol, olean-12-en-3 [3,15 a,24-triol, lupeol, and betulin inhibited the enzymatic activity of topoisomerase II activity with IC50 values in the range of 10 to 39 p.M (38). 

Burseraceae Commiphora (myrrh) Boswellia (olibanum or frankincense) Canarium (elemi) a and (3 amyrin, euphanes, oleananes... 

In the mass spectra of ot-amyrine, a peak was observed at m/z 426, relating to the molecular ion, along with peaks at m/z 411 and 408, arising from the fragmentation of the molecular ion by the loss of a methyl radical and of a water molecule, respectively. The peak at m/z 393 is due to the loss of a methyl radical and a water molecule. 

Figure 3.1 Mass spectra of (a) a amyrine and (b) oleanolic acid obtained by DE MS...

Tirucallol, p amyrin, germanicol, lupeol, 3 hydroxy malabarica 14(26), 1 7 ,21 triene C30H50O... 

Regert et al. studied [9] a series of 30 Neolithic hafting adhesives from lake dwellings at Chalain (France) using an analytical procedure based on GC/MS analysis involving solvent extraction (dichloromethane) and trimethylsilylation. In the majority of the samples a series of triterpenoid compounds with a lupane structure was clearly identified on the basis of their TMS mass spectra. In particular, the presence of betulin, betulone, lupenone, lupeol and lupa-2,20(29)-dien-28-ol allowed birch bark tar to be identified. In other samples the co-occurrence of other plant biomarkers such as a-amyrin,(3-amyrin... 

The use of HMDS as a derivatization reagent in the analysis of triterpenoid resins has been less explored. The TMS derivatives of triterpenoids bearing hydroxyl groups [a-amyrine, p-amyrine and hop-22(29)-en-3p-ol] have been identified in the triterpenic fraction of Burseraceae resins, thus demonstrating that HMDS combined with Py-GC/MS is effective in the derivatization of triterpenoid compounds [59]. However, the range of structures that can be fully derivatized and detected must be extended and, in order to get comprehensive results comparable with those coming from the well assessed off-line GC/MS procedures, general improvements in the on-line trimethylsilylation-pyrolysis method are needed. 

The tetracyclic alcohol 179 is produced by the action of boron trifluoride etherate or tin(IV) chloride on the oxirane 178 (equation 85)95. A similar cyclization of the oxirane 180 yields DL-<5-amyrin (181) (equation 86)96. In the SnCLt-catalysed ring-closure of the tetraene 182 to the all-fraws-tetracycle 183 (equation 87) seven asymmetric centres are created, yet only two of sixty-four possible racemates are formed97. It has been proposed that multiple ring-closures of this kind form the basis of the biosynthesis of steroids and tetra-and pentacyclic triterpenoids, the Stork-Eschenmoser hypothesis 98,99. Such biomimetic polyene cyclizations, e.g. the formation of lanosterol from squalene (equation 88), have been reviewed69,70. 

Characterization of P-Amyrin Synthase from Avena strigosa - A Novel... 

Fig. 5.1 Cyclization of 2,3-oxidosqualene to sterols and triterpenoids. The 2,3-oxidosqualene cyclase enzymes that catalyse the formation of the different products are indicated LS, lanosterol synthase CS, cycloartenol synthase LuS, lupeol synthase PAS, P-amyrin synthase aAS, a-amyrin synthase.

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