Eudesmane sesquiterpenes

The extrapolation of the vinylcyclopropane-cyclopentene rearrangement to a vinyl-cyclobutaiie-cyclohexene synthesis begins to create new insights into the synthesis of six membered ring natural products. The eudesmane sesquiterpene (—)-P-selinene, 217 illustrates such a strategy as summarized in Scheme 14 80). A suitable cyclohexene... 

The construction of the tricyclo[5.2.0.02,6]nonane (26, n = 1) and tricyclo[6.2.0.02,7]decane (26, n = 2) frameworks involved the [2 4- 2] cycloaddition of readily accessible31,32 l,2-bis(trimethyl-siloxy)cyclobutene and cnone 25, n = 1 or 2, respectively.33 The yields (75-80%) were good for adducts 26a, c, e, and g. Lower yields (40-50%) were observed for adducts 26b and 26f, while adduct 26d was only isolated in a trace amount. The most interesting and important reaction, related to the total synthesis of eudesmane sesquiterpenes, was the photochemical reaction of (-)-piperitone (25g) with l,2-bis(trimethylsiloxy)cyclobutene, which gave c/.v,(5wf/u W-2/j,7/i-dimethyl-4/ -isopropyl-l f ,8Jf -bis(triniethylsiloxy)tricyclo[6.2.0.0z 7]dec-3-one (26g) with the relative cis configuration of the methyl (R2) and isopropyl (R3) groups.33,34 Some of the other photochemical [2 + 2] cycloaddition reactions utilizing l,2-bis(trimethyl-siloxy)cyclobutene are shown by the formation of 2735,36 and 28.37... 

The construction of a key intermediate for use in the synthesis of the eudesmane sesquiterpenes starting from 2-methylfuran has been reported (74H(2)639). Metallation of... 

The isoxazolidines derived from aldehydes (17a-b) were converted to eudesmane sesquiterpenes. Thus, quatemization of isoxazolidine (18) was followed by ring expansion via a Stevens rearrangement. 

Reaction of these adducts with a zinc carbenoid is accompanied by a [2,3]-sigmatropic rearrangement of the phenylthio group to generate a new carbon-carbon bond at the original allylic center. This reaction converts 5 stereospccifically into 6, related to eudesmane sesquiterpenes. 

The utility of this stepwise C3 - C4 - C6 ring expansion has been demonstrated by the synthesis of the optically active eudesmane sesquiterpene (—)- 3-selinene 295 starting from the commercially available (—)-perillaldehyde 2871S3). Thus, addition of the 1-lithio-l-methoxycyclopropane 136 (vide supra. Sect. 4.6.3, Eq. (44)) to 287,... 

A1 Dabbas et al. [163] reported the antibacterial activity of the ethyl acetate extract of the whole aerial part of Varthemia iphinoides L. The bioassay-guided fractionation led to the isolation and identification of an antibacterial eudesmane sesquiterpene, selina-4,ll(13)-dien-3-on-12 oic acid. Fig. (10). This compound exhibited potent antimicrobial activity against 6 bacterial species Staphylococcus aureus, Bacillus subtilis. Micrococcus luteus, Escherichia coli. Bacillus cereus and Salmonella enter Hides ). The MIC values of this sesquiterpene, which was determined by the agar dilution method, ranged between 250 and 500 ig/ml. 

Michael addition. TiCl4 was used to effect addition of the silyl enol ether I to 2 to obtain 3. Base could not be used because of the extreme sensitivity of 2. The product was used for synthesis of several eudesmane sesquiterpenes containing an a-methylene-y-butyrolactone unit, such as //-epiatlantolactone (4).5... 

This compound, probably derived from an eudesmane sesquiterpene, is a metabolite of many actino-mycetes and of several blue-green algae. 

Intramolecular cycloaddition reactions are possible in the absence of electron-withdrawing substituents on the dienophile, although more-vigorous conditions are normally required. Cycloaddition of the triene 87 at 200 °C gave, after hydrolysis of the silyl ether, a mixture of the diastereomeric rra s-fused ring systems 88, which were converted into the eudesmane sesquiterpene 89 (3.76). ... 

C15H22O, Mr 218.34. The structural isomers a-V (iso-nootkatone, a-vetiverone, cryst., mp. 51 -51.5 °C, bp. 152-153 °C (5.32 10 Pa), soluble in all common organic solvents, [a]D+225°(C2HjOH) and)3-K [cryst., mp. 44-45 °C, [aJo -38.9° (C2H5OH)] are known. Both isomers occur in vetiver oil. The biosynthesis proceeds from eudesmane sesquiterpenes. For some time a-V. was erroneously considered to be a hydro-azulenone derivative. 

Orabi, K.Y, 2000. Microbial transformation of the eudesmane sesquiterpene plectranthone. J. Nat. Prod., 63 1709-1711. 

The genus Lactuca (L. perennis, L. tatarica, L. indica, L. capensis, L. tenerrima) has been shown to produce sesquiterpene lactones including guaianolides, germacranolides, and some eudesmanolides. Two new eudesmane sesquiterpene lactones show anticancer activity against epithelial carcinoma and colon carcinoma cell lines [77]. 

Total syntheses of the 1-oxygenated eudesmane sesquiterpenes ( )-dihydro-reynosin and ( )-oxocostic acid have appeared.The ester (166) rearranges to the lactone (167), which is obtained (in good yield) as a 2 1 mixture of epimers at the methyl-bearing carbon (Scheme 95). 

Intramolecular Cycloadditions.—Application of certain intramolecular reactions allows the synthetic chemist to generate complex carbon skeletons more readily than by using intermolecular processes, and to exercise considerable control over regio- and stereo-specificity. It is not surprising, therefore, that this area of endeavour has become increasingly popular in recent years. Dominant among the reactions under study has been the intramolecular [4 + 2] cycloaddition (i.e. the intramolecular variant of the Diels-Alder reaction), some examples of which have already been noted in earlier sections. The reaction has also been applied in total syntheses of steroids, ( )-cedrol, eudesmane sesquiterpenes, and norpatchoulenol. The intramolecular [3 + 2] cycloaddition, a related process, has been used by Confalone et al. in a synthesis of ( )-biotin. The key steps are... 

Amazonian species of Emmotum and Poraqueiba two genera of the Icacinaceae family occuring in the Western Hemisphere, contain a class of rearranged eudesmane sesquiterpenes named emmotins that are of higher frequency in (27 compoimds/4 species)... 

A fiirther investigation of the trunkwood of the first specimen of E. nitens (Enl) led to the isolation of three authentic eudesmane derivatives, the new emmotinol-A and -B besides the previously known pterocarptriol (24) (Figure 2) and rearranged eudesmane sesquiterpenes, comprising (+)-rishitinol (Table I), a stress compound from Solanaceae (25), and 14 new emmotins represented by 3 tetralones (Table II), 10 naphthalenes (Table III) and 1 naphthoquinone (Table IV) (27). 

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