Guaiane Sesquiterpene Research Articles

Sesquiterpenes from Roots of Lingularia veitchiana.

AbstractFor Abstract see ChemInform Abstract in Full Text.

New erythroxane-type diterpenoids from Fagonia boveana (Hadidi) Hadidi & Graf.

The aerial parts of Fagonia boveana afforded two new erythroxane-type diterpenes, 3beta,15,16-trihydroxy-erythrox-4(18)-ene (2) and 15,16-dihydroxy-cis-ent-erythrox-3-ene (fagonene) (3) together with two known ones; 16-O-acetylfagonone (1) and 7beta-hydroxy fagonene (8). Also a new guaiane sesquiterpene alcohol, 6,10-epoxy-4alpha-hydroxy guaiane type sesquiterpene (4) has been isolated. In addition three 8-methoxy flavonols, 8-methoxy-quercetin-3,7,3'-trimethyl ether (ternatin) (5), gossypetin, 3,8,3',4' tetramethyl ether (6) and herbacetin-3,8-dimethyl ether (7) were also isolated. The structures of the isolated compounds have been determined on the basis of spectroscopic evidences as well as physical and chemical correlation with known compounds. On performing different assays for biological activities, 6 displayed significant cytotoxic activity against KA3IT and NIH3T3 cell lines, 8 was the most active antiviral against Herpes simplex type 1 while 7 was the most active cancer-preventive agent using protein-tyrosine kinase inhibitory method.

Induced Ionization in 1,4-Diol Monosuylfonate Esters and its Application in the Synthesis of Natural Products

The chemical manifestations of orbital interactions through four σ-bonds in the base-induced and -directed reactions of monosulfonated trans-perhydronaphthalene- and norbornane-1,4-diols are discussed. Through-bond interactions (TBI) and σ-participation are the most important stereoelectronic effects which principally determine their reactivity. Dependent on the geometry of the relaying C-C bonds, these compounds react by three chief pathways: rearrangement, elimination, and homofragmentation. Substituents at carbon atoms adjacent to the carbon atom bearing the sulfonate ester group increase the contribution of σ-participation, which is expressed in a higher reactivity of these compounds. In cases where the ideal W arrangement is not distorted by alkyl substituents, the co-operation of TBI and σ-participation results in a fast homofragmentation. Through-space interactions (TSI), if occurring next to TBI, have only a modest influence on the reactivity of these compounds. Secondary monosulfonate esters of rigid 1,4-diols do show these typical reactions after induced ionization but the ionization of primary sulfonate esters can not be induced in a similar way. The results obtained from the reactions on monomesylated cholestane-3,7-diols, as model systems for cyclic 1,5-diol monosulfonate esters, show that chemical consequences of TBI and σ-participation still can be observed in these systems, but play only a minor role in their reaction patterns. Applications of reaction strategies in which orbital interactions through four σ-bonds play an essential role are demonstrated in the total syntheses of cis-fused guaiane sesquiterpenes, alloaromadendrenes, α- santalanes and marasmanes.

Antimalarial (+)-trans-hexahydrodibenzopyran derivatives from Machaerium multiflorum.

Bioassay-guided fractionation of Machaerium multiflorum yielded the hitherto unreported (+)-trans-hexahydrodibenzopyrans machaeriol A (1) and machaeriol B (2), as well as the known guaiane sesquiterpene (-)-kessane. Structure elucidation was based on (1)H and (13)C NMR data, mainly 2D NMR (1)H-(1)H COSY, (1)H-(13)C HMQC, (1)H-(13)C HMBC, and (1)H-(1)H NOESY experiments. This is the first report of the hexahydrodibenzopyrans from a higher plant other than the genus Cannabis. The cannabimimetic activity was thus evaluated by radioligand binding assay for cannabinoid receptor CB1, which indicated, notably, that both 1 and 2 were inactive. In addition, the cross reactivity of 1 and 2 toward antibodies designed for urinary metabolites of cannabinoids was evaluated with the EMIT and On Line cannabinoids assays. Both compounds showed no response at 100 000 ng/mL in both assays. Machaeriol B (2) demonstrated in vitro antimalarial activity (IC(50) = 120 ng/mL) against Plasmodium falciparum W-2 clone.

Enantiodivergent syntheses of cycloheptenone intermediates for guaiane sesquiterpenes

The syntheses of enantiomeric 6-isopropenyl-3-methyl-2-cycloheptenones 16 and 22 have been effected starting from ( R)-(−)-carvone. In the synthesis of 16, ( R)-(−)-carvone was reduced and the resulting dihydrocarvone transformed regioselectively into silyl enol ethers. Cyclopropanation with dibromocarbene and in situ rearrangement gave an α-bromo-cycloheptenone which was reduced to the ( R)-(+)-cycloheptenone 16. In the synthesis of 22, ( R)-(−)-carvone was cyclopropanated with a sulfur ylide, followed by reduction with LiAlH 4 and acid-catalyzed cyclopropylcarbinyl rearrangement to afford a cycloheptenol. Oxidation and double bond conjugation led to the ( S)-(−)-cycloheptenone 22 in a partially racemized form. Four cycloheptenones have been obtained and are suitable intermediates for the enantiodivergent syntheses of guaiane sesquiterpenes.

Sesquiterpenes fromCurcuma aeruginosa

Curcuma aeruginosa Roxb. (Zingiberaceae) is widely cultivated in Malaysia and is known as temu hitam, owing to the blueish-grey internal colour of the rhizomes, as distinct from the yellow or orange colour of most species of the genus (1). The rhizome is used medicinally to treat asthma and cough (2), and is also applied externally, pounded in coconut oil for scurf (3). Previous studies of C. aeruginosa have resulted in the isolation of aerugidiol (4), difurocumenone (5) and guaiane sesquiterpene lactones (6). The chemical compositions of the essential oil of C. aeruginosa of Malaysia have been reported to comprise mainly curzerenone (7).

Synthesis of (E,E)-Germacrane Sesquiterpene Alcohols via Enolate-Assisted 1,4-Fragmentation.

An efficient method has been developed for the synthesis of (E,E)-germacrane sesquiterpene alcohols. The key step in these syntheses involves the enolate-assisted 1,4-fragmentation of properly functionalized perhydro-1-naphthalenecarboxaldehydes with 1 equiv of sodium tert-amylate as base, to give the corresponding (E,E)-germacrane aldehydes. These aldehydes are not very stable, and in situ reduction of the aldehyde function with Red-Al is required to obtain high yields of the desired germacrane alcohols. This procedure has led to the successful synthesis of 15-hydroxygermacrene B (4) and 15-hydroxyhedycaryol (35) from the mesylates 6 and 33, respectively. When KHMDS is used instead of sodium tert-amylate in the fragmentation reaction of 6, isomerization of the initially formed C(4)-C(5) E double bond cannot be avoided and results, after in situ reduction with Red-Al, in the formation of the (E,Z)-germacrane alcohol 24. The 15-hydroxy-(E,E)-germacranes are excellent starting materials for the selective synthesis of the corresponding 4,5-epoxides, which in turn can perfectly well be used in studies on the biomimetic formation of guaiane sesquiterpenes.

About the Chiral Stability of Germacrene B and the Biomimetic Synthesis of Guaiane Sesquiterpenes.

The planar chirality of 15-hydroxygermacrene B (2) has been examined by means of the asymmetric Sharpless epoxidation, performed as a kinetic resolution. (1)H NMR experiments with Eu(hfc)(3) demonstrate that the recovered 2 is racemic. Consequently, 2 and most likely also germacrene B (1) are not enantiomerically stable at room temperature. The formation of the optically active cis-fused guaiane 4 of high ee with limited Sharpless reagent shows that the asymmetric epoxidation of 2 proceeds highly enantioselectively. The Sharpless epoxidation methodology applied on the (E,Z)-germacrane 3 results in the formation of the stable optically active epoxide 5. Acid-induced cyclization of 5, leading to a mixture of guaianes, probably proceeds via the trans-fused carbocationic intermediate A.

New Sesquiterpenes from TwoLigularia Species

Further phytochemical investigation of the roots of Ligularia sagitta afforded two new eremophilane sesquiterpene acids, and from the roots of Ligularia nelumbifolia, two new guaiane sesquiterpenes were isolated. Their structures were elucidated by spectroscopic methods including 2D NMR techniques and chemical transformations.

The isolation of a guaiane sesquiterpene from fruit bodies of Lactarius sanguifluus

The isolation and structure elucidation of a novel guaiane alcohol, formed together with related aldehydes and alcohols from fatty acid ester precursors in injured fruit bodies of the Basidiomycete Lactarius sanguifluus, is reported.

Terpenoids from Curcuma heyneana

A new guaiane sesquiterpene named oxycurcumenol was isolated from the steam-distilled essential oil fraction of Curcuma heyneana in addition to known sesquiterpenes germacrone, dehydrocurdione, isocurcumenol, curcumenol, curcumanolide A, B and zerumbone. Its structure was elucidated on the basis of spectroscopic and chemical studies, and finally confirmed by X-ray crystallography. ( E)-Labda-8(17),12-diene-15,16-dial was isolated from the benzene extract of the same plant together with dehydrocurdione, curcumenol, curcumanolide A and B. The taxonomic status of C. heyneana is briefly discussed based on the chemotaxonomic significance of these findings.

A brief, stereoselective total synthesis of the guaiane sesquiterpene (±)-gnididione

A total synthesis of the guaiane sesquiterpene (±)-gnididione (1) has been achieved using carbanion chemistry at each key stage.