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1.
The two D:A-friedo-oleanane triterpenes kokzeylanol and kokzeylanonol isolated from the inner bark of Kokoona zeylanica have been characterized as 6β,27-dihydroxy-D:A -friedo-olean-3-one and 6β,27-dihydroxy-D:A-friedo-olean-3,21-dione, respectively, by the deoxygenation of their 27-acetoxy derivatives using lithium-ethylenediamine reduction coupled with spectroscopic and irradiation methods. Kokzeylanonol represents the first tetra-oxygenated D:A-friedo-oleanane triterpene obtained from a nautral source. Significance of some of these D:A-friedo-oleananes in the biosynthesis of quinonoid triterpenes in Celastraceae is discussed. 相似文献
2.
Two steroidal compounds BR-1 (I) and ?2 (II) which had been obtained from the rhizomes of Baker, were isolated also from those of Roth. They were identified, respectively, by X-ray analysis and chemical correlation as 1β,2β,3β,4β,5β,7α-hydroxy-spirost-25(27)-en-6-one and its corresponding 6β-hydroxy compound. 相似文献
3.
Hypobromous acid addition to the diol yields two epimeric dibromo 6β,19a-epoxides and in a 83:17 ratio. Under the same conditions the 6β-acetoxy derivative gives three products: (46%), its epimer (5%) and the spyrocyclic ketone (49%). 相似文献
4.
Michael J. Pearson 《Tetrahedron letters》1985,26(3):377-380
6β(7β)-(-2,2,2-Trichloroethoxycarbonyl--trifluoromethanesulphonylamino) penicillins and cephalosporins have been converted into the corresponding 6α(7α)-formamido-6β(7β)-2,2,2-trichloroethoxycarbonylamino derivatives, by treatment with ,-bis(trimethylsilyl) formamide and triethylamine. 相似文献
5.
Three fungal metabolites with a common structural feature as prenylated phenols were synthesized in their naturally occurring and optically active forms: ascochlorin [(2',4',1',2',6')-(-)-5-chloro-2,4-dihydroxy-6-methyl-3-[5'-(1',2',6'-trimethyl-3'-oxo-cyclohexyl)-3'-methyl-2', 4'-pentadienyl] benzaldehyde], ascofuranone [(2',6',1')-(-)-5-chloro-2, 4-dihydroxy-6-methyl-3-[7'-(3',3'-dimethyl-4'-oxo-2'-oxacyclopentyl)-3',7'-dimethyl -2', 6'-heptadienyl] benzaldehyde] and ascofuranol [(2',6',1',4')-(-)-5-chloro-2,4-dihydroxy-6-methyl-3-[7'-(3', 3'-dimethyl-4'-hydroxy-2'-oxacyclopentyl)-3', 7'-dimethyl-2',6'-hepta-dienyl]benzaldehyde ]. (+)-Ascofuranone and (+)-ascofuranol were also synthesized. By the present synthesis the absolute configuration of the natural (-)-ascofuranol was established as (1',4'). 相似文献
6.
Suzanne Butt H.Geoff Davies Michael J. Dawson Gordon C. Lawrence Jeff Leaver Stanley M. Roberts Michael K. Turner Basil J. Wakefield Wilfred F. Wall John A. Winders 《Tetrahedron letters》1985,26(41):5077-5080
Bicyclo[3.2.0]hept-2-en-6-one (1) was reduced with an alcohol dehydrogenase from and a whole cell system () with excellent substrate enantioselectivity: 7,7-dimethylbicyclo[3.2.0]hept-2-en-6-one (2) was similarly reduced using the 3α,20β-hydroxysteroid dehydrogenase from Streptomyces while furnished both 6S-alcohols (4a), (6b) with high optical purity. 相似文献
7.
A.A.Leslie Gunatilaka N.P.Dhammika Nanayakkara M.Uvais S. Sultanbawa 《Tetrahedron letters》1979,20(19):1727-1730
Three new triterpenes zeylanol, zeylanonol and zeylandiol isolated from have been identified as 6β-hydroxyfriedelan-3-one, 6β-hydroxyfriedelan-3,21-dione and 6β,21β-dihydroxyfriedelan-3-one, respectively by spectroscopic methods and chemical interconversions. 相似文献
8.
The preparation of phosphatidyl-β-glucosyl diglyceride is described. The synthesis of glycophospholipid was accomplished by using: (a) the levulinoyl group for the temporary protection of the glucose hydroxyl functions of , which could then be converted into the dioleoyl substituted derivative ; (b) the tetraisopropyldisiloxane-1,3-diyl (TIPS) group to protect the 3'- and 4'-hydroxyl groups of , in a two step procedure, to afford compound ; (c) a 2,4-dichlorophenyl protected phosphatidic acid derivative . Compound could be selectively coupled to the primary hydroxyl function of to afford the fully protected glycophospholipid . Finally, removal of the 2,4-dichlorophenyl and TIPS protecting groups from was performed with syn-4-nitrobenzaldoximate and fluoride ions, respectively, to afford glycophospholipid . 相似文献
9.
Yoshiro Kobayashi Takeo Taguchi Norio Kanuma Nobuo Ikekawa Jun-ichi Oshida 《Tetrahedron letters》1981,22(43):4309-4312
Two new fluorinated 25-hydroxyvitamin D3 analogs, 26,26,26-trifluoro- 25-hydroxy () and 27-nor-26,26,26-trifluoro-25-hydroxyvitamin D3 (), were prepared from 24-phenylsulfonyl 25,26,27-triorcholest-5-en-3β-yl tetrahydropyranyl ether (). 相似文献
10.
The stereoselective total synthesis of 2β,3β,20β-triacetoxy-5α-pregnan-6-one () via acetylene-cation cyclization of , which was readily derived from the D-ring aromatic steroid , is described and this constitutes a total synthesis of 20-hydroxyecdysone (). 相似文献
11.
Antonio G. Gonzalez Dulce M. Estrada Julio D. Martin Victor S. Martin Cirilo Perez Ricardo Perez 《Tetrahedron》1984,40(20):4109-4113
The methanol extract of the sponge Spongia officinalis from Pt. Guimar, Tenerife (Canary Islands) contained new diterpenoids which inhibited the growth of microbes. The structures of the new diterpenes isolated were determined as; 11β-hydroxyspongi-12-en-16-one (), 11β-acetoxyspongi-12-en-16-one (), 7β,11β-dihydroxy8pongi-12-en-16-one (), and 7β,11α-dihydroxy-spongi-12-en-16-one (), by spectral and chemical degradation studies. The previously reported diterpenes isoagatholactone () and aplysillin () were also found in the extract. 相似文献
12.
A short and convenient synthesis of phosphatidyl-α-diglucosyldiglyceride (i.e. compound ) and two related Streptococci glycolipids (i.e. compounds and ) will be presented. 4',6'-Tetraisopropyl-disiloxane-1,3-diyl (TIPS) protected α-glucosyl diglyceride (i.e. compound ) turned out to be a suitable protected precursor. Thus, compound was selectively condensed with glucosyl bromide to afford . Removal of the protecting groups from gave glycolipid . The “dynamic” properties of the TIPS pro- tecting group were utilized to convert 4',6'-TIPS protected into 3',4'- TIPS protected derivative . Compound could then be condensed with either a stearoyl fatty acid or a phosphatidyl moiety to give the fully protected derivatives and , respectively. Finally, removal of all the protecting groups from and afforded the glycolipid and glycophospholipid , respectively. 相似文献
13.
14.
Anna Bernardi Silvia Cardani Cesare Gennari Giovanni Poli Carlo Scolastico 《Tetrahedron letters》1985,26(52):6509-6512
MgBr2 mediated addition of Methyl α-methylthio propionate silylketene acetal to α and α,β-alkoxy aldehydes is highly 3,4 -selective (18:1). -α- methylene-β- hydroxy-?-alkoxy esters (6) and (8) are synthesized. 相似文献
15.
Claudine Augé Serge David Cécile Mathieu Christine Gautheron 《Tetrahedron letters》1984,25(14):1467-1470
Glycosidation of disaccharides I and III with a system of five immobilized enzymes gave excellent yields of trisaccharides -Gal-(1→4)--GlcNAc-(1→6)--Gal ¦ the I(Ma) determinant ¦ and -Gal-(1→4)--Glc-NAc-(1→3)--Gal, on the milimole scale. 相似文献
16.
Four novel polyoxygenated C28-sterols have been identified from the soft coral (the Gulf of Eilat, the Red Sea): the 22,28-lactol of 24-methylcholest-5-en-3β,22(R),25-triol-28-al (), 24-methylcholest-5-en-3β,22(R),25,28-tetraol() and the corresponding 5,6β-epoxides ( and ). 相似文献
17.
Malcolm M. Campbell Aston D. Kaye Malcolm Sainsbury Roya Yavarzadeh 《Tetrahedron letters》1984,25(15):1629-1630
Two syntheses of (±)-methyl shikimate from the adduct of furan and methyl acrylate are described. One requires the regioselective hydroxylation of (±)-5β,6β-dihydroxy-,-isopropylidene-2-methoxycarbonylcyclohexa-1,3-diene and the other -dihydroxylation of (±)-5-hydroxy-1-methoxycarbonylcyclohexa-1,3-diene. 相似文献
18.
Aminomalonates, e.g., and , smoothly reacted with difluoro- and chlorofluorocarbene to produce the adducts (, , and ) in good yields. These products were successfully converted to various versatile β-fluorinated alanine derivatives, i.e., β,β-difluoroalanine (), N-acyl-β-fluorodehydroalaninate (), and fluoropyruvic acid (). 相似文献
19.
A new purine derivative with cytokinin activity was isolated from the cuckoo-pint fruits () and identified as 6-(o-hydroxybenzylamino)-2-methylthio-9-β-D-glucofuranosylpurine . 相似文献
20.
β-Bromoenamines and α-bromoaldehydes are synthesised from the ambident anions generated from either α-bromoaldimines or α,α-dibromoaldimines . 相似文献