- Different pathways for the deoxygenation of the A-ring of natural triterpene compounds
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Some deoxygenation pathways were tested to remove the hydroxyl groups of the natural triterpenes oleanolic acid and maslinic acid to obtain a practical starting material for the semisynthesis of other interesting organic synthons. Different deoxygenation processes were carried out starting from these triterpenic acids or from several derivatives such as methyl esters and epoxy derivatives. The hydroxyl groups were transformed into some intermediate compounds including xanthyl, thiocarbonyl or tosyl derivatives. The opening of the oxirane ring between C-2 and C-3 was also achieved through different methods using deoxygenating reagents such as Me3SiCl/NaI, WCl 4/n-BuLi and Cp2TiCl.
- Parra, Andres,Lopez, Pilar E.,Garcia-Granados, Andres
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scheme or table
p. 177 - 196
(2010/05/18)
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- Epoxides, cyclic sulfites, and sulfate from natural pentacyclic triterpenoids: Theoretical calculations and chemical transformations
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Several triterpenic derivatives, with the A-ring functionalized, were semisynthesized from oleanolic and maslinic acids. The reactivities of sulfites, sulfate, and epoxides in these triterpene compounds were investigated under different reaction conditions. Moreover, contracted A-ring triterpenes (five-membered rings) were obtained, by different treatments of the sulfate 7. From the epoxide 8, deoxygenated and halohydrin derivatives were semisynthesized with several nucleophiles. Ozonolysis and Beckmann reactions were used to yield 4-aza compounds, from five-membered ring olanediene triterpenes. The X-ray structure of sulfate 7 is given and compared with density functional theory geometries. Theoretical 13C and 1H chemical shifts (gauge-invariant atomic orbital method at the B3LYP/6-31G*//B3LYP/6-31G* level) and 3JH,H coupling constants were calculated for compounds 5-9 and 34-36, identifying the (R)- or (S)-sulfur and α- or β-epoxide configurations together with 4-aza or 3-aza structures.
- Garcia-Granados, Andres,Lopez, Pilar E.,Melguizo, Enrique,Moliz, Juan N.,Parra, Andres,Simeo, Yolanda,Dobado, Jose A.
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p. 4833 - 4844
(2007/10/03)
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