- ESTERS OF Ferula karakalensis. STRUCTURE AND STEREOCHEMISTRY OF KARAFERIN AND KARAFERININ
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Two new guaiane esters - karaferin and karaferinin - have been isolated from Ferula karakalensis, and their structures and stereochemistry have been established.It has been shown that the Ferula sesquiterpene alcohols angrendiol, ugamdiol, and karaferol are biogenetically interconnected and are products of a single chain of the biogenesis of terpenoids in plants.
- Saidkhodzhaev, A. I.,Malikov, V. M.,Pimenov, M. G.
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p. 187 - 190
(2007/10/02)
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- Remarkable Differences in the Reactivity of Echinadiol and Shiromodiol, Biologically Active Epimeric Germacrane Derivatives
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Treatement of echinadiol with a variety of acids gave a 8,9-secoguaiane aldol resulting from the cyclofragmentation of the ten-membered ring.Under these conditions its C-8 epimer (shiromodiol) did not react or underwent esterification of the hydroxy group at C-8.Allylic oxidation of both epimers occurred with oxidation of the allylic methyl to the formyl level and retention of configuration of the endocyclic trans (Z) double bond.However, whereas the enal from shiromodiol was stable, that from echinadiol smoothly underwent Z-E isomerization.Low temperature NMRexperiments showed that echinadiol and shiromodiol exist in solution as a mixture of parallel and crossed rotamers, whose ratio is ca. 1:5 for shiromodiol and 4:1 for echinadiol.Anchimeric stabilization of an incipient positive charge at C-10 or C-14 by the C-8 β-hydroxy group of echinadiol might be responsible for the observed differences in reactivity.
- Appendino, Giovanni,Tettamanzi, Paola,Gariboldi, Pierluigi
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p. 2139 - 2144
(2007/10/02)
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- Structural and Conformational Studies on Sesquiterpenoid Esters from Laserpitium halleri Crantz subsp. halleri
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Investigation of the ripe fruits of Laserpitium halleri Crantz subsp. halleri afforded two pairs of new germacrane and guaiane esters, as well as the daucane derivative vaginatin, whose stereochemistry was assessed by spectral data and correlation with a compound of known configuration.The 1H and 13C n.m.r. spectra of the germacrane esters were characterized by the presence of sharp and broad signals.A conformational study of the natural compounds and several derivatives allowed us to relate the broadening of the n.m.r. lines to conformational motions which are discussed in detail.Among the derivatives of the natural esters, the ketone (8) was found to adopt, in solution, a conformation hitherto unreported for germacrane derivatives .Comparison of the spectral features of some crossed/boat germacra-1(10),4-dienes and their corresponding 4,5-epoxides suggests that homoconjugation plays an important role in stabilizing the crossed/boat conformation of this class of cyclic 1,5-dienes.The biogenetic relationship between the compounds cumulated in the roots and the fruits of L. halleri is discussed.
- Appendino, Giovanni,Valle, Maria Grazia,Gariboldi, Pierluigi
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p. 1363 - 1372
(2007/10/02)
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