Conformation of ring A in triterpenoid ketones. Carbon-13 chemical shifts and spin-lattice relaxation times of lupane and 18α-oleanane derivatives
1989 ◽
Vol 54
(7)
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pp. 1928-1939
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Keyword(s):
The One
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13C NMR spectra of sixteen lupane and 19β,28-epoxy-18α-oleanane triterpenoids I-XVI were measured and a complete structural assignment of chemical shifts was made. For most compounds also the carbon spin-lattice relaxation times T1 were obtained. Characteristic differences in chemical shifts of some carbon atom signals were found between 2α-methyl-3-oxo and 2α-methyl-1-oxo derivatives II, V and VIII with chair conformation of the ring A on the one hand and their 2β-isomers III, VI and IX (boat form) on the other. Using these 2-methyl ketones as models, the chair-boat population in allobetulone (I), 3-oxo-28-lupanenitrile (IV) and 1-oxo derivative VII was determined. The results agree well with the data obtained by other physical methods.
1980 ◽
Vol 58
(23)
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pp. 2709-2713
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1996 ◽
Vol 50
(11)
◽
pp. 1408-1412
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1971 ◽
Vol 44
(11)
◽
pp. 2931-2935
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Keyword(s):
Keyword(s):
1979 ◽
Vol 20
(30)
◽
pp. 2753-2756
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Keyword(s):