| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1346338 | Tetrahedron: Asymmetry | 2011 | 10 Pages |
Herein, we studied the stereoselectivity of the reduction of the 18-oxo group in cytotoxically active des-E lupane derivatives with respect to a dependence on the substituent type at the 17-position by means of sodium borohydride and also in the presence of cerium chloride. It was found that the stereoselectivity of the reduction of the 18-keto group both depended on the type and length of the substituent chain at the 17-position. In most cases, 18α-hydroxyderivatives were obtained by the assumed attack from the upper side. However, in the case of 18-oxo-17α, 17β-disubstituted derivatives and a 17-methylene derivative, a mixture of both epimeric 18α and 18β alcohols was obtained by the reduction with borohydride itself. However, if the reduction of the 18-oxo-17α, 17β-disubstituted derivatives was carried out in the presence of cerium chloride, the corresponding 18α-hydroxyalcohols were obtained exclusively; conversely, if the 17-methylene derivative was reduced, the 18β-epimer prevails.
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Methyl 3β,28-diacetoxy-18α-hydroxy-19,20,21,29,30-pentanorlupan-22-oateC30H48O7[α]D20=+24 (c 0.20, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,17S,18S)
Pivaloyloxymethyl 3β,28-diacetoxy-18α-hydroxy-19,20,21,29,30-pentanorlupan-22-oateC35H56O9[α]D20=+17 (c 0.24, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,17S,18S)
Methyl 3β,28-diacetoxy-18β-hydroxy-19,20,21,29,30-pentanorlupan-22-oateC30H48O7[α]D20=+23 (c 0.30, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,17R,18R)
Methyl 3β,28-diacetoxy-18β-hydroxy-19,20,21,29,30-pentanorlupan-22-oateC30H48O7[α]D20=+23 (c 0.30, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,17R,18R)
Methyl 3β,18α-dihydroxy-19,20,28,29,30-pentanor-17βH-lupan-21-oateC26H44O4[α]D20=+33 (c 0.19, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,17S,18R)
3β,18α-Dihydroxy-19,20,28,29,30-pentanor-17βH-lupan-18α,21-lactoneC25H40O3[α]D20=-30 (c 0.18, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,17S,18R)
Methyl 3β-hydroxy-18-oxo-19,20,28,29,30-pentanor-17αH-lupan-21-oateC25H40O4[α]D20=0 (c 0.20, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,17R)
Methyl 3β,18α-dihydroxy-19,20,28,29,30-pentanor-17αH-lupan-21-oateC28H46O5[α]D20=0 (c 0.31, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,17R,18R)
Pivaloyloxymethyl 3b,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oateC35H54O9[α]D20=+40 (c 0.35, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,17S)
18α-Hydroxy-19,20,21,22,29,30-hexanorlup-17(28)-en-3β-yl acetateC26H42O3[α]D20=+36 (c 0.08, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,18S)
18α-Hydroxy-19,20,21,22,28,29,30-heptanorlupan-3β-yl acetateC25H42O3[α]D20=+19 (c 0.39, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,18R)
18β-Hydroxy-19,20,21,22,29,30-hexanorlup-17(28)-en-3β-yl acetateC26H42O3[α]D20=+41 (c 0.12, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,18R)
18α-Hydroxy-19,20,21,22,29,30-hexanor-17αH-lupan-3β-yl acetateC26H44O3[α]D20=+37 (c 0.14, CHCl3)Source of chirality: chiral substrateAbsolute configuration: (3S,5R,8R,9R,10R,13S,14R,17S,18R)
