C. Triterpenoids
33
'<> H
79
a: R = OH
b: R = H
OH
MeO Q^O^^C,
MeO
0 ^°\U^\__^~
fj ^
inmOH
fl!
"""OH
I l H I J
I I H I
H
Ή H
80
81
MeO °^°\^x_^A
O M e
mmOH
H O ^ y M
/%H
82
firmed by carrying out the hydrolysis in dioxane rather than methanol.
Nmr studies revealed the configuration of the 12-methoxy group to be beta.
On the basis of arguments based on nmr solvent shifts Chanley and Rossi
(1969a) were further led to conclude that the configuration of the C-21 methyl
group was analogous to lanosterol, i.e., behind the plane of the lactone ring.
The great ease with which the 12-hydroxy group in holothurin A is converted to the 12-methoxy compounds suggested to Chanley and Rossi
(1969b) that the configuration of the original hydroxy group might be axial,
i.e., a, and that the ß-methoxy disposition of the neo series of compounds is a
result of epimerization during acid treatment. Chanley and Rossi (1969b)
proved this point by enzymatic hydrolysis of desulfated holothurin A
(holothurin A itself proved to be unsuitable), which led to some aglycones
with the 12a-hydroxy configuration.