24-Norchola-20,22-diene-4-carboxaldehyde,3-(acetyloxy)-14,15:21,23-diepoxy-1,7,19-trihydroxy-4,8-dimethyl-11-oxo-,cyclic 4,19-(2-methyl-1-oxopropyl acetal), [1a,3a,4b(S),5a,7a,13a,14b,15b,17a]-