Epoxides, Cyclic Sulfites, and Sulfate from Natural Pentacyclic Triterpenoids: Theoretical Calculations and Chemical Transformations

Several triterpenic derivatives, with the A-ring functionalized, were semisynthesized from oleanolic
and maslinic acids. The reactivities of sulfites, sulfate, and epoxides in these triterpene compounds
were investigated under different reaction conditions. Moreover, contracted A-ring triterpenes (five-membered rings) were obtained, by different treatments of the sulfate 7. From the epoxide 8, deoxygenated and halohydrin derivatives were semisynthesized with several nucleophiles. Ozonolysis
and Beckmann reactions were used to yield 4-aza compounds, from five-membered ring olanediene
triterpenes. The X-ray structure of sulfate 7 is given and compared with density functional theory
geometries. Theoretical 13C and 1H chemical shifts (gauge-invariant atomic orbital method at the
B3LYP/6-31G*//B3LYP/6-31G* level) and 3JH,H coupling constants were calculated for compounds
5−9 and 34−36, identifying the (R)- or (S)-sulfur and α- or β-epoxide configurations together with
4-aza or 3-aza structures.