Carbon‐13 NMR study of (20,24)‐epoxydammarane triterpenes

Assignments of the 13C NMR signals of the dammarane triterpenes, 3β,25,30‐trihydroxy‐(20R,24R)‐epoxydammaran‐16‐one 3,30‐diacetate (trevoagenin A diacetate) (2), its 20S‐isomer (trevoagenin B diacetate) (3) and their related (20R)‐3β,30‐diacetoxy‐16‐oxo‐25,26,27‐trisnordammarane‐24,20‐lactone (4) and its 20S‐isomer (5) have been achieved. Suitable tetrahydrofuran models have been synthesized in order to aid the 13C NMR assignments of the side‐chain carbons of the above‐mentioned compounds. The remarkable chemical shift differences observed for C‐21 and C‐22 between each pair of the C‐20 epimers (2, 3 and 4, 5) allowed the confirmation of the C‐20 stereochemistry of these ocotillol‐type dammarane triterpenes.