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

Abstract
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.