UNAMBIGUOUS ASSIGNMENT OF C-13 CHEMICAL-SHIFTS OF SOME HOPANE AND MIGRATED HOPANE DERIVATIVES BY 2D NMR

C-13 NMR chemical shifts of some migrated hopane derivatives, vir. boehmeryl acetate (1), neohop-13(18)-en-3 beta-ol (2), neomotiol (3), arborinol (4), isoarborinyl acetate (5), fernenol (6), fernenyl acetate (7), and simiarenol (8), and a hopane derivative, hop-17(21)-en-3 beta-yl acetate (9) have been assigned unambiguously on the basis of detailed 2D NMR analyses. Heteronuclear Multiple Bond Correlation (HMBC) spectrum was found to be most informative not only in the assignment of signals to specific carbons but also in the elucidation of back-bone structure of triterpenoids. The relative stereochemistry of most of the chiral centres of the back-bone could also be established from the NOESY spectra.