NMR CHEMICAL-SHIFT CORRELATIONS IN 16,17-DIHYDROXYKAURANOIDS - IMPLICATION FOR STEREOCHEMICAL ASSIGNMENTS

The unambiguous H-1 and C-13 NMR assignments for 16 a,17-dihydroxy-3-o xo-phyllocladane(calliterpenone) were achieved by the concerted applic ation of homo- and heteronuclear correlation techniques. Comparison of these with the data for related ent-kauranoids established the charac teristic NMR shielding patterns applicable for differentiation between the phyllocladane skeleton and the ent-kauranoid skeleton as well as for the assignment of the stereochemistry of the hydroxyl groups at C- 16 and C-17. These studies also led to a revision of the stereochemist ry of the hydroxy groups at C-16 and C-17 of a diterpenoid isolated fr om Euphorbia sieboldiana.