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

The unambiguous H-1 and C-13 NMR assignments for 16 alpha,17-dihydroxy-3-oxo-phyllocladane(calliterpenone) were achieved by the concerted application of homo- and heteronuclear correlation techniques. Comparison of these with the data for related ent-kauranoids established the characteristic 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 stereochemistry of the hydroxy groups at C-16 and C-17 of a diterpenoid isolated from Euphorbia sieboldiana.