Advances in the universal NMR database approach. 2 '-substituted taxanes as probes for an improved protocol of diastereomeric differentiation

The configuration of the alpha-substituted alpha-hydroxy-beta-aminoester moiety in a series of 2'-substituted taxanes was analyzed according to the recently proposed Universal NMR Database (UDB) approach. A critical analysis of the results showed that modifications regarding chemical shift adjustment (so as to render the shifts virtually connectivity independent) were necessary to get consistent stereoassignments in this set of compounds. On this basis, a modified UDB-based strategy, especially tailored to the configurational assignment of densely substituted diastereomeric fragments, is proposed.