NMR shift data of neo-clerodane diterpenes from the genus Ajuga.

The complete assignment of the NMR spectra of ajugarin I and ajugareptansin, as models for other neo-clerodane diterpenoids isolated from the genus Ajuga, is reported in order to improve their usefulness as reference compounds. Conflicting NMR shift data for some members of this group are discussed, and plausible reassignments are proposed [i.e. the identity of ajugacumbin C and ajugamarin A2; the revision of ajugacumbin D as 12-hydroxyajugacumbin A, and of ajugacumbin E as 12-hydroxy-1-(3-hydroxy-2-methylenebutanoyloxy)ajugarin I] in order to provide a unified basis for future use.