Isolation and identification of neo-clerodane diterpenes from Ajuga remota by high-performance liquid chromatography

In order to explore the suitability of reversed-phase HPLC for the rapid isolation, identification and semi-preparative fractionation of neo-clerodane diterpenes from Ajuga remota, an extract from aerial parts of the plant was examined using a C18 column with UV detection and gradient elution with water:methanol. In addition to the known diterpenes ajugarins I, II, IV and V and clerodin, the presence and chromatographic behaviours of ajugapitin, dihydroajugapitin, dihydroclerodin and deacetylajugarin IV, not previously isolated from A. remota, were established. Presence of the epimeric mixture of 14-hydro-15-hydroxyclerodin (scutecyprol A) was also demonstrated together with that of 14-hydro-15-hydroxyajugapitin, the latter only in trace amounts. The structures of all isolated diterpenes were determined from NMR data. The anti-feedant activities of the isolated compounds against Spodoptera littoralis are also reported here.