Abstract
An extract of the aerial parts of Ajuga nipponensis Makino was examined by HPLC for neo-clerodane diterpenes. The suitability of reversed-phase HPLC for the semi-preparative fractionation of this extract was explored, resulting in the isolation of two new neo-clerodane diterpenes, which we have named ajuganipponin A, (12S)-1β,6α,19-triacetoxy-4α,18-epoxy-12-tigloyl-neo-clerod-13-en-15,16-olide (AJNP A, 1), and ajuganipponin B, (12S)-6α,19-diacetoxy-4α,18-epoxy-12-tigloyl-neo-clerod-13-en-15,16-olide (AJNP B, 6). In addition, ajugamarins A2 and F4, ajugamacrin B, ajugacumbin A and ajugatakasin A, were newly isolated compounds from A. nipponensis, along with the previously reported ajugamarins A1, B2 and L2 (ajugacumbin B). The structures of all the isolated compounds were unambiguously elucidated based on extensive NMR spectral studies (one and two-dimensional experiments) and their reversed-phase chromatographic behavior was established. The antifeedant activity of the isolated diterpenes against Spodoptera littoralis is also reported here.