Viburnum awabuki (Caplifoliaceae) has elaborated a number of rarely occurring vibsane-type diterpenes, which can be subdivided into three types of eleven-membered, seven-membered and rearranged ones. 1,2) In the preceding paper, 3) we demonstrated that an eleven-membered vibsane-type diterpene, vibsanin B (11), exists in solution as two conformational isomers, CT and BC, which can transform to sevenmembered derivatives, vibsanin C (6) and its 5-epimer (6a) by thermal Cope rearrangement, respectively, as shown in Fig. 1. This result suggests the occurrence of natural 5-epimers corresponding to the previously reported sevenmembered vibsanins C (6), H (7), K (8), and 18-Omethylvibsanin K (9) and vibanin E (10) with a trans relationship on the C-5 and C-10 positions.4,5) Herein, we report the isolation and structure of five anticipated isomers, 5-epivibsanin C (1), 5-epi-vibsanin H (2), 5-epi-vibsanin K (3) and 18-O-methyl-5-epi-vibsanin K (4) and 5-epi-vibsanin E (5) from the methanol extract of the leaves of Viburnum awabuki.Compound 1 . These spectral data were very similar to those of vibsanin C (6), which was a typical seven-membered vibsane-type diterpene isolated from the title plant. In fact, analyses of two-dimensional (2D) NMR spectra such as quantum filtered-correlated spectroscopy (DQF-COSY), heteronuclear multiple quantum coherence (HMQC) and heteronuclear multiple bond correla- * To whom correspondence should be addressed. e-mail: fukuyama@ph.bunri-u.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.