Isodon excisoides (Sun ex C. H. Hu) C. Y. Wu et H. W. Li, a perennial herb, is mainly found distribured in Yunnan, Sichuan and Gansu Provinces. 1 Leaves of the plant have been used in folk medicine for the treatment of digestive disorders, dyspepsia and ulcers. Although a large number of ent-kaurane diterpenoids with various biological activities have been isolated from the genus Isodon, the chemical constituents and biological activities of Isodon excisoides (Sun ex C. H. Hu) C. Y. Wu et H. W. Li have not been reported previously. Our search for bioactive diterpenoids from the leaves of I. excisoides (Sun ex C. H. Hu) C. Y. Wu et H. W. Li, collected in Zang County of Gansu Province, led to the isolation of a new diterpenoid, excisoidesin (1), together with the known, kamebacetal B (2), glaucocalyxin A (3), leukamenin E (4), kamebanin (5) and wangzaozin A (6).Excisoidesin (1) was obtained as white needles. The EI-MS spectrum of 1 showed a molecular ion peak at m/z = 348 consistent with a molecular formula of C 20 H 28 O 5 , which was confirmed by the HR-EIMS and NMR spectra. The NMR spectra (Table 1) indicated the presence of two methyls, six methylenes (including one oxygen-bearing methylene), five methines (including two oxygen-bearing methines), three quaternary carbons, two olefinic carbons, one carbonyl carbon and an α, β-unsaturated ketonic carbon [δ C 207.6 (s), δ C 150.1 (s), δ C 116.3 (t), δ H 6.28 (1H, s), δ H 5.37 (1H, s)]. This corresponded to the basic skeleton of ent-kaurane diterpenoids previously described in the genus Isodon. [3][4][5][6][7] A careful analysis of the NMR spectral data revealed that the structure of compound 1 was similar to that of glaucocalyxin A (3) 4 except for one more oxygenated methylene and one less methyl group. Comparison of their 13 C NMR spectral data indicated that the difference between 1 and 3 was only in the ring A. This meant that two hydroxyl groups were located at C-7 and C-14, and a hydroxymethyl group and a
