Diterpene alkaloids and diterpenes from Spiraea japonica and their anti-tobacco mosaic virus activity

Five new naturally occurring natural products, including two atisine-type diterpene alkaloids (1 and 2), two atisane-type diterpenes (3 and 4), and a new natural product spiramine C2 (5), along with nine known ones (6-14), were isolated from the ethanolic extracts of the whole plant of Spiraea japonica var. acuminata Franch. Their structures were elucidated by extensive spectroscopic analysis. The anti-tobacco mosaic virus (TMV) activities of all the compounds were evaluated by the conventional half-leaf method. Six compounds (2, 3, 6, 7, 11, and 12) exhibited moderate activities at 100 μg/mL with inhibition rates in the range of 69.4-92.9%, which were higher than that of the positive control, ningnanmycin. Their preliminary structure-activity relationships were also discussed.