Diterpene Alkaloids Chemistry Research

Eighteen diterpene alkaloids were isolated from the roots of Spiraea japonica L. f. var. fortunel (planchon) Kehd. Fifteen of these had previously unrcported structuresand were designted as spiragine 1 (1)-----spirasine XV(15). of the three remaining alkaloids, two are the previously reported spiradine A (16) and spiredine (17). The third, the N-chloromethyl quaternary salt of spirasine IX (18), is tentatively regarded as an artifact since CH₂Cl₂ was used in the extraction. The structures were elucidated by means of spectroscopy (ms, ir, ¹II-, ¹³C-nmr, 2D-nmr, cd, uv) and chemical correlations. The structures of spirasine III (3), spirasine VI (6) and spirasine 1 (1) were confirmed by x-ray crystallographic analysis.CD has proved very useful for the allocation of certain keto groups in structures of the atisine-type alkaloids. With the normal absolute configuration, C₁₁-carbonyl Rives rise to a positive Cotton effect at 305 nm, while C₆ - and c₁₃-carbonyls give rise to negative Cotton effects at ca. 290 nm and 305 nm respectively, with a weaker amplitude for the C₆-carbonyl. The Cotton effect extremum of the C₆-carbonyl can be eliminated upon acidification. The acid-quenching effect thus assures the allocation...