ABSTRACT
Three Stemona alkaloids named stemotuberines A-C (1-3) with unique C17N frameworks, presumably formed by elimination of the C-11-C-15 lactone ring of the stichoneurine skeleton, were isolated from the roots of Stemona tuberosa. Their structures were elucidated by spectroscopic analysis, X-ray diffraction, and computational methods. Compounds 2 and 3 showed inhibition (IC50 values of 37.1 and 23.2 µM, respectively) against LPS-induced nitric oxide production in RAW 264.7 cells. In addition, concern was expressed about the reported plant origin (S. sessilifolia) of the recently described alkaloids tuberostemonols O-R (4-7), which should be S. tuberosa. NMR calculations indicated structural misassignment of these compounds except for 6. Isolation of tuberostemonol P (5) from our material of S. tuberosa allowed for a close examination of the spectroscopic data leading to the revised structure 5a. Tuberostemonol R (7) was found to have identical 1H and 13C NMR data to the well-known alkaloid croomine, and therefore its structure including relative stereochemistry must be revised as 7a.
ABSTRACT
The structural revision of four Stemona alkaloids from Stemona tuberosa is reported. The misassignment of the tuberostemonine O structure (1) was recognized when a new alkaloid, tuberostemonine P, was isolated and unambiguously assigned structure 1 in this work. Reinvestigation of the spectroscopic data and NMR calculations led to the revised structure 1a for tuberostemonine O. The structural misassignment of dehydrocroomine A as 2 was corrected by reinterpreting the X-ray crystal structure, which was consistent with 2a. The structural reassignments of dehydrocroomine B (3 to 3a) and dehydrocroomine (4 to 4a) were confirmed by X-ray crystallography and NMR calculations, respectively.
Subject(s)
Alkaloids , Stemonaceae , Alkaloids/chemistry , Molecular Structure , Stemonaceae/chemistryABSTRACT
Five Lycopodium alkaloids featuring novel C17N2 (1 and 2), C29N3 (3 and 4), and C15N2 (5) skeletons were isolated from Lycopodium japonicum. Compound 1 is the first natural product containing a 3-aza[3.3.3]propellane motif. The structures of these compounds were elucidated by spectroscopic analysis, X-ray crystallography, and computational methods. Compounds 1 and 3-5 significantly inhibited TGF-ß1-induced fibronectin deposition in HK-2 cells at a nontoxic concentration of 20 µM.
