Leucostinine A from Aconitum barbatum

Abstract

In the search for sources of songorine, we studied Aconitum barbatum Pers. The known alkaloids delcosine, lycoctonine, songorine, and the new base bataconine were isolated earlier from the aerial part of this plant collected near UlanBator during vegetation [1]. Roots of A. barbatum from Altai collected in July contained songorine [2]. According to the literature, the Mongol and Siberian populations of A. barbatum can be used as sources of the biologically valuable alkaloid songorine. Thus, the aerial part of the plant contained 1.5% total alkaloids, of which the songorine fraction was 14%. The alkaloid content of A. barbatum roots is 1.7%. The songorine concentration is 36% of the total bases [3]. We did not find songorine in flowerheads and leaves of A. barbatum collected in Irkutsk Oblast′ during flowering but did isolate leucostinine A. Leucostinine A was first observed in 1996 by Chinese researchers in roots of A. leucostomum [4]. In 1999, Swiss scientists isolated this same alkaloid from flowers of A. lycoctonum but reported it as a new base, 6-O-acetyldemethylenedelcorine [5]. Thus, different names have been given to a single compound [4, 5]. Both groups of researchers established the structure using mass, PMR, and 13C NMR spectra (DEPT, COSY). Chemical shifts in 13C NMR spectra of both alkaloids are practically identical. However, assignments for C-5, C-9 and C-10, and C-13 were interchanged among themselves [4, 5] (Table 1). We used a heteronuclear method (1H—13C HMBC) to assign signals in the PMR and 13C NMR spectra of leucostinine A and to confirm that the Swiss researchers had interpreted correctly the NMR spectra. Figure 1 shows the principal correlations in the 2D HMBC spectrum. The chemical shift of the N atom was obtained from the 15N—1H HMBC spectrum, in which there are correlations with H-17 (3.01), H-19 (2.69), and the ethyl CH3 (1.04). Leucostinine A: C27H43NO8. Mass spectrum (EI, 70 eV, m/z, Irel, %): 509 (4) [M] +, 494 (3) [M 15]+, 478 (100) [M 31]+, 450 (21) [M 60]+, 434 (10) [M 15 60]+. 15N NMR spectrum (40.5 MHz, CDCl3, δ, ppm, CH3NO2 internal standard): 344.0. Table 1 gives the PMR and 13C NMR spectra.