Isotalatisidine Hemihydrochloride Sesquihydrate from Aconitum talassicum

We continued our study of alkaloids from Aconitum talassicum Popov collected in Kamchik pass (Tashkent Oblast, Uzbekistan). Alkaloids of the plant growing in Uzbekistan have not been previously studied. We studied roots of this plant that were collected after the aerial part had died off. The content of total alkaloids was 2.5% of the dry plant weight [1]. A part (4.2 g) of the total alkaloids was dissolved with heating in Me 2 CO and left at room temperature. The resulting crystals were recrystallized from MeOH to afford talatisamine (0.32 g). The mother liquor was chromatographed over a column of silica gel (KSK, 50:1 adsorbent–substance ratio) with elution by CHCl 3 with gradually added MeOH. Elution by CHCl 3 –MeOH (100:1) isolated 14-O-acetyltalatisamine (0.07 g) and talatisamine (0.19 g). Eluates of CHCl 3 –MeOH (30:1) isolated isotalatisidine (0.08 g) and isoboldine (0.05 g); of CHCl 3 –MeOH (20:1), talatisidine (0.03 g). The mother liquor was evaporated, dissolved in EtOH, and treated until weakly acidic with HCl in EtOH. The EtOH was removed. Work up with Me 2 CO produced a crystalline hydrochloride (0.07 g) that had mp 113–115°C, which was close to that of isotalatisidine hydrate [2], after recrystallization from Me 2 CO. The structure of the isolated hydrochloride was studied by x-ray crystal structure analysis (XSA). It was found that the compound was isotalatisidine hemihydrochloride sesquihydrate. The asymmetric (independent) unit contained two alkaloid molecules (one of which was protonated; the other, as the base and numbered with stroke), three water molecules, and a chloride ion. The conformations of the rings and orientations of the hydroxyls agreed in general with those observed in talatisidine [3] except for the C1 (C1) hydroxyl. This hydroxyl had the -orientation in talatisidine whereas it had the -orientation in isotalatisidine. The -orientation of the C1 hydroxyl led to the formation of an intramolecular H-bond. Although the alkaloid in the ionic form formed a H-bond between the hydroxyl O atom (O1) and the protonated N atom (NH + ), the base (unprotonated molecule) formed one between the -hydroxyl H atom (O1H) and the unshared pair of the N atom (N1). Table 1 presents the parameters of the intramolecular H-bonds in the crystal hydrate. Ring A had the boat