Isolation and SAR studies of bicyclic iminosugars from Castanospermum australe as glycosidase inhibitors Kato, Atsushi Hirokami, Yuki Kinami, Kyoko Tsuji, Yutaro Miyawaki, Shota Adachi, Isao Hollinshead, Jackie Nash, Robert J. Kiappes, J. L. Zitzmann, Nicole Cha, Jin K. Molyneux, Russell J. Fleet, George W. J. Asano, Naoki Phytochemistry 2015 2015-03-31 111 124 131 9CQFS [652,753,1051,1071] Magnoliopsida Fabaceae Castanospermum Plantae Fabales 1 125 Tracheophyta species australe  The seeds ( 5.8 kg) of  C. australewere extracted with 50% aqueous EtOH. The chromatographic separation of the extract using various ion-exchange resins led to isolation of eleven alkaloids ( 1–3, 5, 6, 8–12, and 14). The 1H NMR and 13C NMR spectra of alkaloid 1were in accord with those of 2 R-hydroxymethyl-3 S-hydroxypyrolidine (CYB-3), which has been isolated previously from the same plant  C. australe( Nash et al., 1985; Kato et al., 2003). The biosynthesis of the bicyclic indolizidine and pyrrolizidine iminosugars has not been elucidated yet, but CYB-3 ( 1), N-hydroxyethyl-2- hydroxymethyl-3-hydroxypyrrolidine, and N-methyl- trans-4- hydroxy-L- proline ( Molyneux et al., 1991; Haraguchi et al., 2003) can be speculated as being important intermediate compounds because the distributions of these pyrrolidines and of castanospermine are closely related and appear to be restricted to a small taxonomic group. Alkaloids 2and 3were identified as fagomine and 3- epi-fagomine, respectively, from an analysis of their 1H NMR and 13C NMR spectroscopic data. Fagomine ( 2) was first isolated from buckwheat seeds (  Fagopyrum esculentum) ( Koyama and Sakamura, 1974). We have previously reported that fagomine ( 2) and 3- epi-fagomine ( 3) occur abundantly in the leaves and roots of  Xanthocercis zambesiaca, from southern Africa ( Kato et al., 1997). The 1H and 13C NMR spectroscopic data of alkaloids 5, 6, and 8–12were in accord with those of the polyhydroxylated pyrrolizidines, australine, 1- epi-australine, 2,3-di epi-australine, 2,3,7-tri epi-australine, and the polyhydroxylated indolizidines, castanospermine, castanospermine-8- O-b- D- glucoside, 6- epi-castanospermine isolated earlier from  C. australe( Molyneux et al., 1986, 1988; Kato et al., 2003). The 1H NMR and 13C NMR spectra of alkaloid 14were in accord with those of 7-deoxy-6- epi-castanospermine ( Molyneux et al., 1990). Recently, this compound has been synthesized in ten steps from a common chiral building block (+)-tetramic acid derivative ( Liu et al., 2010). The dried leaves ( 360 g) of  C. australewere extracted with 50% aqueous MeOH. The chromatographic separation of the extract using various ion-exchange resins led to isolation of nine alkaloids ( 1, 2, 4–7, 10, 12, and 13). Alkaloids 4and 7were identified as 3,4- di epi-fagomine and 3- epi-australine, respectively, from an analysis of their 1H NMR and 13C NMR spectroscopic data ( Kato et al., 1997, 2003). The structural determination of the new alkaloid 13is described below. Alkaloid 13was determined to have the molecular formula C 8H 15NO 4by HRFABMS. The 13C NMR spectroscopic data of 6,8- di epi-castanospermine were closely related to those of 6- epi-castanospermine. In the 1H NMR spectrum, the H-1 showed similar coupling constants to H-2 and H-8a as those of 6- epi-castanospermine, indicating a common stereochemical configuration for H-1 and H-8a. The stereo configurations of 6,8-di epi-castanospermine were corroborated by definite NOEs between H-7 and H-8a or H-5ax and by the presence of a W-path long-range coupling between H-6 and H-8. Hence, alkaloid 13was shown to be 6,8-di epi- castanospermine.