Homonojirimycin analogues and their glucosides from Lobelia sessilifolia and Adenophora spp. (Campanulaceae)

2,6-Dideoxy-7-O-(β-d-glucopyranosyl) 2,6-imino-d-glycero-l-gulo-heptitol (7-O-β-d-glucopyranosyl-α-homonojirimycin, 1) was isolated from the 50% methanol extract of the whole plant of Lobelia sessilifolia (Campanulaceae), which was found to potently inhibit rice α-glucosidase. Adenophorae radix, roots of Adenophora spp. (Campanulaceae), yielded new homonojirimycin derivatives, adenophorine (2), 1-deoxyadenophorine (3), 5-deoxyadenophorine (4), 1-C-(5-amino-5-deoxy-β-d-galactopyranosyl)butane (β-1-C-butyl-deoxygalactonojirimycin, 5), and the 1-O-β-d-glucosides of 2 (6) and 4 (7), in addition to the recently discovered α-1-C-ethylfagomine (8) and the known 1-deoxymannojirimycin (9) and 2R,5R-bis(hydroxymethyl)-3R,4R-dihydroxypyrrolidine (DMDP, 10). Compound 4 is a potent inhibitor of coffee bean α-galactosidase (IC50=6.4 μM) and a reasonably good inhibitor of bovine liver β-galactosidase (IC50=34 μM). Compound 5 is a very specific and potent inhibitor of coffee bean α-galactosidase (IC50=0.71 μM). The glucosides 1 and 7 were potent inhibitors of various α-glucosidases, with IC50 values ranging from 1 to 0.1 μM. Furthermore, 1 potently inhibited porcine kidney trehalase (IC50=0.013 μM) but failed to inhibit α-galactosidase, whereas 7 was a potent inhibitor of α-galactosidase (IC50=1.7 μM) without trehalase inhibitory activity.