Pentahydroxy-nor-tropane alkaloids, calystegines C-1 and C-2, were isolated from the leaves of greenhouse-cultivated Duboisia leichhardtii, together with calystegines B-1, B-2 and B-4. Calystegine C-1 is a potent inhibitor of beta-glucosidase and beta-galactosidase, whereas calystegine C-2 exhibited no significant inhibitory activity against these enzymes. Only calystegine C-2, the 2-epimer of calystegine C-1, among calystegines isolated to date exhibited an inhibitory activity against all alpha-mannosidases tested. (C) 1997 Elsevier Science Ltd.