Calystegin N-1, a novel nortropane alkaloid with a bridgehead amino group from Hyoscyamus niger: Structure determination and glycosidase inhibitory activities

Seven calystegins were isolated from the whole plant of Hyoscyamus niger. They are calystegins A(3), A(5), A(6), B-1, B-2, B-3, and N-1, The structure of new calystegin A(6) was determined as 1 alpha, 2 beta, 7 alpha-trihydroxy-nor-tropane, and another new calystegein N-1 was elucidated to be a trihydroxy-nor-tropane alkaloid with a bridgehead NH2 group in the place of a bridgehead OH group in calystegin B-2, Very interestingly, on storage for a half year in a refrigerator, approximately 40% of calystegin N-1 was nonenzymically converted into calystegin B-2 Calystegin N-1 was a weaker inhibitor of glycosidases compared to calystegin B-2 but with the same inhibitory spectrum. However, calystegin N-1 inhibited porcine kidney trehalase in a noncompetitive manner, whereas calystegin B-2 inhibited this enzyme in a competitive manner. (C) 1996 Elsevier Science Ltd.