novel bicyclic tetrahydroxylated pyrrolizidines are disclosed which are inhibitors of glycosidase enzymes . a preferred inhibitor is 1α , 2α , 6α , 7α , 7αβ - 1 , 2 , 6 - 7 - tetrahydroxypyrrolizidine . it is synthesized from d - glycero - d - gulo - heptono - 1 , 4 - lactone .