Polyhydroxy 4-azaspiro[2.4]heptane derivatives (spirocyclopropyl iminosugars) were prepared in four to six steps from readily available protected aldoses. The key step of the reaction sequence involves a titanium-mediated aminocyclopropanation of glycononitriles with subsequent cyclization. Five new polyhydroxypyrrolidines so-obtained have been evaluated for their ability to inhibit 16 glycosidases. One of them exhibits selective inhibition Of alpha-L-fucosidase from bovine kidney (K-i = 1.6 mu M, competitive). (c) 2006 Elsevier Ltd. All rights reserved.