Changes in the glycosylation pattern of cellular glycoproteins constitute a hallmark in human cancer and influence tumour progression, suggesting that inhibitors of selected glycosidases may control cancer invasion. Following the studies on swainsonine, a natural inhibitor of Golgi -mannosidase II, which highlighted the inhibition of cellular mannosidases as a potential innovative approach for the treatment of cancer, several dihydroxylated pyrrolidines and analogues were developed as new potent inhibitors of -mannosidases II able to induce antiproliferative effects on human cancer cells.