Improvements in the preparation of a key imidazylate and the reduction of the derived nitrile have led to more efficient syntheses of isofagomine, noeuromycin, azafagomine, and isofagomine lactam. As well, a precursor of azafagomine has been converted into azanoeuromycin, and the nitrogen atom of isofagomine has been incorporated into a guanidine residue.