PURPOSE: To link C-1 to C-5 by N and to obtain the compd. by executing the interconvesion between L-gulono and D-mannono form or between the D-gulono and L-mannono form from 2,3-O-isopropylidene-L- or D-gluono-γ-lactone.

CONSTITUTION: The desired deoxymannojirimycin, i.e., the compds. of formula I and the formula II are obtd. by introducing a silyl protecting group into the C-6 of the 2,3-O-isopropylidene-L-gluono-γ-lactone or the 2,3-O-isopropylidene-D- gluono-γ-lactone, introducing an azide group into the C-5 by executing the inversion of stereocoordination to obtain a piperidine ring, reducing the formed azide lactone to form its 6-lactam, then reducing this lactam to obtain the corresponding amine and removing all the protecting groups. This compd. is useful as an enzyme inhibitor, an inhibitor of human immunodeficiency virus (AIDS), etc. A good yield is obtainable in a short stage by this process.