The potent O-GlcNAcase (OGA) inhibitor GlcNAc-thiazoline has been modified by buffer- or acylation-induced imine-to-enamine conversion, and then electrophile or radical addition (Xn = D3, F, N3, OH, SMe, COCF3, CF3). Several functionalized GlcNAc-thiazolines show highly selective inhibition of OGA vs human hexosaminidase, and thus have promise as tools for targeted investigations of OGA, an enzyme linked to diabetes and neurodegeneration. A new radical addition/fragmentation reaction of the N-(trifluoroacetyl)enamine has been discovered.