A series of new compounds from 1,3,4-thiadiazine class with thiomorpholine fragment at position 2 of the thiadiazine cycle have been synthesized by cyclocondensation of α-haloacetophenones with original 4-morpholinothiosemicarbazide. Two of the new 1,3,4-thiadiazines (IIIa and IIIb, containing phenyl and fluorophenyl fragment, respectiverly) showed the ability to inhibit nonenzymatic glycosylation of proteins in a model system in vitro. The obtained results allow these compounds to be recommended for subsequent experimental testing in vivo.