DUMITRU PETRU IGA, DUMITRU POPESCU, FLORENTINA DUICA THE USE OF EXOGLYCOSIDASES FOR THE ASSAY OF TWO NEW ENZYMATIC SUBSTRATES, B-D-XYLOPYRANOSYL-4-NITROCATECHOL-1-YL AND A-LACTOSYL-4-NITROCATECHOL-1-YL Glycosylation acceptor, 4-nitrocatechol, has been prepared via 4-nitrocatechol sulfate (2-hydroxy-5-nitrophenyl sulfate). The two carbohydrates, D-xylose and lactose, were peracetylated and then served as glycosylation donors in a modified Helferich glycosylation method, by using BF3· OBu2 as a promotor. The new synthesized glycosides were crystallized from ethanol and then submitted to Zémplen saponification and separated by preparative thin layer chromatography (TLC). We have isolated two xylosides. Reaction mixture of lactoside proved to be unitary, a single product could be isolated. Small portions of the synthetic glycosides were re-acetylated and their 1H and 13C NMR spectra registered. The two separated xylosides were b- and a-xylopyranoside-4-nitrocatechol-1-yl. Being submitted to the action of an enzymatic extract from digestive tract of snail (Helix pomatia) only the b-anomer was susceptible to enzymatic hydrolysis. The isolated lactoside proved to be the a-isomer. Under the action of an enzymatic extract from wheat (Triticum aestivum) germs, it was sequencially cleaved, as indicated by a kinetic TLC analysis.