The hydrogen-isotope labeling of nucleic acid bases is sometimes required in nucleic acid research. Many papers have already appeared on deuteration of E-H in purines 2,3) and of 5-H in pyrimidines 4-6) through the ionic exchange processes. This paper describes catalytic hydrogen exchange of nucleosides and nucleotides using Adams platinum. 7) This catalytic method may provide a source of labeled compounds which are difficult to be obtained by other methods. All the materials used were purchased from Kojin Co.,Tokyo, and Sigma Chem. CO., St. Louis. Platinum dioxide (Pt02 -2H20) was purchased from Kawaken Fine Chemicals, Tokyo. Incorporated deuterium was determined by quantitative NNR analysis. Chemical purity of the products was checked by thin-layer chromatography and UV spectroscopy. Appreciable amount of any decomposed by-products was not detected in any of the cases examined in the present study. General Procedure for Hydrogen Exchange _~_l___________"~~llII_ ___ _________ An appropriate amount of platinum oxide (shown in the table) was suspended in 1 ml of D20 in a test tube (10 x 150 rmn) and mechanically vibrated in D2 gas atmosphere for l-3 hr at room temperature. After most of the solvent was removed with a small pipette, nucleoside or nucleotide dissolved in 1 ml of D20 was added. Then the reaction mixture was frozen and degassed up to 10s3 Torr. After this procedure was repeated twice more to eliminate molecular hydrogen involved, the reaction tube was sealed under 10 -3 Torr pressure. The tube was gently shaken in a water bath at 30+0.5° or kept standing ih boiling water for 40 hr. After the catalyst was eliminated by filtration, the NMR spectrum of the filtrate was measured for quantitative analysis of the deuterium incorporated in the respective positions of the molecule. Results The results are shown in the table. __-.I"__ Cytidine and uridine underwent deuteration at 30° in both 5-and 6-positions. The 5-H's were more readily * This paper also constitutes Part XIII of a series of study entitled "Studies on Hydrogen Exchange. Part XII: ref. 3.