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Carbon-13 NMR is utilized to demonstrate the attack of bisulfite anion on uridine, 5-fluorouridine, and uridine 5'-monophosphate. The attack produces a pair of diastereomeric adducts similar in structure to those seen in the uracil series. Intensity data from the equilibrium system give an estimate for the individual equilibrium constants. Thymidine and thymidine 5'-monophosphate show no evidence of nucleophilic attack by bisulfite. This evidence indicates that bisulfite addition to nucleosides and nucleotides models the enzymatic methylation of uridine by the enzyme thymidylate synthetase better than the uracil bisulfite system.

U r a c i l , 6,7-dimethyllumazine, and lumichrome have been l a b e l l e d w i t h carbon-13 a t p o s i t i o n s 6 , 8a, and 10a, respect i v e l y . This w a s accomplished v i a a common i n t e r m e d i a t e , ~y a n o a c e t y l u r e a -6 -~~C . Lumazine and lumichrome w e r e condens a t i o n products of 5,6-diaminouracil and e i t h e r 2,3-butanedione. o r a condensate of i t . U r a c i l w a s produced by a Raney Nickel r e d u c t i o n followed by a c i d c a t a l y z e d c y c l i z a t i o n . This method i s a l s o a p p l i c a b l e t o l a b e l l i n g t h e s e compounds a t o t h e r carbons w i t h i n t h e molecules.

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