Triazolo[4,5-b]- and imidazo[4,5-b]pyridines as substrates of NAD glycohydrolase: Evidence for two competitive transglycosylation reaction sites

The NAD(+) glycohydrolase-catalysed transglycosidation reaction of pyrido-annulated triazole 1 and imidazole 2 was investigated. In both cases two regioisomers, N-1-ribosylated (3 and 5) and N-3-ribosylated products (4 and 6), were efficiently obtained in roughly equal ratio. The regioisomers were distinguished from each other on the basis of N-15-NMR data. The present study furnished evidence of two competitive sites of transglycosidation in the triazole 1 and the imidazole 2. The occurrence of competition is probably attributable to a tautomeric equilibrium between 1a and 1b (2a and 2b).