C-13 AND N-15 NMR CHEMICAL-SHIFT ASSIGNMENTS OF N-1-(2-AZIDOETHYL)-4-R-PYRIMIDIN-2-ONES BY H-1,X HMQ(B)C WITH Z-GRADIENT SELECTION

C-13 and N-15 NMR chemical shift assignments based on z-gradient selec ted H-1,X (X = C-13 and N-15) HMQC and NMBC experiments are reported f or N-1-(2-azidoethyl)pyrimidin-2-one (ring system of cytosine), its fi ve 4-R derivatives [where R = NH2, OCH3, N(CH2)(4), NHCH2CH(CH3)(2) an d N(CH3)(2)] and 2-azidoethyl tosylate. The possibilities of detecting all nitrogens in these molecules containing (i) an azido group at N-1 and (ii) an electronegative substituent at C-4 are limited. First, th e terminal nitrogen of the azido group is difficult to observe because the nearest proton (in a CH2 group) is located four bonds away from i t. Second, in contrast to N-1, N-3 in N-1-(2-azido-ethyl)-4-pyrimidin- 2-ones remained undetected. For that reason, an unsubstituted derivati ve (R = H) was also prepared, where N-3 was easily observed. (C) 1998 John Wiley & Sons, Ltd.