13C and15N NMR chemical shift assignments ofN-1-(2- azidoethyl)-4-R-pyrimidin-2-ones by1H,X HMQ(B)C withz-gradient selection

13C and 15N NMR chemical shift assignments based on z-gradient selected 1H,X (X=13C and 15N) HMQC and HMBC experiments are reported for N-1-(2-azidoethyl)pyrimidin-2-one (ring system of cytosine), its five 4-R derivatives [where R=NH2, OCH3, N(CH2)4, NHCH2CH(CH3)2 and 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, the terminal nitrogen of the azido group is difficult to observe because the nearest proton (in a CH2 group) is located four bonds away from it. Second, in contrast to N-1, N-3 in N-1-(2-azido-ethyl)-4-pyrimidin-2-ones remaine…