Synthesis of [4-15NH2]- and [1,3-15N2]cytidine derivatives for use in NMR-monitored binding tests.

The conversion of 15N-enriched urea to a [1,3-15N2]cytidine derivative is accomplished in nine steps with an overall yield of 67%. Synthesis of a [4-15NH2]cytidine derivative is achieved by thiolation of the corresponding uridine derivative with Lawesson's reagent and amination with 15N-enriched ammonia in a sealed glass vessel.