24. Synthesis of (15N2)[17O]urea, (15N2)[O2,O4-17O 2]uridine, and (15N3)[O2-17O]cytidine

Article abstract of DOI:10.1002/hlca.19960790125

A general synthetic approach for the synthesis of ¹⁵N- and ¹⁷O-doubly labelled pyrimidine nucleosides is described. The ¹⁵N isotopes in uridine and the ¹⁷O isotope in the urea-derived carbonyl group of uridine and cytidine originate from (¹⁵N₂)[¹⁷O]urea (5) which was synthesized from ¹⁵NH₄Cl, thiophosgene (1), and H₂[¹⁷O]. The third ¹⁵N isotope of cytidine in 4-position stems from the substitution of the 1,2,4-triazole moiety of (¹⁵N₂)[O²-¹⁷O]uridine derivative 8a/b with ¹⁵NH₄OH. Hydrolysis of the same key intermediate 8a/b with Na[¹⁷O]H/H₂[¹⁷O] introduced the second ¹⁷O isotope into the 4-position of uridine. The ¹⁵N- and ¹⁷O-NMR spectra of the target compounds 12 and 14 in phosphate-buffered H₂O serve as references for heteronuclear NMR spectra of labelled RNA fragments.