Synthesis and Photochemical Behavior of the Tetrazolo Tautomer of 2-Azido-4-pyrimidinone-2′-deoxyriboside

15N Chemical Shifts and JNN-Couplings as Diagnostic Tools for Determination of the Azide-Tetrazole Equilibrium in Tetrazoloazines

Selectively ¹⁵N-labeled tetrazolo[1,5-b][1,2,4]triazines and tetrazolo[1,5-a]pyrimidines bearing one, two, or three ¹⁵N labels were synthesized. The synthesized compounds were studied by ¹H, ¹³C, and ¹⁵N NMR spectroscopy in DMSO and TFA solutions, where the azide-tetrazole equilibrium can lead to the formation of two tetrazole (T, T') isomers and one azide (A) isomer for each compound. Incorporation of the ¹⁵N-label(s) leads to the appearance of ¹⁵N-¹⁵N coupling constants (J_NN), which can be easily measured via simple 1D ¹⁵N NMR spectra, even at natural abundance between labeled and unlabeled ¹⁵N atoms. The chemical shifts for the ¹⁵N nuclei in the azole moiety are very sensitive to the ring opening and azide formation, thus providing information about the azido-tetrazole equilibrium. At the same time, the ^1-2J_NN couplings between ¹⁵N-labeled atoms in the azole and azine fragments unambiguously determine the fusion type between tetrazole and azine rings in the cyclic isomers T and T'. Thus, combined analysis of ¹⁵N chemical shifts and J_NN values in selectively isotope-enriched compounds provides an effective diagnostic tool for direct structural determination of tetrazole isomers and azide form in solution. This method was found to be the most simple and efficient way to study the azido-tetrazole equilibrium.

Crystal structure of 4,6-dimethyl-2-[(2,3,4,6-tetra-O-acetyl-β-d-galacto-pyranos-yl)sulfan-yl]pyrimidine

In the title com-pound, C20H26N2O9S, the S atom is attached equatorially to the sugar ring. The C-S bond lengths are unequal, with S-Cs = 1.8018 (13) Å and S-Cp = 1.7662 (13) Å (s = sugar and p = pyrimid-yl). In the crystal, a system of three weak hydrogen bonds, sharing an oxygen acceptor, links the mol-ecules to form chains propagating parallel to the b-axis direction.

New synthetic strategies for acyclic and cyclic pyrimidinethione nucleosides and their analogues

Pyrimidinethione nucleosides are effective compounds and have significant and pivotal effects in several fields. New synthetic strategies for many pyrimidinethione nucleosides including acyclic and cyclic derivatives have been reported.

Transformation of a wobble 2-thiouridine to 2-selenouridine via S-geranyl-2-thiouridine as a possible cellular pathway

The newly discovered S-geranylated 2-thiouridines (geS2U) (Dumelin et al., 2012) and 2-selenouridines (Se2U) were recently shown to be synthesized by a single enzyme (selenouridine synthase, SelU) through two distinct pathways using the same 2-thiouridine substrate (S2U); however, no clear catalytic mechanism was proposed. We suggest that S-geranyl-2-thiouridine is an intermediate of the SelU-catalyzed conversion of S2U to Se2U. The successful chemical transformation of S2U→geS2U→Se2U is demonstrated here as an initial approximation of the intracellular pathway. The structure of Se2U was confirmed by spectroscopic methods, which included, for the first time, (77)Se NMR data (δ 354ppm).

Long-range 1H-15N J couplings providing a method for direct studies of the structure and azide-tetrazole equilibrium in a series of azido-1,2,4-triazines and azidopyrimidines

The selectively (15)N labeled azido-1,2,4-triazine 2*A and azidopyrimidine 4*A were synthesized by treating hydrazinoazines with (15)N-labeled nitrous acid. The synthesized compounds were studied by (1)H, (13)C, and (15)N NMR spectroscopy in DMSO, TFA, and DMSO/TFA solutions, where the azide-tetrazole equilibrium could lead to the formation of two tetrazoles (T, T') and one azide (A) isomer for each compound. The incorporation of the (15)N label led to the appearance of long-range (1)H-(15)N coupling constants (J(HN)), which can be measured easily by using amplitude-modulated 1D (1)H spin-echo experiments with selective inversion of the (15)N nuclei. The observed J(HN) patterns enable the unambiguous determination of the mode of fusion between the azole and azine rings in the two groups of tetrazole isomers (2*T', 4*T' and 2*T, 4*T), even for minor isoforms with a low concentration in solution. However, the azide isomers (2*A and 4*A) are characterized by the absence of detectable J(HN) coupling. The analysis of the J(HN) couplings in (15)N-labeled compounds provides a simple and efficient method for direct NMR studies of the azide-tetrazole equilibrium in solution.