Crystal Structure of 3-Amino-1,2,4-triazin-5(2H)-one

Abstract

The 1,2,4-triazine ring system had been suggested for study because of various interesting biological activities. 1 The tautomeric proton is highly effective at making strong intermolecular hydrogen binding with other heteroatoms of molecules involved with biological activity.The title compound 3-amino-1,2,4-triazin-5(2H)-one (6-azaisocytosine, Fig. 1), an isosteric isomer of isocytosine, can exist in several tautomeric forms, which have been discussed in earlier reports. [2][3][4] Ueda and Furukawa 2 concluded that the imino-oxo form is predominant, as shown by infrared spectra. Sasaki and Minamoto 3 used ultraviolet and infrared spectra to show that amino-oxo form (4H-tautomer) to be predominant. Pitha et al. 4 compared ultraviolet spectra and ionization constants to reveal the relative abundances as 100:1, in favor of the amino-oxo form (2H-tautomer). There is a need to obtain more precise information about the most contributed prototropic tautomerism of the title molecule and to confirm the assigned structure. So we have undertaken a critical use of X-ray crystallographic analysis.The title compound was prepared by the method of Sasaki and Minamoto. 3 The physical properties of 3-amino-1,2,4-triazin-5-one had been reported: mp, 4-6 IR, 2,3,5 UV, 3-5 NMR, 5,6 and dissociation exponent. 4 A colorless crystal of dimensions 0.35 × 0.50 × 0.55 mm 3 suitable for single-crystal X-ray diffraction measurements was obtained by recrystallization from H2O solution. The results of the X-ray structure determination are given in Tables 1 -3. The ORTEP diagram for the title compound is shown in Fig. 2.Data from the X-ray structure reveal that the oxidation site is at C-5 position and that the predominant tautomeric structure is amino-oxo form 2H-tautomer (3-amino-1,2,4-triazin-5(2H)-one). This analysis reveals that the 1,2,4-triazine ring structure of 3-amino-1,2,4-triazin-5(2H)-one is slightly distorted due to the asymmetry of the electronegativity of nitrogen. Obviously, the tautomeric proton 2-H is located at N-2 (N2) with 0.885(20)Å bond distance shorter than the bond length of H-N(3) 1.009 Å, 7 which means the H2-N2 single bond is strongly attracted by the greater π-deficiency triazine ring. The same reason also explains the result that the bond distance 0.966(19)Å of C3-H1 is shorter than the bond length 1.083 Å of Car-H. 7 On the other hand, because of the π-electron resonance effect in the triazine ring, the C1-O bond length 1.2413 (18)

Crystal structure of 2-[(2-acetoxyethoxy) methyl]-3-amino-1,2,4-triazin-5(2H)-one

“…From this X-ray analysis of the title compound, revealing the 1,2,4-triazine ring is slightly distorted. Obviously, the extending out acyclic nucleoside chain is located at N1 (i.e., N-2), which is compatible well to the tautomeric proton 2-H located at N-2 of the compound 3-amino-1,2,4-triazin-5(2H)-one (6-azaisocytosine, II), as reported by us (Hwang et al 2002). A comparison of selected bond lengths and angles for compounds I and II in Table 3.…”

Achieving 1% NMR polarization in water in less than 1min using SABRE

“…ATZ exhibits various interesting biochemical properties [29,30] and its structure has been studied in detail [31,32]. ATZ is a heterocyclic aromatic organic compound, containing three nitrogen atoms in the aromatic ring, which are able to bind to the iridium atom of the catalyst precursor.…”

Aromatization and ring cyclization: A reasonable understanding on the ring cyclization mechanism of 3‐amino‐6‐hydrazino‐1,2,4‐triazin‐5(2H)‐one reacted with one‐carbon fragment reagents or nitrous acid

“…When 3-amino-2-benzyl-6-hydrazino-1,2,4-triazin-5(2H)-one (10), the N-2 benzylated derivative of 2, is treated under the same conditions, ring cyclization does not occur; instead, 3-amino-2-benzyl-6-substituted-1,2,4-triazin-5(2H)-ones (11,12,14) and 2-N-(2-amino-1-benzyl-4-oxo-1,2,4-triazin-5-yl)semicarbazide (13) are formed. Alternatively, when 3-amino-6-hydrazino-2-[(2-hydroxyethoxy)methyl]-1,2,4-triazin-5(2H)-one (16), a compound bearing the 2-[(2-hydroxyethoxy)methyl] side-chain at N-2 of 2 by an N-C-O bond, reacts with glacial acetic acid or nitrous acid, the side-chain is cleaved through acidolysis to affford the ring-closed compound 6-amino-3-methyl-1,2,4-triazolo [3,4-f] [1,2,4]triazin-8(7H)-one (3b) or compound 4, respectively.…”

“…Additionally, we studied the prototropic tautomerism of 3-amino-1,2,4-triazin-5(2H)-one (6) and 6-amino-3-ethyl-1,2,4-triazolo[3,4-f][1,2,4]triazin-8(7H)-one (7) by X-ray crystallographic analysis [10,11], which revealed the predominant tautomeric structure of compound 6 as the 2H-tautomer and that of compound 7 as the 7H-tautomer (not the 5H-tautomer as speculated by Lovelette [7]). These results inspired us to understand more about the actual mechanism for this ring cyclization of the compound 2 reacting with one-carbon fragment reagents to afford tautomeric heterobicycles (3).…”

“…type I structure). This is based on the fact that when 3-amino-2-benzyl-6-hydrazino-1,2,4-triazin-5(2H)-one (10), an N-2 benzylated derivative of 2, is treated with N,Ndimethylformamide (DMF) and acetic acid to afford 3-amino-2-benzyl-6-(2-formylhydrazino)-1,2,4-triazin-5(2H)-one (11), no ring cyclization is observed since the N-2 benzyl group prevents the prototropic tautomerism required in the formation of the aromatic intermediate ( Figure 1. type II structure).…”