Nucleic acids components and their analogues. LXXXII. The fine structure of 6-azaisocytosine and its derivatives

Tautomerism: Introduction, History, and Recent Developments in Experimental and Theoretical Methods

“…The quinoxalinones 10a (R 1 = H or CO 2 R, R 2 = CO 2 R or CN) were examined by Kurasawa et al [10] using NMR in dimethyl sulfoxide (DMSO) and DMSO-TFA (trifluoroacetic acid) mixtures and were found to go 100% to 10b despite loss of aromaticity, presumably because of dipolar repulsion in 10a; no quantitative data were reported, however. Pit'ha and coworkers [11] …”

Aromatization and ring cyclization: A better understanding on the ring cyclization mechanism of 3‐amino‐6‐hydrazino‐1,2,4‐triazin‐5(2H)‐one reacted with acetic acid in N,N‐dimethylformamide

“…Many aza and deaza analogues of purine and their nucleosides have attracted considerable interest due to their biological activities. Compound 1, 6-amino-1,2,4-triazolo [3,4-f] [1,2,4]triazin-8(5H)-one (4,8-diaza-9-deazaguanine), the isosteric isomer of guanine, has been previously synthesized by Lovelette [1]. He treated 3-amino-6hydrazino-1,2,4-triazin-5(2H)-one (3) with two equiva-lents of acetic acid in excess N,N-dimethylformamide (DMF) under reflux, and the ring closure at the N-1 nitrogen of the 1,2,4-triazine ring occurred to afford 1.…”

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

“…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.…”

“…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.…”

“…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.…”