The crystal structure of 8-azaadenine hydrochloride

Abstract

The crystal and molecular structure of 8-azaadenine hydrochloride, C4HsN6CI, has been determined from three-dimensional counter X-ray data. The purine derivative crystallizes in the monoclinic space group P2t, with two molecules in a cell of dimensions a=7.728 (4), b=7.177 (4), c=6"122 (4) A,, fl= 91.54 (3) °. The structure has been refined by least-squares techniques using 513 independent data to a conventional R (on F) of 0.038. The structure consists of disordered 8-azaadeninium cations which are hydrogen bonded to chloride anions. The disorder involves two orientations of the cation with C(4) and C(6) common to both, and one orientation is related to the other by an approximately 180 ° rotation around the C(4)-C(6) vector. Consequently, atoms C(2) and N(7) in one orientation occupy the sites of N(7) and C(2) respectively in the other orientation. An examination of the hydrogen bonding suggests that the cationic proton is on N(1). The apparent stability of 8-azaadenine to the acid conditions employed strongly suggests that the previously documented hydrolysis of this purine analogue on coordination to Cu 2+ is primarily due to the interaction with the metal ion. The corresponding hydrobromide salt is isomorphous with the hydrochloride, and disorders in an analogous manner.

Azaguanine: A Theoretical Study of Its Tautomerism and Protonation in the Gas Phase and Aqueous Solution

“…To name the protonated species we used the same notation applied for the neutral forms and are easily recognized by their three numerical indices. The calculated structural parameters (see Table 4) agree reasonably well with the experimental data determined by X-ray diffraction methods from azaguanine hydrochloride and hydrobromide monohydrate (28,29). Unfortunately, no direct comparison can be made in relation with the hydrogen atoms since the extensive hydrogen bonding taking place in the solid state and the uncertainty in the location of the hydrogen attached to the triazolo ring.…”

8-Azapurines as isosteric purine fluorescent probes for nucleic acid and enzymatic research

“…Amino and keto structures predominate in most amino and oxo 8-azapurine derivatives, analogously as in the purine series. 61,62 Such conclusions can be drawn from crystallographic data, available for 8-azaAde hydrochloride, 63 its N(7)-methyl derivative 64 and 8-azaAdo, 65 and 8-azaGua and 8-azaHx derivatives. 63,[66][67][68] Spectroscopic (FT/IR) studies of 8-azapurines also point to predominance of the keto-amino structures.…”

“…61,62 Such conclusions can be drawn from crystallographic data, available for 8-azaAde hydrochloride, 63 its N(7)-methyl derivative 64 and 8-azaAdo, 65 and 8-azaGua and 8-azaHx derivatives. 63,[66][67][68] Spectroscopic (FT/IR) studies of 8-azapurines also point to predominance of the keto-amino structures. 36,69 Crystal structures show the presence of the N( 9)-H in 8-azaGua, 66 while 8-azaGua hydrobromide crystals show the N(8)-H, N(3)-H structure.…”