Since the nitrogens of nucleosides and nucleotides play an important role in the molecular recognition of these compounds, (15)N NMR became a method of choice in this field. Fully (15)N-labeled adenine, required in the latter studies, was obtained in four synthetic steps, in a good yield. Likewise, ((15)N(5))-2-hexylthioether-adenine and ((15)N(5))-8-Br-adenine were obtained in five synthetic steps from the relatively inexpensive (15)N sources: (15)N-NH(4)Cl, (15)N-NH(4)OH, (15)N-NaNO(2). Full (15)N labeling of these adenine prototypes enabled to obtain high-resolution (15)N NMR spectra of these bases at 60.8 MHz. Furthermore, the spectra suggested the existence of the N3-H species in the tautomeric mixtures of these compounds in solution, in addition to the well-reported N9-H (major) and N7-H (minor) tautomers. These observations were also supported by quantum mechanical calculations of the tautomeric equilibria in the gas phase and in solution of the above-mentioned adenine compounds. The gas-phase tautomeric equilibria were estimated using density functional theory and second-order perturbation theory methods. Solvent effects were included by means of both continuum and discrete solvation models. The observation of the existence of the N3-H tautomer has a clear impact on the possible H-bonding patterns of these adenine prototypes and on their molecular recognition by various biological macromolecules. The above(15)N-labeled analogues are expected to find use as (15)N NMR probes for numerous biochemical studies.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

No abstract

No abstract

The elucidation of the molecular recognition of adenosine deaminase (ADA), the interpretation of the catalytic mechanism, and the design of novel inhibitors are based mostly on data obtained for the crystalline state of the enzyme. To obtain evidence for molecular recognition of the physiologically relevant soluble enzyme, we studied its interactions with the in situ formed inhibitor, 6-OH-purine riboside (HDPR), by 1D-15N- and 2D-(1H-15N)- NMR using the labeled primary inhibitor [15N4]-PR. We synthesized both [15N4]-PR and an [15N4]-HDPR model, from relatively inexpensive 15N sources. The [15N4]-HDPR model was used to simulate H-bonding and possible Zn2+-coordination of HDPR with ADA. We also explored possible ionic interactions between PR and ADA by 15N-NMR monitored pH-titrations of [15N4]-PR. Finally, we investigated the [15N4]-PR-ADA 1:1 complex by 2D-(1H-15N) NMR. We found that HDPR recognition determinants in ADA do not include any ionic-interactions. HDPR N1 H is an H-bond acceptor, and not an H-bond donor. Despite the proximity of N7 to the Zn2+-ion, no coordination occurs; instead, N7 is an H-bond acceptor. We found an overall agreement between the crystallographic data for the crystallized ADA:HDPR complex and the 15N-NMR signals for the corresponding soluble complex. This finding justifies the use of ADA's crystallographic data for the design of novel inhibitors.