The "abbreviated" model of NAD, 1-[3-(adenin-9-yl)-2-hydroxypropyl]-3-carbamoylpyridinium chloride (VIIIa), and its 2,6-diaminopurine (VIIIb), 3-deazaadenine (VIIIc), guanine (VIIId) and cytosine (VIIIe) analogues were prepared by the Zincke reaction. The (R)-isomer of the adenine model VIIIa (compound IX) was prepared for chiroptical studies. As shown by NMR, UV and CD spectra, neither in dimethyl sulfoxide nor in water any intramolecular π-π interactions exist between the heteroaromatic systems.
13C NMR spectra of p-nitrobenzoyl 2-, 4-, and 6-aminopyridine-3-carboxylates, their hydrochlorides, trifluoroacetates and 1-benzyl derivatives were studied. As found from the chemical shifts of pyridine carbon atoms C-2, C-4 and C-6, the free bases exist in the amino form whereas hydrochlorides and 1-substituted pyridinium derivatives in the imino form. Trifluoroacetates of the 2- and 6-amino derivatives have structure similar to that of amidiniumcarboxylates (parallel hydrogen bonds and partially ionic character) whereas trifluoroacetate of the 4-amino derivative is structurally close to the corresponding hydrochloride. The found structures were confirmed by 1H NMR and IR spectroscopy.
Amino-Imino Tautomerism in Derivatives of 2-, 4-and 6-Aminonicotinic Acid.-The title derivatives, e.g. (IIIa), (V), (VI), and (VIII), are investigated with the aid of 13C NMR spectroscopy. The main tantomeric form of the products is determined. Depending on the derivative amino or imino forms are observed. -(SMRCKOVA, S.; JURICOVA, K.; PRUTIANOV, V.; Collect.
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