A new antibiotic, aldecalmycin, has been discovered in the culture broth of Streptomyces sp. MJ147-72F6. Aldecalmycin was purified by solvent extraction, Diaion HP-20 chromatography, silica gel chromatography, Sephadex LH-20 chromatography, HPLC and centrifugal partition chromatography. The *H and 13C NMRspectra of aldecalmycin showed the presence of keto-enol tautomers. Aldecalmycin is equipot...

The mol-ecule of the title compound, C(21)H(16)N(2)O, exists in the keto form and the C=O and N-H bonds are mutually cis in the crystal structure, although an enol form would be possible through tautomerism. The dihedral angle between the quinoline and the naphthalene systems is 22.04 (2)°. A bifurcated intramolecular N-H⋯(O,N) hydrogen bond is present.

Substituent, temperature and solvent effects on tautomeric equilibria in several β-ketoamides have been investigated by means of nuclear magnetic resonance spectroscopy (NMR). Keto-enol equilibrium predominates over the amide-imidol one. The relative stability of the individual tautomers and the corresponding equilibrium shifts are explained considering electronic and steric effects and tautome...

Density functional theory (DFT) calculations have been performed to calculate the optimized geometries of stepwise fluorinated methylenecyclopropanes and 1-methylcyclopropenes. Increasing the number of fluorine atoms caused a destabilization of methylenecycopropane. Perfluorinated 1-methylcyclopropene was found to be present in substantial concentration. This is supported by calculations of the...

Ultraviolet and infrared absorption spectroscopy, in aqueous and non-aqueous media, have been employed to study the tautomerism of 9-substituted isoguanines, including the nucleoside isoguanosine. With the aid of a series of model compounds, it was shown that 9-substituted isoguanines, and isoguanosine, in aqueous medium are predominantly in the form N (1) H, 2-keto-6-amino. In dioxane solution...

This thesis presents computational chemistry studies of keto-enol reactions and chromophores of photobiological significance. The first part of the thesis is concerned with two protein-bound chromophores that, depending on the chemical conditions, can exist in a number of different ketonic and enolic forms. The first chromophore is astaxanthin, which occurs in the protein complex responsible fo...