5,6-dihydroxyindole-2-carboxylic acid by treatment of sepiomelanin with sodium borohydride.

Mild treatment of sepiomelanin and biosynthetic eumelanins with NaBH₄ in 0.1 N NaOH leads to the isolation of 5,6-dihydroxyindole-2-carboxylic acid ($\text{3}$), a component of structural interest which may account for most of the degradation products of melanins so far obtained.     

Synthesis of optically active tetrameric melanin intermediates by oxidation of the melanogenic precursor 5,6-dihydroxyindole-2-carboxylic acid under biomimetic conditions

In a recent work addressing the structural characterization of melanin pigments, we reported the isolation and characterization of trimeric oligomers of 5,6-dihydroxyindole-2-carboxylic acid (DHICA), a key intermediate in the biosynthesis of the dark brown eumelanins, by tyrosine catalyzed oxidation of the indole under biomimetic conditions. These oligomers feature atropisomerism and consequently, we wished to investigate chirality in such systems. Herein, we report two significant steps forward in this study: The isolation of a regiosymmetric DHICA tetramer by means of a model approach involving oxidation of the main DHICA dimer, namely 4,4′-biindolyl and the first resolution of eumelanin intermediates. This also allowed the absolute stereochemistry of the newly isolated tetramer to be defined by applying the exiton chirality method.     

4-Hydroxy-2-quinolones 138. Synthesis and study of structure-biological activity relationships in a series of 1-hydroxy-3-oxo-5,6-dihydro-3H-pyrrolo[3,2,1-<Emphasis Type="Italic">ij</Emphasis>]quinoline-2-carboxylic acid anilides

Two methods are discussed and the synthesis of a series of 1-hydroxy-3-oxo-5,6-dihydro-3H-pyrrolo[3,2,1-ij]quinoline-2-carboxylic acid anilides has been carried out. The antitubercular activity and the effect on the urinary function of the kidney have been studied for the compounds prepared. A structure-biological activity relationship is discussed. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1808–1819, December, 2007.