2,6-Pyridinedicarboxylic acid, 4-(2-((2S)-2-carboxy-2,3-dihydro-5,6-dihydroxy-1H-indol-1-yl)ethenyl)-2,3-dihydro-, (2S)-

(2R)-1-[(E)-2-[(2S)-2-carboxy-6-(dihydroxymethylidene)-2,3-dihydro-1H-pyridin-4-yl]ethenyl]-5,6-dioxo-2,3-dihydroindole-2-carboxylic acid