Vulgaxanthin I

1,2,3,4-Tetrahydro-4-[2-(1-carboxy-3-carbamoylpropylimino)ethylidene]-2,6-pyridinedicarboxylic acid

4-[2-[(4-Amino-1-carboxy-4-oxobutyl)imino]ethylidene]-1,2,3,4-tetrahydro-2,6-pyridinedicarboxylic acid

1,2,3,4-Tetrahydro-4-[2-[(4-amino-1-carboxy-4-oxobutyl)imino]ethylidene]pyridine-2,6-dicarboxylic acid