2-carboxy-2,5-dihydro-5-oxofuran-2-acetate 2-carboxy-5-oxo-2,5-dihydrofuran-2-acetate 4-carboxymuconolactone 5-Carboxy-2,5-dihydro-2-oxofuran-5-acetate CPD-761 gamma-carboxymuconolactone