D-Glucuronic acid lactone (Dicurone) is a naturally occurring chemical that is an important structural component of nearly all connective tissues. Glucuronolactone is also found in many plant gums.

2,5-Furandicarboxylic acid (Dehydromucic Acid) is a normal urinary metabolite in humans. 2,5-Furandicarboxylic acid is also a microbial metabolite, a product of the oxidation of hydroxymethylfurfural (HMF) by the enzyme furfural HMF oxidoreductase which is found in the bacterium Cupriavidus basilensis.

5-Hydroxymethyl-2-furancarboxylic acid (5-(Hydroxymethyl)-2-furoic acid) (Sumiki's acid) is a naturally occurring human metabolite. Sumiki's acid was first identified in the urine of a leukemia patient who was excreting an abnormal amount of its glycine derivative. Sumiki's acid has been found to be a byproduct of the fungus Aspergillus and probably other species of fungi and yeast as well.

Furanones (HDMF) are mainly derived from American grape (Vitis labrusca) and its hybrid varieties. As an important aroma compound in fruits, it exhibits strawberry-like aroma characteristics in some wines.

3-Furanoic acid (3-Carboxyfuran) is an organic acid regularly occurring in the urine of healthy individuals. 3-Furanoic acid (3-Carboxyfuran) is also a compound found in honey and honeydew samples.