The observation that F-acids (1) occur in rat chow initiated a search for F-acids in human diet. We observed that the amount of F-acids with a pentyl side chain in alpha-position taken up with a one-day diet correlates well with the amount of excreted degradation products, the pentyl urofuran acids (2), (3) and (4). Therefore it can be concluded that F-acids with a pentyl side chain are not produced in the human body but are introduced through the diet. The origin of F-acids carrying an alpha-propyl side chain is less clear. The amount of propyl-urofuran acids (2) and (3) excreted in urine was found in one case out of three to be five times higher than the amount of F-acids carrying a propyl group in alpha-position taken up by the diet. Therefore, it can presently not be excluded that a portion of the propyl F-acids is produced by the body. F-acids found in human food are mainly introduced into the body by vegetables and fruits. F-acids were found also in birch leaves in considerable amounts, as well as in grasses, dandelion and clover leaves. Thus, we can conclude that F-acids are common constituents of plants.

The possible role of linoleic acid as a biogenetic precursor of the furan fatty acids (F-acids) was investigated in in vivo experiments in the rat, using a C19 analogue of linoleic acid and gas chromatography-mass spectrometry. No evidence of incorporation of this compound into the F-acids was found. Using an improved analysis procedure by converting F-acids into their tetrahydrofuran derivatives (enabling a separation from the large amounts of normal fatty acids), F-acids (F3, F4 and F6) were detected in rat food, correcting earlier results. Quantification of F-acid intake with food and excretion of furandicarboxylic acids in the urine, suggested the possibility that the F-acids are not produced de novo in the rat, but instead accumulate in tissue after nutritional intake.

Furancarbonsäuren (F‐Säuren) 1 wurden jetzt auch im Blutplasma von Mensch und Rind nachgewiesen, wo sie als Phospholipide vorliegen.

Die kürzlich in der Phospholipidfraktion des Blutplasmas identifizierten Furanfettsäuren (F‐Säuren)1) 1a–f liegen vorzugsweise als Cholin‐ und Ethanolaminphospholipide vor. Im Gegensatz dazu sind F‐Säuren in den Neutrallipiden des Blutplasmas ausschließlich an Cholesterol gebunden.

The title compounds (I) are found to be present in human and bovine blood plasma where they occur as phospholipids.