– 1H-Indole-3-carboxaldehyde (3-Formylindole), also known as 3-formylindole or 3-indolealdehyde, belongs to the class of organic compounds known as indoles. Indoles are compounds containing an indole moiety, which consists of pyrrole ring fused to benzene to form 2,3-benzopyrrole. 1H-Indole-3-carboxaldehyde is an extremely weak basic (essentially neutral) compound (based on its pKa). Outside of the human body, 1H-Indole-3-carboxaldehyde has been detected, but not quantified in, several different foods, such as gram beans, brussel sprouts, cucumbers, cereals and cereal products, and white cabbages. This could make 1H-indole-3-carboxaldehyde a potential biomarker for the consumption of these foods. A heteroarenecarbaldehyde that is indole in which the hydrogen at position 3 has been replaced by a formyl group.