<unk>  (IPA), or indole-3-propionic acid, is a potent neuroprotective antioxidant, plant auxin, and natural product in humans that is being studied for therapeutic use in Alzheimer's disease. It is endogenously produced by human microbiota and has only been detected in vivo when the species Clostridium sporogenes is present in the gastrointestinal tract. , C. sporogenes, which uses tryptophan to synthesize IPA, is the only species of bacteria known to synthesize IPA in vivo at levels which are subsequently detectable in the blood plasma of the host. IPA is an even more potent scavenger of hydroxyl radicals than melatonin, the most potent scavenger of hydroxyl radicals that is synthesized by human enzymes. Similar to melatonin but unlike other antioxidants, it scavenges radicals without subsequently generating reactive and pro-oxidant intermediate compounds. In 2017, elevated concentrations of IPA in human blood plasma were found to be correlated with a lower risk of type 2 diabetes and higher consumption of fiber-rich foods.
3-Indolepropionic acid
3-Chloropropanoic acid
Indoxyl sulfate
Corynanthine
Orthosilicic acid
Metirosine
Phenylacetic acid
Choline