EC23, also known as AGN 190205, is photostable synthetic analog of All-trans retinoic acid (ATRA). EC23 is an agonist of retinoic acid receptors: alpha, beta and gamma, while having no appreciable activity for retinoid X receptors and weakly activates aryl hydrocarbon receptor. It was shown, that EC23 induced neural differentiation in human pluripotent embryonic stem cells.

DL-5-hydroxytryptophan, 5-HTP is a serotonin precursor. It was discovered on the rats, that the pharmacological responses and changes in brain 5-hydroxytryptamine (5-HT) concentration elicited following the administration of 5-HTP did not reflect changes in the concentration of endogenous brain 5-HT. The biochemical and pharmacological properties of the 5-HTP-induced increases in brain 5-HT concentration were distinctly different from those of increases in the endogenous content of the amine. In normal rats, administered 5-HTP, observable pharmacological responses were not elicited, despite equal or even larger increases in brain 5-HT concentration.

3-Tyrosine, in contrast to the para isomer, is readily racemized. The majority of the load was metabolized to m-hydroxyphenylacetic acid but m-hydroxymandelic acid and 3,4-dihydroxyphenylacetic acid were also detected. Low circulating levels of m-tyrosine in the plasma suggest that most of the load is held due to a first pass effect somewhere in the enterohepatic system and that this portion of the load is not in equilibrium with the plasma m-tyrosine. The metabolism of a m-tyrosine may give further insight into the deficiencies of the phenylalanine hydroxylating system found in the various phenotypes of phenylketonuria. 3-Tyrosine has been used experimentally as a substitute for L-DOPA in the treatment of Parkinsonism. 3-tyrosine mimics the action of Dopa in two experimental animal models. It was also obvious from the experiments with d,l- and l-m-tyrosine that only the l-isomer (3-Tyrosine) is active.