Racemic phenibut (beta-phenyl-gamma-aminobutyric acid or 4-amino-3-phenylbutyric acid) is a neuropsychotropic drug that was discovered and introduced into clinical practice in Russia in the 1960s. In pharmacological tests of locomotor activity, antidepressant and pain effects, S-phenibut was inactive. In contrast, R-phenibut turned out to be two times more potent than racemic phenibut in most of the tests. Racemic phenibut and R-phenibut demonstrated an affinity for GABAB receptors, in contrast, S-phenibut was not able to bind receptors. Pharmacological activity of racemic phenibut relies on R-phenibut and this correlates to the binding affinity of enantiomers of phenibut to the GABAB receptor. Both S- and R-phenibut bind to the α2-δ subunit of voltage-dependent calcium channels and exert gabapentin-like anti-nociceptive effects. In addition S-isomer was found to be a substrate of gamma-aminobutyric acid aminotransferase, however, the R-isomer is a competitive inhibitor.

Mephenytoin, (+)- is an (S)-enantiomer of anticonvulsant drug mephenytoin. Mephenytoin is usually administrated as a 1:1 racemic mixture of the (R)- and (S)-enantiomers. The marked stereoselectivity of 4’-hydroxylation of the phenyl ring of S-mephenytoin together with the relatively slow N-demethylation to R-PEH (R-5-phenyl-5-ethylhydantom) and even slower renal clearance results in a dramatic difference in the pharmacokinetic disposition of the S- and R-enantiomers of mephenytoin in man. As a consequence, S-mephenytoin provides a negligible contribution to circulating hydantoins, whereas R-mephenytoin is converted to the pharmacologically active demethylated product R-PEH which is the major circulating hydantoin during chronic administration of the racemic drug. Only the 4’-hydroxylation of the (S)-mephenytoin is absent in patents who are poor metabolizers of mephenytoin. It is not clear as to the clinical consequences of the accumulation of (S)-mephenytoin for the poor metabolizer phenotype. Indeed, it may be the extensive metabolizer who is at great risk of adverse effects by the formation of potentially toxic oxidative metabolites of (S)-mephenytoin.

Thiazolyl Blue is a membrane-permeable yellow dye that is reduced by mitochondrial reductases in living cells to form the dark blue product. The net positive charge on Thiazolyl Blue appears to be the predominant factor involved in their cellular uptake via the plasma membrane potential. Thiazolyl Blue is used as a direct indicator of cytotoxicity (such as for screening cancer drugs), proliferation and apoptosis. Thiazolyl Blue is also an electron acceptor used for studying NADP-dependent dehydrogenases. Thiazolyl Blue reduction is associated not only with mitochondria, but also with the cytoplasm and with nonmitochondrial membranes including the endosome/lysosome compartment and the plasma membrane. Biological Applications: cell viability assay; microbial growth assays; DNA quantification assays; tissue viability assays; detecting enzymes; measuring membrane potential; treating Alzheimer’s disease, asthma, cancer. Because Thiazolyl Blue forms an insoluble formazan it has usually been applied in endpoint assays.

S-Adenosyl-L-homocysteine (SAH), a potent methyltransferase inhibitor and a substrate of the s-adenosylhomocysteine hydrolase, is an amino acid derivative and an intermediator or modulator of several metabolic pathways, including the activated methyl cycle and cysteine biosynthesis. It was shown, that the plasma SAH might be a novel biomarker for the early clinical identification of cardiovascular disease. In addition, the elevated SAH in Alzheimer's brain was related to markers of disease progression and cognitive impairment.

Veratramine, a steroidal alkaloid originating from Veratrum nigrum L. CYP2D6 and SULT2A1 mediating hydroxylation and sulfation were identified as the major biotransformation for veratramine. Veratramine significantly inhibits the hedgehog pathway in NIH/3T3 cells. Veratramine is both a release and uptake inhibitor of serotonin. Veratramine exhibits cytotoxic activity against human tumor cell lines A549, PANC-1, SW1990 and NCI-H249. Veratramine has demonstrated distinct anti-hypertension effects in spontaneously hypertensive rats.