Guanosine 3′,5′-cyclic monophosphate (cGMP) is a cyclic nucleotide derived from guanosine triphosphate (GTP). Cyclic GMP is a cellular regulatory agent that acts as a second messenger. Its levels increase in response to a variety of signals (acetylcholine, insulin, oxytocin). cGMP is involved in the regulation of kinases G. cGMP binds to sites on the regulatory units of protein kinase G (PKG) and activates the catalytic units, enabling them to phosphorylate their substrates. cGMP is a common regulator of ion channel conductance, glycogenolysis, and cellular apoptosis. It also relaxes smooth muscle tissues. In blood vessels, relaxation of vascular smooth muscles lead to vasodilation and increased blood flow. cGMP is a secondary messenger in phototransduction in the eye. In the photoreceptors of the mammalian eye, the presence of light activates cGMP phosphodiesterase 5 (PDE5), which degrades cGMP. The sodium ion channels in photoreceptors are cGMP-gated, so degradation of cGMP causes sodium channels to close, which leads to the hyperpolarization of the photoreceptor's plasma membrane and ultimately to visual information being sent to the brain. Mutations in the cGMP phosphodiesterase cause defects in cGMP metabolism leading to retinal disease. Inhibition of cGMP degrading PDE5 by its selective inhibitor sildenafil induced migraine without aura in 10 of 12 migraine patients and in healthy subjects.

Naftopidil,(R)- is an enantiomer of Naftopidil (NAF), a specific subtype selective α1-adrenoceptor blocker. Racemic Naftopidil is frequently used for the treatment of lower urinary tract symptoms/benign prostatic hyperplasia. No significant differences in pharmacokinetic parameters were observed between R(+)- and S(−)-NAF after intravenous administration. However, mean plasma concentrations of S(−)-NAF were higher than those of R(+)-NAF after intragastric administration. S(−)-NAF reached higher plasma concentrations within shorter times and achieved lower plasma CL within 24 h than R(+)-NAF. S(−)-NAF bioavailability in rats was consistently about two-fold higher than that of R(+)-NAF. The major pathways of S(−)-NAF metabolism in vitro were demethylation and hydroxylation. CYP2C9 played the most important role in the demethylation and hydroxylation of both NAF enantiomers.

The methyl ester of ibuprofen is the most common starting material for the enzymatic resolution process based on selective hydrolyses of racemic mictures of ibuprofen esters. Addition of the methyl ester of racemic ibuprofen to growing cultures of Pseudomonas, Mucor, Arthrobacter or Bacillus species produced (S)-(+)-ibuprofen in 74-98% ee. Lipase from Candida rugosa hydrolyses racemic ibuprofen methyl ester to give 95% ee (S)-(+)-ibuprofen.

Pitavastatin lactone is the major metabolite of pitavastatin in humans. Pitavastatin is a potent competitive inhibitor of HMG-CoA reductase, which is indicated for hypercholesterolaemia (elevated cholesterol) and for the prevention of cardiovascular disease. Uridine 5’ -diphosphate (UDP) glucuronosyl transferase (UGT) is critically involved in the lactonization of pitavastatin in man and animals. The metabolic and transporter profiles of pitavastatin in man are complex, involving acid/lactone interconversion. Both forms of pitavastatin are observed in-vivo following oral administration. Lactone form and pitavastatin differ in substrate activity towards uptake and efflux transporters.

(R)-Naproxen is an enantiomer of the more active (S)-Naproxen, the last belongs to the class of Non-Steroidal Anti-Inflammatory Drugs. (S)- and (R)-naproxen represent useful substrates to distinguish different glucuronosyl transferases isozymes.

Naproxen methyl ester, a mixture of two isomers R and S, is the precursor of therapeutically important nonsteroidal anti-inflammatory drug naproxen. Naproxen methyl ester can be enantioselectively hydrolyzed by lipases or (S)-enantioselective esterase could catalyze the selective hydrolysis of the (S)-Naproxen methyl ester, giving optically pure (S)-naproxen. In addition, S-naproxen methyl ester is used as a tool for identification and determination of new stereo selective carboxylesterase activities.

L-Gulonic acid, a diastereomer of d-gluconic acid is the one of a metabolite in the urinate cycle, is a substrate of L-Gulonate 3-dehydrogenase (GDH). This enzyme catalyzes the NAD(+)-linked dehydrogenation of L-gulonate into dehydro-L-gulonate. L-Gulonic acid is also a metabolite of the D-glucuronic acid pathway. It was suggested, that the measurement of a spectrum of urinary D-glucuronic acid metabolites might provide a more reliable index for assessment of the induction of hepatic xenobiotic-metabolizing enzyme activities in man than the determination of urinary D-glucaric acid alone.