Cytidine is a substrate of the uridine-cytidine kinase and is a part nucleic acids. It can serve as a substrate for the salvage pathway of pyrimidine nucleotide synthesis, as a precursor of the cytidine triphosphate (CTP) needed in the phosphatidylcholine (PC) and phosphatidylethanolamine (PE) biosynthetic pathway. Cytidine was also used under the brand name posilent in Germany for the treatment of muscular, accommodative, and nervous eye disorders.

Phenylacetate is the ester of a phenol and acetic acid. It is a metabolite of anticancer drug phenylbutyrate (PB), natural neurotransmitter phenylethylamine. Naturally, it is an odorant found in strawberries, passion fruit, and black tea. Phenylacetate level in urine was used as a marker for the diagnosis of some forms of unipolar major depressive disorders. Phenylacetate is used as a tool substrate to study esterase activity in the blood of patients in clinical studies of the effect of nutritional supplements on paraoxonase-1 levels.

Oxypurinol is an active metabolite of allopurinol and is an inhibitor of xanthine oxidase. Cardiome Pharma developed oxipurinol for the treatment of allopurinol-intolerant hyperuricemia (gout) and for the treatment of congestive heart failure. It is known, that inhibition of xanthine oxidase can improve myocardial work efficiency by sensitizing cardiac muscle cells to calcium ions, which are a key determinant of cardiac muscle function. However, all these studied were discontinued.

11-Deoxycortisol (also known as cortodoxone) is the predominant deoxycorticosteroid and is the immediate precursor of cortisol, which is formed by the enzymatic action of 11beta-hydrozylase (P450). Deficiency of this enzyme causes congenital adrenal hyperplasia, which is characterized by hypertension. 11-deoxycortisol is measured as part of the Metyrapone Test. Metyrapone blocks the formation of cortisol, resulting in increased secretion of Adrenocorticotropic hormone (ACTH) and 11-deoxycortisol in normal individuals.

Mevalonolactone (ML) is a lactone form of mevalonic acid (MA), they exist in equilibrium. Mevalonolactone is used to study the effect of statin on the prenylation of Ras and Rho GTPases. Recently was discovered, that mevalonolactone disrupted mitochondrial functions and induced permeability transition pore opening in rat brain mitochondria, what can be important for the pathogenesis of mevalonic aciduria. Mevalonic aciduria is caused by severe deficiency of mevalonic kinase activity leading to tissue accumulation and high urinary excretion of mevalonic acid and mevalonolactone. It was proved that ML impaired essential brain mitochondrial functions with the involvement of MPT pore opening and that disturbance of brain mitochondrial homeostasis contributed to the neurologic symptoms of MVA.

Threitol is a four carbon sugar primarily used in the chemical synthesis of other compounds. It is a diastereomer of erythritol an FDA approved low-calorie sweetener. Threitol can be found in meaningful concentrations in the edible fungus Armillaria mellea and is used by some organisms as an antifreeze agent, such as the Alaskan beetle. Threitol is a very weak inhibitor of Carbonic anhydrase. Threitol is the main end product of D-xylose metabolism in humans and deficiency is associated with inborn errors of metabolism.

3-Methoxytyramine (3-MT) is a human trace amine that occurs as a metabolite of the neurotransmitter dopamine. It has been shown to act as an agonist of human TAAR1, and an inhibitor of mitochondrial respiration. 3-MT has garnered research interest for its potential links and implications to Parkinson's disease and other Neurological disorders.