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Caffeic acid (CAS: 331-39-5) is a polyphenol present in normal human urine positively correlated to coffee consumption and influenced by the dietary intake of diverse types of food (PMID:16870009). Caffeic acid has been found to be a microbial metabolite of Escherichia (PMID: 28396925).

3-(3-Hydroxyphenyl)propanoic (hMPP) acid is one of the major metabolites of ingested caffeic acid (PMID: 15479001) and of the phenolic degradation products of proanthocyanidins (the most abundant polyphenol present in chocolate) by the microflora in the colon (PMID: 12663291). mHPP is suspected to have antioxidants properties and is actively absorbed by the monocarboxylic acid transporter (MCT) in intestinal Caco-2 cell monolayers (PMID: 15479001, 12663291). hMPP has been found to be a metabolite of Clostridium, Escherichia, and Eubacterium (PMID: 28393285, 19520845). 3-(3-Hydroxyphenyl)propanoic acid is a flavonoid metabolite. 3-(3-Hydroxyphenyl)propanoic acid is a phenolic acid metabolite formed by the gut microflora detected after the consumption of whole grain.

3-(2-Hydroxyphenyl)propanoic acid is found in bilberry. 3-(2-Hydroxyphenyl)propanoic acid is found in Melilotus alba (whilte melilot).

A nitroimidazole used to treat amebiasis; vaginitis; trichomonas infections; giardiasis; anaerobic bacteria; and treponemal infections. It has also been proposed as a radiation sensitizer for hypoxic cells. According to the Fourth Annual Report on Carcinogens (NTP 85-002, 1985, p133), this substance may reasonably be anticipated to be a carcinogen (Merck, 11th ed).

N-Acetyl-L-phenylalanine or N-Acetylphenylalanine, belongs to the class of organic compounds known as N-acyl-alpha amino acids. N-acyl-alpha amino acids are compounds containing an alpha amino acid which bears an acyl group at its terminal nitrogen atom. N-Acetyl-L-phenylalanine can also be classified as an alpha amino acid or a derivatized alpha amino acid. Technically, N-Acetyl-L-phenylalanine is a biologically available N-terminal capped form of the proteinogenic alpha amino acid L-phenylalanine. N-acetyl amino acids can be produced either via direct synthesis of specific N-acetyltransferases or via the proteolytic degradation of N-acetylated proteins by specific hydrolases. N-terminal acetylation of proteins is a widespread and highly conserved process in eukaryotes that is involved in protection and stability of proteins (PMID: 16465618). About 85% of all human proteins and 68% of all yeast proteins are acetylated at their N-terminus (PMID: 21750686). Several proteins from prokaryotes and archaea are also modified by N-terminal acetylation. The majority of eukaryotic N-terminal-acetylation reactions occur through N-acetyltransferase enzymes or NAT’s (PMID: 30054468). These enzymes consist of three main oligomeric complexes NatA, NatB, and NatC, which are composed of at least a unique catalytic subunit and one unique ribosomal anchor. The substrate specificities of different NAT enzymes are mainly determined by the identities of the first two N-terminal residues of the target protein. The human NatA complex co-translationally acetylates N-termini that bear a small amino acid (A, S, T, C, and occasionally V and G) (PMID: 30054468). NatA also exists in a monomeric state and can post-translationally acetylate acidic N-termini residues (D-, E-). NatB and NatC acetylate N-terminal methionine with further specificity determined by the identity of the second amino acid. N-acetylated amino acids, such as N-acetylphenylalanine can be released by an N-acylpeptide hydrolase from peptides generated by proteolytic degradation (PMID: 16465618). In addition to the NAT enzymes and protein-based acetylation, N-acetylation of free phenylalanine can also occur. In particular, N-Acetyl-L-phenylalanine can be biosynthesized from L-phenylalanine and acetyl-CoA by the enzyme phenylalanine N-acetyltransferase (EC 2.3.1.53). N-Acetyl-L-phenylalanine is a potential uremic toxin and is considered as a hazardous amphipathic metabolite of phenylalanine (PMID: 4038506). Many N-acetylamino acids, including N-acetylphenylalanine, are classified as uremic toxins (PMID: 26317986; PMID: 20613759). Uremic toxins are a diverse group of endogenously produced molecules that, if not properly cleared or eliminated by the kidneys, can cause kidney damage, cardiovascular disease and neurological deficits (PMID: 18287557). N-Acetyl-L-phenylalanine appears in large amount in urine of patients with phenylketonuria (PKU), which is a human genetic disorder due to the lack of phenylalanine hydroxylase, the enzyme necessary to metabolize phenylalanine to tyrosine (PMID: 3473611). N-Acetyl-L-phenylalanine is a product of enzyme phenylalanine N-acetyltransferase [EC 2.3.1.53] which is found in the phenylalanine metabolism pathway. N-Acetyl-L-phenylalanine is produced for medical, feed, and nutritional applications such as in the preparation of aspartame. Afalanine (N-Acetyl-DL-phenylalanine) is also approved for use as an antidepressant.

Identified in Anthemis nobilis (Roman chamomile

o-Cresol is a minor urinary metabolite of toluene, O-cresol is a cresol that is phenol substituted by a methyl group at position 2. It is a minor urinary metabolite of toluene. It has a role as a human xenobiotic metabolite. It is widely used chemical with neurotoxicological properties (PMID:15687000). o-Cresol is used commercially as a disinfectant. Exposure may occur by inhalation, by cutaneous adsorption or by oral ingestion. o-Cresol denature and precipitate cellular proteins and thus may rapidly cause poisoning. o-Cresol is metabolized by conjugation and oxidation. Ingestion of o-Cresol cause intense burning of mouth and throat, followed by marked abdominal pain and distress. The minimum lethal dose of cresol by mouth is about 2 g (PMID 15040915). o-Cresol is a microbial metabolite that can be found in Pseudomonas. Besides, o-Cresol is one of the chemical compounds found in castoreum. This compound is gathered from the beaver's castor glands and found in the white cedar consumed by the beavers. Together with many other compounds, o-cresol is traditionally extracted from coal tar, the volatile materials obtained in the production of coke from coal. A similar source material is petroleum residues. These residue contains a few percent by weight of phenol and isomeric cresols. In addition to the materials derived from these natural sources, about two thirds of the Western world's supply is produced by methylation of phenol using methanol.

Phenylalanylproline is a dipeptide composed of phenylalanine and proline. It is an incomplete breakdown product of protein digestion or protein catabolism. Some dipeptides are known to have physiological or cell-signaling effects although most are simply short-lived intermediates on their way to specific amino acid degradation pathways following further proteolysis. It is found in urine (PMID: 3782411).

para-Cresol, also 4-methylphenol, is an organic compound with the formula CH3C6H4(OH). P-cresol is a cresol that consists of toluene substituted by a hydroxy group at position 4. It is a metabolite of aromatic amino acid metabolism produced by intestinal microflora in humans and animals. It has a role as a uremic toxin, a human metabolite and an Escherichia coli metabolite. It is a colourless solid that is widely used intermediate in the production of other chemicals. It is a derivative of phenol and is an isomer of o-cresol and m-cresol. It is a partially lipophilic moiety which strongly binds to plasma protein (close to 100%) under normal conditions. p-Cresol is metabolized through conjugation, mainly sulphation and glucuronization, but removal of the unconjugated p-cresol is, at least in part, via the urine. Therefore it is not surprising that this compound, together with several other phenoles, is retained when the kidneys fail. P-Cresol is an end-product of protein breakdown, and an increase of the nutritional protein load in healthy individuals results in enhanced generation and urinary excretion. The serum p-cresol concentration in uremic patients can be decreased by changing to a low-protein diet. p-Cresol is one of the metabolites of the amino acid tyrosine, and to a certain extent also of phenylalanine, which are converted to 4-hydroxyphenylacetic acid by intestinal bacteria, before being decarboxylated to p-cresol (putrefaction). The main contributing bacteria are aerobes (mainly enterobacteria), but to a certain extent also anaerobes play a role (mainly Clostridium perfringens). In uremia, modifications in the intestinal flora result in the specific overgrowth of bacteria that are specific p-cresol producers. The administration of antibiotics reduces urinary excretion of p-cresol, as a result of the liquidation of the producing bacteria. Environmental factors might also contribute. The liver cytochrome P450 metabolizes toluene to benzyl alcohol, but also to o-cresol and p-cresol. Toluene is not only used industrially, but it is also the most widely abusively inhaled solvent. Furthermore, p-cresol is a metabolite of menthofuran, one of the metabolites of R-(+)-pulegone, which is found in extracts from the plants Mentha pulegium and Hedeoma pulegioides, commonly known as pennyroyal oil and pennyroyal tea. These extracts are popular as unconventional herbal therapeutic agents and are applied as abortiva, diaphoretics, emmenagogues, and psychedelic drugs. Pennyroyal oil is extensively used for its pleasant mint-like smell in the flavoring industry. The toxicity of pennyroyal oil and menthofuran is well known. Another compound used in traditional medicine, especially in Japan, which is a precursor of p-cresol is wood tar creosote. p-Cresol has been reported to affect several biochemical, biological and physiological functions: (i) it diminishes the oxygen uptake of rat cerebral cortex slices; (ii) it increases the free active drug concentration of warfarin and diazepam; (iii) it has been related to growth retardation in the weanling pig; (iv) it alters cell membrane permeability, at least in bacteria; (v) it induces LDH leakage from rat liver slices; (vi) it induces susceptibility to auditive epileptic crises; and (vii) it blocks cell K+ channels. (PMID:10570076). p-Cresol is a uremic toxin that is at least partially removed by peritoneal dialysis in haemodialysis patients, and has been involved in the progression of renal failure (PMID:11169029). At concentrations encountered during uremia, p-cresol inhibits phagocyte function and decreases leukocyte adhesion to cytokine-stimulated endothelial cells. (PMID:14681860). p-Cresol can be found in Bacteroides, Bifidobacterium, Clostridium, Enterobacter and Lactobacillus (PMID:2394806; PMID:30208103). As a volatile organic compound, it has been identified as a fecal biomarker of Clostridium difficile infection (PMID:30986230).

Monomethyl phthalate is a metabolite, or breakdown product, of dimethyl phthalate, used in insect repellant, plastic, and as a rocket propellant.

3,5-Dihydroxycinnamic acid (DHA) (CAS: 28374-93-8) is found in fruits. It can be isolated from peach buds. BioTransformer predicts that 3,5-dihydroxycinnamic acid is a product of 3,​4,​5-​trihydroxycinnamic acid metabolism via a -4p-dehydroxylation-of-substituted-benzene reaction occurring in human gut microbiota and catalyzed by a dehydroxylase enzyme (PMID: 30612223). 3,5-Dihydroxycinnamic acid is an alkylresorcinol metabolite. It is a potential urinary biomarker of whole grain intake (PMID: 28444884).

m-Cresol is an isomer of p-cresol and o-cresol. Cresols are organic compounds which are methylphenols. They are a widely occurring natural and manufactured group of aromatic organic compounds which are categorized as phenols (sometimes called phenolics). Depending on the temperature, cresols can be solid or liquid because they have melting points not far from room temperature. Like other types of phenols, they are slowly oxidized by long exposure to air and the impurities often give cresols a yellowish to brownish red tint. Cresols have an odor characteristic to that of other simple phenols, reminiscent to some of a "medicine" smell. Cresol solutions are used as household cleaners and disinfectants, perhaps most famously under the trade name Lysol. In the past, cresol solutions have been used as antiseptics in surgery, but they have been largely displaced in this role by less toxic compounds. Lysol was also advertised as a disinfecting vaginal douche in mid-twentieth century America. Cresols are found in many foods and in wood and tobacco smoke, crude oil, coal tar, and in brown mixtures such as creosote and cresylic acids, which are wood preservatives. Small organisms in soil and water produce cresols when they break down materials in the environment. Most exposures to cresols are at very low levels that are not harmful. When cresols are breathed, ingested, or applied to the skin at very high levels, they can be very harmful. Effects observed in people include irritation and burning of skin, eyes, mouth, and throat; abdominal pain and vomiting; heart damage; anemia; liver and kidney damage; facial paralysis; coma; and death. Breathing high levels of cresols for a short time results in irritation of the nose and throat. Aside from these effects, very little is known about the effects of breathing cresols, for example, at lower levels over longer times. Ingesting high levels results in kidney problems, mouth and throat burns, abdominal pain, vomiting, and effects on the blood and nervous system. Skin contact with high levels of cresols can burn the skin and damage the kidneys, liver, blood, brain, and lungs. m-Cresol is a microbial metabolite that can be found in Lysinibacillus.

Anisole is a flavouring agent Anisole is a precursor to perfumes, insect pheromones, and pharmaceuticals. For example, synthetic anethole is prepared from anisole. Anisole undergoes electrophilic aromatic substitution reaction more quickly than does benzene, which in turn reacts more quickly than nitrobenzene. The methoxy group is an ortho/para directing group, which means that electrophilic substitution preferentially occurs at these three sites. The enhanced nucleophilicity of anisole vs benzene reflects the influence of the methoxy group, which renders the ring more electron-rich. The methoxy group strongly affects the pi cloud of the ring, moreso than the inductive effect of the electronegative oxygen.

Homoveratric acid is the main metabolite of 3,4-dimethoxyphenylethylamine (DMPEA) in urine. It has been suggested that DMPEA and other amines are in higher concentrations in drug-free schizophrenics than in normal subjects. DMPEA is a the di-methylated metabolite of L-DOPA, the major treatment for Parkinson's disease (PD). (PMID 7059639, 14311254, 588645, 10834300).

5,10-dihydrophenazine-1-carboxylic acid is a member of the class of phenazines that is 5,10-dihydrophenazine substituted at position 1 by a carboxy group. It has a role as a bacterial metabolite. It is a member of phenazines and an aromatic carboxylic acid. It is a conjugate acid of a 5,10-dihydrophenazine-1-carboxylate. 5,10-Dihydrophenazine-1-carboxylic acid is a natural product found in Apis cerana with data available.

2-Acetamido-4-methylphenyl acetate belongs to the class of organic compounds known as phenol esters. These are aromatic compounds containing a benzene ring substituted by a hydroxyl group and an ester group.

2-Methyl-1-phenyl-2-propanyl acetate is a flavouring agent

A member of the class of phenazines that is (10aS)-10,10a-dihydrophenazine substituted at position 1 by a carboxy group" []

derivative Caesalpinia sappan

A member of the class of phenazines that is 5,10-dihydrophenazine substituted at position 1 by a carboxy group." []

4-Phenyl-2-butyl acetate is used as a food additive [EAFUS] ("EAFUS: Everything Added to Food in the United States. [http://www.eafus.com/]")

Genipin is found in beverages. Genipin is a constituent of Genipa americana (genipap) Genipin is an aglycone derived from an iridoid glycoside called geniposide present in fruit of Gardenia jasminoides. Genipin is an excellent natural cross-linker for proteins, collagen, gelatin, and chitosan cross-linking. It has a low acute toxicity, with LD50 i.v. 382 mg/kg in mice, therefore, much less toxic than glutaraldehyde and many other commonly used synthetic cross-linking regents. It is also used for pharmaceutical purposes, such as choleretic action for liver diseases control

4-Hydroxy-4-(3-pyridyl)-butanoic acid is a nitrosonornicotine metabolite derived from tobacco smoke. (PMID: 796709). This nicotine-related compound was separated by HPLC as a cotinine metabolite in human urine and an urinary metabolites of (methylnitrosamino)(pyridyl)butanone in rats. (MID: 10362230).

Xanthoxylin is found in fats and oils. Xanthoxylin is obtained from Zanthoxylum piperitum (Japanese pepper tree) and Sapium sebiferum (Chinese tallowtree

A member of the class of benzimidazoles that is benzimidazole in which the hydrogen at position 2 is replaced by an amino group." []