| Pyroglutamic acid | Organic compounds | Organic acids and derivatives | Carboxylic acids and derivatives | Amino acids, peptides, and analogues | Details |
| Tetrahydrocorticosterone | Organic compounds | Lipids and lipid-like molecules | Steroids and steroid derivatives | Hydroxysteroids | Details |
| Sphinganine | Organic compounds | Organic nitrogen compounds | Organonitrogen compounds | Amines | Details |
| Sarcosine | Organic compounds | Organic acids and derivatives | Carboxylic acids and derivatives | Amino acids, peptides, and analogues | Details |
| Phosphoserine | Organic compounds | Organic acids and derivatives | Carboxylic acids and derivatives | Amino acids, peptides, and analogues | Details |
| Thymidine | Organic compounds | Nucleosides, nucleotides, and analogues | Pyrimidine nucleosides | Pyrimidine 2'-deoxyribonucleosides | Details |
| Sphingosine 1-phosphate | Organic compounds | Lipids and lipid-like molecules | Sphingolipids | Phosphosphingolipids | Details |
| Saccharopine | Organic compounds | Organic acids and derivatives | Carboxylic acids and derivatives | Amino acids, peptides, and analogues | Details |
| Phosphoribosyl pyrophosphate | Organic compounds | Organic oxygen compounds | Organooxygen compounds | Carbohydrates and carbohydrate conjugates | Details |
| D-Ribose | Organic compounds | Organic oxygen compounds | Organooxygen compounds | Carbohydrates and carbohydrate conjugates | Details |
| Uridine triphosphate | Organic compounds | Nucleosides, nucleotides, and analogues | Pyrimidine nucleotides | Pyrimidine ribonucleotides | Details |
| Uridine diphosphate glucose | Organic compounds | Nucleosides, nucleotides, and analogues | Pyrimidine nucleotides | Pyrimidine nucleotide sugars | Details |
| Uridine 5'-monophosphate | Organic compounds | Nucleosides, nucleotides, and analogues | Pyrimidine nucleotides | Pyrimidine ribonucleotides | Details |
| Uric acid | Organic compounds | Organoheterocyclic compounds | Imidazopyrimidines | Purines and purine derivatives | Details |
| Uridine diphosphate-N-acetylglucosamine | Organic compounds | Nucleosides, nucleotides, and analogues | Pyrimidine nucleotides | Pyrimidine nucleotide sugars | Details |
| Vanillylmandelic acid | Organic compounds | Benzenoids | Phenols | Methoxyphenols | Details |
| Xanthine | Organic compounds | Organoheterocyclic compounds | Imidazopyrimidines | Purines and purine derivatives | Details |
| Xanthosine 5-triphosphate | Organic compounds | Nucleosides, nucleotides, and analogues | Purine nucleotides | Purine ribonucleotides | Details |
| Urea | Organic compounds | Organic acids and derivatives | Organic carbonic acids and derivatives | Ureas | Details |
| Uridine 5'-diphosphate | Organic compounds | Nucleosides, nucleotides, and analogues | Pyrimidine nucleotides | Pyrimidine ribonucleotides | Details |
| Uridine | Organic compounds | Nucleosides, nucleotides, and analogues | Pyrimidine nucleosides | Not Available | Details |
| Xanthosine | Organic compounds | Nucleosides, nucleotides, and analogues | Purine nucleosides | Not Available | Details |
| Uracil | Organic compounds | Organoheterocyclic compounds | Diazines | Pyrimidines and pyrimidine derivatives | Details |
| Urocanic acid | Organic compounds | Organoheterocyclic compounds | Azoles | Imidazoles | Details |
| Uridine diphosphategalactose | Organic compounds | Nucleosides, nucleotides, and analogues | Pyrimidine nucleotides | Pyrimidine nucleotide sugars | Details |
| Tryptamine | Organic compounds | Organoheterocyclic compounds | Indoles and derivatives | Tryptamines and derivatives | Details |
| Uridine diphosphate-N-acetylgalactosamine | Organic compounds | Nucleosides, nucleotides, and analogues | Pyrimidine nucleotides | Pyrimidine nucleotide sugars | Details |
| Vitamin A | Organic compounds | Lipids and lipid-like molecules | Prenol lipids | Retinoids | Details |
| Tyramine | Organic compounds | Benzenoids | Benzene and substituted derivatives | Phenethylamines | Details |
| 1b-Hydroxycholic acid | Organic compounds | Lipids and lipid-like molecules | Steroids and steroid derivatives | Bile acids, alcohols and derivatives | Details |
