Reportedly privileged substructures and related compounds. (A) Reportedly privileged substructures. 1,4-benzodiazepin-2-one (1), indole (2), purine (3), spiropiperidine (4) and biphenyl (5) are reported as privileged. The wavy line on spiropiperidine (4) indicates that ring can have variable composition and size. (B) Examples of endogenous molecules containing reportedly privileged substructures. ATP (6) contains purine, the amino acid tryptophan (7) contains indole, and nordiazepam (8), which occurs naturally in mammalian brains, contains 1,4-benzodiazepin-2-one. (C) Examples of drugs with reportedly privileged substructures. Devazepide (9) is a cholecystokinin A antagonist that contains indole and 1,4-benzodiazepin-2-one. Acyclovir (10), used to treat herpes, contains purine. Spiperone (11), a dopamine D2 antagonist, contains spiropiperidine. Diflunisal (12), an anti-inflammatory analgesic, contains biphenyl.