Azapirones are a class of drugs used as anxiolytics, antidepressants, and antipsychotics. They are commonly used as add-ons to other antidepressants, such as selective serotonin reuptake inhibitors (SSRIs).
Bretazenil (Ro16-6028) is an imidazopyrrolobenzodiazepine anxiolytic drug which is derived from the benzodiazepine family, and was invented in 1988. It is most closely related in structure to the GABA antagonist flumazenil, although its effects are somewhat different. It is classified as a high-potency benzodiazepine due to its high affinity binding to benzodiazepine binding sites where it acts as a partial agonist. Its profile as a partial agonist and preclinical trial data suggests that it may have a reduced adverse effect profile. In particular bretazenil has been proposed to cause a less strong development of tolerance and withdrawal syndrome. Bretazenil differs from traditional 1,4-benzodiazepines by being a partial agonist and because it binds to α1, α2, α3, α4, α5 and α6 subunit containing GABAA receptor benzodiazepine receptor complexes. 1,4-benzodiazepines bind only to α1, α2, α3 and α5GABAA benzodiazepine receptor complexes.
Pagoclone is an anxiolytic agent from the cyclopyrrolone family, related to better-known drugs such as the sleeping medication zopiclone. It was synthesized by a French team working for Rhone-Poulenc & Rorer S.A. Pagoclone belongs to the class of nonbenzodiazepines, which have similar effects to the older benzodiazepine group, but with quite different chemical structures. It was never commercialised.
DMCM is a drug from the β-carboline family that induces anxiety and convulsions by acting as a negative allosteric modulator of GABAA receptors — functionally opposite to benzodiazepines and related drugs which are positive allosteric modulators — and is used in scientific research for these properties to test new anxiolytic and anticonvulsant medications, respectively. It has also been shown to produce analgesic effects in animals, which is thought to be the drug's induced panic reducing the perception of pain.
Fenobam is an imidazole derivative developed by McNeil Laboratories in the late 1970s as a novel anxiolytic drug with an at-the-time-unidentified molecular target in the brain. Subsequently, it was determined that fenobam acts as a potent and selective negative allosteric modulator of the metabotropic glutamate receptor subtype mGluR5, and it has been used as a lead compound for the development of a range of newer mGluR5 antagonists.
Panadiplon (U-78875) is an anxiolytic drug with a novel chemical structure that is not closely related to other drugs of this type. It has a similar pharmacological profile to the benzodiazepine family of drugs, but with mainly anxiolytic properties and relatively little sedative or amnestic effect, and so is classified as a nonbenzodiazepine anxiolytic.
Pazinaclone (DN-2327) is a sedative and anxiolytic drug in the cyclopyrrolone family of drugs. Some other cyclopyrrolone drugs include zopiclone and eszopiclone.
Imidazenil is an experimental anxiolytic drug which is derived from the benzodiazepine family, and is most closely related to other imidazobenzodiazepines such as midazolam, flumazenil, and bretazenil.
Abecarnil (ZK-112,119) is an anxiolytic drug from the β-Carboline family. It is one of a relatively recently developed class of medicines known as the nonbenzodiazepines, which have similar effects to the older benzodiazepine group, but with quite different chemical structures. It is a partial agonist acting selectively at the benzodiazepine site of the GABAA receptor.
L-838,417 is an anxiolytic drug used in scientific research. It has similar effects to benzodiazepine drugs, but is structurally distinct and so is classed as a nonbenzodiazepine anxiolytic. The compound was developed by Merck, Sharp and Dohme.
CL-218,872 is a sedative and hypnotic drug used in scientific research. It has similar effects to sedative-hypnotic benzodiazepine drugs such as triazolam, but is structurally distinct and so is classed as a nonbenzodiazepine hypnotic.
Y-23684 is an anxiolytic drug with a novel chemical structure, which is used in scientific research. It has similar effects to benzodiazepine drugs, but is structurally distinct and so is classed as a nonbenzodiazepine anxiolytic.
Premazepam is a Pyrrolodiazepine class of drug. It is a partial agonist of benzodiazepine receptors and was shown in 1984 to possess both anxiolytic and sedative properties in humans but was never marketed.
ELB-139 (LS-191,811) is an anxiolytic drug with a novel chemical structure, which is used in scientific research. It has similar effects to benzodiazepine drugs, but is structurally distinct and so is classed as a nonbenzodiazepine anxiolytic.
TPA-023 (MK-0777) is an anxiolytic drug with a novel chemical structure, which is used in scientific research. It has similar effects to benzodiazepine drugs, but is structurally distinct and so is classed as a nonbenzodiazepine anxiolytic. It is a mixed, subtype-selective ligand of the benzodiazepine site of α1, α2, α3, and α5-containing GABAA receptors, where it acts as a partial agonist at benzodiazepine sites of the α2 and α3-containing subtypes, but as a silent antagonist at α1 and α5-containing subtypes. It has primarily anxiolytic and anticonvulsant effects in animal tests, but with no sedative effects even at 50 times the effective anxiolytic dose.
TP-003 is an anxiolytic drug with a novel chemical structure, which is used in scientific research. It has similar effects to benzodiazepine drugs, but is structurally distinct and so is classed as a nonbenzodiazepine anxiolytic.
Viqualine (INN) is an antidepressant and anxiolytic drug that was never marketed. It acts as a potent and selective serotonin releasing agent (SRA) and serotonin reuptake inhibitor (SRI) similarly to para-chloroamphetamine (PCA). In addition, viqualine displaces diazepam from the GABAA receptor and produces benzodiazepine-like effects, indicating that it is also a positive allosteric modulator of the benzodiazepine site of the GABAA receptor. The drug has mainly been researched as a potential treatment for alcoholism.
Ricasetron (BRL-46470) is a drug which acts as a selective antagonist at the serotonin 5-HT3 receptor. It has antiemetic effects as with other 5-HT3 antagonists, and also has anxiolytic effects significantly stronger than other related drugs, and with less side effects than benzodiazepine anxiolytics. However, it has never been developed for medical use.
Umespirone (KC-9172) is a drug of the azapirone class which possesses anxiolytic and antipsychotic properties. It behaves as a 5-HT1A receptor partial agonist (Ki = 15 nM), D2 receptor partial agonist (Ki = 23 nM), and α1-adrenoceptor receptor antagonist (Ki = 14 nM), and also has weak affinity for the sigma receptor (Ki = 558 nM). Unlike many other anxiolytics and antipsychotics, umespirone produces minimal sedation, cognitive/memory impairment, catalepsy, and extrapyramidal symptoms.
Adatanserin is a mixed 5-HT1A receptor partial agonist and 5-HT2A and 5-HT2C receptor antagonist. It was under development by Wyeth as an antidepressant but was ultimately not pursued.
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