File:Benzodiazepine3.alt=On the left is the chemical structure of the parent<unk>  ring system, which consists of a seven-membered ring containing two nitrogen atoms fused to a six-membered ring. The two nitrogen atoms are labeled one and four. On the right is the chemical structure of a pharmacologically active<unk>  in which alkyl, phenyl, and halogen groups attach to the one, five, and seven positions, respectively, and the carbon atom at position two is double-bonded to an exocyclic oxygen atom. The ortho and para positions of the phenyl substituent are labeled two-prime and 4-prime, respectively.|Left: The 1,4-benzodiazepine ring system. Right: 5-phenyl-1H-benzoe 1,4diazepin-2(3H)-one forms the skeleton of many of the most common<unk>  pharmaceuticals, such as diazepam (7-chloro-1-methyl substituted). A pharmacophore model of the<unk>  binding site on the GABAA receptor. White sticks represent the carbon atoms of the<unk>  diazepam, while green represents carbon atoms of the nonbenzodiazepine CGS-9896. Red and blue sticks are oxygen and nitrogen atoms that are present in both structures. The red spheres labeled H1 and H2/A3 are, respectively, hydrogen bond donating and accepting sites in the receptor, while L1, L2, and L3 denote lipophilic binding sites.<unk> s share a similar chemical structure, and their effects in humans are mainly produced by the allosteric modification of a specific kind of neurotransmitter receptor, the GABAA receptor, which increases the overall conductance of these inhibitory channels; this results in the various therapeutic effects as well as adverse effects of<unk> s. Other less important modes of action are also known. The term<unk>  is the chemical name for the heterocyclic ring system (see figure to the right), which is a fusion between the benzene and diazepine ring systems. Under Hantzsch–Widman nomenclature, a diazepine is a heterocycle with two nitrogen atoms, five carbon atom and the maximum possible number of cumulative double bonds. The "benzo" prefix indicates the benzene ring fused onto the diazepine ring.<unk>  drugs are substituted 1,4-benzodiazepines, although the chemical term can refer to many other compounds that do not have useful pharmacological properties. Different<unk>  drugs have different side groups attached to this central structure. The different side groups affect the binding of the molecule to the GABAA receptor and so modulate the pharmacological properties. Many of the pharmacologically active "classical"<unk>  drugs contain the 5-phenyl-1H-benzoe 1,4diazepin-2(3H)-one substructure (see figure to the right).<unk> s have been found to mimic protein reverse turns structurally, which enable them with their biological activity in many cases. Nonbenzodiazepines also bind to the<unk>  binding site on the GABAA receptor and possess similar pharmacological properties. While the nonbenzodiazepines are by definition structurally unrelated to the<unk> s, both classes of drugs possess a common pharmacophore (see figure to the lower-right), which explains their binding to a common receptor site. Types * 2-keto compounds: ::clorazepate, diazepam, flurazepam, halazepam, prazepam, and others * 3-hydroxy compounds: ::lorazepam, lormetazepam, oxazepam, temazepam * 7-nitro compounds: ::clonazepam, flunitrazepam, nimetazepam, nitrazepam * Triazolo compounds: ::adinazolam, alprazolam, estazolam, triazolam * Imidazo compounds: ::climazolam, loprazolam, midazolam * 1,5-benzodiazepines: ::clobazam
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