Anxiolytic, Sedative, and Hypnotic Agents: Medicinal Chemistry and Pharmacology

Comprehensive vocabulary flashcards covering GABA-A receptor modulators, benzodiazepine SAR, Z-drugs, H1 antagonists, and melatonin receptor agonists based on PHAR 441 lecture notes.

Gamma-Aminobutyric Acid ($\text{GABA}$)

The primary inhibitory neurotransmitter in the central nervous system that mediates rapid neuronal inhibition via activation of ionotropic $\text{GABA}_A$ receptors.

$\text{GABA}_A$ Receptor

A ligand-gated chloride channel that increases $\text{Cl}^-$ influx upon activation, causing neuronal membrane hyperpolarization and inhibition.

Benzodiazepines ($\text{BZDs}$)

Positive allosteric modulators of the $\text{GABA}_A$ receptor that bind at the interface between $\alpha$ and $\gamma$ subunits to increase the receptor's affinity for $\text{GABA}$.

$\text{BZD}$ Structure-Activity Relationship (Position 7)

Requires an electron-withdrawing group ($\text{EWG}$) such as $\text{Cl}$, $\text{F}$, or $\text{CF}_3$; higher electronegativity at position 7 directly increases pharmacological activity.

$\text{BZD}$ Structure-Activity Relationship (Position 3)

Substitution with a $3\text{-OH}$ group yields polar compounds that rapidly undergo glucuronidation and excretion ($\downarrow \text{DOA}$), whereas non-hydroxylated analogs undergo hepatic oxidation to active metabolites ($\uparrow \text{DOA}$).

Diazepam

A long-acting, highly lipophilic ($\text{Log P} = 3.86$) benzodiazepine ($t_{1/2} \approx 46\,\text{h}$) used for anxiety, seizures, and spastic disorders, which undergoes $N\text{-demethylation}$ to active Nordazepam.

Nordazepam

A long-acting active metabolite ($t_{1/2} = 40\text{-}50\,\text{h}$) formed from diazepam and clorazepate that can accumulate in the blood for over a week post-discontinuation.

Clorazepate Dipotassium

A polar, inactive prodrug containing a $3\text{-carboxylic acid}$ potassium salt that rapidly decarboxylates in gastric acid to produce active, nonpolar Nordazepam.

Flurazepam

A benzodiazepine marketed for insomnia whose active metabolite, $N_1\text{-dealkylflurazepam}$, has an elimination half-life of $50\,\text{h}$, leading to cumulative clinical effects.

Temazepam

An intermediate-acting benzodiazepine hypnotic ($t_{1/2} = 8\text{-}15\,\text{h}$) containing a $3\text{-OH}$ group that undergoes direct glucuronidation conjugation as its major metabolic route.

Alprazolam

A potent short-to-intermediate-acting triazolobenzodiazepine ($t_{1/2} \approx 12\,\text{h}$) containing a 1,2-fused triazole ring, which is metabolically hydroxylated at its benzylic methyl group to active $\alpha\text{-hydroxyalprazolam}$.

Lorazepam

A short-acting benzodiazepine anxiolytic ($t_{1/2} = 2\text{-}6\,\text{h}$) containing a $3\text{-OH}$ group and an $ortho\text{-chloro}$ phenyl substitution, indicated for acute seizures and status epilepticus.

Triazolam

An ultra-short-acting triazolobenzodiazepine sleep-inducing agent ($t_{1/2} \approx 4\,\text{h}$) rapidly metabolized by $\text{CYP3A4}$, minimizing residual daytime sedation.

Zolpidem

A short-acting non-benzodiazepine $\text{GABA}_A$ receptor agonist ($t_{1/2} = 2.5\,\text{h}$, $\text{Log P} = 2.61$) belonging to the Z-drug class, indicated for insomnia.

Zaleplon

A short-acting non-benzodiazepine hypnotic with a mean half-life of $1\,\text{h}$ and 30% absolute bioavailability, effective specifically for sleep initiation.

Eszopiclone

A moderate-acting non-benzodiazepine hypnotic ($t_{1/2} = 5\text{-}6\,\text{h}$) useful for sleep maintenance in patients who wake up during the night.

Flumazenil

An imidazobenzodiazepinone derivative that acts as a competitive antagonist at the benzodiazepine receptor site to reverse overdoses from benzodiazepines and Z-drugs.

Propofol

A highly lipophilic phenolic general anesthetic that acts as a positive modulator at a $\text{GABA}_A$ receptor site distinct from the benzodiazepine binding site.

Disodium Ethylenediaminetetraacetic Acid (EDTA)

A metal chelator added to propofol oil-in-water formulations to retard microbial growth, which can increase urinary excretion of zinc and iron during extended therapy.

Histamine

An endogenous amine synthesized from L-histidine via L-histidine decarboxylase that plays a key role in promoting wakefulness in the central nervous system.

Diphenhydramine

A first-generation $\text{H}_1$ receptor antagonist ($\text{Log P} = 3.66$) with central sedative properties, used widely in over-the-counter sleep aids.

Melatonin

An endogenous neurohormone biosynthesized from serotonin and released at night that activates central $\text{MT}_1$ receptors to promote sleep.

Ramelteon

A selective $\text{MT}_1$ receptor agonist featuring an indene ring structure, approved for insomnia with no addiction liability or controlled substance designation.