Chemical Structure:
C8H12N2O3
Mechanism of Action:
Barbital is a barbiturate that works by enhancing the action of GABA, a neurotransmitter that inhibits brain activity.
This results in sedative and hypnotic effects.
Structure-Activity Relationship (SAR) of Barbital:
1.Barbituric Acid Core:
Barbital, like all barbiturates, is derived from barbituric acid, which consists of a urea and malonic acid derivative forming a pyrimidine-dione ring system.
This core is crucial for the biological activity of barbiturates.
2.Substitutions at C5:
The presence of alkyl or aryl groups at the C5 position of the barbituric acid ring enhances the lipid solubility and, consequently, the potency and duration of action.
Barbital has ethyl groups at this position.
3.Hydrogen Bonding:
The ability of barbiturates to engage in hydrogen bonding through the NH groups in the barbituric acid ring influences their interaction with the GABA-A receptor and their potency.
4.Lipophilicity:
The overall lipophilicity of the molecule affects its onset and duration of action.
For Barbital, the ethyl groups provide moderate lipophilicity, contributing to its sedative effect.
Synthesis of Barbital (Chemical Reaction):
The synthesis of Barbital is a classic example of barbiturate synthesis, involving the condensation of urea with diethyl malonate:
1.Condensation Reaction:
Diethyl malonate + Urea → (acidic conditions) Barbital
In this reaction, diethyl malonate and urea are combined under acidic conditions.
The malonate provides the carbon skeleton for the barbituric acid core, while urea provides the nitrogen atoms.
The reaction typically involves heating the reactants with an acid catalyst to facilitate the condensation and cyclization into the barbiturate ring system.
Uses:
It was formerly used as a sedative and hypnotic.
However, it's seldom used today due to the risk of abuse and the availability of safer alternatives.
Side Effects:
Potential side effects include drowsiness, dizziness, nausea, and in severe cases, respiratory depression, dependence, and withdrawal symptoms.