Cimetidine SAR, Physicochemical Properties, IUPAC Nomenclature, Mechanism of action and Uses

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IUPAC nomenclature
1-cyano-2-methyl-3-[2-[(5-methyl-1H-imidazol-4-yl)methylsulfanyl]ethyl]guanidine

Physicochemical Properties
Chemical Structure:

Molecular structure of Cimetidine
Chemical formula: C₁₀H₁₆N₆S
Molar mass: 252.34 g/mol.
Physical State: Cimetidine is typically found as a white to pale yellow, crystalline powder or colorless crystals.
Melting Point: The melting point of cimetidine is reported to be around 140-144 °C (284-291 °F).
Solubility: Cimetidine is sparingly soluble in water, but it is soluble in alcohol and slightly soluble in chloroform.
pKa: Cimetidine has a pKa value of approximately 6.8, indicating its behavior as a weak base. This property is relevant to its activity as a histamine H2 receptor antagonist, as it interacts with acidic conditions in the stomach.
LogP (Partition Coefficient): The logarithm of the octanol/water partition coefficient (LogP) of cimetidine is approximately 0.70, indicating it has a higher affinity for water than for lipids. This property can influence its absorption, distribution, and elimination in the body.
Stability: Cimetidine is stable under normal storage conditions and is sensitive to light. It should be stored in a cool, dry place, protected from light and moisture.

SAR of Cemitidine
1. Imidazole Ring: The imidazole ring in cimetidine is essential for its H2 receptor binding activity. Substituents on this ring can influence the compound’s potency and selectivity for the H2 receptor.
2. Aromatic Ring Substituents: Various substitutions on the aromatic ring attached to the imidazole moiety can affect the potency and pharmacokinetic properties of cimetidine.
3. Guanyl Group: Cimetidine contains a guanyl group, which is crucial for its H2 receptor binding affinity. Modifications to this group may impact the compound’s activity.
4. Side Chain Modifications: Cimetidine has a side chain that is important for its interactions with the receptor. Alterations in the length or nature of this side chain can lead to changes in the compound’s activity and pharmacological properties.
5. Stereochemistry: The stereochemistry of chiral centers, if present, can influence the compound’s activity. However, cimetidine does not have chiral centers.
6. Electronic and steric effects: Electron-donating or electron-withdrawing substituents on the aromatic ring can influence the electronic properties of the molecule, impacting its receptor binding affinity. Steric effects from bulky substituents can also affect the molecule’s interactions with the receptor.

Mechanism of Action
a. Cimetidine blocks the histamine effects by binding to the H2-receptors found on the baso-lateral membra ne of gastric parietal cell.
b. Reduction in gastric acid secretion, gastric volume and acidity are the results of this competitive inhibition.

Uses
1) It is used for treating certain types of ulcer.
2) It is used for treating the conditions in which too much acid is secreted by the stomach.
3) It is also used for treating acid-reflux disorders ( like GERD), peptic ulcer disease, heartburn, and acid indigestion.

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