Sildenafil (CAS No. 139755-83-2) is a white crystalline powder with the molecular formula C22H30N6O4S and a density of 1.39 g/cm3. It is a drug for treating erectile dysfunction in men, accidentally discovered during the development of drugs for cardiovascular diseases. It is generally known by its commercial name Viagra. It is a selective inhibitor of phosphodiesterase (PDE) V, enhancing the physiological response of penile erection induced by NO release in response to sexual stimulation. It is primarily used for erectile dysfunction.
Dosage and Administration
1. For most patients, the recommended dose is 120 mg, taken as needed approximately 1 hour before sexual activity, with sexual stimulation required after administration. However, it can be taken at any time within 0.5–4 hours before sexual activity. Based on efficacy and tolerability, the daily dose may be adjusted to between 150 mg, but should not be taken more than once a day.
- Dosage for renal insufficiency: The recommended starting dose for patients with severe renal insufficiency (where creatinine clearance is less than or equal to 30 ml/min, and AUC and cmax are almost doubled) is 25 mg.
- Dosage for hepatic insufficiency: The recommended starting dose for patients with hepatic impairment (such as cirrhosis, where AUC and cmax are increased by 84% and 47%, respectively) is 80 mg.
2. Dosage for the elderly: The recommended starting dose for patients aged 65 years and older is 100 mg.
Product Specifications and Properties
- CAS No.: 139755-83-2;
- Chemical Name: Sildenafil;
- Molecular Formula: C22H30N6O4S;
- Purity: 99%;
- Appearance: White powder;
- Melting Point: 187-189°C;
- Detection Method: High Performance Census Spectrometry;
- Standard: USP (United States Patent and Trademark Office)
Product Development and Application
Ethyl 3-n-propylpyrazole-5-carboxylate and dimethyl sulfate are mixed and reacted to obtain ethyl 2-methyl-3-n-propylpyrazole-5-carboxylate. This is then suspended in sodium hydroxide solution and hydrolyzed to obtain 2-methyl-3-n-propylpyrazole-5-carboxylic acid. The hydrolysis product is added in portions to a mixed acid and nitrated to obtain 1-methyl-4-nitro-3-n-propylpyrazole-5-carboxylic acid. The nitration product is chlorinated with thionyl chloride to an acyl chloride, and then aminated with concentrated ammonia to obtain 1-methyl-4-nitro-3-n-propylpyrazole-5-carboxamide. The carboxamide and tin dichloride dihydrate were suspended in ethanol and reduced under reflux to give 4-amino-1-methyl-3-n-propylpyrazole-5-carboxamide. The reduced product, 4-dimethylaminopyridine, and triethylamine were dissolved in dichloromethane, and then a dichloromethane solution of 2-ethoxybenzoyl chloride was added, followed by acylation to give 4-(2-ethoxybenzoylamino)-1-methyl-3-n-propylpyrazole-5-carboxamide. This acylated product was cyclized in aqueous sodium hydroxide and hydrogen peroxide to give 5-(2-ethoxyphenyl)-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyridin-7-one. The cyclized product was added in portions to chlorosulfonic acid to give 5-(5-chlorosulfonyl-2-ethoxyphenyl)-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyridin-7-one. The chlorosulfonated product was suspended in ethanol, and 4-methylpiperazine was added and stirred to obtain sildenafil.
Mechanism of action
During sexual stimulation, nitric oxide synthase in non-adrenergic, non-cholinergic neurons of the corpus cavernosum and vascular endothelial cells catalyzes the synthesis of nitric oxide from L-arginine. Nitric oxide activates guanylate cyclase, increasing the synthesis of cyclic guanosine monophosphate (cGMP), which in turn causes relaxation of the smooth muscle of the corpus cavernosum and small arteries, allowing blood to flow into the cavernous sinus and resulting in penile erection. Simultaneously, cGMP is hydrolyzed by phosphodiesterase.
Therefore, theoretically, both increasing the activity of guanylate cyclase and inhibiting the activity of phosphodiesterase can increase the level of cGMP, contributing to the relaxation of the smooth muscle of the corpus cavernosum and small arteries. Viagra (Sildenafil) increases cGMP levels by inhibiting the hydrolytic activity of phosphodiesterase without affecting cGMP, thereby increasing the nitric oxide synthase/cGMP cascade effect induced by sexual stimulation, relaxing the smooth muscle of the corpus cavernosum, and achieving the purpose of treating erectile dysfunction.
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