Chemical Synthesis
The preparation steps for synthesis of sildenafil are as follows:
- Methylation of 3-propylpyrazole-5-carboxylic acid ethyl ester with hot dimethyl sulfate
- Hydrolysis with aqueous NaOH to free acid
- Nitration with oleum/fuming nitric acid
- Carboxamide formation with refluxing thionyl chloride/NH4OH
- Reduction of nitro group to amino
- Acylation with 2-ethoxybenzoyl chloride
- Cyclization
- Sulfonation to the chlorosulfonyl derivative
- Condensation with 1-methylpiperazine.
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