FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
PROVISIONAL SPECIFICATION
(SeesectionlO]
1. Title of the invention: "A novel process for the preparation of Sildenafil Citrate"
2. Macleods Pharmaceuticals Ltd., an Indian Company, having its Registered Office at 304 - Atlanta Arcade, Opp. Leela Hotel, Marol Church Road, Andheri (East), Mumbai - 400 059, Maharashta, India.
3. The following specification describes the invention.



A NOVEL PROCESS FOR THE PREPARATION OF SILDENAFIL CITRATE
The present invention provides a simple and commercially viable process for the preparation of sildenafil citrate of Formula I.

Formula I
Sildenafil is chemically known as 5-(2-ethoxy-5- (4-methylpiperazin-l-ylsulfonyl) phenyl)-l-methyl-3-propyl-lH-pyrazolo [4, 3-d] pyrimidin-7 (6H)-one and is known from U.S. Patent No. 5,250,534. U.S. Patent 5,250,534 describes the multi step synthesis of Sildenafil with a yield of-27%.
A first aspect of the present invention is to provide a novel process for the preparation of sildenafil citrate of Formula I comprising the steps of:
a) converting 4-(2-ethoxy-5- (4-methylpiperazin-1 -ylsulfonyl) benzamido)-1 -methyl-3-propyl-lH-pyrazole-5-carboxylic acid of Formula II to sildenafil of Formula III.
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b) and optionally converting sildenafil of Formula III to sildenafil citrate of Formula I or a pharmaceutically acceptable salt thereof
A second aspect of the present invention is to provide a 4-(2-ethoxy-5- (4-methylpiperazin-1-ylsulfonyl) benzamido)-l-methyl-3-propyl-lH-pyrazole-5-carboxylic acid of Formula II .

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A third aspect of the present invention is to provide a 4-(2-ethoxyo- (4-
methylpiperazin-1-ylsulfonyl) benzamido)- l-methyl-3 -propyl- lH-pyrazole-5-
carboxylic acid of Formula II

used for the preparation of sildenafil citrate of Formula I


Formula II
A fourth aspect of the present invention is to provide a process for the preparation of 4-(2-ethoxy-5- (4-methylpiperazin-1 -ylsulfonyl) benzamido)-1 -methyl-3-propyl-1H-pyrazole-5-carboxylic acid of Formula II

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Dated this 16* day of July, 2008.
Signature:
Name: Dr. Rajendra Agarwal
To
The Controller of Patents The patent Office, At Mumbai.

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