First Publication Date: 20th December 2009
The case related to a patent in respect of the manufacture of new sulphonyl-ureas, salts of those compounds and of anti-diabetic preparation containing such compounds. One of the chemical compounds comprised in the said patent was Tolbutamide, and since 1957 the patent holder had been marketing the same as an anti-diabetic drug in India and all over the world under the trade mark “Rastinon”. The patent holder filed an infringement suit against the Respondents claiming that the manufacture, preparation and sale of Uni-Tolbid tablets or Tolbutamide by the Respondents infringes its patent. In response to the suit, the Respondents claimed that their activities were based on a patent held by one of the Respondents for the preparation of substituted benzonesulphonyl ureas from the corresponding substituted benzonesulphonylthioureas by desulphurisation with hydrogen peroxide and therefore, they were not liable for infringement.
The Court construed the claims before deciding on infringement. Claim 1 of the patent read as follows:
“A process for the manufacture of sulphonylureas of the general formula R-SO. 2-NH-CO-NH-R. 1 in which R represents a phenyl radical which may contain one or two substitutes selected from alkyl and alkoxy residues, the alkyl group of which containing at most 8 Carbon atoms, and halogen atoms, or represents an aliphatic or cycloaliphatic Hydro-Carbon radical containing 3 to 8 Carbon atoms and R. 1 represents an aliphatic or cycloaliphatic Hydra-Carbon radical containing 2 to 8 Carbon atoms, and of the salts thereof, where in compounds of the formula R – SO. 2.-X and Y-R.1 are reacted together in which X and Y are groups which ion reaction together form a urea linkage as defined above or a linkage readily convertible thereto”.
Furthermore, Claim 11 of the patent read as follows:
“A process as claimed in claim 1 wherein thioureas of the formula R-SO. 2-NH-CS-NH-R. 1 are treated with agents eliminating the sulphur, R and R. 1 having the meanings given above.”
The Court stated that Claim No.1 was the main claim of the patent, which covers compounds obtained by the chemical reaction specified in it, either directly to form a urea linkage, or indirectly to form a linkage readily convertible into urea linkage. As per the Court, Claim No.11 falls within the scope of claim No.1 in so far as it deals with the processes by which thioureas were converted to the corresponding urea linkage by being treated with agents eliminating sulphur and the radicals R and R.1 had for the purpose of claim No.11 the same limitations in regard to the number of Carbon atoms as they were required to have for the purposes of claim No.1.
As the Respondents were preparing the compound Tolbutamide by the process of desulphurisation of benzene-sulphonyl thioureas with Hydrogen peroxide, the Court stated that such a process falls within the scope of claim 11 because the claim includes desulphurisation of thioureas by any chemical substance, including Hydrogen peroxide, which was used by the Respondents. The Court stated that Claim No. 11 was wide enough to cover all methods of eliminating sulphur from thioureas, whether the desulphurisation was effected,, by means of Hydrogen peroxide, or by the use of any other substance. As claim 11 depended on claim 1, the court held that claim 1 was also infringed by the Respondents’ process. Though one of the Respondents held a patent for the preparation of substituted benzonesulphonyl ureas from the corresponding substituted benzonesulphonylthioureas by desulphurisation with hydrogen peroxide, the Court stated that holding a patent over a step in the process would not avoid liability for patent infringement if the process falls within the scope of a patent claim.

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