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22. The Plaintiff contends that the plea that Erlotinib would be an isostere of known compounds is a speculation. A person skilled in the art knows that the smallest change in a molecule can have dramatic effects and can totally change the efficacy of a molecule. Many examples in the pharmaceutical industry show that a small change in an active molecule can lead to an inactive or toxic molecule. Thus, changing the smallest Chemical group or a molecule cannot be seen as obvious. The person skilled in the art a priori never considers that it would have been obvious to change a Chemical group for another. The Defendant's argument, the Plaintiff contends, is artificial and can only be the result of an ex post facto analysis. In the case of pharmaceutical products such 'reverse engineering' is employed with great effect. 'Inventive step' must be examined at the time of filing of the Tarceva patent. At that time and without the knowledge of Erlotinib, there was no motivation to replace the methyl group by a C=N group either in the general formula or in the specific formulae of EP 0566 226. The suggestion that that the Plaintiff used the Methyl prior art, progressed to the Cyano state (i.e. C=N) and then arrived at the Ethynyl stage, is pure speculation and false. The simple point is that prior art is Methyl and Gefitinib used the Methyl route. The defendant, contends the plaintiff, suggested the Cyano route in the Gefitinib patent. However, the plaintiffs have simply used the Ethynyl model and not the Methyl model. Indeed, all these arguments have already been taken into account in the pre grant opposition proceedings and the patent was granted nonetheless by the Indian patent office. The defendant does not bring any new prior art document or argument in this respect.

30. Dr. Singhvi next relied upon Dunlop Pneumatic Tyre Co. Ltd v. Neal 1899 (1) Ch. D. 807. In that decision it was held that the purchaser of a patented article can carry out repairs to it; however, he cannot manufacture a new article and claim that he had not infringed the patent because in the manufacture he had used an article derived from a patented article sold by its patentee. It was contended that the defendants cannot similarly claim, by process of 'reverse engineering' that their products were new and invented goods. They were clearly inspired by the plaintiff's products and after purchasing them, copied the main elements; their effort was an act of infringement, which had to be injuncted.