Background

In an Appeal from refusal Order of a Patent Application the Delhi High court clarified that even for Intermediate chemical compounds, it is important to show enhanced therapeutic efficacy to overcome objection under section 3(d) and Inventive step of the Intermediate compounds. Intermediate compounds are the compounds which are generated during a chemical reaction.

The patent appeal was filed by Zeria Pharmaceutical Co. Ltd (Appellant) before Delhi High Court against the refusal order of the Indian Patent Office.

The patent application (3630/DELNP/2011) filed as a divisional patent application by Zeria Pharmaceutical Co. Ltd (Appellant) from the parent Indian Patent Application number 1090/DELNP/2007, related to a novel intermediate compound formula (5a). The parent application included a claim related to the process however the Divisional patent application claimed only a compound.

During the Examination, there were objections under section 3(d) and Inventive step of the Intermediate compounds on the basis of 2 prior arts. The prior arts were Appellant/Zeria’s own patent application.

Appellant’s arguments:

1. The methyl ester having the methoxycarbonyl group as claimed is not produced in the prior art document D2, and such compound is not specifically described.
2. Also, when starting from the generic disclosure of formula (II) to arrive at the claimed compound it takes a selection from multiple lists, which cannot be considered obvious to PSITA.
3. Because intermediate compound will not be directly used/ applied for the treatment of the disease, thus, it will not be feasible to determine the therapeutic efficacy of the intermediate compound.

Patent Office’s arguments:

1. The prior art document D2 discloses 2- [N-(4,5-dimethoxy-2- hydroxybenzoyl) amino]-4-(ethoxycarbonyl)-1, 3-thiazole acetate in Example 6. The only difference between Example 6 with the claimed compound of the subject application is the presence of “ethoxycarbonyl” in the prior art document D2 instead of “methoxycarbonyl”.
2. The prior art documents D1 and D2 relate to the same field of invention, and moreover, the applicant in both the prior art documents D1 as well as D2 and the applicant in the subject application is the same. Therefore, it appears to be an attempt by the appellant for mere extension of protection for known process intermediates, which is not permissible.

The data provided by the appellant during the written submission is about making the hydrochloride form of a compound called formula (7). However, the main focus of the application is on making the compound of formula (7) or 7(a), not specifically the hydrochloride form. The claim in the main or parent application is about a process to make the compound of formula (7), which can optionally be converted to the hydrochloride form Court’s reasoning for the refusal of patent application and the patent appeal:

1. The appellant claimed that the compound is a novel intermediate and not a new form of a known substance and therefore the provisions of Section 3(d) of the Act were not applicable, the Controller held that Claim 1 of the subject application fell within the scope of Section 3(d) of the Act as the claimed compound was a mere discovery of new form and a derivative of known compound disclosed in the prior art document D2, having no enhanced efficacy in terms of its effect.
2. Further, both the prior art documents D1 and D2 define lower alkoxy group as methoxy and ethoxy, etc. and therefore, using methoxy in place of ethoxy is one of the straightforward possibility, while developing alternative intermediate compounds based on the compound disclosed in Example 6 of the prior art document D2 as part of routine experimentation.
3. The only structural difference between the two compounds is in the ester group, which is the presence of an ethoxycarbonyl group in the prior art document D2 and a methoxycarbonyl group in the claimed compound under the subject application. These compounds differ by only one CH2 unit in their ester groups. Under Section 3(d) of the Act, these two compounds are derivatives of each other as they are differing only by methoxy and ethoxy group and the appellant was unable to show the enhanced efficacy in the claimed compound of the subject application over the compounds in the prior art documents.
4. Thus, the claim of the appellant that the compound (5a) claimed under the subject application, when reacted with N, N- diisopropylethylenediamine (6), the corresponding compound of formula (7a) is obtained at a yield of 97% and the property of the reaction with N, N-diisopropylethylenediamine is specific to the methoxycarbonyl derivative and that using the claimed compound, formula (7a) is obtained at a yield of 97%, and that the subject application is better in terms of reduced reaction time, and has higher isolation yield and reduction in impurities, altogether fails.
5. The court finally concluded that the prior art document D2 suggests that such compounds, specifically “compound 38”, are useful in the synthesis of aminothiazole derivatives recorded, and which is sufficient to motivate a PSITA to choose compounds therein, including Example 6 thereof being the closest compound. This is sufficient to conclude that it is obvious for a PSITA to replace “ethoxy” with “methoxy” to provide alternative intermediates useful in the synthesis of aminothiazole derivatives. The prior art documents D1 and D2 and the subject application relate to the same field of invention, and in each of them, one of the inventors, Mr. Masaaki Nagasawa, is the same, which is of much relevance.

Our observation:

• The parent patent application has a claim related to the process however the Divisional patent application claimed only a compound. Appellant’s argument before the Patent Office as well as the High court was that the intermediate compound is novel which is useful in obtaining the final product with advantages like reduced reaction time, higher isolation yield etc. However, as the intermediate chemical compounds are temporary in existence, it may not be feasible to compare the therapeutic efficacy of the compound as this intermediate compound is not being directly used for the treatment of a disease.

We understand that the chances of securing a patent grant would have been higher if the claims in the divisional application had been directed to the process for producing the intermediate compound. It is well established that, for process claims, demonstrating technical advantages such as improved yield or enhanced purity is generally sufficient. However, in light of the recent judgment, it has been clarified that when a compound itself is being claimed—particularly if it is already known in some way—it is essential to demonstrate enhanced therapeutic efficacy over the known compound, in accordance with Section 3(d) requirements.

*Matter Details: Zeria Pharmaceutical Co. Ltd vs The Controller Of Patents on 27 May, 2025 (C.A.(COMM.IPD-PAT) 452/2022)