Under the European Patent Convention, a patent application must meet the requirements of sufficiency, that is the application must disclose the invention in a manner sufficiently complete and clear for it to be carried out by a person skilled in the art (Article 83 EPC). The plausibility of the invention must also be taken into consideration.

European patent EP1651658 concerned aryl C-glycoside derivatives and their use as SGLT inhibitors for the treatment of diabetes mellitus and associated complications. Reference was made to SGLT receptors being present in the intestine (SGLT1) and in the kidney (SGLT2), with the SGLT2 receptor being of interest as this mediates the excretion of excess glucose in the urine.

The application as filed disclosed and claimed certain aryl C-glycoside derivatives and pharmaceutically acceptable salts, a process for their synthesis, as well as medical uses and pharmaceutical compositions. No data demonstrating the effectiveness of the claimed compounds as SGLT1 or SGLT2 inhibitors were present in the application as filed. However, the application as filed made reference to a prior disclosure which disclosed other aryl C-glycoside derivatives as SGLT2 inhibitors with details of a suitable assay. The applicant also filed during prosecution comparative test data showing superior activity of certain claimed compounds against the closest prior art.

The appellant claimed that, in the absence of test data, it was implausible that the claimed compounds were suitable for the claimed use and the skilled person would not know what test to use.  Furthermore, the disclosure was insufficient as the skilled addressee would need inventive skill to synthesise most of the claimed compounds as the Examples did not cover compounds with large substituents, some of the claimed compounds could not form salts, and the skilled person would not know how to synthesise prodrugs for the claimed compositions.

Plausibility

The Board, summarising established case law, noted that for plausibility to be acknowledged, there must be no reason a priori to regard the claimed effect as being implausible and no indication in the common general knowledge of a lack of plausibility.

The Board agreed that in order for post-published data to be take into account, it must be plausible at the filing date that the claimed effect was obtained.  As there were no experimental data in the application as filed, if plausibility were to be acknowledged, this had to be in view of common general knowledge and prior art.  As the prior disclosure acknowledged in the application as filed disclosed compounds which were structurally sufficiently similar to the claimed compounds and provided details of an assay for SGLT2 inhibition, the Board considered it plausible that the desired therapeutic effect was obtained. Therefore the post-published evidence could also be taken into account.

Sufficiency

For the remaining sufficiency objections, the Board found no lack of sufficiency and noted that not only does the burden of proof lie with the party making the assertions and that no such proof had been provided, but that, in accordance with established principles, a skilled person should try, with synthetical propensity, to arrive at an interpretation of the claim which is technically sensible and takes into account the whole disclosure of the patent.

In conclusion, although it is not necessary to provide experimental data in a patent application provided there is sufficient information in the common general knowledge or an acknowledged prior publication, there is a risk that a disclosure could be found implausible and insufficient in particular in new fields of technology where there is little or no prior-published information, for example a previously unexplored therapeutic mechanism.  It is best practice therefore to provide supportive data in the application as filed to demonstrate that the applicant was in possession of a working invention at the time of filing and remove the risk that the application could be viewed as mere speculation.