T 1919/23 - When is an enantiomer 'implicitly' disclosed in the eyes of the EPO?

In a recent decision, the EPO's Board of Appeal considered the question of when does a prior art disclosure of a named molecule, which is agnostic to any particular stereochemistry, implicitly disclose a particular enantiomer of that molecule? According to this recent decision, the answer is when you can persuasively demonstrate that the general name of a molecule would be understood by the skilled person, according to their common general knowledge, to implicitly require particular sterochemistry.

In T 1919/23, the Board considered the novelty of claim 1 as granted of EP 3 656 765. Claim 1 was directed to "a salt or cocrystal of (a) (1R,2R)-3-(3-dimethylamino-1-ethyl-2-methyl-propyl)-phenol, and (b1) L-(+)-tartaric acid". Novelty was challenged on the basis of a prior art document (D1) which disclosed “tartaric acid”, but did not explicitly state whether this term referred to a racemate, the meso form, the L enantiomer, or the D enantiomer.

With reference to three textbooks, which were submitted as evidence by the Respondent (Opponent), the Board concluded that in the common general knowledge, where tartaric acid is referred to without specification of stereochemistry, then it “invariably” refers to the L-(+)-enantiomer only, as required by claim 1.  The Board concluded that claim 1 therefore lacked novelty.

The Proprietor attempted to argue against this position with reference to several (seven) patent literature documents which suggested otherwise, but the Board was not persuaded on the grounds these documents only demonstrate that “in patent literature, various stereoisomeric forms of tartarate may be used in the pharmaceutical field. However, these documents to not call into question the common general knowledge” established by the aforementioned textbooks.

The Proprietor also referred to various decisions in the case law, but the Board observed that those decisions relate to the situation where “an alleged disclosure can only be regarded as implicit if it is immediately apparent to the skilled person that nothing other than the alleged implicit feature forms part of the subject-matter disclosed”. The Board found that their reasoning was entirely consistent with earlier case law on this point, stating that “it is unequivocally derivable from D1 in light of common general knowledge (D2 to D4), and it is immediately apparent to the skilled person, that nothing other than L-(+)-tartaric acid forms part of the subject-matter disclosed in D1”.

This case has interesting consequences for the question of an implicit disclosure of a compound. If a party to proceedings successfully finds a small collection of documents that are readily accepted as common general knowledge (e.g. textbooks as in this case), which collectively support a common ‘implicit’ meaning attributable to a term, then in the eyes of the Board, this ‘unequivocally’ demonstrates that meaning is applied by the skilled person. In this case, it was incumbent on the Proprietor to demonstrate that the alleged implicit meaning was not accepted across the common general knowledge at all, for instance by presenting a counter document which provided an alternative definition of “tartaric acid” that encompassed stereoisomers other than L-(+)-tartaric acid. However, in the absence of a counter document that the Board could readily accept as common general knowledge, the patent was ultimately revoked on the basis of lack of novelty over an implicit disclosure. Access to textbooks can be difficult for parties to opposition and appeal proceedings, owing to their generally academic nature and limited online availability. However, this is a cautionary tale where if a definition to be relied upon hinges on an understanding according to the common general knowledge, a deep dive into the library stack may be rewarding.