T 0728/98 (Pure terfenadine/ALBANY) of 12.05.2000

1. It follows from the requirement of legal certainty that a claim cannot be considered clear in the sense of Article 84 EPC if it comprises an unclear technical feature (here "substantially pure") for which no unequivocal generally accepted meaning exists in the relevant art. This applies all the more if the unclear feature is essential for delimiting the subject-matter claimed from the prior art. (see reasons point 3)

2. Where the claimed purity level of a low molecular chemical compound (here a terfenadine derivative) turns out to be successfully achieved by applying a conventional purification method on a reaction mixture disclosed in the prior art, an exceptional situation such as addressed in the decision T 990/96 does not exist. This would have required evidence that conventional methods could not achieve that purity level. Therefore the general rule applies that the level of purity of that low molecular compound cannot entail novelty. That general rule is valid also in the case of a product-by-process claim where that purity level is the inevitable result of the preparation process indicated in the claim. (see reasons point 6)