With regard to the inventiveness requirement of a selection invention that falls within a broader or generic concept disclosed in the prior art, the Supreme Court had previously ruled that the selection invention should exhibit a criticality (i.e., an effect qualitatively different from or quantitatively remarkable over that of the prior art) throughout the entire range claimed, and such criticality should be clearly demonstrated in the specification (see, e.g., Supreme Court Case Nos. 2008 Hu 736 and 743 rendered on October 15, 2009). 

In a recent decision, however, the Supreme Court, in upholding the inventiveness of a selection invention, departed from the previous approach; and held that: in order to determine the inventiveness of a selection invention, the difficulty to conceive the selection invention should be first examined; and if the difficulty to conceive the selection invention cannot be shown, the inventiveness of the selection invention may then be assessed based on the existence of a criticality of the selection invention (Supreme Court Case No. 2019 Hu 10609 rendered on April 8, 2021). 

▶Background of the Case 

The subject patent (KR Patent No. 908176) relates to novel lactam-containing compounds and derivatives thereof that are useful as inhibitors of factor Xa, and is based on the discovery that certain compounds having a lactam ring () are useful as inhibitors of factor Xa and exhibit superior pharmacokinetic properties. Specifically, claim 1 of the subject patent is directed to a particular compound having the lactam ring (i.e., apixaban, ) or a pharmaceutically acceptable salt thereof. 

Meanwhile, the prior art reference (WO 00/39131) discloses nitrogen containing heterobicyclic compounds that are useful as inhibitors of factor Xa, and specifically discloses 66 core structures for the nitrogen-containing heterobicyclic compounds. As the prior art reference defines such compounds by a Markush grouping of various substituents applicable to the 66 core structures, an enormous number of compounds can be theoretically covered by the prior art reference, depending on the selection of a core structure and the combination of substituents applicable thereto.

Several generic companies lodged invalidation trials against the subject patent and the Trial Board rendered a decision invalidating the subject patent for lack of inventiveness over the prior art reference. The patentee filed an appeal with the Patent Court. 

▶The Patent Court Decision 

The Patent Court first noted that the subject patent involved a selection invention because the claimed compounds fell within the broad scope encompassed 1 by the Markush grouping defined in the prior art reference. Applying a strict patentability requirement to the subject patent as a selection invention, the Patent Court denied the inventiveness of the subject patent because the specification failed to describe any effect qualitatively different from, or quantitatively remarkable over, that of the prior art reference, and such effect had not been corroborated. 

▶The Supreme Court Decision 

On appeal, however, the Supreme Court reversed the Patent Court decision. In doing so, the Supreme Court first indicated that difficulty to conceive an invention, which is generally considered in determining the inventiveness of an invention, should equally be considered first when determining the inventiveness of a selection invention like the one of the subject patent directed to specific species falling within the scope theoretically covered by the Markush formula provided in the prior art reference but not specifically disclosed therein. In particular, the Supreme Court stated that the difficulty to conceive the subject invention shall be determined in light of the number of compounds theoretically included in the scope of the 66 core structures and the substituents applicable thereto defined by the Markush formula of the prior art reference; existence of motivation, suggestion or reason for the selection of the specific compounds or substituents; and the structural similarity between the patented compounds and those specifically disclosed in the prior art reference.

Further, the Supreme Court added that the superior effect of a selection invention may be regarded as a material factor in assessing the difficulty to conceive the selection invention, especially in the fields of chemical and pharmaceutical inventions whose effects are difficult to predict. 

Based on the above reasoning, the Supreme Court found that, in order to arrive at claim 1 of the subject patent from the Markush formula of the prior art reference, a particular core structure () needed to be first selected from the 66 core structures listed in the prior art reference and then all relevant substituents amenable to this core structure in a materially efficacious manner. In particular, the Supreme Court noted that the lactam ring in claim 1 of the subject patent, which is the key substituent responsible for exhibiting the effect of the subject invention, needs to be attached to the core structure at substituent B linked to substituent A; however, the prior art reference does specifically disclose the lactam ring, there is no teaching or suggestion pointing to the lactam ring in a preferred embodiment of the prior art reference enumerating 34 structures among the 66 core structures; and no compound that has a similar structure to the claimed compounds of the subject patent or contains a lactam ring as substituent B is among those 107 individual compounds specifically listed therein. 

In addition, the Supreme Court noted that the subject invention has an improved inhibiting activity and selectivity for factor Xa as compared to known inhibitors of factor Xa, exhibits improved pharmacokinetic effects, and shows improved effects for combination with other therapeutic agents in light of the disclosures given in the specification of the subject patent and experimental data submitted after the filing date. 

For the foregoing reasons, therefore, the Supreme Court held that 1) a person skilled in the art would have to experiment with numerous combinations of selections through repetitive trial and error in the course of searching for the correct combination in order to arrive at the subject invention from the prior art reference, since the prior art reference points to a different compound from the subject invention and there is no motivation, suggestion or reason for the selection of the subject invention in the prior art; 2) the inventiveness of the subject invention over the prior art reference cannot be denied since it would not be obvious to conceive the subject invention from the prior art reference without the benefit of hindsight knowledge of the subject invention, and 3) the subject invention produces certain improved effects over the prior art. 

Accordingly, the Supreme Court reversed the Patent Court decision which had denied the inventiveness of the subject invention for the sole reason that the patentee failed to show any qualitatively different or quantitatively remarkable effect of the subject invention over the prior art reference. 

▶Significance of the Decision 

The upshot of the Supreme Court decision is to likely decrease the invalidation rate of selection patents or increase the allowability of patent applications pertaining to selection inventions, since the difficulty to conceive an invention may be used to determine the inventiveness of a selection invention, even when the critical effect thereof cannot be shown.