Written by:Chen Wenping Ma Hui (Intellectual Property)





The Reexamination and Invalidation Department of the Chinese patent office (CNIPA) announced the 10 guiding cases of the year 2021.  These cases have always been authoritative interpretations of legal provisions involved in hot patent law issues.  In the three chemical field cases, two of them involved examination of Markush claims.

“Markush” claims, as a special claim drafting manner in the field of chemistry, have been controversial during prosecution and post-grant proceedings. Due to generalities contained in the Markush claims, the examining opinions usually relates to issues of support, unity, novelty, inventiveness, etc. To overcome these examination opinions, applicants usually make limitations to the protection scope of Markush claims in order to obtain patent right. During post-grant proceedings, the priority of Markush claims is often part of the dispute. Since authoritative decisions or clear rules on priority of Markush claims have not been seen, when being challenged, patentee usually has unfavorable expectations on the priority issue of a Markush claim. On the other hand, subject to restrictions in the manner of amendments in the patent invalidation proceedings, the amended Markush claims can barely be accepted at the invalidation stage typically for the reason of not complying with the provisions of the Chinese Guidelines for Examination on amendment at the invalidation stage.

The Invalidation Decision No.48183 of the 10 cases of 2021 (on the patent entitled “novel sulfamides and their use as endothelin receptor antagonists”) relates to a pulmonary arterial hypertension drug. In the granted patent, claim 1 is directed to compounds of a general formula, and claims 2-9 further specify the range of substituents of the compounds of the general formula, or defines a general formula with fewer variables. Claims 10 and 11 further define a list of specific compounds.  The active pharmaceutical compound in the marketed drug falls into the range of Markush claims, and is also recited in claim 11. One of the invalidation grounds raised by the petitioner is that the subject patent does not possess inventiveness over the reference documents existing after the priority date but before the filing date of the disputed patent. Therefore, the priority is an unavoidable issue to be determined in the case. In the Response, the patentee narrowed the scope of claim 1 to two compounds only. As such, the focus of the priority problem is to determine whether specific compounds can have the priority. In this regard, the panel held that:

“if the prior application relates to a Markush formula and the subsequent application is directed to specific compounds of the formula, determination as to whether the subsequent application can enjoy the priority of the prior application should be made based on whether the specific compounds are explicitly or implicitly recited in the prior application, and the compounds not explicitly or implicitly recited in the prior application may not enjoy the priority of the prior application.”  

In other words, if the priority document does not recite the specific compounds as claimed in the subsequent application, priority determined based on “the invention-creation with the same subject” will not be supported.

The criterion for determining the priority of compounds in this case is substantially consistent with the conclusion in the Decision No.46047 (on the patent entitled “Substituted oxazolidinones and their use in the field of blood coagulation”, which is one of the 10 guiding cases of the year 2020). In the Decision No.46047, the patentee also amended the claim to protect a specific compound structure and argued that the subject patent possessed inventiveness even if the priority cannot be supported. The panel then determined that although priority claim is not supported, the patent possesses inventiveness.

In both cases, the patentees all adopted a relatively conservative defense strategy, possibly because the patentee does not want to trigger the unfavorable determination of the rule for evaluating priority of Markush claims in the invalidation procedure. However, the question arises how the priority should be evaluated if those claims are still Markush claims? Considering that whether Markush claims can enjoy priority is closely related to the amending manner, we would like to discuss this issue in light of the Supreme People’s Court opinions on amendments from one of the 10 guiding intellectual property cases in 2017.

From the perspective of legislative intent, Markush claims are intended to solve the problem of lacking a common general term for multiple substituent groups in the field of chemistry. Therefore, “reasonable” generalization is critical to the examination of Markush claims. In addition, from the perspective of technical research and development, when the applicant submits a patent for compounds defined in Markush claims, research is usually in the early preclinical stage where the applicant does not have a clear and full picture about the structure-activity relationship of the compound. It is therefore impossible to accurately predict the compound that will eventually enter the clinical stage and show therapeutic effects.  At this time, the existence of Markush claims allows the applicant to delineate a certain scope of protection based on the research results. As such, the examination on Markush claims is an evaluation with hindsight, while drafting of Markush claims requires the applicant to have certain foresight about the future development of the research. The discussion on the application of legal provisions with respect to Markush claims should be balanced between these two perspectives.

First of all, according to the rules as stated by the panel in the Decision No.48183, if a specific compound is not recited explicitly or implicitly in a priority document, the subsequent patent may not enjoy priority. When making this decision, the panel somehow adopted a nocelty test. Specifically, if the specific compound in the subsequent patent was not recited in the priority document, it possesses novelty over the Markush claims in the priority document, and thus possibly can constitute a new invention. As such, if the patentee is allowed to reserve the priority date, the date of delimiting the prior art will be brought forward, which goes against the intent of the priority system.

Markush claims are different from a specific compound or a combination of specific compounds. This has been confirmed in (2016) Supreme People’s Court Retrial Verdict No. 41 (one of the Ten Guiding Intellectual Property Cases in 2017).  The Supreme People’s Court (“SPC”) holds,

Markush claims should be regarded as a collection of Markush elements, rather than a collection of many compounds, and the Markush elements can only be embodied as a single compound under certain circumstances and should be interpreted as a class of compounds with common properties and effects”.

In practice, more often seen is a scope of Markush claims being narrower than the scope of disclosure of the document published on the priority date, or overlapping with the scope of the original disclosure.

In the former case, compared with the scope of the disclosure of the priority document, the narrowed Markush claims typically possess novelty. If possessing novelty is considered as undermining the priority, excessive burden will be imposed on the applicant while drafting the claims, rendering the generalization function of the Markush claims meaningless. This is because during prosecution, Markush claims are always amended, rendering the amended claims inconsistent with those contained in the priority document. If a subsequent application may not enjoy priority simply due to narrowing amendments, applicants will be hindered from disclosing the invention as early as possible. To solve this dilemma, we believe a two-way novelty test could be considered: if the specific compound disclosed in the priority document still falls within the scope of protection of the amended Markush claims, it can be reasonably inferred that, upon filing the priority application, the applicant has not only conceived a reasonable scope of protection but also recited one or more compound, which indicates that the applicant has substantially completed the invention. If Markush claims as amended, either during substantive examination or during invalidation procedure still contain a specific compound disclosed in the priority document, the amendments made are for obtaining an appropriate and stable scope of protection and for avoiding prior art documents that were not discovered by the priority date. Therefore, such amended Markush claims should enjoy priority. This is echoed in a way in the Reexamination Decision No.103348 (on an invention entitled “High performance solution processable seminconductor based on dithieno[2,3-d:2′,3′-d’]benzo[1,2-b:4,5-b’] dithiophene”). The panel holds that to determine whether a patent application may enjoy priority of the prior application, determination should be focused on the question if they relate to the same invention subject, rather than being restricted to comparison of the drafting language of the respective claims of the two, or even the number of substituents; for Markush claims, if amended claims are arrived at by deleting some substituents in the prior application, without including a new invention subject, the subsequent application should be allowed to enjoy priority. Notably in this patent application, specific examples fall within the scope of protection of the modified Markush claims. By allowing such modifications, the interests of the applicant can be reasonably protected, and the unreasonable situation that the applicant deliberately designs general modifications according to the commercial behavior of competitors rather than the disclosure of the instructions can be prevented.

The other circumstance is much more complicated. If the subsequent application overlaps with the priority application in protection scope of the Markush formula, it remains in question whether the amended Markush claims necessarily may not enjoy priority due to inclusion of contents not recited in the priority document.  In the regard, we believe that, considering the purpose of establishing priority system, not all Markush claims including contents beyond the priority document are prevented from enjoying priority; rather, conclusion should be varied with the individual case.  It is not allowed to improperly use the priority system for unreasonable predominance, nor is it reasonable to require an applicant to draft claims in a perfect manner at the very beginning at the time of priority date.

Markush claims are inevitably subject to revision during substantive examination. Applicants usually have higher flexibility to amend claims during substantive examination, for example, by deleting some candidates defined in multiple variable definitions. However, due to the restrictions on amendments in the invalidation procedure, Markush claims can be amended only in limited manner, and deletion of candidates from variable definition is barely allowed. In the (2016) Supreme Court Retrial Verdict No. 41, as mentioned above, the Supreme People’s Court holds, “amendments to Markush claims in the invalidation procedure must be strictly limited.  The principle of allowing Markush claim amendments should be that no new class of compounds or a single compound with new properties and effects is produced due to the amendment; nonetheless, factors particular to each single case should also be fully considered“.

In this case, the applicant made the following amendments during invalidation procedure, specifically:


















The panel only accepted deletion of “or ester” and rejected other amendments.  This decision is supported by the Supreme People’s Court. The Supreme People’s Court holds that that, if the above amendments were allowed in the invalidation procedure, “there would be uncertainty as to whether a new scope of protection would be generated due to this deletion even though such deletion only involved narrowing the scope of protection of the claims and would not damage the rights and interests of the public, which not only failed to give the public an ascertained expectation, but also would not be conducive to maintaining the stability of the patent validation system”.

Bearing this in mind, if some substituents in the Markush claims are deleted, rendering the protection scope narrowed but a new protection scope not generated accordingly, the concerns of the Supreme People’s Court in the above verdict could be removed.

Turning to the above discussion on the disclosure of the priority document, if the priority document recites the compound of the general formula and gives one or more exemplified compounds, the applicant has substantially completed the invention upon filing the priority document. Therefore, irrespective of being in substantive examination procedure or in the invalidation procedure, if Markush claims amended by the applicant/patentee still cover specific compounds disclosed in the priority document, the amended Markush claims will not incur a scope of protection with novelty, and the essence of such amendments is to avoid prior art documents having not been discovered by the filing date or priority date, so as to obtain a more stable and reasonable scope of protection.

Above all, all rules are conceived and discussed within the legislative frame of the Patent Law, that is, “disclosure in exchange for protection”. Currently with the restrictions posed in amendments after patent grant, the Markush claims become a not so ideal option for patentees to protect their inventions. The industry is expecting the CNIPA to clarify the examination criterion and evaluation elements about Markush claims, thus making it possible to bring the reasonable generalization role of the Markush claims into full play.