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6.57 A Markush claim is a claim that defines multiple “functionally equivalent” alternative entities for one or more of the features of the invention. This type of claim is mainly encountered in the chemistry field.
6.58 Generally, there will be a consistent core structure that provides the activity of a compound. However even relatively straightforward Markush structures might comprise several thousand compounds, while more complex structures have been estimated to include in the order of 1061 compounds. By way of reference, the number of actual known compounds number in the order of 107
6.59 As previously noted, guidance can be taken from the PCT Guidelines, where the key consideration for unity is whether there is a common or corresponding special technical feature between alternatives. In the case of a Markush structure this requirement is met when the alternatives (that is the compounds defined by the claim) are of a similar nature.
6.60 The PCT Guidelines also set out that compounds are regarded as being of a similar nature where the following criteria are fulfilled:
(a) all alternatives have a common property or activity, and
(b) (1) a common structure is present, that is, a significant structural element is shared by all of the alternatives, or
(2) in cases where the common structure cannot be the unifying criteria, all alternatives belong to a recognized class of chemical compounds in the art to which the invention pertains.
6.61 In paragraph (b)(1), “significant structural element is shared by all of the alternatives” means that the compounds share a common chemical structure which occupies a large portion of their structures. Where the compounds have only a small portion of their structures in common, the commonly shared structure must constitute a structurally distinctive portion in view of existing prior art, and the common structure must be essential to the common property or activity. The structural element may be a single component or a combination of individual components linked together.
6.62 In paragraph (b)(2), “recognized class of chemical compounds” means that there is an expectation from the knowledge in the art that members of the class will behave in the same way in the context of the claimed invention. In other words, each member could be substituted one for the other, with the expectation that the same intended result would be achieved.
6.63 An objection of lack of unity should not be taken only on the basis that the alternatives of a Markush grouping belong to different IPC classes. If at least one Markush alternative is not novel over the prior art, an a posteriori lack of unity may be a consideration. However, it should be noted that the mere existence of compound(s) falling within the scope of a claim is not unusual and will rarely result in an objection of lack of unity. This may be an over-technical approach which at its most extreme would result in an objection of lack of unity. When in such cases, a novelty objection will be taken that will generally result in the applicant amending the claim to remove the prior art compound(s). The Examiner should take a broad consideration of the relationship between the alternatives. In these situations the issue may be closely linked to inventive step.
6.64 Example 1:
The invention relates to novel compounds of the following formula:
wherein R1 is selected from the group consisting of phenyl, pyridyl, thiazolyl, triazinyl, alkylthio, alkoxy, and methyl; R2-R4 are methyl, benzyl, or phenyl. The compounds are useful as pharmaceuticals for the purpose of enhancing the capacity of the blood to absorb oxygen.
In this case, there is a common activity or property and a common structure is present that appears to be essential to the activity. Accordingly, the Markush grouping has unity.
6.65 Example 2:
The following Markush group does not represent a single invention:
A is selected from C1-C10 alkyl or alkenyl or cycloalkyl, substituted or unsubstituted aryl or C5-C7 heterocycle having 1-3 heteroatoms selected from O and N;
B is selected from C1-C6 alkyl or alkenyl or alkynyl, amino, sulfoxy, C3 C8 ether or thioether;
C is selected from C5-C8 saturated or unsaturated heterocycle having 1 4 heteroatoms selected from O, S or N or is a substituted or unsubstituted phenyl;
D is selected from B or a C4-C8 carboxylic acid ester or amide; and
E is selected from substituted or unsubstituted phenyl, naphthyl, indolyl, pyridyl, or oxazolyl.
The key issue here is that the different combinations encompassed by the claim can lead to a large diversity of different compounds having no common structural feature. Furthermore, all of the circumstances of the case should be taken into account. For example, if the specification provides only one specific group of compounds, then there may be an issue of whether the claims are supported and such an objection could be taken instead of, or in addition to, the unity objection.
6.66 In chemical cases, a claim directed to a genus expressed as a group consisting of certain specified materials is allowable, provided it is clear from the known nature of the alternative materials or from the prior art that the materials in the group possess at least one property in common which is mainly responsible for their function in the claimed relationship. Therefore, a Markush claim will generally be construed with a generic expression covering a group of two or more different materials (elements, radicals, compounds) as illustrated in the following examples:
“A solvent selected from the group consisting of alcohol, ether and acetone …”
“A strip of a conductive metal selected from the group consisting of copper, silver and aluminium …”
6.67 Occasionally, the Markush format may be used in claims directed to subject matter in the mechanical or electrical fields in a manner such as that illustrated in the example below:
“A means for attaching a wall panel to a framework wherein the attaching means is selected from group consisting of nails, rivets and screws …”
6.68 While an objection should be as detailed as possible, in more extreme cases such as this, there is little benefit in detailing every permutation that falls within the scope of the claim. If there are only a limited number of classes specifically exemplified, then these may be identified in the objection and only a general comment made as to the others. Moreover, the examination should attempt to be of as much benefit as possible to the applicant, as well as avoiding unnecessary or wasted effort through examining embodiments that the applicant ultimately may not pursue. To this end, if the description is directed primarily to one particular group of compounds, then examination should be carried out on that group.