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2.76 In many cases some or all of the features of an invention may be substituted by similar or technically equivalent alternatives, but the properties of the product are still retained. Such claims are often referred to as Markush claims (named after the applicant on an early case of this type), and may be based on a relatively small number of alternatives or in some cases may extend to many millions of possible alternatives.
2.77 Markush claims are often used in chemical cases where different functional groups may be substituted at various positions and expected to retain the same properties, e.g. biological activity. In most cases the general formula will contain a consistent core element that provides the basic activity while other parts of the molecule may vary depending on the types of substituents the person skilled in the art would consider could be accommodated in the molecule.
2.78 A simple example of a Markush formula is as follows:
R1 – R2
wherein R1 is phenyl or 1-naphthalene, and R2 is chlorine or bromine.
2.79 This claim would include chlorobenzene, bromobenzene, 1-chloronaphthalene and 1- bromonaphthalene. For novelty purposes, a disclosure of even just one of these compounds in the prior art would render the claim lacking in novelty.
2.80 Markush claims can be difficult to search and often a risk-management approach is required in order to search the claims efficiently. In some cases the broad nature of the claims may raise issues of lack of unity, sufficiency and support. However it should be noted that the breadth of the claim alone is not objectionable provided these requirements are satisfied.