Where a single claim defines several (chemical or non-chemical) alternatives, e.g. it contains a so called "Markush grouping", the requirement of Rule 44(1) for same or corresponding special technical features is considered met if the alternatives are of a similar nature (see F‑IV, 3.7).
When the Markush grouping is for alternatives of chemical compounds, they should be regarded as being of a similar nature where:
Thus, common matter is provided for a Markush grouping by the common property or activity of the alternatives (see (i) above) and the common structure defined by (ii) above.
A "significant structural element is shared by all of the alternatives" if the compounds share a common chemical structure that occupies a large portion of their structures, or, if the compounds have in common only a small portion of their structures, the commonly shared structure constitutes a structurally distinctive portion, and this structure or portion leads to a technical contribution in view of existing prior art. The structural element may be a single component or a combination of individual components linked together.
There is no need for a significant structural element to be novel in absolute terms (i.e. novel per se). Rather, the term "significant" means that in relation to the common property or activity, there must be a common part of the chemical structure that distinguishes the claimed compounds from any known compounds having the same property or activity.
In other words, the significant structural element defines the technical contribution which the claimed invention, considered as a whole, makes over the prior art.
The alternatives belong to a "recognised class of chemical compounds" if 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, i.e. that each member could be substituted one for the other, with the expectation that the same intended result would be achieved.
However, if it can be shown that at least one Markush alternative is not novel, unity of invention must be reconsidered. In particular, if the structure of at least one of the compounds covered by a Markush claim is known, together with the property or technical effect under consideration, this is an indication of lack of unity of the remaining compounds (alternatives).
This is because the Markush alternatives comprises no same (c.f. common structure) or corresponding (c.f. same property or technical effect) technical features that are "special".