How does the Markush practice relate to unity of invention?

The Markush practice, which involves claiming a group of alternative chemical compounds, is subject to unity of invention requirements in PCT applications. According to MPEP 1850, for Markush groups:

• Unity of invention is considered to be present when the alternatives are of a similar nature.
• When the Markush grouping is for alternatives of chemical compounds, they are regarded as being of a similar nature when:
  1. All alternatives have a common property or activity, AND
  2. A common structure is present (i.e., a significant structural element is shared by all of the alternatives) OR all alternatives belong to a recognized class of chemical compounds in the art to which the invention pertains.

The phrase “significant structural element is shared by all of the alternatives” refers to cases where the compounds share a common chemical structure which 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 in view of existing prior art.

If these criteria are not met, unity of invention may be lacking among the Markush alternatives.

To learn more:

• Markush practice
• unity of invention
• chemical compounds
• similar nature