A chemist shown the structure of a new molecule having a single chiral centre will understand that two enantiomers, being mirror images of one another, may exist.  If the molecule exhibits activity a question arises whether that activity is mostly due to only one of the enantiomers and, if so, which one? If the racemate demonstrates strong therapeutic activity there may be pressure to file a patent application quickly to establish rights before competitors identify the same molecule independently or the information is made public. This may not allow time, before filing, for the separation and testing of enantiomers to enable the more active enantiomer to be identified. This begs the question as to whether a subsequent patent application, by the same applicant or a competitor, could be validly filed directed only to the more active and clinically important enantiomer?

The Australian Patent Office position is that if only the racemate is known then, without an enabling disclosure e.g. directions to isolate the enantiomers, a subsequent claim to a single enantiomer is ‘arguably’ novel. This position reflects the inherent unpredictability of the biological activity of individual enantiomers and also the practical difficulties often encountered in their separation.

To obtain strong patent protection for a new chiral molecule demonstrating therapeutic efficacy it is therefore desirable to have separated and individually tested the enantiomers for activity. In this way protection can be put in place for both the racemate and the therapeutically relevant enantiomer thereby reducing patenting opportunities for competitors. If an early stage patent application must be filed based upon racemate activity data only, then a second filing relating to the separation and activity of the individual enantiomers should be made, as soon as possible. In this way full commercial advantage can be taken of those molecules in the mirror.

Author: Dr Declan McKeveney  
Conact: +61 3229 2655, dmckeveney@fak.com.au