Optical Isomers

Date Published

The novelty of an isomer can be determined by applying the approach to generic disclosures.

The following information relates specifically to the situation where there is only one chiral centre and thus only two isomers. However, the principles can be extended to situations involving more chiral centres (e.g. diastereomers).

  • If the other isomer, and the racemate, have not been previously disclosed, then the isomer is novel.

  • If the racemate is previously known, it can be argued that the single isomer has been generically disclosed, since a person skilled in the art would appreciate that a compound having a chiral centre exists in two optically active forms. However, without anything further, it is doubtful whether the single isomer has been disclosed in a technical sense, or whether there is an enabling disclosure (see Imperial Chemical Industries Ltd (Howe's) Application [1977] RPC 121).

Examiners may also have to consider whether there is a valid selection.

  • If the other isomer is previously known, but the racemate is not known, the problem appears somewhat different. This situation can arise in cases of naturally occurring compounds, such as steroids. It is unlikely there has been even a generic disclosure of the other isomer and consequently novelty is not an issue.