“Understanding Patentability Considerations for Chemical Inventions: A Focus on Purity, Enantiomers and Polymorphs”

Understanding the Patentability of Chemical Inventions: A Deep Dive into Chemical Purity, Enantiomeric Form, and Polymorph Structure

Chemical inventions often present unique challenges when it comes to patentability. This article delves into the complexities of patent law, focusing on claims distinguished from the prior art by their chemical purity, enantiomeric form, and polymorph structure.

Chemical Purity

Chemical purity refers to the absence of impurities in a chemical sample. A 100% pure sample contains only one molecule or compound, devoid of any impurities or side-products. The patentability of compounds based on their purity has been a subject of debate in both Europe and the UK.

Historically, any document disclosing a method of producing a low molecular weight chemical compound was assumed to anticipate the production of this molecule in all grades of purity, unless evidence suggested otherwise (T 990/96). However, a more recent case, T 1085/13, deviated from this view, stating that a claimed purity is only implicitly disclosed if the method of preparation described in the prior art inevitably results in the claimed level of purity.

Despite this, to be patentable, the claim must also involve an inventive step. This is assessed by considering whether a skilled person could achieve the claimed higher purity using conventional techniques, such as recrystallisation, distillation, and chromatography.

Considerations for Drafting Patent Applications Relating to Compositions or Compounds with Improved Purity

When drafting patent applications for compositions or compounds with improved purity, it is crucial to provide evidence demonstrating that obtaining a high level of purity is not possible using conventional methods. The novel level of purity should be specified in the claim, and if possible, the impurities present when the compound is purified using routine methods should be identified.

Enantiomers

Enantiomers are compounds with a chiral centre, meaning they can exist as optical isomers. Each isomer is a mirror image of the other, and a mixture of enantiomers is referred to as a “racemic mixture”. According to T 296/87, a disclosure of a racemic mixture of enantiomers does not anticipate the novelty of each enantiomer that forms the mixture.

However, case law suggests that the enantiomer of a compound, where the racemic mixture is known, would typically not be held to be inventive, as resolving enantiomers from a racemic compound is often an obvious or routine step.

Considerations for Drafting Patent Applications Relating to Specific Enantiomers

When drafting patent applications for specific enantiomers, it is important to provide evidence demonstrating that one enantiomer has particularly surprising or different properties compared with the other enantiomer(s) or the racemic mixture. If difficulties were encountered when separating the two enantiomers, evidence that standard resolution methods could not be used should be provided.

Polymorphism

Polymorphism refers to the existence of more than one form or crystal structure of a solid material. A particular polymorph of a compound is considered to be novel over the prior art if the prior art does not provide an enabling disclosure of a particular polymorphic form.

However, merely claiming the crystalline form of a compound is unlikely to be considered inventive if the advantage is one that is expected to arise. An inventive step has been acknowledged in cases where the new polymorph has an unexpected property.

Considerations for Drafting Patent Applications Relating to a New Polymorph of a Known Product

When drafting patent applications for a new polymorph of a known product, it is crucial to provide evidence demonstrating that the polymorph is new over prior disclosure. For inventive step, comparative data showing that there is a surprising technical effect associated with a particular polymorph as compared with previously known polymorphs should be provided.

This article provides a general guide to the subject matter. For specific circumstances, it is recommended to seek specialist advice.