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The Supreme Court of Korea adds technical difficulty to polymorph patent considerations

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Min Son of Hanol IP & Law reports on a ruling by the Supreme Court of Korea that will make it easier to obtain polymorph patents of known chemicals in the country


Patenting polymorphs of crystalline forms of chemical compounds is a very important patent strategy, particularly for pharmaceutical companies when they wish to make their patent portfolios strong and long-lasting. However, obtaining such patents has not been easy in Korea, because the Supreme Court has set a higher hurdle for the patentability of this type of invention.

The Korean courts have long demanded that crystalline polymorph patents prove technical effects that are “qualitatively different” from the prior art technology or “quantitatively remarkable”, on the assumption that crystalline form inventions in general lack technical difficulty. This generalised assumption, however, made it very difficult to obtain any polymorph patents of known chemicals in Korea.

Fortunately, the Korean Supreme Court has recently overturned this old practice in its decision on the drug Tylan®, making it clear that the “technical difficulty” of a polymorph patent should also be considered when determining an inventive step.

The Supreme Court’s decision

In the past, the Supreme Court did not consider that polymorph inventions had technical difficulty, unless there were special circumstances, reasoning as follows:

  • Investigating crystalline polymorphism is a routine task of pharmaceutical companies since it is widely known in the field of medicinal chemistry that (i) a single compound may have multiple crystalline forms, and (ii) pharmaceutical properties such as solubility and stability may differ depending on the particular crystalline form;

  • Therefore, for a so-called crystalline polymorph invention (an invention in which the only distinguishable technical feature is a different crystalline form from the known compound), an inventive step can be recognised only if it has qualitatively different or quantitatively remarkable effects compared with the known compound, “unless special circumstances exist”.

Obviously, under these old criteria, the inventiveness of a polymorph patent heavily depended upon proving its superior technical effects, whereas in actual cases, it was quite difficult to prove that properties of specific crystalline forms are remarkably different from those of other crystalline forms that have the same chemical structure.

In the new decision (2018Hu10923 on March 31 2022), the Supreme Court clearly noted that even if “polymorph screening” had been carried out routinely, this routine practice does not necessarily mean that a “specific form” of a crystal would have been obvious and easily derivable from the known compound.

In this regard, the court has set forth the following factors to be considered when determining the technical difficulty of a crystalline polymorph invention:

  • Whether polymorphism of the prior art compound was known or expected;

  • Whether the prior art disclosed any teachings, suggestions, or motivations to lead to the claimed crystalline form;

  • Whether the claimed crystalline form falls within the scope of polymorphs that can be investigated through routine polymorph screening of the prior art compound; and

  • Whether the claimed crystalline form has any unexpected advantageous effects.

The Supreme Court has applied these factors to the Tylan® case and reversed the lower court decision that denied the inventive step of the drug, reasoning that:

  • The prior art does not in any way disclose whether the compound is of a crystal form or an amorphous form, and no other records indicate the existence of the polymorphism of the compound;

  • The claimed crystalline form and the prior art compound differ in starting materials as well as specific crystallisation parameters such as solvent, temperature, and time;

  • It is not certain whether one of ordinary skill in the art would easily conceive the claimed crystalline form from the prior art by modifying crystallisation parameters or through routine polymorph screening; and

  • The effect of the claimed crystalline form would not be expected from the prior art.

Final remarks

After the decision cited above, the inventive step of polymorph patents will be judged on the same principle as other inventions. Furthermore, it is worth noting that this decision is in line with last year’s Supreme Court decision that required the court to take into account the technical difficulty of a selection invention in its determination of an inventive step.

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