## Facts

- Prior art taught that DMSO (dimethyl sulfoxide) could serve as a chiral auxiliary to separate amlodipine isomers from a chemical mixture.
- Xitian Zhang obtained a Chinese patent claiming a separation process using DMSO‑d6, a deuterated version of DMSO, as the chiral auxiliary for resolving amlodipine isomers.
- Zhang argued that replacing DMSO with DMSO‑d6 produced better optical purity and higher yield than the known DMSO-based process, even though DMSO‑d6 was more expensive.
- Shijiazhuang Ouyi Pharmaceutical Co., Ltd. petitioned China’s patent reexamination authority to invalidate (revoke) Zhang’s patent.
- Ouyi contended that, given the close chemical relationship between DMSO and DMSO‑d6 and the prior art’s use of DMSO for the same function, a skilled person would consider DMSO‑d6 for amlodipine separation without inventiveness.
- Ouyi submitted comparative experimental data, generated under comparable laboratory conditions, indicating that DMSO‑d6 produced only marginal gains in purity and yield relative to DMSO.
- The patent reexamination committee revoked the patent.
- After losing an initial challenge to the revocation decision, Zhang appealed to the Beijing Higher People’s Court in 2007.

## Issues

1. Whether, in light of prior art using DMSO to separate amlodipine isomers, substituting DMSO‑d6 in an otherwise similar separation process involves an inventive step under Chinese patent law.
2. Whether marginal improvements in optical purity and yield, shown by comparative testing, are sufficient to establish inventiveness for a close chemical substitution.

## Decision

- The Beijing Higher People’s Court affirmed the revocation of Zhang’s patent.
- The court treated the move from DMSO to DMSO‑d6 as a substitution suggested by their chemical similarity and the prior art’s teaching that DMSO could perform the same separation role.
- Based on the comparative evidence in the record, the court concluded that the reported gains in purity and yield were too small to show a technical effect that would distinguish the claimed process from what a skilled person would expect from routine experimentation.

## Legal Principles

- A claimed method lacks inventive step when the prior art teaches the same technical purpose and the claim differs mainly by substituting a closely related chemical that a skilled person would reasonably try.
- For chemical modification or selection-type inventions, inventiveness often turns on whether the applicant can show a technical effect that is more than the small differences typically expected from routine substitution.
- Comparative test data is most useful when generated under comparable conditions and directed to the exact performance claims advanced to show inventiveness.
- Higher cost or rarity of a substitute material does not, by itself, establish inventiveness if the substitution is technically predictable and yields only limited performance change.

## Conclusion

In *Zhang, Xitian v. Shijiazhuang Ouyi Pharmaceutical Co., Ltd.* (Beijing Higher People’s Court, 2007), the court affirmed the administrative revocation of Zhang’s patent for resolving amlodipine isomers using DMSO‑d6, concluding that the prior art’s DMSO-based separation method and the close similarity between DMSO and DMSO‑d6 made the substitution obvious, and that the comparative evidence showed only marginal gains in optical purity and yield insufficient to support an inventive step.


Zhang, Xitian v. Shijiazhuang Ouyi Pharmaceutical Co., Ltd., China (2007)