## Facts

- Viktor Papesch sought patent claims to a class of trialkyl pyrazolopyrimidine-5,7-diones, including a genus where each substituent was a lower alkyl (more than one and less than five carbons) and species claims to triethyl and tri-n-butyl compounds.
- The patent examiner rejected all claims as obvious over a single reference disclosing a closely related trimethyl compound, reasoning the claimed alkyl substituents were “obvious homologs” of methyl groups and the preparation method was substantially the same.
- The Patent Office Board of Appeals affirmed, concluding that discovery of beneficial properties could not support patentability of the compound itself where the structure was considered an obvious homolog.
- Papesch submitted experimental evidence (including affidavits) that his trialkyl compounds, particularly the triethyl compound, had strong anti-inflammatory activity and diuretic properties, contrasting with the prior-art trimethyl compound.
- Papesch appealed to the United States Court of Customs and Patent Appeals.

## Issues

1. Whether a prima facie case of obviousness based on close structural similarity and “obvious homolog” reasoning can be overcome by evidence that the claimed compound has different and unexpected properties compared with the prior art.
2. Whether chemical obviousness under 35 U.S.C. § 103 must consider the compound’s properties and effects, not merely the apparent obviousness of its structural formula.

## Decision

- The court reversed the Board’s affirmance of the § 103 rejection.
- The court held that, for patentability, a chemical compound cannot be treated as only a structural formula; its properties are part of the claimed subject matter.
- The court held that “obvious homolog” reasoning establishes at most a prima facie case that may be rebutted by competent evidence of unexpected advantageous properties.
- The court found Papesch’s evidence of unexpectedly different biological properties sufficient to overcome the structural-similarity-based rejection.

## Legal Principles

- For patent purposes, a chemical compound and its properties are inseparable; the “invention” is the compound as a whole, including what it does.
- Structural similarity (including homology) may support a prima facie case of obviousness, but that assumption of similarity in relevant characteristics may be disproved by evidence.
- Evidence of unexpected results (in kind or degree), such as materially different biological activity, can rebut a prima facie § 103 case even when the claimed compound is structurally close to the prior art.
- The Patent Office may not categorically disregard property evidence on the ground that the structure appears to be an obvious homolog; the property evidence bears directly on whether the claimed subject matter as a whole would have been obvious.

## Conclusion

The court held that chemical nonobviousness cannot be decided from structure alone: where an “obvious homolog” rejection rests on structural similarity, credible proof that the claimed compound exhibits unexpected advantageous properties can rebut the prima facie case and support patentability under § 103.


In re Papesch, 315 F.2d 381 (C.C.P.A. 1963)