Similarity principle in legal cases
Read enough cheminformatics papers and you'll eventually come across
the a variation of the
similarity principle or
property principle or
molecular similarity principle. Here's
a 2020 example from the JCIM paper
Under the framework of the similarity principle property,5 which assumes that similar compounds should have similar properties, a plethora of methods have been developed to disclose structure-activity relationships, derive pharmacophores to rationalize the biological activity, and perform similarity measurements in the search of novel chemical scaffolds.and here's the only one in J. Cheminformatics, titled
The underlying assumption of ligand-based approach is that similar structures have similar biological activity. Maggiora and Johnson  introduced the similarity-property principle that implies that the chemical similarity can be related to the biological activity of structures.In both cases that citation is to Johnson and Maggiora's (ed.) seminal work Concepts and Applications of Molecular Similarity.
That book is clear that they are not making new observations
about the association between molecular similarity and property
similarity. Indeed, the first sentence of the preface is
Applications that make use, either explicitly or implicitly, of the
concept of molecular similarity in chemistry are numerous, and indeed
lie at the heart of a significant body of chemical research.
The book is focused on the scientific applicability of molecular and
chemical similarity (it distinguishes between the two), with an
emphasis on the types of molecular similarity which can be automated,
the (as Maggiora, Vogt,
Stumpfe, and Bajorath comment in
cognitive algorithms by which medicinal chemists
perceive similarity are largely unknown.
Legal citations of the similarity principle
A point of my previous few essays was to add to the historical discussion in Johnson and Maggiora's book, with one essay on patents and the other on drug analogue laws. I'll end my series of legal quotes with a few citations using the similarity principle, drawn from US case law from before 1980, so well before Johnson and Maggiora. In the following, the bold emphasis is mine.
in re Hoch
It appears in the US the similarity principle is referred to as
re Hoch because of the Application of Paul E. Hoch, 428 F.2d 1341 (C.C.P.A. 1970):
Such actual differences in properties are required to overcome a prima facie case of obviousness because the prima facie case, at least to a major extent, is based on the expectation that compounds which are very similar in structure will have similar properties.
References to in re Hoch
This decision and summary is cited often in later judgments, as the following few examples show:
- Application of Payne, 606 F.2d 303, 203 USPQ 245 (CCPA 1979)
An obviousness rejection based on similarity in chemical structure and function entails the motivation of one skilled in the art to make a claimed compound, in the expectation that compounds similar in structure will have similar properties. In re Gyurik, 596 F.2d 1012, 1018, 201 USPQ 552, 557 (CCPA 1979); See In re May, 574 F.2d 1082, 1094, 197 USPQ 601, 611 (CCPA 1978); In re Hoch, 428 F.2d 1341, 1344, 57
- Application of Wilder, 563 F.2d 457 (1977)
Wilder's discovery of the absence of skin toxicity in the claimed compound does not end the inquiry, because one who claims a compound, per se, which is structurally similar to a prior art compound must rebut the presumed expectation that the structurally similar compounds have similar properties. In re Hoch, supra.
- Application of May, 574 F.2d 1082 (1978)
As alluded to by the court, the basis of the prima facie case of obviousness, at least to a major extent, is based on the presumed expectation that compounds which are similar in structure will have similar properties.
The Papesch Obviousness Regime
I found an essay titled
The law of obviousness of a chemical compound evolved from late nineteenth century structural obviousness case law that became highly defined in the 1940's and was modified in the early 1960's to provide a balanced two part analysis: The Examiner has the initial burden to establish prima facie orThat section of the essay is:structuralobviousness, but where this is established, it is up to the patent applicant to present rebuttal evidence demonstrating actual differences between the claimed compound and the prior art. See § II, The Papesch Obviousness Regime.
After a generation of uncertainty and then several years of challenges, Papesch3 became the core foundation for modern chemical obviousness practice, seemingly untouched by KSR.
Under the Papesch regime, obviousness of a new chemical compound proceeds through two stages. First, is there a prior art compound sufficiently close in structure to the claimed compound to suggest that the claimed structure would have the same properties? If the answer is negative, then the inquiry is completed: There is no obviousness for such a compound. But, as is particularly the case in a mature field, there is a high degree of predictability of properties of a compound keyed to structure, such that the disclosure of a prior art compound suggests that the claimed compound can and should be synthesized to achieve like results. Here, the claimed compound is prima facie obvious based upon the concept ofstructural obviousness. …
Which leads us to the Application of Viktor Papesch, 315 F.2d 381 (C.C.P.A. 1963)
The examiner's statements about the existence of a family of other properties common to the claimed compounds and the compound of the prior art finds support in the record, however, only on the basis of assumptions in turn based on assumedhomology.In his answer, the examiner cited a new reference, WertheimTextbook of Organic Chemistry(2d Ed.), page 37 (1945). From it he quoted the following statement about members ofany one homologous series:"These compounds have similar chemical traits, because their structures are closely related; therefore we can learn the chemistry of the entire group with no more effort than would otherwise be required to study a single compound."
… Wertheim, at the point from which the above quotation was taken, was discussing the samemethane series of hydrocarbonsas Fieser and Fieser. The examiner stopped his quotation just before the sentence reading,Of course we may anticipate certainWe are not here dealing with the methane series or with the type ofexceptionsto this general rule, but such exceptions will make very little trouble.homologywhich it illustrates.
We have had sufficient contact withhomologyon this court to agree with the examiner that such similarity in structure as exists here probably indicates similarity in some undisclosed properties; but we are past giving too much legal significance to the bare termhomolog,even where there is an admission of homology, as there appears to be here. The term is often used loosely. So far as we know, the assumed similarities referred to by the examiner are of little or no practical or commercial significance. Certainly he has pointed to none. On the other hand, the proven dissimilarity is a matter of pharmacological significance, on which the examiner would be quite willing to grant a patent if the invention were claimed as a process. As to the other properties, nothing in the record gives us any information, not even the Robins et al. reference.
Andrew Dalke is an independent consultant focusing on software development for computational chemistry and biology. Need contract programming, help, or training? Contact me
Copyright © 2001-2020 Andrew Dalke Scientific AB