2144.09 Close Structural Similarity Between Chemical Compounds (Homologs, Analogues, Isomers)
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This MPEP section is applicable to applications subject to the first inventor to file (FITF) provisions of the AIA except that the relevant date is the "effective filing date" of the claimed invention instead of the "time the invention was made," which is only applicable to applications subject to pre-AIA 35 U.S.C. 102.
I. REJECTION BASED ON CLOSE STRUCTURAL SIMILARITY IS FOUNDED ON THE EXPECTATION THAT COMPOUNDS SIMILAR IN STRUCTURE WILL HAVE SIMILAR PROPERTIES
A prima facie case of obviousness may be made when chemical compounds have very close structural similarities and similar utilities.
- “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.”
II. HOMOLOGY AND ISOMERISM ARE FACTS WHICH MUST BE CONSIDERED WITH ALL OTHER RELEVANT FACTS IN DETERMINING OBVIOUSNESS
Compounds which are position isomers (compounds having the same radicals in physically different positions on the same nucleus) or homologs (compounds differing regularly by the successive addition of the same chemical group, e.g., by -CH2- groups) are generally of sufficiently close structural similarity that there is a presumed expectation that such compounds possess similar properties.
Isomers having the same empirical formula but different structures are not necessarily considered equivalent by chemists skilled in the art and therefore are not necessarily suggestive of each other.
Homology and isomerism involve close structural similarity which must be considered with all other relevant facts in determining the issue of obviousness.
Homology should not be automatically equated with prima facie obviousness because the claimed invention and the prior art must each be viewed “as a whole.”
III. PRESENCE OF A TRUE HOMOLOGOUS OR ISOMERIC RELATIONSHIP IS NOT CONTROLLING
Prior art structures do not have to be true homologs or isomers to render structurally similar compounds prima facie obvious.
Compare In reGrabiak, (substitution of a thioester group for an ester group in an herbicidal safener compound was not suggested by the prior art);
IV. PRESENCE OR ABSENCE OF PRIOR ART SUGGESTION OF METHOD OF MAKING A CLAIMED COMPOUND MAY BE RELEVANT IN DETERMINING PRIMA FACIE OBVIOUSNESS
“[T]he presence—or absence—of a suitably operative, obvious process for making a composition of matter may have an ultimate bearing on whether that composition is obvious—or nonobvious—under 35 U.S.C. 103.”
“[I]f the prior art of record fails to disclose or render obvious a method for making a claimed compound, at the time the invention was made, it may not be legally concluded that the compound itself is in the possession of the public. In this context, we say that the absence of a known or obvious process for making the claimed compounds overcomes a presumption that the compounds are obvious, based on the close relationships between their structures and those of prior art compounds.”
It may be proper to apply “methodology in rejecting product claims under 35 U.S.C. 103, depending on the particular facts of the case, the manner and context in which methodology applies, and the overall logic of the rejection.”
V. PRESUMPTION OF OBVIOUSNESS BASED ON STRUCTURAL SIMILARITY IS OVERCOME WHERE THERE IS NO REASONABLE EXPECTATION OF SIMILAR PROPERTIES
The presumption of obviousness based on a reference disclosing structurally similar compounds may be overcome where there is evidence showing there is no reasonable expectation of similar properties in structurally similar compounds.
VI. IF PRIOR ART COMPOUNDS HAVE NO UTILITY, OR UTILITY ONLY AS INTERMEDIATES, CLAIMED STRUCTURALLY SIMILAR COMPOUNDS MAY NOT BE PRIMA FACIE OBVIOUS OVER THE PRIOR ART
If the prior art does not teach any specific or significant utility for the disclosed compounds, then the prior art is unlikely to render structurally similar claims prima facie obvious in the absence of any reason for one of ordinary skill in the art to make the reference compounds or any structurally related compounds.
Similarly, if the prior art merely discloses compounds as intermediates in the production of a final product, one of ordinary skill in the art would not ordinarily stop the reference synthesis and investigate the intermediate compounds with an expectation of arriving at claimed compounds which have different uses.
VII. PRIMA FACIE CASE REBUTTABLE BY EVIDENCE OF SUPERIOR OR UNEXPECTED RESULTS
A prima facie case of obviousness based on structural similarity is rebuttable by proof that the claimed compounds possess unexpectedly advantageous or superior properties.
However, a claimed compound may be obvious because it was suggested by, or structurally similar to, a prior art compound even though a particular benefit of the claimed compound asserted by patentee is not expressly disclosed in the prior art.
- It is the differences in fact in their respective properties which are determinative of nonobviousness.
- If the prior art compound does in fact possess a particular benefit, even though the benefit is not recognized in the prior art, applicant’s recognition of the benefit is not in itself sufficient to distinguish the claimed compound from the prior art.
