Homologs, Isomers and Analogs

Abstract

Compounds standing in an adjacent homology relationship are often basis for a prima facie obviousness rejection. A classic definition of homology is found in In re Henze 181 F.2d 196, 200–01, 85 USPQ 261, 264 (CCPA 1950), quoted in Brenner v. Manson 383 U.S. 519, 148 USPQ 589 (1966) (discussed in H.A. Wegner, “Prima Facie Obviousness of Chemical Compounds”, 6 APLA Quart. J. 271 at 273 (1978)):

A homologous series is a family of chemically related compounds, the composition of which varies from member to member by CH₂ * * *. Chemists knowing the properties of one member would in general know what to expect in adjacent members.

In the Henze case, certain propoxymethyl-hydantoins were found obvious over corresponding ethoxymethyl-hydantoins. There have been numerous other cases where the change from one adjacent homolog to another has been held obvious, but this alone is not conclusive if there is no motivation to make a change of any kind, as seen from In re Stemniski, 444 F.2d 581, 170 USPQ 343 (CCPA 1971), In re Lalty, 747 F.2d 703, 223 USPQ 1257 (Fed. Cir. 1984).