Obviousness in Chemical Compound Patents

There is a very high standard set for patenting novel chemical compounds. If the compound sought to be patented is structurally similar to a prior art compound, the PTO does not have to also show that there is prior art that teaches that the claimed compounds will have the same or similar activity, according to In re Dillon. That case involved the patenting of tetraorthoesters and their use in lowering soot emissions when added to gasoline. The prior art showed TRIorthoesters and their use as dewatering agents (i.e. they help remove water from the gasoline). It just so happens that the tetraorthoesters are also capable of acting as dewatering agents. Even though that wasn’t the claimed utility, the claims were still rejected as obvious because they just so happened to share that utility – whether anyone knew it or not.

Apparently the court thinks that the difference between tetraorthoesters and triorthoesters is the sort of difference that amounts to “structural similarity”. The difference between them is that tetraorthoesters have a carbon atom attached to four carbons. Guess how many oxygens are attached to carbon in triorthoesters? Three. See how easy that is? They must be structurally similar after all.

The problem is that what might appear to be small differences between structures to the layman might actually make a huge difference in properties. On the other hand, differences in structure that appear very great to the layman might have no effect whatsoever on the properties.

For example – take structural homologs (i.e. merely inserting an extra CH2 group somewhere.) For a compound that has to fit into a tiny pocket in an enzyme, an extra carbon atom might mean the difference between great activity and no activity. On the other hand, making a drastic change to a group of atoms that is on the other end of the molecule may make no difference at all to the ability of the compound to bind to the enzyme.

In re Deuel dealt with DNA molecules. Although the facts that gave rise to the obviousness issue were different, the Federal Circuit suggested that changing base pairs in a DNA molecule is not the sort of change that amounts to a compound that is “structurally similar”.

Look here for another post related to enzymes: Synthetic Compounds Emulate Enzymes.