A special case takes place when a compound is an optically active enantiomer110 of a compound previously known only in racemic form. While some patent offices, such as EPO, have ruled that such enantiomers may be deemed novel, the existence of inventive step has been denied, since it is obvious that in such types of molecules optically active forms can exist and it is routine to test whether one or the other enantiomers in isolation is more active than the mixture of both (“racemic mixture”). Today, it is generally accepted that one optical isomer will typically have much higher activity than the other, so that superior activity for at least one of the isomers as compared to the racemate is to be expected111.
110 Enantiomers are chemical compounds which behave in relation to one another as an image does to its mirror image. In organic chemistry, enantiomers occur for example in compounds which comprise a carbon atom with four different substituents. See, e.g., Hansen and Hirsch, 1997, p. 113. It is estimated that over a quarter of known pharmaceuticals present that property. See, e.g., Cook, Doyle and Jabbari, 1991, p. 84.
111 See, e.g., Grubb, 1999, p. 199-200; Hansen and Hirsch, 1997, p. 113-118.