Absent any unexpected advantages, a less-than-pure material in terms of the active component is an obvious variant of a corresponding pure material. Here, for example, the claimed “substantially pure” pharmaceutical compound that was 92–95% pure material was found to have been obvious because both a 50/50 mixture and the pure compound were known in the art when no unexpected advantages were shown over the prior art pure material. “[I]f the pure material is known, no reason has been shown why one would want to have an impure material.” This would be a good case to consult before responding to an obviousness rejection where the claimed composition falls within a range between two known but non-overlapping mixtures.
Background / Facts: The patent being asserted here in response to a generic drug ANDA submission is directed to pharmaceutical compositions of substantially pure levoleucovorin (e.g., 92–95% pure), which is used to ameliorate certain cancer treatment regimens. Due to an asymmetric C6 carbon, leucovorin naturally exists as a 50/50 mixture of two diastereoisomers, the (6S) and (6R) isomers. The (6S) diastereoisomer is also known as levoleucovorin or l-leucovorin, and is the isomer with the desired biological activity. The prior art discloses both the naturally occurring 50/50 mixture of isomers and a pure compound.
Issue(s): Whether the claimed “substantially pure” compound that is 92–95% pure material would have been nonobvious when both the 50/50 mixture and the pure compound were known in the art.
Holding(s): No. “[I]f the pure material is known, no reason has been shown why one would want to have an impure material. Although one may not be motivated to obtain an impure material and, in effect, it therefore can be argued to have been nonobvious—which is [the patentee’s] position here, that the 92–95% pure material was nonobvious over the known pure material—that position, despite its superficial appeal, is not persuasive. As the district court correctly decided, because the desirable properties of the prior art 50/50 mixture are attributable to only one component, and the slightly impure mixture—one that contains the substantially pure (6S) isomer in an amount of at least 92–95%—has not been shown to possess unexpected advantages over the prior art pure material, the less-than-pure material, and any others of similar concentration, cannot be found to have been nonobvious.”