Motivation to resolve enantiomers – eszoplicone (LUNESTA)


On May 31, 2012, Judge Dennis M. Cavanaugh denied two competing summary judgment motions in a Hatch-Waxman proceeding involving Sunovian and Mylan, the drug eszoplicone (LUNESTA) and U.S. Patent Nos. 6,319,926, 6,444,673, 6,864,257 and 7,381,724. Although the motions were denied for failing to meet the legal test for summary judgment, the circumstances are somewhat unusual in that Sunovian was seeking to disprove the priority of one its own patent applications relative to that of the patents in suit.


In the early 1990’s Sunovian and Rhone-Poulenc Rorer (“RPR”) were each seeking to develop enantiomers of the racemic drug zoplicone. On January 17, 1991 RPR filed a French patent application generally related to (+) zoplicone (also known as eszoplicone) “essentially free” of the (-) enantiomer. The four patents asserted against Mylan all claimed priority back to this French application.

On December 1991, Sunovian filed a number of prophetic U.S. patent applications separately directed to (+) and (-) enantiomers of zoplicone. The Court characterized the circumstances behind the filing of these applications as follows:

In the late 1980s and early 1990s, Sunovian began individually evaluating racemic compounds. According to Sunovian, during this time it was the company’s practice to file “prophetic” patent applications on enantiomeric forms of racemic drugs that Sunovian believed could constitute improved drugs. Such prophetic patents were filed before the enantiomers of a given racemic compound were actually separated.


According to Sunovian, the simultaneous filing of the four patents was done because Sunovian did not know which isomer constituted an improvement over the racemate and had not yet resolved racemic zopiclone to make this determination.

In August 2000, one of Sunovian’s prophetic applications (the “Young ‘312 Application”) issued and was involved in an interference proceeding with the RPR applications.  Sunovian asked that an adverse judgment be entered against it and the Board of Patent Appeals and Interferences awarded priority to RPR’s application.  As part of the resolution of the interference, Sunovian agreed to acquire rights in the patent in suit from RPR for payments that have, according to the Court, exceeded more than $150 million.

Novelty – 35 U.S.C. § 102(g)(2)

Mylan had sought summary judgment on the basis that the Young ‘312 application demonstrates that Sunovian had invented eszoplicone essentially free of the (-) enantiomer in the United States before RPR’s invention was made on January 17, 1991.  Further, it argued that Sunovian had not abandoned, suppressed, or concealed its invention and had also exercised reasonable diligence in reducing its invention to practice.  In response, Sunovian disputed that the Young ‘312 Application enabled one skilled in the art to make the claimed invention, notwithstanding statements in the Young ‘312 Application that (+) zoplicone could be resolved by “conventional means”. Having determined that the evidence did not clearly and convincingly demonstrate which patent is entitled to priority, the Court denied Mylan’s motion for summary judgment.

The Court also denied Sunovian’s motion for summary judgment for a finding of no invalidity, holding that there were questions of material fact as to whether the inventors of the Young ‘312 Application had exercised reasonable diligence in reducing the invention to practice.

A copy of the summary judgment opinion may be found here.