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March 15, 2004.


The opinion of the court was delivered by: RICHARD A. POSNER, Circuit Judge


Abbott Laboratories filed suit for patent infringement in 1997 against TorPharm, a manufacturer of generic pharmaceutical drugs, and affiliates of TorPharm unnecessary to discuss separately. 35 U.S.C. § 271(e)(2)(A). The district court granted summary judgment in favor of Abbott on both validity and infringement. 156 F. Supp.2d 738 (N.D. Ill. 2001). The Federal Circuit affirmed the validity of Abbott's patent but remanded for a trial on infringement. 300 F.3d 1367 (Fed. Cir. 2002). I was designated to conduct the trial pursuant to 28 U.S.C. § 291(b) — a bench trial, because Abbott is seeking only equitable relief. Indeed, it could not seek damages, because TorPharm has not yet begun to market its generic substitute for Abbott's product. The trial was conducted between February 23 and Page 2 February 27 of this year, and I now set forth my findings of fact and conclusions of law.

The patent (actually two patents, U.S. Patent Nos. 4,988,731 and 5,212,326, but they differ in only one material respect, discussed later, so in most of the opinion I shall treat them as one) is on a chemical called divalproex sodium, which Abbott sells under the trade name Depakote for the treatment of epilepsy and other ailments. The chemical formula is (C16H31NaO4)n, with the "n" signifying that the chemical unit is repeated n times. Divalproex sodium, the unit, is a combination, of a type commonly called a "complex," of two molecules, one of sodium valproate and the other of valproic acid. Each molecule contains valproate, an organic compound composed of carbon, oxygen, and hydrogen atoms, and it is the valproate that is responsible for the therapeutic properties of the drug. The other constituents of the complex — a sodium ion in the sodium valproate molecule and an extra hydrogen atom in the valproic acid molecule — do no therapeutic work. The chart at the end of this opinion ("Atwood 1" — a demonstrative exhibit used by Abbott's expert witness at the trial) contains a diagram of divalproex sodium and its constituent molecules (with the valproate itself designated "V") together with some of the other data referred to in this opinion.

  Although either sodium valproate or valproic acid would have all the therapeutic properties of divalproex sodium, neither is as easy to manufacture into pills — valproic acid because it is a liquid and sodium valproate because it is hygroscopic, that is, attracts moisture from the atmosphere, which makes it semi-liquid unless costly efforts are undertaken to remove the moisture from the atmosphere of the manufacturing plant. When sodium valproate and valproic acid combine to form divalproex sodium, however, the result is a nonhygroscopic, crystalline solid (powder or flakes) better suited for manufacturing into pills than either of its constituents.

  What holds the sodium valproate molecule to the valproic acid molecule? A normal atom has a neutral charge because it has the same number of protons and electrons and because the other atomic particle, the neutron, has no charge. An ion is an Page 3 atom that has a different number of protons and electrons and therefore carries a positive charge (if it has more of the former) or a negative charge (if it has more of the latter). The sodium atom in the sodium valproate molecule is a positively charged ion, because the oxygen in the valproate "steals" an electron from that atom. The ion is attracted to the (negatively charged) electrons in the oxygen atoms of the valproic acid molecule (see Atwood 1), bonding the two molecules.

  For reasons that have never been adequately explained, the patent examiner before whom Abbott prosecuted its patent application insisted that the patent claims include a specification of the chemical structure of divalproex sodium beyond what I have just described. Abbott obliged by claiming that divalproex sodium is an oligomer consisting of about 4 to 6 units of the divalproex sodium. In one of the patents, the number of units is not specified, but the parties make nothing of this; in effect they have agreed that if TorPharm's product contains no fewer than 4 and no more than 6 or 7 units, it infringes both patents.

  Just as the two molecules combine to form the divalproex sodium complex, so two or more of these complexes might join together to form a larger structure, such as a crystal, which might consist of millions or billions of identical units, whether atoms, molecules, or looser complexes. A polymer, usually a "soft" structure (many proteins are polymers) compared to a crystal, and usually classified as a molecule — although a very loosely bound polymer might instead be described as a "coordination polymer" — is an assemblage of a large number of smaller molecules. It is like a crystal (indeed sodium valproate, which is a crystal, was also described by one of the expert witnesses as a coordination polymer), but it needn't be solid and it will usually not be as extensive, although some proteins consist of thousands of lesser molecules.

  At the opposite extreme is a monomer. If the divalproex sodium complex — this bound pair of valproate molecules — does not have any discernible linkage with neighboring divalproex sodium complexes, so that a batch of divalproex sodium would be a loose mixture, like the grains of sugar in a teaspoonful of sugar (which is a mixture of sugar crystals — the mixture itself Page 4 having no structure, whether crystalline or otherwise), then di-valproex sodium is a monomer.

  An oligomer, as the name implies, is an assemblage of several rather than, as in the case of a polymer, many identical units, in this case divalproex sodium complexes. In other words, it is a small polymer. TorPharm's product must be an oligomer of about 4 to 6 units to infringe Abbott's product. Divalproex sodium in the solid state is a crystal, and a crystal is a structure of many repeating units, but it could be composed of oli-gomers loosely connected to each other to form the crystal. Alternatively, it could be composed of monomers, as I have already noted, or it could be a polymer; in either event it would not be infringing.

  TorPharm insists that to count as an oligomer the units constituting the aggregate in question must be connected "end to end" in the special sense of forming a row, rather than a circle or sphere or any other shape other than simple horizontality. There is no basis in the scientific literature, the patent itself, the proceedings before the patent office, or the Federal Circuit's opinion for so restrictive a definition.

  Although the exact structure of the divalproex sodium complex is, as I'll explain, unknown, the expert testimony indicates that each of the two molecules composing it has a "head" and a "tail." The tail is a chain of carbon and hydrogen atoms constituting part of the valproate; in the diagram at the end of this opinion, the tail is shown as the top layer of the upper molecule, the sodium valproate molecule, and the lower layer of the lower molecule, the valproic acid molecule. The "head" is mainly sodium and oxygen in the case of sodium valproate and oxygen and hydrogen in the case of the valproic acid molecule. Because sodium "loves" oxygen (chemists actually talk this way), and its affection is reciprocated, the heads of the two molecules want to nestle together. The carbon and hydrogen atoms in the tails are less passionately attracted to each other, but likes do sometimes attract (though sometimes repel, as when two particles have either a positive or a negative electrical charge), and so they want to be touching each other too. The tails of the two molecules composing the divalproex sodium Page 5 complex cannot touch each other, but each tail can touch a tail of an adjacent divalproex sodium complex. The affinities of the heads for one another and, perhaps as well (though the record is unclear on this point), the weaker affinities of the tails for one another bind the divalproex sodium complexes into an oli-gomeric structure. The heads and the tails are the ends of the divalproex sodium complexes, and so the complexes are connected "end to end," just not horizontally, and so satisfy the legal (patent office and Federal Circuit) and scientific definition of oligomer.

  The tails of the divalproex sodium complexes are larger than the heads. There are 44 atoms in the two tails (which incidentally are forked, as shown in the diagram), compared to only 8 atoms in the two heads. After the divalproex sodium complex has repeated itself four to seven times, the tails become as it were entangled and lose most of their ability to attract neighboring complexes, while after a certain point the crowding of sodium ions in the heads creates a repulsive force, since like-charged particles repel each other. Hence the oli-gomeric structure: a structure that peters out after a few repetitions of its constituent units. But remember that divalproex sodium is a crystal. Each tiny crystal (and the crystals are tiny, as we'll see, unlike a diamond, for example, which is a crystal of carbon) contains a large number of oligomers. Since a crystal has a definite and uniform structure, there must be some attractive force holding the oligomers in that structure, but it is weaker than the forces holding the units within each oligomer together.

  Such at least is Abbott's theory of why divalproex sodium is an oligomer rather than a polymer or a monomer. At the first round in the district court and before the Federal Circuit on appeal, TorPharm vigorously contested the validity of Abbott's patent, contending that divalproex sodium is not, as the patent claimed, an oligomer. But the Federal Circuit held unequivocally that divalproex sodium, or more precisely Abbott's divalproex sodium, is an oligomer. 300 F.3d at 1372, 1378. That is the law of the case, and it binds me. E.g., United States v. Husband, 312 F.3d 247, 250 (7th Cir. 2002). Page 6

  But the qualification (Abbott's divalproex sodium) is vital. Only if TorPharm's product, which is also divalproex sodium, is an oligomer is TorPharm infringing. Now one way in which TorPharm's product might not be an oligomer, even though it has the same chemical constituents as Abbott's, is that it might not consist of a 1:1 ratio of sodium valproate to valproic acid at the molecular level, that is, might not consist of paired molecules of sodium valproate and valproic acid. If its product consisted, say, of two sodium valproate molecules bound to one valproic acid molecule, it might not form up into an oligomer. But this issue too is foreclosed by the Federal ...

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