9.4 case comment

4 BSLR [2006/2007] : CASE COMMENT : JACKSON, WHITEHEAD AND KEMPNER : ON THE OTHER HAND: IS THIS THE LAST WORD ON PATENTING ENANTIOMERS? as a 50:50 mixture of the two enantiomers. Such mixtures are termed racemic mixtures or racemates. It is possible to separate the two enantiomers from a racemate by a process termed resolution, although doing so may be difficult.
The individual enantiomers of a chiral compound exhibit identical physical properties such as boiling points and react in an identical manner (and at identical rates) with non-chiral molecules. However, individual enantiomers differ in two key respects. First, they rotate the plane of polarised light in opposite directions: they are optically active. The direction in which the individual enantiomers rotate light is often notated by a (+) or (–) sign, meaning that light is rotated to the right and left respectively. Secondly, and importantly from the point of view of pharmaceutical chemistry, the reactions of the separate enantiomers with other chiral molecules are often dramatically different. Most drug targets within the human body (for example, proteins) are chiral. Consequently, if a The judgment of the Court of Appeal in H Lundbeck a/s v chiral drug is administered as a racemate, typically only one Generics UK Ltd and others1 may turn out to be the last word of the enantiomers will display the required pharmaceutical on the important issue of the patentability of individual activity, while the other may be inactive or may even display enantiomers. This is perhaps more likely to be the case than undesirable side effects. Consequently, the preference in it would usually be for a decision of the Court of Appeal, on recent times has been for chiral drugs to be prepared and account of Lord Hoffmann taking the highly unusual step of administered as a single enantiomer.
joining two Lord Justices of Appeal, Smith and Jacob LLJ, and giving the leading judgment. The interpretation and application of the law by these eminent judges cannot be faulted. Yet no chemist would hesitate to declare the result to A number of manufacturers of generic pharmaceuticals took action to revoke the patent. In the proceedings in the Patents The Danish pharmaceutical company Lundbeck invented a Court before Kitchin J,2 the claimants did not argue that the drug, citalopram, which is an anti-depressant in the class prior art disclosed the single enantiomer, escitalopram, but known as selective serotonin reuptake inhibitors. Lundbeck’s contended that the scope of claim 1 extended to the single patent for citalopram expired several years ago, since when enantiomer when present (in a 50:50 mixture with the other generic citalopram has been sold by a number of enantiomer) in the racemate. Lundbeck conceded the manufacturers. However, Lundbeck subsequently obtained the existence of a prior enabling disclosure of racemic citalopram, grant of a patent for the (+) or ‘S’ enantiomer of citalopram but contended that claim 1 of the patent was limited to the alone, generally known as escitalopram. This patent, EP(UK) single enantiomer in question, excluding the racemate.
0347066 (‘the patent’) claims not only a method for resolution Applying the approach to patent construction set out in of citalopram (claim 6), but also escitalopram itself and Kirin-Amgen,3 that is, what would a person skilled in the art pharmaceutical compositions containing it (claims 1 and 3).
understand the patentee to have used the language of the claim to mean, the judge, after hearing expert evidence, held that the patent claimed only the isolated enantiomer and that the racemate did not fall within claims 1 or 3. The attack on the A little background chemistry may be helpful. Certain grounds of anticipation therefore failed.
chemical compounds exhibit a property known as chirality, which means that they can exist in two molecular structures In their judgments on the appeal, both Lord Hoffmann and which are mirror images of each other, but are non- Lord Justice Jacob dismissed very swiftly any argument of lack superimposable (and therefore not identical). Many naturally of novelty, and agreed with Kitchin J that the skilled person occurring compounds are chiral but, unless special steps are would not have understood claim 1 of the patent to have taken during preparation, synthetic versions of them will exist encompassed the unresolved half of the racemate.
Kirin-Amgen Inc. v Hoechst Marion Roussel Limited [2005] 1 All ER 667.
Generics (UK) Limited and others v H. Lundbeck A/S [2007] EWHC 1040.
BIO-SCIENCE LAW REVIEW PUBLISHED BY LAWTEXT PUBLISHING LIMITED CASE COMMENT : JACKSON, WHITEHEAD AND KEMPNER : ON THE OTHER HAND: IS THIS THE LAST WORD ON PATENTING ENANTIOMERS? : [2006/2007] 4 BSLR mechanism that preserves stereochemistry (known as an SN2reaction) would be favoured. Ironically, it was these very rules The claimants also argued that the patent lacked an inventive that led to Kitchin J finding that the method was not obvious, step, because it was obvious to try to separate the a finding followed by Lord Hoffmann and Jacob LJ. This came enantiomers of citalopram, and at the priority date (1988) it about because Lundbeck’s expert witness, Professor Davies, was obvious to use the method of resolution disclosed in disagreed with Dr Newton’s interpretation of Baldwin’s Rules.
claim 6. The judge accepted that in 1988 it had been an In Professor Davies’ opinion, which was accepted by the obviously desirable aim to prepare and test the single judge, Baldwin’s Rules suggested that the desired reaction enantiomer, but then held that the fact that there was no was unfavourable, and would be expected to proceed instead known means to effect the separation meant that the product by the alternative SN1 reaction mechanism, in which stereochemistry is lost. As we now know, irrespective of what Baldwin’s Rules might have predicted, the desired reaction The method of claim 6 is not a direct resolution of the racemic clearly was favoured, because that is what happens, and it is mixture, but relies instead on the separation of the enantiomers of the precursor of citalopram (using the usual synthetic route) which is referred to as the diol, followed by Professor Davies eventually provided an explanation for his conversion of each enantiomer of the diol to citalopram ‘correct’ application of Baldwin’s Rules giving an incorrect separately. The judge held that the critical issue was whether prediction. However, that can hardly be relevant. If it takes it would have been obvious to the skilled person that the diol even Oxford’s Waynflete Professor of Chemistry two attempts could be converted to escitalopram without losing its to get the prediction right by applying Baldwin’s Rules, they stereochemistry. This particular issue was hotly disputed, are not going to be much help to the average addressee of the with each side’s experts disagreeing over the expectations of patent. That is the point. In the real world of the industrial the skilled person in 1988. Kitchin J agreed with the patentee, laboratory rather than the court room, the practical chemist is holding that the skilled person would have believed that the unlikely even to have bothered to think about Baldwin’s attempted conversion of the chiral intermediate to the final Rules. Separating enantiomers may be notoriously difficult, product would yield a racemic mixture, rather than the single but everyone knows that eventually it is going to be done. enantiomer (escitalopram). The attack on claim 6 on the It has long been well known that one way of making a grounds of obviousness therefore also failed.
single enantiomer of a compound is to start with a precursor that is already a single enantiomer, and then make the Jacob LJ had no hesitation in agreeing with Kitchin J’s finding desired compound from it in a way that preserves the of lack of obviousness, because he agreed that the skilled stereochemistry. If a resolution is proving particularly man would have had no expectation that the method of intractable, it must therefore be obvious to go back a step in resolution that was ultimately successful would have worked.
the synthetic route, and try separating the enantiomers of the Lord Hoffmann went into greater detail, but came to the same immediate precursor, in the present case the diol. The method conclusion. He made the point that although the diol was for the crucial reaction described in the patent uses known prior art, as was its conversion to citalopram, there was no reagents, and, above all, was very quick and easy to try, so the teaching of how to separate the enantiomers of the diol, nor average skilled chemist would have found it quicker and how to convert them into the individual enantiomers of citalopram. The separation could be achieved by known and tried methods, but the potential problem of the conversion to The principal reason for the judges all failing to find citalopram without loss of stereochemistry remained.
obviousness was their acceptance of the rather surprising Depending upon which of two types of reaction mechanism evidence of an eminent professor, who was rather more occurs, the stereochemistry may either be preserved to give a qualified than the intended addressee of the patent. However, single enantiomer, or lost to give the racemate. The generic they may still have come to the same conclusion on the basis manufacturers had accepted that no one would have known of the new test in Saint-Gobain,4 that has been followed in whether the method was going to work, but the opinion of cases such as Angiotech,5 which requires that for a result to their expert witness, Dr Newton, was that the reaction looked be obvious, it must be more or less self-evident that it will promising, so the skilled man would have tried it. In support work. The chemist might have looked at the question of this, Dr Newton said that the skilled man would have differently: to him it was obvious because he had no doubt known from guidelines set out in two papers by Sir Jack that one or other of the standard methods in his repertoire Baldwin (known as ‘Baldwin’s Rules’) that the type of reaction would work, and if the first one he tried didn’t, then he would Saint-Gobain v Fusion Provida [2005] EWCA Civ 177.
Angiotech Pharmaceuticals Inc. v Conor Medsystems [2007] RPC 20.
BIO-SCIENCE LAW REVIEW PUBLISHED BY LAWTEXT PUBLISHING LIMITED 4 BSLR [2006/2007] : CASE COMMENT : JACKSON, WHITEHEAD AND KEMPNER : ON THE OTHER HAND: IS THIS THE LAST WORD ON PATENTING ENANTIOMERS? have tried another until he found one that did. Prior to actually gets rather more than he has invented. First, such a Saint-Gobain the English Patents Court was sometimes claim will have the effect of covering all ways of making the thought to make it too easy to find obviousness. Now the product, including ways which may be inventive and quite Patents Court has become more friendly to patentees by different from the patentee’s route. Secondly, it would give going to the other extreme. Wherever the line for what is him a monopoly over all uses of the patented compound, obvious is drawn, strange results will sometimes emerge.
including uses that he has never thought of. However, Jacob LJ saw nothing wrong in the fact that compound claims may give a patentee ‘more than he deserves’, which, he considered, had not in practice proved to be much of a problem.
The final attack made by the generic manufacturers was that the product claims (1 and 3), which claimed escitalopram Once again, the chemist might find the judgment surprising.
however obtained, were far too broad to be supported by the In the case of the isolation of a naturally occurring compound disclosure and were therefore invalid for insufficiency. Kitchin for the first time (for example, from a plant) and the discovery J held that it was obviously desirable, as at 1988, to separate that such a compound has a useful pharmaceutical effect, it the enantiomers of citalopram. The inventive step was not in has long been accepted that if the relevant compound had not deciding to separate the enantiomers, but in finding a way it previously been known, the patentee would be entitled to an could be done. He then considered the House of Lords’ absolute monopoly of that compound and its use for any decision in Biogen v Medeva,6 in which Lord Hoffmann held purpose. The position is rather different when a single that the patent specification must enable the invention to be enantiomer is isolated from a racemic mixture. A patentee performed to the full extent of the monopoly claimed and that who has isolated a compound from a plant extract may have a patentee who has found a way of achieving an obviously little idea that any particular compound (among, possibly, desirable goal should not be permitted to monopolise every thousands present) will have any useful quality, whereas it other way of doing so. The patent does not teach any general was known that at least one of the two enantiomers present method of preparing the single enantiomers, other than by in racemic citalopram was an effective anti-depressant.
the single method described in claim 6. In consequence, Indeed, nobody, including the prospective patentee, knows whereas he held claim 6 to be valid, he found claims 1 and 3 a priori what compounds are even present in the plant extract, and even less what their structures are. By contrast, the fact that escitalopram was present in racemic citalopram was It was on the issue of sufficiency that the Court of Appeal known, its structure was known, and all of its properties were differed from Kitchin J’s decision, and upheld the validity of known except for the way in which it rotated a beam of the claims in the patent to escitalopram and pharmaceutical polarised light, and how it reacted with other chiral compositions containing escitalopram. It had generally been understood, not least by Kitchin J, that the principle of what has become known as ‘Biogen insufficiency’ has general applicability. Lord Hoffmann himself, however, explained that this was not so, and that, in general, a product claim is fully As we said in the opening paragraph, this may turn out to be enabled so long as one method of making that product is the last word on the patenting of enantiomers. However, the disclosed. Lord Hoffmann went on to explain that the position result may, in practice, not make much difference, because in Biogen itself had been different because the DNA molecule there will not be many cases in which the method used to for which the inventor had disclosed one method of resolve the racemate is not held to be obvious.
preparation, had previously existed, albeit not isolated but as A somewhat surprising consequence of the decision of the a mixture together with many other substances in people Court of Appeal in this case is that the patentee’s contribution suffering from hepatitis B. One could forgive Kitchin J for to the art (for the purposes of considering sufficiency) is not believing that the same reasoning applied in the present case, necessarily the same as the inventive step underlying a in which the product, namely escitalopram, was already patent. As Lord Hoffmann explained, if a product claim known and had previously existed, albeit as a mixture with its satisfies the requirements of section 1 of the 1977 Act, the technical contribution is the product and not the process Jacob LJ elaborated somewhat on the consequence that when by which it was made, even if that process was the only a patentee successfully has a product claim granted, then he BIO-SCIENCE LAW REVIEW PUBLISHED BY LAWTEXT PUBLISHING LIMITED CASE COMMENT : JACKSON, WHITEHEAD AND KEMPNER : ON THE OTHER HAND: IS THIS THE LAST WORD ON PATENTING ENANTIOMERS? : [2006/2007] 4 BSLR The requirements of section 1 include novelty and inventive known racemic mixture as being novel and inventive. The step, which probably explains the discrepancy between the enantiomer, he would say, has been known for years, and it judges’ conclusion and that of the chemist referred to in the has been sold by the ton, albeit as a 50:50 mixture with the opening paragraph. The average chemist would, we believe, other enantiomer. The law, however, is made by lawyers, and have some difficulty in regarding one of the enantiomers of a legal cases are argued and decided by lawyers.
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