{"id":9004111222139088,"date":"2026-02-11T09:33:45","date_gmt":"2026-02-11T09:33:45","guid":{"rendered":"https:\/\/www.hgf.com\/?p=9004111222139088"},"modified":"2026-03-18T15:15:01","modified_gmt":"2026-03-18T15:15:01","slug":"the-patentability-of-deuterated-pharmaceuticals-insights-from-the-epo-2","status":"publish","type":"post","link":"https:\/\/www.hgf.com\/knowledge-hub\/articles\/the-patentability-of-deuterated-pharmaceuticals-insights-from-the-epo-2\/","title":{"rendered":"The Patentability of Deuterated Pharmaceuticals: Insights from the EPO"},"content":{"rendered":"

Deuteration has emerged as a valuable strategy for tailoring the properties of pharmaceutical compounds.\u00a0 With its expanding role in drug development, it is important to consider how the European Patent Office (EPO) assesses the patentability of deuterated analogues of known compounds.\u00a0 This article examines the EPO\u2019s approach to the novelty and inventive step of such analogues, drawing on trends observed in both examination and opposition proceedings, and aims to provide guidance to applicants seeking to patent deuterated pharmaceuticals in Europe.<\/p>\n

Deuteration, also known as the \u201cdeuterium switch\u201d, refers to the substitution of protium (\u00b9H) for its heavier isotope, deuterium (\u00b2H, or D), within a molecular structure.\u00a0 Due to the strength of the C-D bond this modification can lead to improvements in a drug\u2019s pharmacological properties, pharmacokinetic profile, and toxicity.[1]<\/a><\/p>\n

Deuteration, therefore, represents a powerful tool not only for enhancing the properties of existing drugs but also for supporting the discovery and development of new pharmaceuticals.\u00a0 The deuterated drugs market size was valued at $368.6 million in 2024 and is estimated to reach $795.7 million by 2031.[2]<\/a><\/p>\n

However, as the field continues to expand, a pertinent question arises: To what extent are deuterated pharmaceuticals patentable?<\/strong><\/em><\/p>\n

This article addresses patentability issues of deuterated pharmaceuticals in Europe, where the non-deuterated parent compound already forms part of the state of the art.<\/p>\n

Although there is a lack of European case law regarding the patentability of deuterated pharmaceuticals, an analysis of the prosecution of several applications before the Examining Division (ED) of the EPO, along with two decisions by the more authoritative Opposition Division (OD), offers insight into the EPO\u2019s position and provides guidance for applicants seeking patent protection for deuterated compounds.[3]<\/a><\/p>\n

Novelty<\/u><\/em><\/p>\n

To be patentable before the EPO, a claimed invention must be both novel and inventive.<\/p>\n

A claimed deuterated compound will generally be deemed novel so long as the specific deuterated form was not publicly disclosed before the filing date of the patent application.<\/p>\n

It may be that a previously published patent application includes a general statement that aims to cover any deuterated analogue of a compound disclosed therein.\u00a0 Where the compound contains multiple positions that could be deuterated, such a general statement should not destroy the novelty of a subsequently claimed specifically deuterated analogue.\u00a0 However, if the compound has only a single possible site for deuteration, such a general statement may destroy the novelty of a compound deuterated at that position.<\/p>\n

Since deuterium occurs naturally at low abundance, trace amounts of various deuterated isotopologues will be present in a sample of the previously disclosed \u201cnon\u2011deuterated\u201d parent compound.\u00a0 Even if it were statistically likely that the sample contained a particular claimed deuterated compound, under EPO practice this would typically not constitute a novelty\u2011destroying disclosure, as such a sample would generally be treated as lacking any direct and unambiguous disclosure of that specific deuterated compound.<\/p>\n

Nevertheless, it remains good practice to include language in a patent specification to explain that a position designated as \u201cD\u201d in a chemical structure would be understood by a skilled person to be occupied by deuterium at an isotopic abundance above its natural level, followed by fallbacks that allow higher isotopic purities to be defined, e.g., greater than 50%, 90%, 95%, etc.<\/p>\n

Inventive step<\/u><\/em><\/p>\n

When assessing inventiveness, the EPO will consider what \u201ctechnical effect\u201d is achieved by a claimed deuterated compound over the closest prior art.\u00a0 The closest prior art will typically be a disclosure of the non-deuterated parent compound.\u00a0 In the majority of cases, such a technical effect is established by providing data demonstrating that the claimed compound offers some advantage over the parent compound.\u00a0 In the absence of such data, the EPO is likely to conclude that no technical effect is achieved and, consequently, that the claimed compound is an obvious alternative to the parent.\u00a0 For example, in EP 3810134 A1, CeleCor Therapeutics failed to provide data showing that the claimed deuterated RUC-4 (zalunfiban) derivatives offered any improvement over zalunfiban.\u00a0 As no technical advantage was demonstrated, the EPO could not recognise an inventive step.\u00a0 The application was subsequently withdrawn.<\/p>\n

Even if a technical effect is established, e.g., via the provision of data, the EPO will still ask whether such a technical effect would have been obvious in light of the prior art at hand and the skilled person\u2019s common general knowledge.\u00a0 The following cases illustrate how this assessment can vary depending on both the supporting data and the nature of the prior art landscape.<\/p>\n

EP 3713557 B1 (Sun Pharmaceutical Industries) was granted with claims directed to a pharmaceutical composition comprising D<\/em>-serine deuterated at the \u03b1-carbon:<\/p>\n

\"\"<\/a><\/p>\n

The application included data showing that this analogue retained similar in vitro<\/em> NMDA receptor binding affinity, while exhibiting advantageous pharmacokinetic properties and reduced nephrotoxicity, compared to non-deuterated D<\/em>-serine.<\/p>\n

The ED found the claimed compound to be inventive, noting that although it was well known at the time of filing that selective deuteration of bioactive compounds can, in some cases, improve safety, efficacy, or tolerability, the magnitude and occurrence of such benefits are inherently unpredictable<\/em>, requiring individual assessment<\/em>.\u00a0 In this case, the observed beneficial properties were deemed unpredictable and thus gave rise to an inventive step.<\/p>\n

This view was also shared by the OD in the opposition to Vertex Pharmaceuticals\u2019 patent EP 3352757 B1, relating to a second medical use of a deuterated ivacaftor analogue:<\/p>\n

\"\"<\/a><\/p>\n

The OD contended that while deuteration is a well-known strategy to reduce drug clearance and increase half-life, the effects of deuteration on a drug\u2019s metabolic profile are unpredictable<\/em> and must be evaluated on a case-by-case basis<\/em>. The OD therefore concluded that the skilled person would not have reasonably expected the claimed deuteration to improve ivacaftor\u2019s metabolic properties and pharmacokinetics, supporting the inventiveness of the claims.\u00a0 The opposition was ultimately dismissed.<\/p>\n

The EPO\u2019s reasoning in these two cases reflect its general approach to assessing the inventiveness of deuterated compounds, i.e. although it is widely recognised that deuteration can improve certain drug properties, whether any such improvement will in fact arise, and, if so, to what extent, remains inherently unpredictable and must therefore be evaluated on a case\u2011by\u2011case basis. \u00a0However, as the following decisions illustrate, the analysis can be more nuanced depending on the specific facts and evidence at hand.<\/span><\/p>\n

In EP 2326643 B1, Auspex Pharmaceuticals obtained protection for deutetrabenazine, the first FDA-approved deuterated drug.\u00a0 Structures of tetrabenazine and deutetrabenazine are provided below:<\/p>\n

\"\"<\/a><\/p>\n

The ED initially rejected a broader claim set covering all deuterated forms of tetrabenazine.\u00a0 They argued that it was speculative to assume that each claimed compound would exhibit reduced metabolic degradation based on data provided solely for deutetrabenazine.\u00a0 Since the claims covered compounds that had not been tested, the EPO did not recognise an inventive step across the entire claimed scope, particularly as the general strategy of reducing metabolic degradation through deuteration was already known in the art.<\/p>\n

In response, Auspex limited the claims to deutetrabenazine.\u00a0 They argued that deuteration near metabolic sites does not guarantee improved overall stability due to metabolic switching<\/em>.\u00a0 This is where reduced metabolism at one site is offset by increased metabolism elsewhere.\u00a0 Thus, improved overall metabolic stability due to deuteration could not be predicted for compounds like tetrabenazine with multiple known metabolic pathways.\u00a0 However, the data in the application showed that specifically deuterating the methoxy groups of tetrabenazine improved overall metabolic stability.\u00a0 The EPO found this evidence and argument to be persuasive and granted the patent.<\/p>\n

In a subsequent application, EP 2576552 A2, Auspex sought protection for dihydrotetrabenazine (HTBZ), an active metabolite of tetrabenazine, with the same methoxy deuteration as in deutetrabenazine.<\/p>\n

However, the ED cited an FDA publication on tetrabenazine, which identified the methoxy groups as the principal metabolic sites.\u00a0 The ED argued that, starting from HTBZ, a skilled person would have had a reasonable expectation that methoxy deuteration would improve metabolic stability.\u00a0 Auspex\u2019s arguments concerning metabolic switching were not found persuasive, and the claims were deemed to lack an inventive step.\u00a0 The application was subsequently withdrawn following a summons to oral proceedings and a negative preliminary opinion from the ED.<\/p>\n

A key distinction between these two cases is that, in the latter, prior art had identified that metabolic deactivation occurred primarily via the methoxy groups of tetrabenazine.\u00a0 Such prior knowledge of key metabolic pathways may therefore present a difficult inventive step hurdle to overcome.<\/p>\n

Janssen Pharmaceuticals obtained protection for d<\/em>1<\/sub>-JNJ38877605 in EP 3227296 B1:<\/p>\n

\"\"<\/a><\/p>\n

The compound is selectively deuterated at a key aldehyde oxidase metabolic site of the parent molecule.<\/p>\n

Data in the application showed that this deuteration led to the formation of fewer undesirable metabolites associated with renal toxicity.\u00a0 Crucially, the data also showed that the deuteration triggered a metabolic switch, resulting in increased formation of an active metabolite, thereby allowing a lower therapeutically effective dose to achieve the desired c-Met inhibitory effect.<\/p>\n

The ED concluded that this type of metabolic switch was not predictable from the prior art and therefore found d<\/em>1<\/sub>-JNJ38877605 to be inventive.<\/p>\n

This case highlights the unpredictability of metabolic switching triggered by deuteration.\u00a0 This unpredictability can support an inventive step, especially when the switch leads to a favourable effect, such as an increase in conversion to an active metabolite.<\/p>\n

A Hinova Pharmaceuticals application[4]<\/a> provided pharmacokinetic data for deuterated derivatives of defactinib.\u00a0 Some of these derivatives were shown to improve the half\u2011life of defactinib, whereas another derivative, comprising a different deuteration pattern, was found to adversely<\/em> affect its half\u2011life.<\/p>\n

This evidence supported Hinova\u2019s position that metabolic processes are complex, and that the effects of deuteration on a drug\u2019s pharmacokinetics are influenced by multiple interacting factors and therefore remain inherently unpredictable.\u00a0 The examining division agreed and found the deuterated derivatives that improved the pharmacokinetics of defactinib to be inventive.<\/p>\n

This case illustrates that \u201cnegative data\u201d can accentuate the unexpected nature of an improvement in a given property resulting from deuteration at a specific position.\u00a0 It is therefore advisable to include such data in a patent specification, if available.<\/p>\n

Immunomodulatory imide drugs (IMiDs), such as thalidomide, lenalidomide, pomalidomide, and avadomide, contain a chiral centre at the \u03b1-position relative to the carbonyl group of the glutarimide moiety.\u00a0 The hydrogen at this \u03b1-carbon chiral centre can be involved in enolization, which leads to interconversion between the sedative (R)-enantiomer and the teratogenic (S)-enantiomer.<\/p>\n

Deuteria Pharmaceuticals filed an application[5]<\/a> claiming pomalidomide deuterated at its chiral centre.\u00a0 The ED cited prior art demonstrating that deuteration at lenalidomide\u2019s chiral centre slows racemisation and concluded that it would have been obvious to apply the same strategy to pomalidomide.<\/p>\n

In 2018, DeuteRx\u2019s European patent EP 2943201 B1 was opposed. The granted patent claimed avadomide deuterated at its chiral centre:<\/p>\n

\"\"<\/a><\/p>\n

During opposition proceedings, the claims were limited to the (-)-enantiomer.\u00a0 The patent specification included data showing that the claimed compound was resistant to racemization at its chiral centre.\u00a0 Additionally, in vivo<\/em> data demonstrated that this compound was more effective at inhibiting tumour growth than both a racemic mixture of avadomide and the corresponding deuterated (+)-enantiomer.<\/p>\n

The opponent cited prior art on deuterated lenalidomide and thalidomide, arguing that deuteration at the chiral centre was known to slow racemization and favour the active enantiomer.<\/p>\n

However, the OD considered the claim to be inventive, stating that in vivo<\/em> efficacy cannot be reliably predicted and an improved absorption pattern does not necessarily translate into improved anti-tumour activity.\u00a0 They asserted that in vivo<\/em> effects result from a complex interplay of multiple factors, and may vary significantly even with small chemical modifications.\u00a0 Accordingly, the OD concluded that the in vivo<\/em> effect demonstrated for the claimed deuterated (-)-enantiomer constituted an inventive contribution over the prior art.<\/p>\n

The decision illustrates that in vivo<\/em> data demonstrating enhanced efficacy of a claimed deuterated compound may help establish inventiveness, even if it is known that deuteration might improve stability against stereochemical inversion or metabolism.<\/p>\n

Summary<\/u><\/em><\/p>\n

Deuterated derivatives of known pharmaceutical compounds are patentable in Europe.\u00a0 However, patentability must be assessed on a case-by-case basis, taking into account the available experimental data, the relevant prior art, and any preexisting knowledge regarding the lability of the parent compound.\u00a0 In light of the discussion above, key take-home points are as follows:<\/p>\n