Challenges and trends in pharma NMR
Against a background where analysts in the pharmaceutical industry are increasingly looking for accurate, easy-to-use and scalable methods throughout the R&D, quality control (QC) and drug manufacture pipeline, nuclear magnetic resonance spectroscopy (NMR) has become established as a leading technique. NMR gives an unmatched breadth of information on the sample, including strikingly detailed structural elucidation. When properly implemented, the technique also offers straightforward method development, allows rapid throughput without destroying the samples used and, importantly, is a direct quantitative method with no requirement for response factors and calibration curves.
As regulators expect a company to know much more about their drug compounds – and to have this information early in the development process – NMR is now often used in parallel with mass spectrometry so that discovery and development scientists can access structural information and mass data at the same time.
In recent times, fluorine-containing compounds have become increasingly important. By 2011, more than 200 marketed medicines, and approximately one third of the most successful – so called, ‘blockbuster’ – drugs contained fluorine atoms in their structure (1). Moreover, around 40% of small molecules entering advanced (phase III) clinical trials in 2012 and 2013 were fluoro-organic compounds (2).
Fluorine chemistry is used in a wide variety of drug applications, including: antibiotics, antacids, antibiotics, anti-depressants, antihistamines, arthritis/anti-inflammatory agents and psychotropics, for example (3).
Consequently, the spotlight has fallen on the techniques used for the analysis of fluorine-containing pharmaceutical substances – including active pharmaceutical ingredients, branded and generic finished products.
Traditionally, NMR analysis is based on carbon (13C) and hydrogen (1H), however, fluorine (19F) NMR of fluorine-containing compounds can be very useful because of much higher 19F NMR sensitivity. 19F also has less risk of signal overlap due to its broad response range in comparison to 1H. Moreover, 19F NMR provides a wealth of detail, including the coupling (between fluorine nuclei and other atoms), and chemical shift data that provides the assignment of both the location and nature of fluorine atoms within a molecule.
We recently spoke with an NMR user who works on structural elucidation in the early development group at a major US-based pharmaceutical company. He explained the increasing need for a robust approach to fluorine detection: “Five years ago, we could see fluorine coming; today – with more than 50% of the new compounds that come to me from discovery being fluorinated – it’s in your face every day! Moving to my current lab around three years ago, I wanted to add a third channel to one of the existing spectrometers; in my opinion it’s an absolute requirement for modern pharma R&D.”
But 19F also exhibits some specific NMR properties that make it difficult to excite and decouple from other nuclei. Importantly, any new ‘multinuclear NMR spectroscopy’ approach, centred on 19F NMR, has lacked a robust routine HFX probe that could do every experiment well.
Modern NMR probes often allow easy, straightforward use of 19F NMR or 1H and 13C NMR, but not all three at the same time. Instrument manufacturers are continually working on new and innovative hardware and software to address such challenges and there is now a probe on the market with a dedicated matrix of complementary 1D and 2D NMR experiments. It offers the ability to manipulate the 1H, 19F, and 13C spins simultaneously without the typical loss in performance associated with traditional NMR probes designed for proton-fluorine NMR spectroscopy.
Talking about the evolution in instrument capabilities, the NMR user said: “We now have a hardware platform that allows us to do investigations that were never available before – and we have a library of well worked out experiments that just work right out of the box – so we are at the stage of exploring the new limits and defining best approaches. As a result, I expect to see significant new data, and new publications, coming out from my team in the coming months and years.”
Installing new NMR hardware should be a straightforward process – it’s a mature technique and the physical platform is solid and secure. Even adding automation to a set-up is now routine. But implementing new methodology can be more challenging, and the heart of the system – the control and data processing software – has become the vital component for a successful installation in practice.
Different manufacturers take dramatically different approaches to software architecture. Many users report that multi-instrument labs – or partners within a company that work at different sites – want to exchange results, share optimized methods with minimum input at each individual system and do simple housekeeping tasks, such as using descriptive rather than numerical file names.
This NMR user summarises the impact of technological advances across the years: “We are spoilt by how far software has developed on the devices we use every day. Software systems are so intuitive, so easy to use. NMR instrument software – from all vendors – has a way to go to approach this modern state but, in my experience, the underlying architecture available from our NMR vendor gives us some significant advantages in terms of networkability and the ability to share method files in a multi-instrument set-up. In my experience, this is not a trivial matter.”
With fluorine established as a major elemental component in many new chemical entities coming through pharma R&D, scientists are again relying on NMR as a frontline analytical technique. Now, the introduction of unique technologies establishes an essential upgrade path for the rapid, straightforward analysis of these important new drug candidates.
1. Wang et al, Chem. Rev. 2014, 114, 2432-2506
2. Zhou et al, Chem. Rev. 2016, 116, 422-518
3. Fluoride Toxicity Research Collaborative (FTRC), Index of Fluorinated Pharmaceuticals http://www.slweb.org/ftrcfluorinatedpharm.html