The IQ Consortium reports on the current state of process analytical technology (PAT) for active pharmaceutical ingredient (API) development in branded pharmaceutical companies. The article uses an API process workflow (process steps from raw material identification through to finished API) to provide representative examples, including why and how the pharmaceutical industry uses PAT tools in API development. The use of PAT can improve R&D efficiency and minimize personnel hazards associated with sampling hazardous materials for in-process testing. Although not all steps or chemical processes are readily amenable to the use of the PAT toolbox, when appropriate, PAT enables reliable and rapid (real or near time) analyses of processes that may contain materials that are highly hazardous, transient, or heterogeneous. These measurements can provide significant data for developing process chemistry understanding, and they may include the detection of previously unknown reaction intermediates, mechanisms, or relationships between process variables. As the process becomes defined and understanding is gained through these measurements, the number of parameters suspected to be critical is reduced. As the process approaches the commercial manufacturing stage and the process design space is established, a simplification of the monitoring and control technology, as much as is practical, is desired. In many cases, this results in controls being either off-line, or if in situ control is required, the results from PAT are correlated with simple manufacturing measurements such as temperature and pressure.

In this paper we describe the development of a 5 mm NMR flow tube that can be used in a standard 5 mm NMR probe, enabling the user to conduct experiments on flowing samples or, more specifically, on flowing reaction mixtures. This enables reaction monitoring or kinetic experiments to be conducted by flowing reaction mixtures from a reaction vessel to detection in the coil area of the NMR, without the need for a specialized flow NMR probe. One of the key benefits of this flow tube is that it provides flexibility to be used across a range of available spectrometers of varying magnetic field strengths with a standard 5 mm probe setup. The applicability of this flow tube to reaction monitoring is demonstrated using the reaction of p-phenylenediamine and isobutyraldehyde to form the diimine product.

We report findings from the qualitative evaluation of nuclear magnetic resonance (NMR) reaction monitoring techniques of how each relates to the kinetic profile of a reaction process. The study highlights key reaction rate differences observed between the various NMR reaction monitoring methods investigated: online NMR, static NMR tubes, and periodic inversion of NMR tubes. The analysis of three reaction processes reveals that rates derived from NMR analysis are highly dependent on monitoring method. These findings indicate that users must be aware of the effect of their monitoring method upon the kinetic rate data derived from NMR analysis. Copyright © 2015 John Wiley & Sons, Ltd.

Detector response is not always equivalent between detectors or instrument types. Factors that impact detector response include molecular structure and detection wavelength. In liquid chromatography (LC), ultraviolet (UV) is often the primary detector; however, without determination of UV response factors for each analyte, chromatographic results are reported on an area percent rather than a weight percent. In extreme cases, response factors can differ by several orders of magnitude for structurally dissimilar compounds, making the uncalibrated data useless for quantitative applications. While impurity reference standards are normally used to calculate UV relative response factors (RRFs), reference standards of reaction mixture components are typically not available during route scouting or in the early stages of process development. Here, we describe an approach to establish RRFs from a single experiment using both online nuclear magnetic resonance (NMR) and LC. NMR is used as a mass detector from which a UV response factor can be determined to correct the high performance liquid chromatography (HPLC) data. Online reaction monitoring using simultaneous NMR and HPLC provides a platform to expedite the development and understanding of pharmaceutical reaction processes. Ultimately, the knowledge provided by a structurally information rich technique such as NMR can be correlated with more prevalent and mobile instrumentation [e.g., LC, mid-infrared spectrometers (MIR)] for additional routine process understanding and optimization.

On-flow ReactIR and (1)H NMR reaction monitoring, coupled with in situ intermediate characterization, was used to aid in the mechanistic elucidation of the N-chlorosuccinimide mediated transformation of an α-thioamide. Multiple intermediates in this reaction cascade are identified and characterized, and in particular, spectroscopic evidence for the intermediacy of the chlorosulfonium ion in the chlorination of α-thioamides is provided. Further to this, solvent effects on the outcome of the transformation are discussed. This work also demonstrates the utility of using a combination of ReactIR and flow NMR reaction monitoring (ReactNMR) for characterizing complex multicomponent reaction mixtures.