Real time pharmaceutical reaction monitoring by electrospray ion mobility-mass spectrometry

Abstract

Reaction monitoring is a critical step in the synthesis of new drug entities, and many pharmaceutical companies spend significant resources on equipment and new methods to perform this task. The potential of electrospray ion mobility-mass spectrometry (ESI-IMMS) as a method for monitoring pharmaceutical reactions in real time is demonstrated with a reductive amination reaction that is commonly used in the synthesis of amines for drug discovery but poses problems for detection with current analytical instrumentation. Data were collected on the timescale of 300s and reaction completion time was determined by monitoring the starting, intermediate and product materials during the reaction. The detection limits for nicotinaldehyde (starting material 1), 4-picolylamine (starting material 2), and di-(2-picolyl)amine (the product) were 0.32, 0.10 and 0.05μM, respectively, with a linear dynamic range of more than 2 orders of magnitude for each analyte. Starting materials were not separated by their mobility in a nitrogen buffer gas, but could be separated in a buffer gas of carbon dioxide. In the nitrogen buffer gas, the reduced mobility (Ko) values for the reaction starting materials (nicotinaldehyde, 4-picolylamine, 4-pyridinementhanol) were 1.86cm2/Vs and the reduced mobility value for the product (di-(2-picolyl)amine) was 1.69cm2/Vs. In carbon dioxide the Ko values for the reaction starting materials were 1.43cm2/Vs and 1.38cm2/Vs for nicotinaldehyde and 4-picolylamine, respectively. The coupling of IMS to MS enabled the discovery of a hemiacetal complex forming between nicotinaldehyde and methanol, limiting the availability of nicotinaldehyde for the reaction. Thus use of IMS in conjunction with MS provided information about the reaction mechanism that would not have been possible with MS alone. The complexation prevented the formation of the intermediate species, presumably due to the formation of the hemiacetal from SM1; however, the intermediate species could be formed when the nicotinaldehyde concentration was increased by 10-fold. While either IMS or MS alone could be used to monitor this and similar reactions, the combined ESI-IMMS approach offered more complete information about the reaction, demonstrating potential as a rapid and selective technique to aid pharmaceutical process control.