In Situ Monitoring of Competitive Coformer Exchange Reaction by ¹H MAS Solid-State NMR.

Area of Science:

• Pharmaceutical Science
• Solid-State Chemistry
• Materials Science

Background:

• Coformer exchange reactions are critical in pharmaceutical cocrystal research for enhancing stability.
• Understanding the mechanism of these reactions is vital to prevent product destabilization during processing and storage.
• 1H nuclear magnetic resonance (NMR) is a key technique for monitoring reaction dynamics.

Purpose of the Study:

• To investigate the mechanistic pathways of competitive coformer exchange reactions.
• To elucidate the influence of stoichiometry, temperature, and polymorphism on cocrystal formation.
• To monitor the in situ transformation of caffeine-based cocrystals during coformer exchange.

Main Methods:

• In situ monitoring of coformer exchange reactions using 1H magic angle spinning (MAS) solid-state NMR (SSNMR).
• High-speed MAS (60 kHz) was employed to capture dynamic changes.
• Reactions involved caffeine maleic acid cocrystals with glutaric acid and vice versa.

Main Results:

• Caffeine glutaric acid Form I was consistently formed as the end product.
• Metastable 1:1 caffeine glutaric acid Form I formed rapidly under centrifugal pressure when glutaric acid was added to 2:1 caffeine maleic acid.
• Stoichiometry significantly impacts the completeness of coformer replacement, with 1:1 stoichiometry ensuring full replacement of maleic acid.

Conclusions:

• The polymorphic transition of caffeine glutaric acid Form II to Form I at elevated temperatures drives the exchange reaction.
• Stoichiometry, temperature, and polymorphism are crucial factors governing competitive coformer exchange reactions.
• This study provides novel insights into reaction pathways, enhancing the understanding of cocrystal stabilization strategies.