Eastern Analytical Symposium. (Nov. 12-16, 2006, Somerset, NJ, USA)

Mechanisms that Determine the Stable-Isotopic Composition of the API, Topiramate:
Implications for Process Analytical Chemistry (PAC) and Patent Protection
John P. Jasper1, Robbe C. Lyon2, Larry E. Weaner3, and John M. Hayes4

1Molecular Isotope Technologies, LLC, 8 Old Oak Lane, Niantic, CT 06357-1815, USA;
2Division of Product Quality Research, CDER, FDA, Silver Spring, MD 20993-0002 USA;
3Johnson, Johnson Pharmaceutical Research and Development, L.L.C., PO Box 776, Welsh; and McKean Roads, Spring House, PA 19477-0776, USA; and,
4Woods Hole Oceanographic Institution, Accelerator Mass Spectrometry Lab, Woods Hole, MA 02543 USA.

The stable-isotopic composition of pharmaceutical materials derives from two sources of variation:  the natural stable-isotopic composition of the reagents and intermediates used and any isotopic fractionation that occurs during the synthesis process.  A recent study of the isotopic composition of a suite of archive samples of the Active Pharmaceutical Ingredient, Topiramate showed differences in isotopic compositions that varied based on the synthetic pathway by which they were produced [Jasper et al., 2005, J. Pharm. Biomed. Anal. 39:66-75].  To differentiate the contributing factors for the observed isotopic compositions a multi-stable isotopic (δ13C, δ15N, δ18O, δD) study of the reactants and reagents (acetone, fructose, sulfamide etc.), synthetic intermediate (diacetone fructose), and synthetic product (Topiramate) was performed.  For the synthetic pathways examined, both types of isotopic effects were observed.  We suggest that elucidation of these isotopic effects on the final composition of products may prove useful in monitoring industrial processes and (a.k.a., process consistency or Process Analytical Chemistry).   In some cases, understanding the source of isotopic variations may provide a quantitative method for process patent protection.