NMR spectrometry isotopic fingerprinting: a tool for the manufacturer for tracking active pharmaceutical ingredients from starting materials to final medicines.

In the frame of increasingly stringent quality assessment required by the regulators, the pharmaceutical industry has to face increasingly sophisticated counterfeiting practices. Counterfeits based on deliberate copying of processes or on the infringement of current patents for generic medicines are not straightforward to detect, unless the molecular probe is the active molecule itself. In this context, impurity profiling is limited. A tool based on the determination of intramolecular isotopic profiles has been developed to provide manufacturers of APIs (Active Pharmaceutical Ingredients) with a new solution to meet this double requirement. Stable isotope analyses by NMR gives direct access to site-specific isotope content at natural abundance. In this report, it is shown how both ²H and ¹³C NMR spectrometry can provide complementary and valuable information that could be applied to link APIs to their manufacturing source. Isotopic ¹³C NMR offers additional benefits over ²H NMR in using robust adiabatic polarization transfer methods, leading to a tremendous reduction in experimental time. Two approaches are illustrated. Firstly, the use of ²H and single pulse ¹³C NMR spectra obtained on 20 commercial ibuprofen samples from different origins show that this combined strategy leads to (i) a unique intramolecular isotope identification and (ii) a preliminary classification of the samples according to the synthetic pathways of the main industrial processes. An approach employing polarization transfer methods applied to 11 commercial naproxen samples, for which ²H and single pulse ¹³C NMR spectra are not exploitable and/or are not accessible in reasonable time. The relative and partial intramolecular ¹³C distribution obtained on naproxen by applying this methodology is sufficiently informative to allow the same conclusions as for ibuprofen. The additional benefits that these approaches should bring to API manufacturers are discussed.

Isotopic finger-printing of active pharmaceutical ingredients by 13C NMR and polarization transfer techniques as a tool to fight against counterfeiting.

The robustness of adiabatic polarization transfer methods has been evaluated for determining the carbon isotopic finger-printing of active pharmaceutical ingredients. The short time stabilities of the adiabatic DEPT and INEPT sequences are very close to that observed with the one pulse sequence, but the DEPT long time stability is not sufficient for isotopic measurements at natural abundance or low enrichment. Using the INEPT sequence for (13)C isotopic measurements induces a dramatic reduction in the experimental time without deterioration in short time or long time stability. It appears, therefore, to be a method of choice for obtaining the isotopic finger-print of different ibuprofen samples in a minimum time. The results obtained on 13 commercial ibuprofen samples from different origins show that this strategy can be used effectively to determine (13)C distribution within a given molecule and to compare accurately differences in the isotopic distribution between different samples of the given molecule. The present methodology is proposed as a suitable tool to fight against counterfeiting.

ZrCl4-promoted halogen migration during an electrophilic amination of halogenated phenols.

An electrophilic amination of halogenated phenols with diisopropyl diazenedicarboxylate in the presence of ZrCl4 as a Lewis acid, accompanied by a halogen migration, was demonstrated for the first time; the fluorine, chlorine, bromine, or iodine atom migrated during the amination process under mild reaction conditions.