NMR regulatory analysis: determination and characterization of S-adenosyl-L-methionine in dietary supplements

1H NMR methodology is described for the determination and characterization of the dietary supplement S-adenosyl-L-methionine (SAM), recently introduced to the US market, utilizing a 400 MHz spectrometer without the need of pure reference standards. The developed methodology is able to assess chemical structure, differentiate between biologically-active (S)-diastereomer and biologically-inactive (R)-diastereomer, and determine the ratio of each in the dietry supplement formulation. The determination of the percentage of declared SAM was based on the integrals for the methyl proton of 2-methyl-2-propanol served as an internal standard at delta 1.24 and the methine proton H1' of SAM ribose ring at delta 6.06. The percentage of the active diastereomer was calculated from the relative intensities of the sulfonium methyl singlets corresponding to the major component (S)-diastereomer at delta 2.98 and the minor (R)-counterpart at delta 2.93. The accuracy was established by analyzing synthetic mixtures of the analyte and the internal standard. Excellent agreement was verified between the assay results and the quantities of analyte in the mixture. The mean +/- SD recovery values for SAM and its (R)-diastereomer impurity from a set of 10 synthetic mixtures were 99.6 +/- 0.8% and 22.5 +/- 0.1%, respectively. Using 10 lots, the percentage of SAM ranged from 0 to 110.7% of the declared value and the percentage of the active (S)-diastereomer ranged from 0 to 82.3%.