Low-field 1H NMR of Theanine: A High Concentration Amino Acid Supplement

The amino acid derivative γ-L-glutamylethylamide, also known as theanine, got this trivial name from its discovery in tea plants.^[1] Interesting fact - tea is solely the only plant where this ingredient has been found in so far.^[2] It is known for its relaxation effect in humans, proven by the measurement of brain waves after oral administration of theanine. Now, although such waves cannot be measured with the NMReady-60, no question that we can observe the ¹H NMR spectrum of theanine (Figure 1).

FIGURE 1. 1H NMR OF THEANINE IN D2O

As we recorded theanine in deuterated water, the acidic and basic protons scrambled with deuterium and their signals are not observed in the ¹H NMR spectrum anymore (for more details see our blog post: To D2O or not to D2O). With the J couplings and the integrals of the signals, the assignment can be done only with the 1D proton spectrum. The triplet ‘C’ at 1.17 ppm with a coupling constant of J_HH = 7.3 Hz is clearly connected to the quartet ‘B’ at 3.27 ppm with the same J coupling constant. The CH(CO)N signal ‘A’ is shifted downfield in comparison to the quartet ‘B’ due to the presence of a carbonyl function in the alpha position.

So, although we cannot (yet – who never knows what the future will bring) assign the interaction of theanine with receptors in the human brain with NMR spectroscopy, we can easily assign the ¹H NMR signals to the molecular structure of theanine.

References

^[1] Y. Sakato, J. Agri. Chem. Soc. 1949, 23, 262-267.
^[2]L. R. Juneja, D.-C. Chu, T. Okubo, Y. Nagato, H. Yokogoshi, Trends in Food Science & Technology 1999, 10, 199-204.