Amino Acid Synthesis through C-N Coupling between α-Ketoacids and Hydroxylamine from Nitrate Reduction

The artificial synthesis of amino acids is an important yet challenging subject. Electrocatalytic C-N coupling from organic acids and nitrogen sources provides an opportunity for this target but with the difficulty of C-N bond formation toward the production of amino acids. Herein, we report the synthesis of amino acids (alanine, glutamic acid, glycine, leucine, valine) from nitrate and alpha-ketoacids with a hybrid catalyst, cobalt phthalocyanine immobilized on carbon nanotubes (CoPc/CNT). The Faradaic efficiency for alanine production with CoPc/CNT is as high as 61%. The CoPc catalyst integrated with CNTs can catalyze nitrate reduction to hydroxylamine, which is switched from a thermodynamically uphill to a downhill process. The hydroxylamine intermediate attacks the alpha-carbon of an alpha-ketoacid to form an oxime. Amino acids are produced by the reduction of oximes catalyzed by CNTs. The bifunctionality of CoPc/CNT steers the tandem catalytic reaction toward the efficient production of amino acids in one pot. This work identifies that enhancing the reduction of nitrate to hydroxylamine is the key to C-N bond formation in amino acid synthesis.