Production of a novel tryptophan analog, β‐1‐indazole‐L‐alanine with tryptophan synthase of Escherichia coli

The tryptophan synthase alpha 2 beta 2 complex from Escherichia coli has been found to catalyze the beta-replacement reaction of L-serine with indazole, an indole analog which has a nitrogen atom at the 2-position (pyrazole ring). The reaction product was isolated and identified as beta-indazolealanine by mass spectrometric, elemental and NMR analyses. Careful assignment of 1H- and 13C-signals with several NMR techniques revealed that the beta-carbon of the product alanine moiety was bound to the 1-N-position of the indazole ring. This is the first example of the beta-replacement reaction catalyzed by tryptophan synthase occurring at any other position than the 3-position of indole analogs.