Microbial Biotransformation of 1-Methyl-L-tryptophan into Herbicidal Indole Alkaloids by Endophytic Fungus GGY-3.

Indole alkaloids are privileged secondary metabolites, and their production may be achieved by the microbial biotransformation of tryptophan analogues. By feeding 1-methyl-L-tryptophan (1-MT) into the culture of endophytic GGY-3, six novel (-) and seven known indole alkaloids (-) were generated. Their structures were elucidated by means of NMR spectroscopy, experimental electronic circular dichroism (ECD) spectra, and X-ray crystallography analysis. A Friedel-Crafts reaction was proposed as the key reaction responsible for the formation of the new compounds. Racemates and were separated into isomers by chiral HPLC, with their absolute configurations determined by X-ray and ECD calculation. Compounds , , and display good herbicidal activity against dicotyledon weed , of which and exhibited 88.50% and 100% inhibition rates on the radicle at 200 μg/mL, respectively, a similar effect compared to the positive control penoxsulam.