Enantioselective total synthesis, divergent optimization and preliminary biological evaluation of (indole-N-alkyl)-diketopiperazines.

The first enantioselective total synthesis of the antifungal natural product (indole-N-isoprenyl)-tryptophan-valine diketopiperazine 5 was accomplished. Four stereoisomers of 5 were intentionally prepared, and the (R, R)-isomer is more favorable in enhancing the antifungal bioactivity. Divergent structural optimization of this attractive model was conducted from the chiral pool amino acids. Fine-tuning of the structure protruded the broad-spectrum antifungal 6b, which also showed good preventative efficacy against Sclerotinia scleotiorum. Compound 5d could accelerate both hypocotyl elongation and root growth of Eclipta prostrata even at the concentration of <2.5 ppm. This unique and easily accessible scaffold will be of prime importance in achieving agrochemical candidates with the novel scaffold.