The first and facile total synthesis of thaxtomin A and its three stereoisomers has been achieved. The synthetic approach involves intramolecular nucleophilic cyclization of an amide toward a ketoamide group to produce a C-hydroxydiketopiperazine scaffold. The most amazing discovery was that each of the four stereoisomers of TA exhibits different phytotoxic, fungicidal, and antiviral activities.

Thaxtomins are a unique family of phytotoxins with unique 4-nitroindole and diketopiperazine fragments possessing potential herbicidal activities. This work presents the total synthesis of natural product thaxtomin C and its analogues. The extensive structure-activity relationship study screens four effective compounds, including thaxtomin A and thaxtomin C. It is indicated that 4-nitro indole fragment is essential for phytotoxicity, while benzyl and m-hydroxybenzyl substituents on the diketopiperazine ring are favorable for the efficacy. The N-methylations on indole and diketopiperazine show weak influence on the herbicidal activities. The four selected compounds show effective herbicidal activities against Brassica campestris, Amaranthus retroflexus, and Abutilon theophrasti, which are comparable or better than dichlobenil, even at a dosage of 187.5 g ha(-1). Moreover, these four compounds show good crop-selective properties to different crops and exhibit moderate protoporphyrinogen oxidase (PPO) enzyme inhibition. The antifungal results indicate that thaxtomin C displays inhibition to a wide range of fungi.

A highly efficient and convenient method for the construction of C‐hydroxydiketopiperazines has been developed using Lanthanum(III) triflate as a recyclable reagent. Microwave heating dramatically enhances the reaction rate without the epimerization of the existing chiral center in the substrate.

Microwave-Assisted Construction of C-Hydroxydiketopiperazines Using Lanthanum(III) Triflate. -A highly efficient and convenient method for the construction of C-hydroxydiketopiperazines is developed using Lanthanum(III) triflate as a recyclable reagent. Microwave heating dramatically enhances the reaction rate without the epimerization of the existing chiral center in the substrate. -(WANG, Q.-P.; ZHANG, H.-B.; NING, X.; HANG, H.; HUANG, Z.-L.; SONG, H.-R.; WANG, X.; WANG*, P. G.; Asian J. Org. Chem. 4 (2015) 2, 132-136, http://dx.