Several recent studies have lent evidence to the fact that certain so-called plant metabolites are actually biosynthesized by associated microorganisms. In this work, we show that the original source organism(s) responsible for the biosynthesis of the important anticancer and cytotoxic compound maytansine is the endophytic bacterial community harbored specifically within the roots of Putterlickia verrucosa and P. retrospinosa plants. Evaluation of the root endophytic community by chemical characterization of their fermentation products using HPLC-HRMS(n), along with a selective microbiological assay using the maytansine-sensitive type strain Hamigera avellanea revealed the endophytic production of maytansine. This was further confirmed by the presence of AHBA synthase genes in the root endophytic communities. Finally, MALDI-imaging-HRMS was used to demonstrate that maytansine produced by the endophytes is typically accumulated mainly in the root cortex of both plants. Our study, thus, reveals that maytansine is actually a biosynthetic product of root-associated endophytic microorganisms. The knowledge gained from this study provides fundamental insights on the biosynthesis of so-called plant metabolites by endophytes residing in distinct ecological niches.

The active complexes of chiral N,N'-dioxide ligands with dysprosium and magnesium salts catalyze the hetero-Diels-Alder reaction between 2-aza-3-silyloxy-butadienes and alkylidene oxindoles to selectively form 3,3'- and 3,4'-piperidinoyl spirooxindoles, respectively, in very high yields and with excellent enantioselectivities. The exo-selective asymmetric cycloaddition successfully regaled the construction of sp -rich and highly substituted natural-product-based spirooxindoles supporting many chiral centers, including contiguous all-carbon quaternary centers.

A highly enantioselective copper-catalyzed vinylogous propargylic substitution has been developed. Aromatic and aliphatic propargylic esters react smoothly with substituted coumarins under mild reaction conditions to give the desired products with excellent yields and enantioselectivities. Subsequent single-step transformations enable the synthesis of a wide range of multifunctional and diverse compounds, and allow the efficient combination of different natural product fragments. Investigation of the obtained compound collection in cell-based assays monitoring changes in phenotype led to the discovery of a novel class of autophagy inhibitors.

A series of diverse heterocycles containing spirooxindole, isoxazoline/triazole, and isoxazole rings has been synthesized via an efficient three‐component reaction of (E)‐2‐(1‐propargyl‐2‐oxoindoline‐3‐ylidene)acetophenones 1, arylnitrile oxides 2, and arylazides 3 using Cu(I) as catalyst. The regiochemistry and stereochemistry of cycloadducts 4a and 5a have been confirmed by X‐ray diffraction studies. The heterocycles were screened against Gram‐positive and Gram‐negative bacteria and fungi. Several compounds exhibit moderate to excellent activities comparable to those of established standard drugs.

Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.