A Tunable and Enantioselective Hetero-Diels-Alder Reaction Provides Access to Distinct Piperidinoyl Spirooxindoles.

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 sp3 -rich and highly substituted natural-product-based spirooxindoles supporting many chiral centers, including contiguous all-carbon quaternary centers.

Highly Enantioselective Catalytic Vinylogous Propargylation of Coumarins Yields a Class of Autophagy Inhibitors.

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.

Endophytes are hidden producers of maytansine in Putterlickia roots.

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.

Crystal structure and Hirshfeld surface analysis of 1-[(benzyl-dimethyl-sil-yl)meth-yl]-1-ethyl-piperidin-1-ium ethane-sulfonate.

The title mol-ecular salt, C17H30NSi+·C2H5O4S-, belongs to the class of a-amino-silanes and was synthesized by the alkyl-ation of 1-[(benzyl-dimethyl-sil-yl)meth-yl]piperidine using diethyl sulfate. This achiral salt crystallizes in the chiral space group P21. One of the Si-C bonds in the cation is unusually long [1.9075 (12) Å], which correlates with the adjacent quaternary N+ atom and was verified by quantum chemical calculations. In the crystal, the components are linked by weak C-H⋯O hydrogen bonds: a Hirshfeld surface analysis was performed to further investigate these inter-molecular inter-actions and their effects on the crystal packing.

Crystal structures of [Li7(i-PrO)3(C4H10NO)3]2O and [Na(i-PrOH)2(C8H18NO2)]2.

The title compounds, hexa-kis-[µ3-2-(di-methyl-amino)-ethano-lato]hexa-µ2-iso-propano-lato-µ4-oxido-tetra-deca-lithium(I), [Li7(i-PrO)3(C4H10NO)3]2O (1), and {3-[(2-meth-oxy-eth-yl)(meth-yl)amino]-1,1-dimethylpropano-lato}diiso-prop-an-o-lsodium(I), [Na(i-PrOH)2(C8H18NO2)] (2), were crystallized in the presence of 2-propanol (i-PrOH, C3H7OH). The structure 1 has monoclinic symmetry (C2/c) and the asymmetric unit contains half of the compound. Title compound 2 has triclinic symmetry (P ) and the asymmetric unit is half of an inversion-symmetric aggregate. Both compounds consist of an alkali metal, an amino-alkoxide and a 2-propanol compound. Furthermore, the dimeric sodium aggregate 2 is build up by hydrogen bonding through the 2-propanol and the alkoxides. Compound 1 does not exhibit hydrogen bonding, due to the fact that the 2-propanol is deprotonated. In compound 1, benzene appeared as co-crystallate, but was suppressed by solvent masking because of strong disorder. The formula mass and density do not take account of the solvent.

Synthesis and crystal structure of [Zn6Br4(C9H18NO)4(OH)4]·2C3H6O2.

The complete mol-ecule of the hexa-metallic title complex, namely, tetra-bromido-tetra-µ-hydroxido-hexa-kis-[µ-2-methyl-3-(pyrrolidin-1-yl)propan-2-olato]hexa-zinc(II) acetone disolvate, [Zn6Br4(C9H18NO)4(OH)4]·2C3H6O2, is generated by a crystallographic centre of symmetry. Two of the unique zinc atoms adopt distorted ZnO2NBr tetra-hedral coordination geometries and the other adopts a ZnO3N tetra-hedral arrangement. Both unique alkoxide ligands are N,O-chelating and both hydroxide ions are µ2 bridging. The crystal structure displays an O-H⋯O hydrogen bond between a µ2-OH group and an acetone solvent mol-ecule. The Hirshfeld surface has been calculated and is described.

Crystal structure of borated N,N,N',N'-tetra-methyldi-amino-methane.

In the title compound, {[(di-methyl-amino)-meth-yl]di-methyl-amine}-trihydridoboron, C5H17BN2, the tetra-hedral geometry of the N-C-N unit is slightly disorted. As a result of the bulky amine substituents, a wider N-C-N angle of 113.6 (1)° is observed. The bond lengths between the N atom and methyl groups are slighly elongated to 1.481 (2) and 1.482 (2) Šat the borated N atom, whereas the distances between the other N atom and its methyl groups are only 1.461 (2) and 1.462 (2) Å. The studied crystal was twinned. The twin data refinement was subsequently carried out with a scale factor of 0.263 (1). The two lattices of the twin domains were rotated by 179.84°.