Bisindole Alkaloids from the Alstonia Species: Recent Isolation, Bioactivity, Biosynthesis, and Synthesis

Bisindoles are structurally complex dimers and are intriguing targets for partial and total synthesis. They exhibit stronger biological activity than their corresponding monomeric units. Alkaloids, including those containing C-19 methyl-substitution in their monomeric units, their synthetic derivatives, and their mismatched pairs can be attractive targets for synthesis and may unlock better drug targets. We herein discuss the isolation of bisindoles from various Alstonia species, their bioactivity, putative biosynthesis, and synthesis. The total synthesis of macralstonidine, macralstonine, O-acetylmacralstonine, and dispegatrine, as well as the partial synthesis of alstonisidine, villalstonine, and macrocarpamine are also discussed in this review. The completion of the total synthesis of pleiocarpamine by Sato et al. completes the formal synthesis of the latter two bisindoles.

Benchmark ab initio stationary-point characterization of the complex potential energy surface of the multi-channel Cl + CH3NH2 reaction

We characterize the exothermic low/submerged-barrier hydrogen-abstraction (HCl + CH2NH2/CH3NH) as well as, for the first time, the endothermic high-barrier amino-substitution (CH3Cl + NH2), methyl-substitution (NH2Cl + CH3), and hydrogen-substitution (CH2ClNH2/CH3NHCl...

Crystal structure and Hirshfeld analysis of 3′-bromo-4-methylchalcone and 3′-cyano-4-methylchalcone

Two crystal structures of chalcones, or 1,3-diarylprop-2-en-1-ones, are presented; both contain a methyl substitution on the 3-Ring, but differ on the 1-Ring, bromo versus cyano. The compounds are 3′-bromo-4-methylchalcone [systematic name: 1-(2-bromophenyl)-3-(4-methylphenyl)prop-2-en-1-one], C16H13BrO, and 3′-cyano-4-methylchalcone {systematic name: 2-[3-(4-methylphenyl)prop-2-enoyl]benzonitrile}, C17H13NO. Both chalcones meaningfully add to the large dataset of chalcone structures. The crystal structure of 3′-cyano-4-methylchalcone exhibits close contacts with the cyano nitrogen that do not appear in previously reported disubstituted cyanochalcones, namely interactions between the cyano nitrogen atom and a ring hydrogen atom as well as a methyl hydrogen atom. The structure of 3′-bromo-4-methylchalcone exhibits a type I halogen bond, similar to that found in a previously reported structure for 4-bromo-3′-methylchalcone.

Benchmark ab initio characterization of the abstraction and substitution pathways of the OH + CH4/C2H6 reactions

We report benchmark ab initio stationary-point properties for the hydrogen-abstraction, hydrogen-substitution, and methyl-substitution pathways of the OH + CH4/C2H6 reactions.

Methyl substitution effects on the non-adiabatic dynamics of benzene: lifting three-state quasi-degeneracy at conical intersections

Time-resolved photoelectron spectra of benzene and its methyl-derivatives (toluene and o-xylene) measured with a vacuum-UV laser clearly reveal both fast (A → B → C → D) and slow (B → C′ → D) relaxation channels from the S2 state.

On single-electron magnesium bonding formation and the effect of methyl substitution

The complexes formed between MgX2 (X = F, H) molecules and alkyl radicals Y [Y = CH3, CH2CH3, CH(CH3)2, and C(CH3)3] have been characterized by using quantum chemical methods.