Photodehydrocyclizations of stilbene-like compounds VIII: Synthesis of hexaheliceno[3,4-c]hexahelicene
The synthesis of a new double helicene, hexaheliceno[3,4-c]hexahelicene, has been described. Of two possible diastereomers only one has been obtained. Presumably the product has the racemic configuration but this assignment is not yet definite.
Reinvestigation of the photoreaction of 1,4-bis(2,4,6-triphenylpyridinio)benzene: Synthesis of a diazonia derivative of hexabenzoperylene by multiple photocyclization
Abstract The photo-induced oxidative cyclization of the 1,1′-p-phenylene-bis(2,4,6-triphenylpyridinium) was reinvestigated. While mono-cyclization was claimed to be the photoproduct in a previous report, it was found that the diazonia derivative of hexabenzoperylene can be formed as the final photoproduct by four-fold cyclization. The photoreaction affords one of the two possible stereoisomers (twisted and anti forms), and the stereostructure of the product is assigned to the twisted form by 1H NMR titration study with a chiral complexing reagent and by analysis of the absorption spectrum using TD-DFT calculations. The diazonia derivative of hexabenzoperylene exhibits yellow and red luminescence in the solution and solid states respectively and possesses well-separated four-reversible one-electron reduction potentials.
Calyculins and Related Marine Natural Products as Serine-Threonine Protein Phosphatase PP1 and PP2A Inhibitors and Total Syntheses of Calyculin A, B, and C
Calyculins, highly cytotoxic polyketides, originally isolated from the marine sponge Discodermia calyx by Fusetani and co-workers, belong to the lithistid sponges group. These molecules have become interesting targets for cell biologists and synthetic organic chemists. The serine/threonine protein phosphatases play an essential role in the cellular signalling, metabolism, and cell cycle control. Calyculins express potent protein phosphatase 1 and 2A inhibitory activity, and have therefore become valuable tools for cellular biologists studying intracellular processes and their control by reversible phosphorylation. Calyculins might also play an important role in the development of several diseases such as cancer, neurodegenerative diseases, and type 2-diabetes mellitus. The fascinating structures of calyculins have inspired various groups of synthetic organic chemists to develop total syntheses of the most abundant calyculins A and C. However, with fifteen chiral centres, a cyano-capped tetraene unit, a phosphate-bearing spiroketal, an anti, anti, anti dipropionate segment, an α-chiral oxazole, and a trihydroxylated γ-amino acid, calyculins reach versatility that only few natural products can surpass, and truly challenge modern chemists’ asymmetric synthesis skills.