Cover Picture: Development of Chemical Probes for Functional Analysis of Anticancer Saponin OSW‐1 (Chem. Rec. 12/2019)

Abstract

This cover picture shows that an anticancer saponin OSW‐1 from Ornithogalum saundersiae was derivatized through site‐selective modification to provide a set of chemical probes for biological analysis. See the Personal Account by Rina Komatsu and Kaori Sakurai (DOI: 10.1002/tcr.201900042).

Redox‐Active Hydrocarbons: Isolation and Structural Determination of Cationic States toward Advanced Response Systems

“…Cations with azulene moieties, which are non-benzenoid aromatics, have been reported for a long time. [78][79][80][81][82] Ito et al reported the redox behavior of several derivatives with multiple azulene skeletons, and their electrochemical properties have been investigated in detail. [83,84] Upon one-electron oxidation of a seven-membered ring, a nonbenzenoid tropylium cation, which acquires Hückel aromaticity, is generated.…”

“…Azulene is a molecule of historical interest because of its abnormal photophysical properties; [76,77] it exhibits a deep blue color due to its narrow HOMO–LUMO energy gap and anti‐Kasha fluorescence from S 2 to S 0 . Cations with azulene moieties, which are non‐benzenoid aromatics, have been reported for a long time [78–82] . Ito et al.…”

Synthesis and Properties of Azahomocorannulenyl Cations and Radicals

“…The tropylium cation (C 7 H 7 + ; A ; Figure 1A), first discovered in 1891, [1,2] stands as a cyclic, planar molecule endowed with 6π electrons and a positive charge delocalized over the entire 7‐membered ring. According to the Hückel rule, this species is classified as aromatic and displays notable stability, as demonstrated by the isolation of stable tropylium compounds [3–7] . Despite their aromaticity, tropylium cations exhibit electrophilic reactivity as Lewis acids and oxidants, which has led to their utilization as catalysts and stoichiometric reagents in a diverse array of organic transformations [8,9] and as functional organic dyes/chromophores in material sciences [10–17] …”