Benzo[X]quinoline (X = g or f: BQX) derivatives bearing bistrifluoromethyl and amine groups have been designed as push−pull-type fluorescent dyes. Through the synthesis of BQX derivatives from 2,7-diaminonaphthalene, lineartype (BQL) and angular-type (BQA) structural isomers were obtained. X-ray structures of single crystals from six given BQX derivatives revealed that the BQL and BQA series adopt planar-and bowl-shaped structures. In the fluorescence spectra, interestingly, the BQL series emitted in the near-infrared region over 700 nm in polar solvents. Based on the visible absorptions and base properties related to the amine moiety, the ammonia responsiveness was investigated using an ion-exchange reaction by the BQX-HCl salt. By exploiting the environmentally responsive fluorescence probe, cell imaging through confocal laser microscopy was conducted using HeLa and 3T3-L1 cells, emitting specific lipid droplets. The results indicate that BQX derivatives have multiple functions and may be applied in materials chemistry and biochemistry.

A chiral cyclic α,α-disubstituted α-amino acid, (S)-(−)-cucurbitine, which has a pyrrolidine ring with a chiral center at the α-position, was synthesized, and its homopeptides were prepared. (S)-(−)-Cucurbitine homopeptides with a Boc-protecting group formed helical structures with slight control of the helical screw sense to the left-handed form. The state of the pyrrolidine ring in (S)-(−)-cucurbitine was important for the control of the helical structures and helical screw sense of its homopeptides.

Helical peptide foldamer catalyzed Michael addition reactions of nitroalkane or dialkyl malonate to α,β-unsaturated ketones are reported along with the mechanistic considerations of the enantio-induction. A wide variety of α,β-unsaturated ketones, including β-aryl, β-alkyl enones, and cyclic enones, were found to be catalyzed by the helical peptide to give Michael adducts with high enantioselectivities (up to 99%). On the basis of X-ray crystallographic analysis and depsipeptide study, the amide protons, N(2)-H and N(3)-H, at the N terminus in the α-helical peptide catalyst were crucial for activating Michael donors, while the N-terminal primary amine activated Michael acceptors through the formation of iminium ion intermediates.

Small chiral organic molecules with CD properties are in high demanded due to their potential use in promising electronic and biological applications. Herein, we reveal a system in which the oxidation of a phosphino group to the corresponding phosphine oxide on the inner rim of a helicene derivative induces a CPL response. Laterally π-extended 7,8dihydro[5]helicenes bearing phosphine and phosphine oxide groups on their inner helical rims (i. e., the C1 position) were synthesized, and their helical structures were unambiguously determined by X-ray crystallography. The photophysical (UV/ visible and emission) and chiroptical properties of these compounds were investigated in various solvents. Despite their structural similarities, phosphine oxide showed a significantly better CPL response than phosphine, with a high dissymmetry factor for emission (j g lum j = (1.3-1.9) × 10 À 3 ) that can be attributed to structural changes in the interior of the helicene helix.

N-terminal thiourea-modified l-Leu-based peptide {(3,5-diCF 3 Ph)NHC(=S)-(l-Leu-l-Leu-Ac 5 c) 2 -OMe} with fivemembered ring α,α-disubstituted α-amino acids (Ac 5 c) catalyzed a highly enantioselective 1,4-addition reaction between β-nitrostyrene and dimethyl malonate. The enantioselective reaction required only 0.5 mol % chiral peptide-catalyst in the presence of i Pr 2 EtN (2.5 equiv.), and gave a 1,4-adduct with 93 % ee of an 85 % yield. As Michael acceptors, various β-nitrostyrene derivatives such as methyl, p-fluoro, p-bromo, and p-methoxy substituents on the phenyl group, 2-furyl, 2thiophenyl, and naphthyl β-nitroethylenes could be applied. Furthermore, various alkyl malonates and cyclic β-keto-esters could be used as Michael donors. It became clear that the length of the peptide chain, a right-handed helical structure, amide NÀ Hs, and the N-terminal thiourea moiety play crucial roles in asymmetric induction.