Strained-Cyclophane-Induced β-Turn Template:  Design, Synthesis, and Spectroscopic Characterization

Abstract

[structure: see text] Three tetrapeptides incorporating a 14-membered (R(i+1), S(i+2)) cycloisodityrosine at the i + 1 and i + 2 positions were designed and synthesized. Conformational analysis by (1)H NMR and CD spectra as well as molecular modeling indicated that they all adopt a beta-turn conformation. While the CD spectrum of compound 2 is characteristic of the typical type-II beta-turn (maximum at approximately 200 nm and a minimum at approximately 220 nm), that of 1a (atropisomer of 2) is opposite in sign to the expected spectrum of the type-II beta-turn.

Fluorescent Acridine-Based Receptors for H2PO4–

“…Fluorescent receptors have important applications in a wide range of areas such as supramolecular, synthetic, bioorganic, medicinal, and biological chemistry. − Processes such as protein binding to specific ligands or molecular recognition of DNA can be studied with the help of fluorescent systems. − The recognition of acids is an interesting field that has been widely investigated. − However, in most cases, the recognition event is based on the interaction between the hydrogen ions generated upon acid dissociation and the molecular receptor. A direct and specific interaction of the receptor with the corresponding conjugate base is often lacking in the recognition process.…”

Atropoisomerismo: o efeito da quiralidade axial em substâncias bioativas

“…A técnica de DC também pode ser utilizada em alguns casos para se determinar excesso enantio-ou diastereoisomérico de misturas atropoisoméricas 28,29 . Em estudos de indução de desracemização de derivados 2'-alquilóxi-2-carboxi-6-nitrobifenilas 22 e 23 através da formação de agregados em presença de surfactantes quirais 30 (Figura 10), Mancini e colaboradores utilizaram a técnica de DC para determinação do excesso enantiomérico formado após a quebra da emulsão.…”

Synthesis and NMR Studies on a C3-Symmetrical Triquinolina Triscationic Bicyclophane

“…Their NMR studies have been recently recorded . The synthesis and structures of several neutral cyclophanes, including tetrapeptides incorporating 14-membered-cycloisodityrosine moieties, and [6.6]- and [8.8]cyclophanes with 1,4-dioxabut-2-yne and 1,6-dioxahexa-2,4-diyne bridges have been reported . The synthesis and structural studies of some cationic cyclophanes were previously reported by Cabildo et al Other tetracationic species containing furan, thiophene, and benzo[ b ]thiophene-bridged macrocycles of 4,4‘-bipyridine were reported by Scheytza and Reissig .…”