TITLE:
Synthesis of Branch-Type Cyclophane Tetramers Having a Multivalently Enhanced Guest-Binding Ability
AUTHORS:
Osamu Hayashida, Chihiro Nada, Shuhei Kusano
KEYWORDS:
Cyclophane, Host-Guest Chemistry, Multivalent Effect
JOURNAL NAME:
Advances in Chemical Engineering and Science,
Vol.9 No.1,
January
23,
2019
ABSTRACT: A cationic branch-type cyclophane tetramer (1a) was synthesized by introducing three Boc-protected cyclophane derivatives into a N-acetylated tetraaza[6.1.6.1]paracy-clophane derivative as a core skeleton through DCC condensation, followed by removal of the external Boc-protecting groups. Cationic cyclophane tetramer 1a exhibited a high affinity toward an anionic and hydrophobic fluorescent guest, TNS, with binding constant of 4.8 × 105 M-1. This value of 1a was about 80-fold larger than that of the corresponding monomeric cyclophane for the identical guest, reflecting multivalent effect on the guest binding. As for electrostatic recognition, the obtained binding constant of 1a was one order of magnitude larger than that of an analogous
anionic cyclophane tetramer (1b) for the identical guest. These enhanced guest-binding abilities of 1a were easily evaluated by fluorescence titration experiments.