Cyclodextrin-Based Catenanes Platformed with meso-Arylporphyrin

Among mechanically interlocked supramolecular systems with cyclodextrins (CDs), successful examples of CD-based catenanes are limited compared to a number of CD rotaxanes owing to the synthetic difficulties. We herein demonstrate an efficient synthesis of a CD-based catenane using a meso-arylporphyrin (Por) platform. Using Por modified with two olefin-terminated oxyethylene chains at the cis-meso-positions, an interlocked Por-CD catenane was synthesized via olefin metathesis in the presence of per-O-methylated beta-CD (TMe-beta-CD) in water. The novel Por-CD catenane was obtained in 30 % isolated yield, which was characterized by MALDI-TOF mass and NMR spectroscopies. In the latter part, we demonstrate determination of the binding constants between TMe-beta-CD and meso-(4-sulfonatophenyl)porphyrin using Por-CD catenane, 2,6-di-O-methyl-beta-CD (DMe-beta-CD), and C-13-labeled TMe-beta-CD (C-13-TMe-beta-CD). The host-guest exchange reaction from the Por-CD catenane/DMe-beta-CD to the Por-CD catenane/TMe-beta-CD complexes was directly monitored through 1D HMQC spectroscopy. The ratio of these complexes revealed the difference in the binding affinities of DMe-beta-CD and TMe-beta-CD to Por. The stable 1 : 2 inclusion complex between meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and TMe-beta-CD has been well-studied for many years. This study is the first to determine the respective binding constants, K-1 and K-2, using the model system, to be 3.0x10(7) M-1 and 3.4x10(7) M-1, respectively.