Fluorescence sensing and selective binding of L- and D-tryptophan-modified permethylated beta-cyclodextrins for aliphatic oligopeptides.

Two tryptophan-modified permethylated beta-cyclodextrins, 6I-L-Trp-6I-deoxy-2I,3I-di-O-methyl-hexakis(2II-VII,3II-VII,6II-VII-tri-O-methyl-beta-cyclodextrin (3) and 6I-D-Trp- 6I-deoxy-2I,3I-di-O-methyl-hexakis(2II-VII,3II-VII,6II-VII-tri-O-methyl)-beta-cyclodextrin (4), were synthesized, and their binding behaviors were investigated with the aliphatic oligopeptides, Leu-Gly, Gly-Leu, Gly-Pro, Glu-Glu, and Gly-Gly. Fluorescence spectrophotometric studies indicated that 3 and 4 can act as efficient fluorescence sensors for aliphatic oligopeptides. Due to their intermolecular co-inclusion binding mode with substrates, 3 and 4 not only afforded high binding constants of up to 10(3)-10(4) M(-1) for guest oligopeptides but also good molecular selectivities of up to ca. 7 for Gly-Gly/Leu-Gly and Glu-Glu/Gly-Gly pairs.