Synthesis of a water-soluble 2,2'-biphen[4]arene and its efficient complexation and sensitive fluorescence enhancement towards palmatine and berberine.

Xiayang Huang,Tianxin Qian,Xinghua Zhang,Chunju Li,Junwei Ma,Lei Cui

doi:10.3762/bjoc.14.198

Abstract

A water-soluble 2,2′-biphen[4]arene (2,2’-CBP4) containing eight carboxylato moieties was synthesized and characterized. Its complexation behavior towards two alkaloids, palmatine (P) and berberine (B), was investigated by means of fluorescence and 1H NMR spectroscopy in aqueous phosphate buffer solution (pH 7.4). In the presence of 2,2’-CBP4, 1H NMR signals of P and B displayed very large upfield shifts, indicating the formation of inclusion complexes with strong binding affinities. Fluorescence titration experiments showed that P and B exhibited dramatic fluorescence enhancement of more than 600 times upon complexation with 2,2’-CBP4. Particularly, the fluorescence intensity is strong enough to be readily distinguished by the naked eye. Although the two guests have similar structures, the association constant of B with 2,2’-CBP4 (Ka = (2.29 ± 0.27) × 106 M−1) is 3.9 times larger than that of P (Ka = (5.87 ± 0.24) × 105 M−1).

Highlights

Host–guest chemistry in water is significantly important due to its extensive applications in biology, medicine, and environment
The chemical shifts for the middle protons, H1–6, and H10–11, are larger than those for the ending H7–9. These results indicate that berberine was engulfed by the cavity of 2,2’-CBP4 to form a pseudorotaxane-type inclusion complex
We have synthesized a water-soluble 2,2’biphen[4]arene, 2,2’-CBP4, for the first time and studied its complexation towards two alkaloid guests, P and B. 1H NMR and fluorescence results indicate the formation of inclusion complexes with strong stability

Summary

Introduction

Host–guest chemistry in water is significantly important due to its extensive applications in biology, medicine, and environment. Our group demonstrated a direct host–guest complexation-based drug delivery system for oxaliplatin by carboxylatopillar[6]arene [36]. We wish to report the synthesis of the first watersoluble 2,2’-biphen[4]arene bearing multiple carboxylato moieties, 2,2’-CBP4 (Scheme 1), and its binding behavior and fluorescent spectrum characteristic towards two alkaoilds, palmatine (P) and berberine (B), in water solution.

Results

Conclusion