Aminoglycosylation can enhance the G-quadruplex binding activity of epigallocatechin

Abstract

With the aim of enhancing G-quadruplex binding activity, two new glucosaminosides (16, 18) of penta-methylated epigallocatechin were synthesized by chemical glycosylation. Subsequent ESI-TOF-MS analysis demonstrated that these two glucosaminoside derivatives exhibit much stronger binding activity to human telomeric DNA and RNA G-quadruplexes than their parent structure (i.e., methylated EGC) (14) as well as natural epigallocatechin (EGC, 6). The DNA G-quadruplex binding activity of 16 and 18 is even more potent than strong G-quadruplex binder quercetin, which has a more planar structure. These two synthetic compounds also showed a higher binding strength to human telomeric RNA G-quadruplex than its DNA counterpart. Analysis of the structure-activity relationship revealed that the more basic compound, 16, has a higher binding capacity with DNA and RNA G-quadruplexes than its N-acetyl derivative, 18, suggesting the importance of the basicity of the aminoglycoside for G-quadruplex binding activity. Molecular docking simulation predicted that the aromatic ring of 16 π-stacks with the aromatic ring of guanine nucleotides, with the glucosamine moiety residing in the groove of G-quadruplex. This research indicates that glycosylation of natural products with aminosugar can significantly enhance their G-quadruplex binding activities, thus is an effective way to generate small molecules targeting G-quadruplexes in nucleic acids. In addition, this is the first report that green tea catechin can bind to nucleic acid G-quadruplex structures.

Figure 1. Figure

1. Synthesis of glucosaminosides of EGC.

Figure 2. Synthesis of glucosaminosides of penta-methylated EGC.

Figure 3. ESI-TOF-MS spectra of telomeric DNA d[(TTAGGG)₄TTA] (Q) in the absence and presence of drugs.

Negative ESI-TOF-MS spectra of human telomeric DNA sequence d[(TTAGGG)₄TTA] were recorded under conditions of (A) without drug, (B) with quercetin, (C) with compound 16, (D) with compound 18, (E) with compound 14 and (F) with EGC. The inserts in spectra A and C are the enlargements of free G-quadruplex and complex ions with 1∶1 binding stoichiometry, respectively. The numbers in the inserts represent the number of ammonium ion adducts. Spectra were recorded with a molar ratio of DNA/drug of 1∶1 (C = 50 µM) in 50 mM ammonium acetate buffer (pH 7.6) containing 50% methanol.

Figure 4. Relative binding affinities of drugs with intramolecular human telomeric DNA G-quadruplex.

The numbers indicated on the top of each column showed the mean values from two determinations.

Figure 5. Molecular modeling of 16 binding with the human intramolecular telomeric G-quadruplex (PDB code: 1KF1).

Oxygen atoms are highlighted in red, nitrogen atoms in blue, phosphorus atoms in yellow and carbon atoms in beige.

Figure 6. Relative binding affinities of 16 and 18 with different intramolecular oncogene G-quadruplexes.

The experiments were conducted with a molar ratio of DNA/drug of 1∶1 (100 µM:100 µM) in 100 mM ammonium acetate (pH 7.6) containing 50% methanol. The numbers indicated on the top of each column showed the mean values from two determinations.

Figure 7. Relative binding affinities of drugs with intramolecular human telomeric RNA G-quadruplex.

The numbers indicated on the top of each column showed the mean values from two determinations.

Figure 8. Relative binding affinities of drugs with DNA and RNA G-quadruplex in competitive binding experiments.

The numbers indicated on the top of each column showed the mean values from two determinations.