Synthesis of Macrocyclic Hexaoxazole (6OTD) Dimers, Containing Guanidine and Amine Functionalized Side Chains, and an Evaluation of Their Telomeric G4 Stabilizing Properties

Abstract

Structure-activity relationship studies were carried out on macrocyclic hexaoxazole (6OTD) dimers, whose core structure stabilizes telomeric G-quadruplexes (G4). Two new 6OTD dimers having side chain amine and guanidine functional groups were synthesized and evaluated for their stabilizing ability against a telomeric G4 DNA sequence. The results show that the 6OTD dimers interact with the DNA to form 1:1 complexes and stabilize the antiparallel G4 structure of DNA in the presence of potassium cation. The guanidine functionalized dimer displays a potent stabilizing ability of the G4 structure, as determined by using a FRET melting assay (ΔTm = 14°C).

Solution Structure of an Intramolecular (3 + 1) Human Telomeric G-Quadruplex Bound to a Telomestatin Derivative

“…On the basis of our resolved structure of the HT-L2H complex, we believe that the second ligand molecule interacts with the Gtetrad core through π-stacking via the 3′ bottom G-tetrad. This finding would encourage the G-quadruplex ligand design strategy of Iida et al 39,60 to improve the binding affinity and selectivity using macrocyclic hexaoxazole dimers. Indeed, the second binding site (likely by stacking at the bottom tetrad) was also observed for the intramolecular G-quadruplex of HT when titrated with high concentrations of L2H (Figure S17D of the SI).…”

Macrocycles Are Great Cycles: Applications, Opportunities, and Challenges of Synthetic Macrocycles in Drug Discovery

“…G-Quadruplexes are involved in the structure and function of telomeres, in promoter gene regions of oncogenes, and in subsequent transcription. Stabilization of G-quadruplexes is a potential approach against cancer. , Hexaoxazole analogues of the natural product 94 (telomestatin, Figure ) were reported by Tera et al , Analogue 95 bearing cationic side chains displayed potent DNA sequence selectivity for the telo24 sequence, in sharp contrast to their neutral side chain analogues that were devoid of activity. A similar heptaoxazole analogue bearing only one side chain also bound strongly and selectively with the ss-telo24 sequence and induced a conformational change in the antiparallel G-quadruplex structure .…”

Evaluation of the Interaction between Long Telomeric DNA and Macrocyclic Hexaoxazole (6OTD) Dimer of a G-quadruplex Ligand

“…Synthesis of L2H2-6OTD dimer ( 3 ) is depicted in Scheme 1 . The Cbz group in diamine 4 [ 37 ] was selectively deprotected with hydrogen in the presence of Pd(OH) 2 , and the resulting amine was protected with a 2-nitrobenzenesulfonyl (Ns) group to give 5 in 69% yield from 4 . The diamine 5 was linked with 1,2-bis(2-iodoethoxy)ethane in the presence of potassium carbonate to give dimer 6 in 53% yield.…”

“…Consequently, various telomestatin-related macrocyclic polyoxazole compounds have been synthesized [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. We have independently developed macrocyclic hexaoxazole-type telomestatin derivatives of 6OTDs as G4 ligands, and some of them showed potent telomerase-inhibitory activity, as well as G4-stabilizing activity ( Figure 2 a) [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ].…”

“…, each telo24 unit in the long telomeric DNAs interacted with two molecules of L2H2-6OTD ( 2 ) in an end-stacking mode, and were induced to take anti-parallel-type topology, as shown in Figure 3 b [ 53 ]. Based on this schematic interacting model of L2H2-6OTD ( 2 ) with long telomeric DNAs, we expected that the dimer-type of 6OTD might more effectively stabilize the “flexible” long telomeric DNA by interaction of one molecule of 6OTD-dimer with each telo24 unit in a sandwich manner ( Figure 3 ) [ 36 , 37 , 38 ]. In the present work, we evaluated the interaction mode and efficacy of L2H2-6OTD-dimer ( 3 ) with long telomeric DNAs by means of electrophoresis mobility shift assay (EMSA), circular dichroism (CD) titration analysis, CD melting experiments and TRAP assay.…”