title: Highly fluorescent guanosine mimics for folding and energy transfer studies.
abstract: Guanosines with substituents at the 8-position can provide useful fluorescent probes that effectively mimic guanine residues even in highly demanding model systems such as polymorphic G-quadruplexes and duplex DNA. Here, we report the synthesis and photophysical properties of a small family of 8-substituted-2'-deoxyguanosines that have been incorporated into the human telomeric repeat sequence using phosphoramidite chemistry. These include 8-(2-pyridyl)-2'-deoxyguanosine (2PyG), 8-(2-phenylethenyl)-2'-deoxyguanosine (StG) and 8-[2-(pyrid-4-yl)-ethenyl]-2'-deoxyguanosine (4PVG). On DNA folding and stability, 8-substituted guanosines can exhibit context-dependent effects but were better tolerated by G-quadruplex and duplex structures than pyrimidine mismatches. In contrast to previously reported fluorescent guanine analogs, 8-substituted guanosines exhibit similar or even higher quantum yields upon their incorporation into nucleic acids (Φ = 0.02-0.45). We have used these highly emissive probes to quantify energy transfer efficiencies from unmodified DNA nucleobases to 8-substituted guanosines. The resulting DNA-to-probe energy transfer efficiencies (η(t)) are highly structure selective, with η(t)(duplex) < η(t)(single-strand) < η(t)(G-quadruplex). These trends were independent of the exact structural features and thermal stabilities of the G-quadruplexes or duplexes containing them. The combination of efficient energy transfer, high probe quantum yield, and high molar extinction coefficient of the DNA provides a highly sensitive and reliable readout of G-quadruplex formation even in highly diluted sample solutions of 0.25 nM.
authors.affiliation: Institute of Organic Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
authors.forename: Anaëlle
authors.initials: A
authors.lastname: Dumas
authors.forename: Nathan W
authors.initials: NW
authors.lastname: Luedtke
mesh_terms: D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000528:radiation effects; D004735:Energy Transfer; D005456:Fluorescent Dyes / Q000737:chemistry*; D054856:G-Quadruplexes; D006801:Humans; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009841:Oligonucleotides / Q000737:chemistry; D055668:Photochemical Processes; D016615:Telomere / Q000737:chemistry; D013696:Temperature
chemical_list: D005456:Fluorescent Dyes; D009841:Oligonucleotides; D003849:Deoxyguanosine