title: 4-amino-1H-benzo[g]quinazoline-2-one: a fluorescent analog of cytosine to probe protonation sites in triplex forming oligonucleotides.
abstract: We developed a new fluorescent analog of cytosine, the 4-amino-1H-benzo[g]quinazoline-2-one, which constitute a probe sensitive to pH. The 2'-O-Me ribonucleoside derivative of this heterocycle was synthesized and exhibited a fluorescence emission centered at 456 nm, characterized by four major excitation maxima (250, 300, 320 and 370 nm) and a fluorescence quantum yield of Phi = 0.62 at pH 7.1. The fluorescence emission maximum shifted from 456 to 492 nm when pH was decreased from 7.1 to 2.1. The pK(a) (4) was close to that of cytosine (4.17). When introduced in triplex forming oligonucleotides this new nucleoside can be used to reveal the protonation state of triplets in triple-stranded structures. Complex formation was detected by a significant quenching of fluorescence emission (approximately 88%) and the N-3 protonation of the quinazoline ring by a shift of the emission maximum from 485 to 465 nm. Using this probe we unambiguously showed that triplex formation of the pyrimidine motif does not require the protonation of all 4-amino-2-one pyrimidine rings.
authors.affiliation: INSERM U-386, IFR Pathologies Infectieuses, 146 rue Léo Saignat, Université Victor Segalen, 33076 Bordeaux Cedex, France.
authors.forename: F
authors.initials: F
authors.lastname: Godde
authors.forename: J J
authors.initials: JJ
authors.lastname: Toulmé
authors.forename: S
authors.initials: S
authors.lastname: Moreau
mesh_terms: D001483:Base Sequence; D003596:Cytosine / Q000031:analogs & derivatives*; D005456:Fluorescent Dyes; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D015345:Oligonucleotide Probes / Q000737:chemistry*; D011522:Protons; D011799:Quinazolines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: C415242:4-amino-1H-benzo(g)quinazoline-2-one; D005456:Fluorescent Dyes; D015345:Oligonucleotide Probes; D011522:Protons; D011799:Quinazolines; D003596:Cytosine