Fluorescent and circular dichroic detection of monosaccharides by molecular sensors: bis[(pyrrolyl)ethynyl]naphthyridine and bis[(indolyl)ethynyl]naphthyridine

The push-pull conjugated molecules 2,7-bis-(1H-pyrrol-2-yl)ethynyl-1,8-naphthyridine (BPN) and 2,7-bis(1H-indol-2-yl)ethynyl-1,8-naphthyridine (BIN) adopting daad relays of proton donors (d) and acceptors (a) form multiple hydrogen-bonding complexes with various monosaccharides that possess complementary adda sequences. Although the free BPN emits blue light at lambda(max) = 475 nm in CH(2)Cl(2), its complexation with octyl beta-d-glucopyranoside gives green fluorescence at lambda(max) = 535 nm. The excellent photophysical properties make BPN a highly sensitive probe for monitoring glucopyranoside to a detection limit of approximately 100 pM. On the other hand, the CD-silent BIN molecule binds with monosaccharides to form the CD-active multiple hydrogen-bonding complexes, which exhibit the remarkable chirality dependent helicities consistent with the prediction by the ab initio approaches. On the basis of the similar daad cleft and hence the binding property, the fluorescence and CD absorption methods in BPN and BIN, respectively, are complementary, which, in combination with computational molecular modeling, not only give a detailed insight into the structures of the receptor-saccharide complexes in solution, but also differentiate octyl beta-d-glucopyranoside from its enantiomer and other monosaccharides.     

COMPLEXES OF 1,8-NAPHTHYRIDINES IX. GROUP VIb METAL CARBONYL COMPLEXES CONTAINING 1,8-NAPHTHYRIDINE, 2-METHYL-1,8-NAPHTHYRIDINE OR trans-DECAHYDRO-1,8-NAPHTHYRIDINE

Abstract

Complexes of the type M(CO)₅(N-N), M(CO)₄(N-N) and M(CO)₃(N-N)₂, where M is Cr, Mo or W and N-N is 1,8-naphthyridine(napy), 2-methyl-1,8-naphthyridine(2-mnapy) or trans-decahydro-1,8-naphthyridine(dhnapy), have been prepared and characterized by infrared and proton magnetic spectroscopy. Complexes of the type Mo(CO)₃(N-N)(napy), where N-N is 1,10-phenanthroline(phen), 2,2′-bipyridine(bipy), 2,9-dimethyl-1,10-phenanthroline(2,9-dmphen) or 2,7-dimethyl-1,8-naphthyridine (2,7-dmnapy), were also prepared and characterized by infrared spectroscopy. In these systems, the various naphthyridine donors exhibit the unique ability to behave as both mono- and bidentate ligands. The mode of bonding between the metal and heterocycles is determined by proton magnetic resonance data.     

Luminescence-based colorimetric discrimination of single-nucleotide transversions by the combined use of the derivatives of DOTA-conjugated naphthyridine and its terbium complex

We newly synthesized a nucleobase-binding ligand, ND-DOTA, in which 2-amino-5,7-dimethyl-1,8-naphthyridine (ND) was conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DOTA) via an amide linker, and found that its terbium(III) complex (ND-DOTA-Tb) showed green emission based on an energy transfer from the naphthyridine moiety to Tb³⁺. The blue emission of ND-DOTA was selectively quenched by adding abasic site-containing DNA duplexes that have pyrimidine bases opposite to the abasic site. In contrast, at the same excitation wavelength, ND-DOTA-Tb showed green emission independently of the bases opposite to the abasic site. Thus, a mixed solution of ND-DOTA and ND-DOTA-Tb enabled the luminescence-based colorimetric discrimination of single-nucleotide transversions with the naked eye at a single excitation wavelength.     

A highly selective Cd sensor of naphthyridine: fluorescent enhancement and red-shift by the synergistic action of forming binuclear complex

A new series of fluorophore derivatives from 1,8-naphthyridine have been developed. Compound D1 is the first naphthyridine PET sensor that can signal Cd²⁺ selectively with fluorescent enhancement and red-shift. A binuclear complex structure has been demonstrated in the D1-Cd²⁺ complex.     

2,7-Disubstituted proton sponges as borderline systems for investigating barrier-free intramolecular hydrogen bonds. Protonated 2,7-bis(trimethylsilyl)- and 2,7-di(hydroxymethyl)-1,8-bis(dimethylamino)naphthalenes

Protonated 2,7-bis(trimethylsilyl)- and 2,7-di(hydroxymethyl)-1,8-bis(dimethylamino)naphthalenes have been prepared and studied by a combination of X-ray crystallography at room and low temperatures, IR and NMR spectroscopic techniques in conjunction with quantum-chemical calculations. It was demonstrated that the intramolecular [NHN]⁺ hydrogen bond in the 2,7-bis(trimethylsilyl) system, being sterically compressed, is the shortest among all known aromatic diamine systems. Nevertheless, as it is evidenced by the primary ¹H/²H isotope effect, IR spectra and MP2 calculations, a double minimum potential for the proton motion still exists with a very low barrier estimated to be about 0.7 kcal/mol. An influence of a counter-anion on the NH proton involving the spatially hindered H-bond is also considered.     

Induction of a remarkable conformational change in a human telomeric sequence by the binding of naphthyridine dimer: inhibition of the elongation of a telomeric repeat by telomerase

The binding of a dimeric form of the 2-amino-1,8-naphthyridine derivative (naphthyridine dimer) to a human telomeric sequence, TTAGGG, was investigated by UV melting, CD spectra, and CSI-MS measurements. Both the 9-mer d(TTAGGGTTA) and the 15-mer d(TTAGGGTTAGGGTTA) showed apparent melting temperatures (T(m)) of 45.6 and 63.6 degrees C, respectively, in the presence of naphthyridine dimer (30 microM) in sodium cacodylate buffer (50 mM, pH 7.0) containing 100 mM NaCl. The CD spectra at 235 and 255 nm of the 9-mer increased in intensity accompanied with strong induced CDs at 285 and 340 nm upon complex formation with naphthyridine dimer. UV titration of the binding of naphthyridine dimer to the 9-mer at 320 nm showed a hypochromism of the spectra. A Scatchard plot of the data showed the presence of multiple binding sites with different association constants. Cold spray ionization mass spectrometry of the complex between naphthyridine dimer and the 9-mer clearly showed that one to three molecules of the ligand bound to the dimer duplex of the 9-mer. Telomeric repeat elongation assay showed that the binding of naphthyridine dimer to the telomeric sequence inhibits the elongation of the sequence by telomerase.     

Elaboration of 1,8‐naphthyridine‐2,7‐dicarboxaldehyde into novel 2,7‐dimethylimine derivatives

The known 1,8‐naphthyridine‐2,7‐dicarboxaldehyde was prepared by SeO₂ oxidation of 2,7‐dimethyl‐1,8‐naphthyridine. The dimethylated naphthyridine molecule was assembled from an adaptation of the Skraup synthesis using 2‐amino‐6‐methylpyridine and crotonaldehyde to afford a reproducible 37% yield, and constitute a significant advance over the literature of this reaction. The condensation of 1,8‐naph‐thyridine‐2,7‐dicarboxaldehyde with various primary amines (R = ‐C₆H₁₁, ‐CH₂C₆H₅, ‐C(CH₃)₃, ‐C₁₀H₁₅, and CH₂CH₂SCH₂CH₃) in alcohol affords diimines 1(a‐e) . The inherent crystallinity of 1(a‐e) affords pure compounds in reasonable to excellent yields (ca. 70%) after evaporation of solvent and recrystallization. The anticipated spectroscopic features of (N=C‐H) ¹H nmr shift and v(C=N) in the ir spectrum appear around 8.50 δ and 1640 cm^?1, respectively, for the series 1(a‐e) . These novel naph‐thyridines typically display the signature ¹H nmr doublets at ca. 8.15‐8.30 δ ascribed to the 3 and 4 naphthyridine protons, consistent with a mirror plane (through the quaternary carbons) perpendicular to the naphthyridine plane, and syn, syn relationships of the naphthyridine moiety with each imine nitrogen lone pair. Complexation studies of 1(a‐e) with transition metals of biological relevance such as copper(I) and copper(II) will be reported elsewhere.     

Coordination of 2-phosphorylalkyl-substituted 1,8-naphthyridines in complexes with lanthanide nitrates

The reaction of 2-phosphorylalkyl-substituted 1,8-naphthyridines, viz., 2-[2-(diphenylphosphoryl)propan-2-yl]-1,8-naphthyridine (L ¹ ) and 2-[2-(diphenylphosphoryl)ethyl]-1,8-naph-thyridine (L ² ), with lanthanide nitrates (Nd, Eu, or Lu) afforded complexes with the metal-to-ligand molar ratio of 1: 1 and 1: 2. Based on the IR and Raman spectroscopic data, it was found that the coordination of the ligands L ¹ and L ² in all complexes occurs through the P=O group and the nitrogen atoms of the naphthyridine moiety.     

Synthesis and characterization of new complexes of the type [Ru(CO)2Cl2 (2‐phenyl‐1,8‐naphthyridine‐kN) (2‐phenyl‐1,8‐naphthyridine‐kN′)]. Preliminary applications in homogeneous catalysis

Novel ruthenium (II) complexes were prepared containing 2‐phenyl‐1,8‐naphthyridine derivatives. The coordination modes of these ligands were modified by addition of coordinating solvents such as water into the ethanolic reaction media. Under these conditions 1,8‐naphthyridine (napy) moieties act as monodentade ligands forming unusual [Ru(CO)₂Cl₂(η¹‐2‐phenyl‐1,8‐naphthyridine‐ kN )(η¹‐2‐phenyl‐1,8‐naphthyridine‐kN′)] complexes. The reaction was reproducible when different 2‐phenyl‐1,8‐naphthyridine derivatives were used. On the other hand, when dry ethanol was used as the solvent we obtained complexes with napy moieties acting as a chelating ligand. The structures proposed for these complexes were supported by NMR spectra, and the presence of two ligands in the [Ru(CO)₂Cl₂(η¹‐2‐phenyl‐1,8‐naphthyridine‐ kN )(η¹‐2‐phenyl‐1,8‐naphthyridine‐kN′)] type complexes was confirmed using elemental analysis. All complexes were tested as catalysts in the hydroformylation of styrene showing moderate activity in N,N′‐dimethylformamide. Copyright © 2008 John Wiley & Sons, Ltd.     

Pd（OAc）2 catalyzed synthesis of heteroaryl-substituted 1,8-naphthyridine derivatives via C-N-coupling reactions of chloronaphthyridines

An efficient route to synthesize the heteroaryl-substituted 1,8-naphthyridine derivatives was described.Eight 2-heteroaryl-and 2,7-diheteroaryl-1,8-naphthyridine derivatives were obtained through palladium-catalyzed C-N-coupling reactions of chloro-naphthyridines with imidazole,benzimidazole,morpholine,3,5-dimethylpyrazole,and phthalimide in moderate to good yields.     

Fluorescent trimethyl-substituted naphthyridine as a ligand for C-C mismatch detection in CCG trinucleotide repeats

We report on the selective binding of 2-amino-5,6,7-trimethyl-1,8-naphthyridine (ATMND) to C-C mismatch present in the hairpin structures of (CCG)(n) trinucleotide repeats that are associated with neurological diseases; this binding is accompanied by significant fluorescence quenching of ATMND.     

Electrocatalytic Water Oxidation by a Dinuclear Copper Complex in a Neutral Aqueous Solution

Electrocatalytic water oxidation using the oxidatively robust 2,7‐[bis(2‐pyridylmethyl)aminomethyl]‐1,8‐naphthyridine ligand (BPMAN)‐based dinuclear copper(II) complex, [Cu₂(BPMAN)(μ‐OH)]³⁺, has been investigated. This catalyst exhibits high reactivity and stability towards water oxidation in neutral aqueous solutions. DFT calculations suggest that the O? O bond formation takes place by an intramolecular direct coupling mechanism rather than by a nucleophilic attack of water on the high‐oxidation‐state Cu^IV?O moiety.     

2,7-Bis(1H-pyrrol-2-yl)ethynyl-1,8-naphthyridine: an ultrasensitive fluorescent probe for glucopyranoside

[structure: see text] A push-pull conjugated molecule, 2,7-bis(1H-pyrrol-2-yl)ethynyl-1,8-naphthyridine (BPN), has been designed to bind selectively with octyl glucopyranoside (OGU). The BPN/OGU quadruple hydrogen-bonding complex adopts a rigid BPN conformation in which the proton donor (d) and acceptor (a) relays (daad) are resonantly conjugated through the ethynyl bridge, inducing pi-electron delocalization, i.e., a charge transfer effect. The excellent photophysical properties make BPN a highly sensitive probe for monitoring glucopyranoside to a detection limit of approximately 100 pM.     

Excimer kinetics in di(naphthyl)propane

The kinetics of excimer formation in 1,3-di(1-naphthyl)propane (DPN) in isooctane were investigated. Time-resolved fluorescence measurements carried out as a function of temperature and emission wavelength were successfully analysed in terms of a simple kinetic scheme, involving two ground state DNP conformations, an excimer and a contribution from photodimer formation.     

Synthesis and characterization of new π‐conjugated polymers containing 1,8‐naphthyridine in the main chain: Role of the 1,8‐naphthyridine unit in π‐conjugated polymers

Alternating π‐conjugated copolymers of 1,8‐naphthyridine‐2,6‐diyl ( 1,8‐Nap ) with 9,9‐dioctylfluorene‐2,7‐diyl ( P(Flu‐Ph‐1,8‐Nap) ) and 2,5‐didodecyloxy‐1,4‐phenylene ( P(ROPh‐Ph‐1,8‐Nap) ) have been synthesized by Pd‐catalyzed organometallic polycondensation. The copolymers showed UV‐vis absorption peaks at around 390 nm in o‐dichlorobenzene. The polymers were photoluminescent both in o‐dichlorobenzene and in the solid state. In o‐dichlorobenzene, the emission peaks of P(Flu‐Ph‐1,8‐Nap) and P(ROPh‐Ph‐1.,8‐Nap) appeared at λ_EM = 440 and 471 nm, with quantum yields of 87% and 66%, respectively. Electrochemical data revealed that 1,8‐Nap behaved as a typical electron‐accepting unit. When P(Flu‐Ph‐1,8‐Nap) was treated with 10‐camphorsulfonic acid, the emission peak shifted to λ_EM = 598 nm. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Extraction of lanthanides(III) by phosphorylated naphthyridine ligands from carbonate solutions

The extraction capacities and selectivities of 1,8-naphthyridine-based neutral organophosphorus reagents in extracting trivalent lanthanides (Ln, Nd, Ho, Yb) from carbonate solutions were studied. The length and nature of the linker between the naphthyridine and phosphoryl moieties were found to have considerable influence on the efficiency and selectivity of lanthanide extraction.     

Recognition of guanine-guanine mismatches by the dimeric form of 2-amino-1,8-naphthyridine.

Dimeric 2-amino-1,8-naphthyridine selectively binds to a G-G mismatch with high affinity (K(d) = 53 nM). We have investigated a binding mechanism of naphthyridine dimer 2 to a G-G mismatch by spectroscopic studies, thermodynamic analysis, and structure-activity studies for the thermal stabilization of the mismatch. 1H NMR spectra of a complex of 2 with 9-mer duplex d(CATCGGATG)2 containing a G-G mismatch showed that all hydrogens in two naphthyridine rings of 2 were observed upfield compared to those of 2 in a free state. The 2D-NOESY experiments showed that each naphthyridine of 2 binds to a guanine in the G-G mismatch within the pi-stack. In CD spectra, a large conformational change of the G-G mismatch-containing duplex was observed upon complex formation with 2. Isothermal calorimetry titration of 2 binding to the G-G mismatch showed that the stoichiometry for the binding is about 1:1 and that the binding is enthalpy-controlled. It is clarified by structure-activity studies that show (i) the linker connecting two naphthyridine rings was essential for the stabilization of the G-G mismatch, (ii) the binding efficiency was very sensitive to the linker structure, and (iii) the binding of two naphthyridines to each one of two Gs in the G-G mismatch is essential for a strong stabilization. These results strongly supported the intercalation of both naphthyridine rings of 2 into DNA base pairs and the formation of a hydrogen bonded complex with the G-G mismatch.     

A quadruply hydrogen bonded heterocomplex displaying high-fidelity recognition

An exceptionally strong quadruply hydrogen-bonded complex is formed between 2,7-diamido-1,8-naphthyridine 3 (DAN) and the butylurea of guanosine 6 (UG) in chloroform. The UG unit can be prepared in four steps from guanosine on a 10 g scale in excellent yields without chromatographic purification. The association constant (Kassoc approximately 5 x 10(7) M(-1)) for the UG.DAN complex determined by fluorescence energy transfer from the naphthyridine unit of 3 to coumarin 343 covalently linked UG (18) is among the highest reported for a neutral DNA base-pair analogue. The weak self-association of DAN (Kdimer < 10 M(-1)) and UG (Kdimer ca. 200-300 M(-1)) means that the UG.DAN complex forms with unparalleled fidelity.     

Enhancement of affinity in molecular recognition via hydrogen bonds by POSS-core dendrimer and its application for selective complex formation between guanosine triphosphate and 1,8-naphthyridine derivatives

We report that a polyhedral oligomeric silsesquioxane (POSS) core in a dendrimer can enhance the affinity of the molecular recognition via hydrogen bonds between 1,8-naphthyridine and guanosine nucleotides. The complexation of the naphthyridine ligands with a series of guanosine nucleotides was investigated, and it is shown that the POSS core should play a significant role in the stabilization of the complexes via hydrogen bonds. Finally, we demonstrate that the 1,8-naphthyridine ligand can selectively recognize guanosine triphosphate by assisting with the POSS-core dendrimer.     

New polynuclear carbonyl ruthenium (II) complexes derived from 1,8‐naphthyridine

This work shows the synthesis and characterization of new carbonyl complexes derived of 1,8‐naphthyridine. Covalently bonded complex can be successfully employed in building of supramolecular structures. Copyright © 2005 John Wiley & Sons, Ltd.