Synthesis and complexation properties of DTPA-N,N''-bis[bis(n-butyl)]-N'-methyl-tris(amide). Kinetic stability and water exchange of its Gd3+ complex

A novel DTPA-tris(amide) derivative ligand, DTPA-N,N'-bis[bis(n-butyl)]-N'-methyl-tris(amide)(H2L3) was synthesized. With Gd3+, it forms a positively charged [Gd(L3)]+ complex, whereas with Cu2+ and Zn2+ [ML3], [MHL3]+ and [M2L3]2+ species are formed. The protonation constants of H2L3 and the stability constants of the complexes were determined by pH potentiometry. The stability constants are lower than those for DTPA-N,N'-bis[bis(n-butyl)amide)](H3L2), due to the lower negative charge and reduced basicity of the amine nitrogens in (L3)2-. The kinetic stability of [Gd(L3)]+ was characterised by the rates of metal exchange reactions with Eu3+, Cu2+ and Zn2+. The exchange reactions, which occur via proton and metal ion assisted dissociation of [Gd(L3)]+, are significantly slower than for [Gd(DTPA)]2-, since the amide groups cannot be protonated and interact only weakly with the attacking metal ions. The relaxivities of [Gd(L2)] and [Gd(L3)]+ are constant between 10-20 degrees C, indicating a relatively slow water exchange. Above 25 degrees C, the relaxivities decrease, similarly to other Gd3+ DTPA-bis(amide) complexes. The pH dependence of the relaxivities for [Gd(L3)]+ shows a minimum at pH approximately 9, thus differs from the behaviour of Gd3+-DTPA-bis(amides) which have constant relaxivities at pH 3-8 and an increase below and above. The water exchange rates for [Gd(L2)(H2O)] and [Gd(L3)(H2O)]+, determined from a variable temperature (17)O NMR study, are lower than that for [Gd(DTPA)(H2O)]2-. This is a consequence of the lower negative charge and decreased steric crowding at the water binding site in amides as compared to carboxylate analogues. Substitution of the third acetate of DTPA5- with an amide, however, results in a less pronounced decrease in kex than substitution of the first two acetates. The activation volumes derived from a variable pressure (17)O NMR study prove a dissociative interchange and a limiting dissociative mechanism for [Gd(L2)(H2O)] and [Gd(L3)(H2O)]+, respectively.     

Synthesis of bis(bromomethyl) dimethyl crown ethers and complexation properties of their derivatives having electron-donating sidearms

Several bis(bromomethyl) dimethyl 15-crown-5, 18-crown-6, and 21-crown-7 were prepared according to two methods without protecting reactive bromo substituents. Cis and trans isomers of la are separated and the structures are inferred by considering the complexation property of their derivatives having electron-donating sidearms toward sodium and potassium cations.     

NMR relaxometric study of new Gd(III) macrocyclic complexes and their interaction with human serum albumin

Five novel Gd(iii) complexes based on the structure of the heptadentate macrocyclic 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) ligand have been synthesized and their (1)H and (17)O NMR relaxometric properties investigated in detail. The complexes have been functionalised on the secondary nitrogen atom of the macrocyclic ring with different pendant groups for promoting their ability to interact non-covalently with human serum albumin (HSA). The analysis of the proton relaxivity, measured as a function of pH and magnetic field strength, have revealed that the three complexes bearing a poly(ethylene glycol)(PEG) chain possess a single coordinated water molecule, whereas the complexes functionalised with 1-[3-(2-hydroxyphenyl)]-propyl and 1-[3-(2-carboxyphenyloxy)]-propyl pendant groups have two inner sphere water molecules. The water exchange rates, measured by variable temperature (17)O NMR, cover a broad range of values (from 18 to 770 ns) as a function of their charge, the chemical nature of the substituent and its ability to organize a second sphere of hydration near the water(s) binding site. All the complexes have shown some degree of interaction with HSA, with a stronger binding affinity measured for those bearing an aromatic moiety on the pendant group. However, upon binding the expected relaxation enhancement has not been observed and this has been explained with the displacement of the coordinated water molecules by the protein and formation of ternary adducts.     

Competitive binding affinity of two lanthanum(III) macrocycle complexes toward DNA and bovine serum albumin in water

In the present study, two water-soluble lanthanum(III) hexaaza Schiff base complexes were synthesized and characterized and also theoretically investigated. The interactions of these complexes with DNA and bovine serum albumin (BSA) were studied using different spectroscopic assessments and docking simulation analysis. The DNA docking studies suggested that these two complexes are able to interact with DNA through the minor groove, and also the binding affinity is in the order of La(L¹) > La(L²). Furthermore, the spectral titration was carried out and viscosity measurements were taken. In this regard, protein-binding studies revealed that these complexes quench the intrinsic fluorescence of BSA, and indicated that the possible binding site is located on the vicinity of Trp 213, which is further validated by docking simulation analysis. The in vitro anticancer activities of these complexes indicated that the La(L¹) complex is more effective than the other one and also exhibits a better interaction with DNA.     

Hetero-tripodal hydroxypyridonate gadolinium complexes: syntheses, relaxometric properties, water exchange dynamics, and human serum albumin binding

The synthesis and relaxometric properties of hetero-tripodal hydroxypyridonate-terephthalamide gadolinium (Gd(3+)) chelates with differing structural features for probing human serum albumin (HSA) interactions are reported. The Gd(3+) complexes are divided into two series. The first series (3-5) features a benzyl derivative connected to the hydroxypyridonate (HOPO) moiety. The second series of complexes (6-10) has the common feature of a poly(ethylene glycol) (PEG) attached to the terephthalamide (TAM) moiety and is nonbenzylated. The water exchange of the complexes is in the fast exchange regime with rates (k(ex)) in the range 0.45-1.11 x 10(8) s(-1). The complexes have a moderate interaction with HSA with association constants (K(A)'s) in the range 0.7-8.6 x 10(3) M(-1). Protein binding results in an enhancement in proton relaxivity from 7.7-10.4 mM(-1) s(-1) (r(1p)) to 15-29 mM(-1) s(-1) (r(1p)(b)). It is concluded that the interaction of the complexes with HSA (i) is enhanced by the presence of benzyl groups, (ii) is entropically driven, and (iii) results in a lower hydration number (q).     

Competition binding experiments for rapidly ranking lead molecules for their binding affinity to human serum albumin

Many lead molecules that have high affinity for a therapeutic target in vitro exhibit a reduced efficacy in vivo. Drug binding to human serum albumin is a major contributor to this reduction in potency, and many drug discovery programs expand significant resources preparing compounds that have decreased albumin binding. As rational and structure-based approaches have already been demonstrated to design compounds that have reduced affinity for albumin, the ability to rapidly and accurately assess protein binding will be valuable in lead optimization. This review will summarize some of the NMR-based efforts towards developing universal, rapid, accurate, and site-specific assays for estimating protein binding.     

Prediction of human serum albumin-drug binding affinity without albumin

A new liquid chromatographic system was developed to measure protein-drug binding affinity indirectly without albumin and was evaluated using log nK values of drugs measured by a modified Hummel-Dreyer method using purified human serum albumin. The retention factors of acidic and basic drugs were measured by reversed-phase and ion-exchange liquid chromatography in sodium phosphate buffer, pH 7.40, containing 50 vol.% methanol at 37 °C. The bonded phases were pentyl, guanidino and carboxyl phases. The combined retention factors were correlated with the log nK values measured by a modified Hummel-Dreyer method because glycosylation of human serum albumin did not significantly affect log nK value. The correlation coefficients were 0.949 (n=7) for acidic drugs and 0.978 (n=5) for basic drugs. The log nK values of 26 acidic and 18 basic drugs were predicted from their retention factors measured by reversed-phase and ion-exchange liquid chromatography.     

Synthesis of volatile bis[bis(trimethylsilyl)amide]-substituted boron derivatives

Russian Journal of General Chemistry - General strategy for the synthesis of organoboron compounds containing bis(trimethylsilyl)amide substituents has been suggested.     

Synthesis of hydroxycinnamic acid glucuronides and investigation of their affinity for human serum albumin

Hydroxycinnamic acids (HCAs) are among the most abundant dietary polyphenols. Recent bioavailability studies have shown that HCAs enter the blood circulation mainly as glucuronides, which are thus most likely to express their potential health effects. In this work, an efficient synthesis of HCA O-arylglucuronides is developed. As for many xenobiotics, the resilience of HCA O-arylglucuronides in plasma and subsequent delivery to tissues could be governed by their binding to human serum albumin (HSA). Hence, the affinity of HCA O-arylglucuronides for HSA and its possible binding site were investigated by fluorescence spectroscopy. HCA O-arylglucuronides turn out to be moderate HSA ligands (K in the range 1-4 x 10(4) M(-1)) that bind HSA in sub-domain IIA, competitively or noncompetitively with other sub-domain IIA ligands such as dansylamide and the flavonol quercetin.     

Aggregation of two carboxylic derivatives of porphyrin and their affinity to bovine serum albumin

Aggregation of two porphyrin derivatives with carboxylic groups, 4-oxo-4-((4-(10,15,20-triphenyl-21H,23H-porphin-5-yl)phenyl)amino)butanoic acid (MAC) and 4,4',4',4'-[21H,23H-porphine-5,10,15,20-tetrayltetrakis(4,1-phenyleneimino)]tetrakis(4-oxo-butanoic acid) (TA4C), and their affinity to bovine serum albumin were investigated via absorption spectrometry, (1)H NMR and fluorescence spectrometry. MAC and its complexes with beta-cyclodextrin could form aggregates in an aqueous solution while TA4C was self-associated loosely. From the absorbance profiles of MAC in the titration of bovine serum albumin, hypochromicity was observed without any shift of the maximum absorbance wavelength. In both absorption spectra of TA4C in aqueous solutions and in solid state, three Q bands appeared in the visible region. In the measurements of absorption and fluorescence spectra upon titration of BSA, some spectral changes of TA4C were observed. The whole procedure of titration could be divided into three successive stages. The three-banded profiles of TA4C might be explained according to a loose dimer model.     

Synthesis of lanthanide(III) complexes appended with a diphenylphosphinamide and their interaction with human serum albumin

Two DOTA-based proligands bearing a pendant diphenylphosphinamide 4a and 4b were synthesised. Their Eu(III) complexes exhibit sensitised emission when excited at 270 nm via the diphenylphosphinamide chromophore. Hydration states of q = 1.5 were determined from excited state lifetime measurements (Eu.4a $ k_{{{\text{H}}_{ 2} {\text{O}}}} = 2. 1 4 \,{\text{ms}}^{ - 1} ,\;k_{{{\text{D}}_{ 2} {\text{O}}}} = 0. 6 4 \,{\text{ms}}^{ - 1} $ ; Eu.4b $ k_{{{\text{H}}_{ 2} {\text{O}}}} = 2. 6 7\, {\text{ms}}^{ - 1} ,\;k_{{{\text{D}}_{ 2} {\text{O}}}} = 1. 1 8 \,{\text{ms}}^{ - 1} $ ). In the presence of human serum albumin (HSA) (0.1 mM Eu.4a/b, 0.67 mM HSA, pH 7.4) q = 0.4 for Eu.4a ( $ k_{{{\text{H}}_{ 2} {\text{O}}}} = 1. 3 4\, {\text{ms}}^{ - 1} ,\;k_{{{\text{D}}_{ 2} {\text{O}}}} = 0. 7 5\, {\text{ms}}^{ - 1} $ ) and q = 0.6 for Eu.4b ( $ k_{{{\text{H}}_{ 2} {\text{O}}}} = 1. 8 3\, {\text{ms}}^{ - 1} ,\;k_{{{\text{D}}_{ 2} {\text{O}}}} = 1.0 5 \,{\text{ms}}^{ - 1} $ ). Relaxivites (pH 7.4, 298 K, 20 MHz) of the Gd(III) complexes in the absence and presence of HSA (0.1 mM Gd.4a/b, 0.67 mM HSA) were: Gd.4a (r ₁ = 7.6 mM^?1s^?1 and r ₁ = 11.7 mM^?1s^?1) and Gd.4b. (r ₁ = 7.3 mM^?1s^?1 and r ₁ = 16.0 mM^?1s^?1). These relatively modest increases in r ₁ are consistent with the change in inner-sphere hydration on binding to HSA shown by luminescence measurements on Eu.4a/b. Binding constants for HSA determined by the quenching of luminescence (Eu) and enhancement of relaxivity (Gd) were Eu.4a (27,000 M^?1 ± 12%), Eu.4b (32,000 M^?1 ± 14%), Gd.4a (21,000 M^?1 ± 15%) and Gd.4b (26,000 M^?1 ± 15%).     

Thermodynamics of porphyrin binding to human serum albumin using affinity capillary electrophoresis

Summary The interaction thermodynamics of heptacarboxylporphyrin (HCP) and protoporhyrin (PP) with human serum albumin (HSA) was studied by affinity capillary electrophoresis (ACE) over the temperature range of 25–50°C, where HCP and PP bound to HSAvia 1:1 molecular association. The binding equilibrium constants (pH 7.4, phosphate buffer) for the binding of HCP with HSA were found to decrease with an increase in temperature, whereas the binding constants of the PP/HSA system appeared to be independent of temperature changes over the range studied. The van’t Hoff relationship (25–50°C) was found to be linear for the interaction of either HCP or PP with HSA. However, the interaction thermodynamics for both of these porphyrins with HSA were found to be quite different. In particular, the interaction of HCP (a hydrophilic porphyrin) with HSA appeared to be based on an enthalpy-driven process, whereas the binding between PP (a hydrophobic porphyrin) and HSA driven by a favorable change in entropy. The ability of using ACE to evaluate the interaction thermodynamics of serum proteins (e.g., HSA) with ligands (e.g., porphyrins and related compounds) should aid in the development of new and more effective photosensitizers in the photodynamic therapy of cancer.     

Pyridine- and phosphonate-containing ligands for stable Ln complexation. Extremely fast water exchange on the Gd(III) chelates

Two novel ligands containing pyridine units and phosphonate pendant arms, with ethane-1,2-diamine (L2) or cyclohexane-1,2-diamine (L3) backbones, have been synthesized for Ln complexation. The hydration numbers obtained from luminescence lifetime measurements in aqueous solutions of the Eu(III) and Tb(III) complexes are q = 0.6 (EuL2), 0.7 (TbL2), 0.8 (EuL3), and 0.4 (TbL3). To further assess the hydration equilibrium, we have performed a variable-temperature and -pressure UV-vis spectrophotometric study on the Eu(III) complexes. The reaction enthalpy, entropy, and volume for the hydration equilibrium EuL <--> EuL(H2O) were calculated to be DeltaH degrees = -(11.6 +/- 2) kJ mol(-1), DeltaS degrees = -(34.2 +/- 5) J mol(-1) K(-1), and = 1.8 +/- 0.3 for EuL2 and DeltaH degrees = -(13.5 +/- 1) kJ mol(-1), DeltaS degrees = -(41 +/- 4) J mol(-1) K(-1), and = 1.7 +/- 0.3 for EuL3, respectively. We have carried out variable-temperature 17O NMR and nuclear magnetic relaxation dispersion (NMRD) measurements on the GdL2(H2O)q and GdL3(H2O)q systems. Given the presence of phosphonate groups in the ligand backbone, a second-sphere relaxation mechanism has been included for the analysis of the longitudinal (17)O and (1)H NMR relaxation rates. The water exchange rate on GdL2(H2O)q, = (7.0 +/- 0.8) x 10(8) s(-1), is extremely high and comparable to that on the Gd(III) aqua ion, while it is slightly reduced for GdL3(H2O)q, = (1.5 +/- 0.1) x 10(8) s(-1). This fast exchange can be rationalized in terms of a very flexible inner coordination sphere, which is slightly rigidified for L3 by the introduction of the cyclohexyl group on the amine backbone. The water exchange proceeds via a dissociative interchange mechanism, evidenced by the positive activation volumes obtained from variable-pressure 17O NMR for both GdL2(H2O)q and GdL3(H2O)q (DeltaV = +8.3 +/- 1.0 and 8.7 +/- 1.0 cm(3) mol(-1), respectively).     

Synthesis and physicochemical characterization of two gadolinium(III) TTDA-like complexes and their interaction with human serum albumin

Two novel derivatives of TTDA (3,6,10-tri(carboxymethyl)-3,6,10-triazadodecanedioic acid), TTDA-BOM and TTDA-N'-BOM, each having a benzyloxymethyl group, were synthesized. (17)O NMR longitudinal and transverse relaxation rates and chemical shifts of aqueous solutions of their Gd(III) complexes were measured at variable temperature with a magnetic field strength of 9.4 T. The water exchange rate (k(ex)(298)) values for [Gd(TTDA-BOM)(H(2)O)](2-) (117 x 10(6) s(-1)) and [Gd(TTDA-N'-BOM)(H(2)O)](2-) (131 x 10(6) s(-1)) are significantly higher than those of [Gd(DTPA)(H(2)O)](2-) (4.1 x 10(6) s(-1)) and [Gd(BOPTA)(H(2)O)](2-) (3.45 x 10(6) s(-1)). The rotational correlation time (tau) values for [Gd(TTDA-BOM)(H(2)O)](2-) (119 ps) and [Gd(TTDA-N'-BOM)(H(2)O)](2-) (125 ps) are higher than those of [Gd(DTPA)(H(2)O)](2-) (103 ps) and [Gd(TTDA)(H(2)O)](2-) (104 ps). The stepwise stoichiometric binding constants of [Gd(TTDA-BOM)(H(2)O)](2)(-) and [Gd(TTDA-N'-BOM)(H(2)O)](2)(-) bound to HSA are obtained by ultrafiltration studies. Fluorescent probe displacement studies exhibit that [Gd(TTDA-BOM)(H(2)O)](2-) and [Gd(TTDA-N'-BOM)(H(2)O)](2-) can displace dansylsarcosine from HSA with inhibition constants (K(i)) of 1900 and 1600 microM, respectively; however, they are not able to displace warfarin. These results indicate that [Gd(TTDA-BOM)(H(2)O)](2-) and [Gd(TTDA-N'-BOM)(H(2)O)](2-) have a weak binding to site II on HSA. In addition, the mean bound relaxivity (r(1b)) and bound relaxivity (r(1)(b)) values for the [Gd(TTDA-BOM)(H(2)O)](2-)/HSA and [Gd(TTDA-N'-BOM)(H(2)O)](2-)/HSA adducts are obtained by ultrafiltration and relaxivity studies, respectively. The bound relaxivity of these adducts values are significantly higher than those of [Gd(BOPTA)(H(2)O)](2-)/HSA and [Gd(DTPA-BOM(3))(H(2)O)](2-)/HSA. These results also suggest that bound relaxivity is site dependent. In binding sites studies of Gd(III) chelates to HSA, a significant decrease of the relaxation rates (R(1obs)) was observed for the [Eu(TTDA-BOM)(H(2)O)](2-) complex which was added to the [Gd(TTDA-N'-BOM)(H(2)O)](2-)/HSA solution, and this indicated that these Gd(III) complexes share the same HSA binding site. Finally, as measured by the Zn(II) transmetalation process, the kinetic stability of these Gd(III) complexes are significantly higher than that of [Gd(DTPA-BMA)(H(2)O)].     

Betulinic acid binding to human serum albumin: a study of protein conformation and binding affinity

Betulinic acid (BA) has anti cancer and anti-HIV activity and has been proved to be therapeutically effective against cancerous and HIV-infected cells. Human serum albumin (HSA) is the predominant protein in the blood. Most drugs that bind to HSA will be transported to other parts of the body. Using micro TOF-Q mass spectrometry, we have shown, for the first time that BA isolated from a plant (Tephrosia calophylla) binds to HSA. The binding constant of BA to HSA was calculated from fluorescence data and found to be K(BA)=1.685+/-0.01 x 10(6) M(-1), indicating a strong binding affinity. The secondary structure of the HSA-BA complex was determined by circular dichroism. The results indicate that the HSA in this complex is partially unfolded. Further, binding of BA at nanomolar concentrations of BA to free HSA was detected using micro TOF-Q mass spectrometry. The study revealed a mass increase from 65199 Da (free HSA) to 65643 Da (HSA+drug), where the additional mass of 444 Da was due to bound BA. Based on the results of this study, it is suggested that micro TOF-Q mass spectrometry is useful technique for drug binding studies.     

Synthesis and properties of bis(pyridylmethylene)mercury derivatives

The action of ammonia on - and -monomercurimethylenePyrylium perchlorates gave bis(pyridylmethylene)mercury derivatives, which undergo decomposition to the corresponding pyridine derivatives and mercuric chloride.See [1] for our preceding communication.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 887–888, July, 1981.     

Synthesis and psychotropic properties of bis(2-thenylidene)diamines and their silyl derivatives

Summary The condensation of diamines with the corresponding aldehydes gave bis(2-thenylidene)diamines and their silyl derivatives. The structure of the compounds has been confirmed by their PMR spectra. It has been shown that the introduction of the trimethylsilyl group increases the toxicity, prolongs the hexenal narcosis and the antihypoxy activity, has a positive effect on the memory processes, and has no influence on the coordination of movements, the muscle tone, and the body temperature. All compounds possess an antialcohol activity, whereby the silyl derivatives have the stronger one.Translated from Khimiya Geterotsikiicheskikh Soedinenii, No. 3, pp. 316–320, March, 1994.     

Exploring binding properties of gliclazide with human serum albumin

Journal of Thermal Analysis and Calorimetry - The thermodynamic parameters of the binding of gliclazide (GL) with human serum albumin (HSA) have been discussed along with the insight into the...