Succinate Linker Research Articles

Site-Dependent Substitutions in Mixed-Metal Metal–Organic Frameworks: A Case Study and Guidelines for Analogous Systems

Complex architectures are often found among metal–organic framework (MOF) compounds. The mixed-metal approach to this type of material offers an additional degree of structural complexity, and potential tunability of their properties, which remains largely unexplored. We present an in-depth investigation of the crystal chemistry of mixed-metal MOFs based on succinate linkers (C4H4O4) and having the general formula (M′1–xM″x)5(OH)2(C4H4O4)4 with M′/M″ = Mn/Co, Fe/Co, and Mn/Fe. The distribution of the metallic elements over three crystallographic sites throughout the different substitutions is finely characterized by resonant contrast diffraction (RCD) experiments corroborated by neutron diffraction (ND) measurements. We observe a size-effect in the filling of the oxygen octahedra, leading to the existence of compounds in which a partial order of the cations over the different metallic sites exists for some compositions of the Co/Mn solid solution. This points out the existence of complex structural phenomena potentially able to influence the physical behavior of such phases and that might, so far, have been overlooked in MOFs. In order to facilitate future studies on mixed-metal MOFs, we consider the possibility of using conventional single-crystal X-ray diffraction (SCXRD) to locate cations of close electronic densities in such cases. The comparison with the results from dedicated measurements based on synchrotron (RCD) and neutron (ND) radiations indicates guidelines for the use of laboratory SCXRD to address mixed-metal MOFs where metal distribution is fundamental to tuning physical properties.

Pharmacokinetic and pharmacodynamic properties of calaspargase pegol Escherichia coli L-asparaginase in the treatment of patients with acute lymphoblastic leukemia: results from Children's Oncology Group Study AALL07P4.

Asparaginase is a critical agent used to treat acute lymphoblastic leukemia (ALL). Pegaspargase (SS-PEG), a pegylated form of Escherichia coli L-asparaginase with a succinimidyl succinate (SS) linker, is the first-line asparaginase product used in Children's Oncology Group (COG) ALL trials. Calaspargase pegol (SC-PEG) replaces the SS linker in SS-PEG with a succinimidyl carbamate linker, creating a more stable molecule. COG AALL07P4 was designed to determine the pharmacokinetic and pharmacodynamic comparability of SC-PEG to SS-PEG in patients with newly diagnosed high-risk (HR) B-cell ALL. A total of 165 evaluable patients were randomly assigned at a 2:1 ratio to receive SC-PEG at 2,100 (SC-PEG2100; n = 69) or 2,500 IU/m(2) (SC-PEG2500; n = 42) versus SS-PEG 2,500 IU/m(2) (SS-PEG2500; n = 54) as part of an otherwise identical chemotherapy regimen. The groups were similar demographically, except more female patients received SC-PEG2500. The mean half-life of plasma asparaginase activity for both SC-PEG doses was approximately 2.5× longer than that of SS-PEG2500. The total systemic exposure, as defined by induction area under the curve from time 0 to 25 days, was greater with SC-PEG2500 than with SS-PEG2500 or SC-PEG2100. The proportion of patients with plasma asparaginase activity ≥ 100 mIU/mL and ≥ 400 mIU/mL was higher in patients who received SC-PEG as compared with SS-PEG2500. After one dose of pegylated asparaginase on induction day 4, plasma asparagine was undetectable for 11 days for SS-PEG2500 and 18 days for both SC-PEG groups. SC-PEG2500 achieves a significantly longer period of asparaginase activity above defined thresholds and asparagine depletion compared with SS-PEG2500 and has a comparable toxicity profile in children with HR B-cell ALL.

A tandem in situ peptide cyclization through trifluoroacetic acid cleavage.

We present a new approach for peptide cyclization during solid phase synthesis under highly acidic conditions. Our approach involves simultaneous in situ deprotection, cyclization and trifluoroacetic acid (TFA) cleavage of the peptide, which is achieved by forming an amide bond between a lysine side chain and a succinic acid linker at the peptide N-terminus. The reaction proceeds via a highly active succinimide intermediate, which was isolated and characterized. The structure of a model cyclic peptide was solved by NMR spectroscopy. Theoretical calculations support the proposed mechanism of cyclization. Our new methodology is applicable for the formation of macrocycles in solid-phase synthesis of peptides and organic molecules.

The synthesis, self-assembling, and biocompatibility of a novel O-carboxymethyl chitosan cholate decorated with glycyrrhetinic acid

O-carboxymethyl chitosan (OCMC) was firstly decorated with cholic acid (CA) to acquire an amphiphilic polymer under alkaline condition. Then glycyrrhetinic acid (GA) was conjugated to the polymer via a succinate linker and finally treated with NaCO3 solution to obtain new conjugates for potential liver targeted delivery. These conjugates formed uniform aggregates with low critical aggregation concentrations (0.028–0.079mg/mL) in PBS. The average diameter of cholic acid modified carboxymethyl chitosan (CMCA) aggregates (110–257nm) decreased with the increase of CA substitution degree and became slightly larger after GA modification. Negative zeta potential (−15mV) of GA decorated CMCA (GA-CMCA) revealed that the formation of negatively charged shells and spherical morphology was observed under transmission electron microscopy. Furthermore, hemolysis test, in vitro cytotoxicity assay and cellular uptake study all demonstrated the safety and feasibility of these conjugates as a promising carrier for liver targeted drug delivery.

Synthesis, characterization and in vitro evaluation of novel vitamin D3 nanoparticles as a versatile platform for drug delivery in cancer therapy.

Development of novel nanotechnology based platforms can impact cancer therapeutics in a paradigm shifting manner. The major concerns in drug delivery in cancer therapy are the biocompatibility, biodegradability, non-toxic nature, easy and short synthesis and versatility of the nanovectors. Herein we report the engineering of versatile nanoparticles from biocompatible, biodegradable and non-toxic lipid soluble vitamin D3. We have conjugated different clinically used cytotoxic drugs (paclitaxel and doxorubicin) as well as PI3 kinase inhibitor (PI103) with vitamin D3 using a succinic acid linker. Sub-200 nm, monodispersed nanoparticles with high drug loading were engineered from the vitamin D3-succinic acid-drug conjugates. These nanoparticles released the active drugs at pH 5.5 in a slow and sustained manner over 100 h. Furthermore, these nanoparticles were taken up by HeLa cells into the low pH lysosomal compartments through an endocytosis mechanism in 6 h. Finally, these drug loaded vitamin D3 nanoparticles induced HeLa cervical cancer cell death in a dose dependent manner at 48 h to show their potential in cancer therapeutics.

Pharmacokinetic (PK) and pharmacodynamics (PD) properties of SC-PEG e. coli L-asparaginase (EZN-2285) in the treatment of patients with acute lymphoblastic leukemia (ALL): Results from Children's Oncology Group (COG) study AALL07P4.

9543 Background: Asparaginase is a critical therapeutic agent in the treatment of childhood ALL, and pegaspargase (Oncospar, ONC) is now the preferred product in COG frontline ALL trials. EZN-2285 replaces the succinimidyl succinate linker in ONC with a succinimidyl carbamate linker creating a more stable molecule. AALL07P4 was designed to determine the PK comparability of EZN-2285 to ONC when given intravenously in newly diagnosed patients with NCI high-risk (HR) B-precursor ALL. Methods: 162 eligible patients were randomized to receive EZN-2285 at 2100 (LD, n=66) or 2500 (HD, n=42) IU/m2 vs. 2500 IU/m2 of ONC (n=51) in a 2:1 manner based on the prednisone/Capizzi methotrexate arm of COG AALL0232. All groups were similar demographically with the exception of number of patients over the age of 16 years were 6, 5, and 19 in the ONC, HD and LD, respectively. Results: PK, PD and targeted AEs (Gr 3-5) after the first doses of study drug are presented in the table below. Adverse events in induction were not significantly different between arms with the exception of a higher incidence of hyperglycemia (p=0.042). Conclusions: Based on Cmax , AUC0-25d , and asparaginase activity 25 days post drug, EZN-2285 2500 IU/m2 appears to have an improved PK/PD profile compared to pegaspargase 2500 IU/m2 and a comparable toxicity profile in children with HR ALL. [Table: see text]

Synthesis and anti-hepatitis B virus activity of acyclovir conjugated stearic acid- g-chitosan oligosaccharide micelle

The controlled release of chemotherapeutical reagent with high water solubility was a challenge for targeting drug delivery. In this article, an antiviral agent, acyclovir was conjugated to chitosan- g-stearate via a succinate linker. Chitosan- g-stearate was synthesized by the reaction between the amino group of chitosan oligosaccharide and the carboxyl group of stearic acid. Both chitosan- g-stearate and acyclovir-chitosan- g-stearate could self aggregate to form micelles in aqueous solution. Acyclovir-chitosan- g-stearate micelle had smaller size (24.9 ± 1.1 nm), lower positive zeta potential (24.4 mV) and higher critical micelle concentration (123.23 mg mL −1) in distilled water, compared with those of chitosan- g-stearate (34.2 ± 3.8 nm, 46.9 ± 6.2 mV and 90.07 mg mL −1, respectively). Acyclovir release from acyclovir-chitosan- g-stearate micelles could prolong to 24 h in vitro. For the free acyclovir and acyclovir-chitosan- g-stearate micelle with acyclovir concentration of 0.044 μM mL −1, the inhibition of acyclovir on hepatitis B surface antigen was increased from 12.7% to 22.3% from 5 d to 9 d, while the inhibition of acyclovir-chitosan- g-stearate was increased from 58.2% to 80.3% from 5 d to 9 d. The cellular uptake and antiviral activity of acyclovir was successfully increased and improved through chemical conjugation of acyclovir to chitosan- g-stearate.

PAMAM-camptothecin conjugate inhibits proliferation and induces nuclear fragmentation in colorectal carcinoma cells.

To synthesize and characterize a poly (amido amine) dendrimer-camptothecin (PAMAM-CPT) conjugate and evaluate its activity on human colorectal carcinoma cells (HCT-116). The attachment of CPT to amine-terminated PAMAM was facilitated through a succinic acid-glycine linker. The conjugate was characterized for absence of small molecular weight impurities, size and drug content. Stability of the conjugate in PBS and growth media and its in vitro activity on HCT-116 were studied. Cell cycle arrest and nuclear fragmentation upon PAMAM-CPT treatment were investigated. The conjugate was stable under physiological pH (7.4) in PBS and in growth media (with 10% FBS) with minimal release of 4% and 6% drug, respectively, at 48 h. PAMAM-CPT inhibited proliferation of HCT-116 cells with an IC50 value of 1.6 ± 0.3 µM. The conjugate induced signs of cell cycle arrest with up to 68% of cells blocked in the G(2) phase. Confocal images of cells treated with PAMAM-CPT suggest nuclear fragmentation and formation of apoptotic bodies. Results show that the PAMAM-CPT conjugate was active against colorectal cancer cells in vitro, inhibiting their growth and inducing nuclear fragmentation. Coupled with the ability to target macromolecular therapeutics to tumors, this conjugate shows promise for cancer chemotherapy.

Selective targeting of 2′-deoxy-5-fluorouridine to urokinase positive malignant cells in vitro

A urokinase targeting conjugate of 2′-deoxy-5-fluorouridine (5-FUdr) was synthesized and tested for tumor-cell selective cytotoxicity in vitro. The 5-FUdr prodrug 2′-deoxy-5-fluoro-3′- O-(3-carboxypropanoyl)uridine (5-FUdrsuccOH) containing an ester-labile succinate linker was attached to the specific urokinase inhibitor plasminogen activator inhibitor type II (PAI-2) and was found to preferentially kill urokinase-over expressing cancer cells. Up to 7 molecules of 5-FUdr were incorporated per PAI-2 molecule without affecting protein activity. This is the first time a small organic cytotoxin has been conjugated to PAI-2.

Soluble polyphenols: Synthesis and bioavailability of 3,4′,5-tri(α- d-glucose-3- O-succinyl) resveratrol

We report the development of a chemical modification method of general applicability to polyphenols, which increases solubility to influence absorption. Glucosyl groups were added to the resveratrol kernel via a succinate linker, yielding 3,4′,5-tri-(α- d-glucose-3- O-succinyl) resveratrol. The construct was only slowly hydrolyzed in acid and at pH 6.8, but it was destroyed by blood esterases in less than 1 h. In rats its administration resulted in a blood concentration versus time curve shifted to longer times in comparison to resveratrol, a useful modulation of pharmacokinetics. The area-under-curve parameter and the metabolite mix were similar to those of resveratrol. The method may be advantageously employed to solubilize other polyphenols and to make them more palatable.

X-ray Photoelectron Spectroscopy- and Surface Plasmon Resonance-Detected Photo Release of Photolabile Protecting Groups from Nucleoside Self-Assembled Monolayers on Gold Surfaces

The formation of self-assembled monolayers (SAMs) on gold by 2-(5-iodo-2-nitrophenyl) propoxycarbonyl (I-NPPOC)-protected thymidine with an attached mercaptohexyl succinate linker and the kinetics of photochemical release of the I-NPPOC group were monitored using X-ray photoelectron spectroscopy (XPS) and surface plasmon resonance (SPR) detection. In the XPS spectra, the iodine peaks allowed for specific and accurate monitoring of the presence and loss of I-NPPOC groups on the surface. In the SPR experiment, the overall signal change on photoillumination is in accord with a theoretical estimation of the density of I-NPPOC groups in a dense monolayer. The kinetics roughly follow a biexponential time dependence with two very different time constants, corresponding to photochemical quantum yields of 0.22 and 0.0032, respectively.

Efficiency of succinylated-olive stone biosorbent on the removal of cadmium ions from aqueous solutions

Chemical functionalization of olive stone wastes with succinate linkers can potentially improve the performance of wastewater treatment technologies via enhanced adsorption and high affinity of the covalently attached succinate groups for heavy metals. In this study, a novel reusable adsorbent material based on agricultural waste has been synthesized by esterifying the lignocellulosic matrix of olive stones with succinic anhydride in toluene under basic conditions. Characterization of the as-prepared material by FTIR and solid-state MAS 13C NMR spectroscopies and TGA confirmed that the heterogeneous esterification has proceeded very efficiently to yield the succinylated-olive stone (S–OS). Subsequent alkaline treatment of S–OS with saturated NaHCO 3 aqueous solution led to the resulting sodic material (NaS–OS), which was subjected to batch experiments in order to evaluate its cadmium-removing efficiency from aqueous solutions at realistic concentrations of cadmium found in industrial effluents. The results obtained from the sorption characteristics have revealed that NaS–OS material is highly effective in removing cadmium from aqueous solutions, with a maximum uptake capacity of 200 mg g −1 (1.78 mmol g −1). The Langmuir isotherm model was found to fit adequately the equilibrium isotherm data. Cadmium adsorption occurs rapidly and the adsorption mechanism is a chemical sorption via ionic exchange between the adsorbate and adsorbent. Thermodynamic parameters were also evaluated from the effect of temperature studies. Regenerability of NaS–OS material was ascertained by quantitative desorption of cadmium with 1 M aqueous NaCl and the reusability of the matrix after five repeated cycles led to nearly no attenuation in its performance (less than 2% in the sorption capacity), indicating that repeated use of NaS–OS is quite feasible. Compared to other low-cost adsorbents utilized for the removal of Cd(II) from water/wastewater, NaS–OS shows higher sorption capacity. These results have important implications for the design of low-cost adsorbents based on agricultural wastes.

5-Amino-2-pyridyl 1-thioglycosides in synthesis of analogs of glycosyltransferases substrates

We present the synthesis of 1-thioglycosyl derivatives of uridine, which were designed to act as potential donor substrates for glycosyltransferases. We constructed such analogs using 5-amino-2-pyridyl 1-thioglycosides as glycosyl units which were connected to uridine via succinic linker. For preparation of the amide bonds we applied different condensation procedures.

Towards the conformational mimicry of the measles virus HNE loop: design, synthesis and biological evaluation of a cyclic bile acid–peptide conjugate

The current article reports the design, synthesis and biochemical evaluation of a cyclic bile acid-peptide conjugate as a mimic of the loop-like structure of the measles virus haemagglutinin noose epitope (HNE). This macrocyclic structure was assembled by solid phase synthesis. Scaffold-peptide ring closure was achieved via the introduction of a succinate linker. After disulfide bridge formation with iodine, the desired 14 amino acid cyclic conjugate was obtained with overall yields between 15 and 35%. NMR analysis supports the presence of a helical conformation in the Q384-G388 pentapeptide portion, in agreement with the organisation of this chain in the native protein. The compound was found to have increased biostability compared to stabilised linear peptides, displayed good binding towards monoclonal antibodies known to bind to HNE and thus has potential in an alternative peptide-based measles vaccine.

Characterization of amphiphilic hydrocarbon modified Poly(ethylene glycol) synthesized through ring-opening reaction of 2-(1-octadecenyl)succinic anhydride

Poly(ethylene glycol) (PEG) triblock and diblock amphiphilic block copolymers were synthesized from poly(ethylene glycol) and poly(ethylene glycol) monomethyl ether, respectively. The hydroxyl groups of PEG readily react with 2-(1-octadecenyl) succinic anhydride (OSA) at 140 °C through ring-opening reaction of the succinic anhydride. Both the PEG–OSA diblock and triblock copolymers are produced without use of any solvent or catalyst. The molecular structure of the copolymers was characterized by 1H NMR and FTIR spectroscopy, and the thermal properties by DSC. The behavior of the copolymers in selective and nonselective solvents was studied by 1H NMR spectroscopy in deuterium oxide and d-chloroform. The aggregation of the polymers in water was studied with a particle size analyzer and a transmission electron microscope (TEM) in bright field mode. The results show that the hydrophobic C 18 chain with intramolecular succinic anhydride linker can be attached to the hydrophilic PEG chain, an ester bond forming between the blocks. The copolymers exhibit flexible, liquid-like hydrophobic blocks even in water, which is a nonsolvent for OSA. PEG–OSA block copolymers self-organize in water, forming micellar polymer aggregates in nanoscale.

Synthesis of 6-amino-6-deoxyhyaluronan as an intermediate for conjugation with carboxylate-containing compounds: application to hyaluronan–camptothecin conjugates

A novel methodology for making drug conjugates using hyaluronan as a carrier was developed. This strategy involves a completely regioselective two-step synthesis of 6-amino-6-deoxyhyaluronan, which is then easily functionalized with drugs through a suitable linker. The case of hyaluronan–camptothecin conjugates is described, making use of a simple succinate linker. The antitumor activity of new hyaluronan derivatives prepared is at present under evaluation.

Synthesis of a new mPEG-dexamethasone conjugate and preliminary bioavailability studies in rabbits

Poly(ethylene glycol) esters have been proposed as a potential oral-controlled drug delivery system for dexamethasone (DXM). The drug was covalently attached to monomethoxypolyethylene glycol amine (mPEG-NH 2 ) (Mw = 10,000 Da) using a succinate linker. A new PEG-based prodrug system was designed using ester derivatives. The drug-polymer conjugate (mPEG-DXM) was freely water soluble at room temperature. First of all, the adduct hydrolytic stability was assessed at physiological pH. Then, the bioavailability was evaluated by orally administering the mPEG-DXM conjugate in rabbits and comparing to that obtained by the intravenous route. The area under the concentration-time curve (AUC) of PEGylated drug was twice as large as that of the parent drug after oral administration. In conclusion, PEGylated DXM was useful for maintaining the DXM concentration in the blood after oral administration.

Synthesis, Analysis, in Vitro Characterization, and in Vivo Disposition of a Lamivudine–Dextran Conjugate for Selective Antiviral Delivery to the Liver

A liver-selective prodrug (3TCSD) of the antiviral drug lamivudine (3TC) was developed and characterized. 3TC was coupled to dextran ( approximately 25 kDa) using a succinate linker, and the in vitro and in vivo behavior of the conjugate was studied using newly developed size-exclusion and reversed-phase analytical methods. Synthesized 3TCSD had a purity of >99% with a degree of substitution of 6.5 mg of 3TC per 100 mg of the conjugate. Furthermore, the developed assays were precise and accurate in the concentration ranges of 0.125-20, 0.36-18, and 1-50 microg/mL for 3TC, 3TC succinate (3TCS), and 3TCSD, respectively. In vitro, the conjugate slowly released 3TC in the presence of rat liver lysosomes, whereas it was stable in the corresponding buffer. In vivo in rats, conjugation of 3TC to dextran resulted in 40- and 7-fold decreases in the clearance and volume of distribution of the drug, respectively. However, the accumulation of the conjugated 3TC in the liver was 50-fold higher than that of the parent drug. The high accumulation of the conjugate in the liver was associated with a gradual and sustained release of 3TC in the liver. These studies indicate the feasibility of the synthesis of 3TCS-dextran and its potential use for the selective delivery of 3TC to the liver.

Study of peptide oligomer derived from HIV-1 integrase molecular modelling

Three synthetic oligopeptides (EAA26, K156 and E156) mutant of the α-4 helix of the HIV-1 integrase and having, respectively, 26, 24 and 24 aminoacids showed variable oligomerisation trend as detected by the ESI-MS (electrospray mass spectrometry) or CD (circular dichroism) methodologies. These peptides oligomers were modelled as potential inhibitors of this enzyme through coiled–coil interactions. The dimer, trimer and tetramer aggregate energies for these synthetic peptides were calculated and their stability discussed. One of these peptides, EAA26 shows some propensity to form a tetrameric structure when attached to the calix[4]arene frame through a succinic linker; the possibility to form the quadruple peptide helix, an entity which was not obtained from peptide systems, was evaluated.

Solid-Phase Synthesis of Photochromic Spiropyrans

A convenient solid-phase synthesis of spiropyrans is described. A succinate linker was employed, which allows base-catalyzed cleavage of the desired photochromophore derivatized with a succinimide. Excellent yields and purities were obtained for the compounds that comprise a library of 23 spiropyrans. Opening of the succinimide ring in spiropyran could be realized under mild conditions.