Synthesis of tritium-labeled Semax

The tert-butyloxycarbonyl derivative of Met-Glu-His-Phe-Pro-Gly was prepared and condensed with either unsaturated or labeled proline. The unsaturated peptide protected by the tert-butyloxycarbonyl group was hydrogenated with gaseous tritium in the presence of a catalyst. The Semax analog labeled in the proline fragment was deprotected by acid hydrolysis. The molar radioactivity of the product (PBq mol^?1) reached 0.93 in the route via labeled proline and 0.37 in the route via unsaturated Semax analog.     

Synthesis of tritium-labeled Ganciclovir

The influence of temperature on the solid-phase isotope exchange of Ganciclovir with tritium was studied. Synthesis conditions were found, and tritium-labeled Ganciclovir with the molar radioactivity of 25 Ci mmol⁻¹ (0.925 PBq mol⁻¹) and purity higher than 98% was prepared.     

Synthesis of tritium-labeled Selank

A scheme was developed for the synthesis of Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) and its precursor (Thr-Lys-Pro-Arg-Pro-Gly). Condensation of the tert-butyloxycarbonyl derivative of Thr-Lys-Pro-Arg-Pro-Gly with labeled proline yielded Selank labeled in the C-terminal proline fragment. The molar radioactivity of tritium-labeled Selank was 56 Ci mmol^?1, which corresponded to the molar radioactivity of proline.     

Synthesis of deuterium- or tritium-labeled acetylcholine

Halogenated acetylcholine precursors were synthesized. The prepared deuterium analogs of acetylcholine were characterized by HPLC and mass spectrometry. Uniformly tritium-labeled acetylcholine with the radiochemical purity of no less than 97–98% and molar radioactivity of 20–40 Ci mmol^–1 was prepared at 190°С on a Lindlar catalyst. The molar radioactivity of [³H]acetylcholine allows using it for evaluating the specific binding on plasmatic membranes of striatum cells of intact rats by radioligand–receptor binding assay. Two sites of specific binding of acetylcholine, high-affinity (binding constant K _d = 12 nmol L^–1, possible number of radioligand specific binding sites B _max = 3 pmol mg^–1) and low-affinity (binding constant K _d = 72 nmol L^–1, possible number of radioligand specific binding sites B _max = 13 pmol mg^–1), were characterized.     

1-Alkylcarbonyl-5-fluorouracil Prodrugs: Synthesis,Thermal and Hydrolytic Stability

Abstract

Six homologous 1 -alkylcarbonyl derivatives of 5-fluorouracil (5-FU) have been synthesized and characterized by ¹H NMR, infrared and UV spectroscopy. The derivatives were found to hydrolyze rapidly in pH 7.1 buffer at 32°C (t_1/2 = 3-5 min). Although the hydrolysis was found to be catalyzed by hydrated formaldehyde, only 5-FU was observed as a product of the hydrolysis: no 1- or 3-alkylcarbonyloxymethyl products were observed. The 1 -alkylcarbonyl derivatives were recovered intact upon heating at 145°C for 1 h, but, upon heating at 205°C for 1 h, 25% of the sample decomposed to 5-FU with the assumed loss of ketene. The 1-alkylcarbonyl derivatives were stable when stored in a desiccator but decomposed to carboxylic acid and 5-FU upon exposure to atmospheric moisture.     

Synthesis of tritium-labeled 2′,3′-dideoxy-2′,3′-didehydrothymidine and 3′-azidothymidine-5′-phosphamide

Tritium-labeled 2′,3′-dideoxy-2′,3′-didehydrothymidine and 3′-azidothymidine-5′-phosphamide were prepared by isotope exchange with highly enriched tritium water. Tritium water was prepared by oxidation of high-percentage tritium on PdO. The isotope exchange was performed at 100°C in the dioxane-triethylamine mixed solvent (9: 1 by volume). The molar radioactivities (GBq mol^?1) and yields (%) of the products were, respectively, as follows: 2′,3′-dideoxy-2′,3′-didehydrothymidine, 82, 44; 3′-azidothymidine-5′-phosphamide, 200, 71.     

5-氟尿嘧啶载药微球的制备工艺及性能研究

以PLA为载体材料,以5-Fu为模型药物,制备5-Fu/PLA载药微球,通过正交设计优化微球制备工艺.另外,检测了载药微球的回收率、稳定性、缓释性能等物理性质.用紫外分光光度计测定药物含量,激光粒度仪分析粒径. 结果表明,载药微球的平均粒径为(133.2±32.5)nm,平均包封率为(11.3±5.0)%,缓释时间延长至80～100h,具有良好的缓释功能.     

主动靶向5-氟尿嘧啶聚乳酸微球的研究

通过对5-u聚乳酸载药微球接PEI进行表面胺解、接枝靶向基团Folate以及荧光物质FITC，制备了靶向5-u聚乳酸微球，并研究了微球的缓释性能、荧光效应和主动靶向性．结果表明，靶向5-u聚乳酸微球具有良好的缓释性能，缓释时间可达到105h；未改性的载药微球对Hela细胞的抑制作用有限，无主动靶向性：改性的载药微球具有明显的荧光效应和良好的主动靶向性．     

Synthesis of tritium-labeled dermorphin fragments and kinetics of radioactivity distribution in rat organs upon intramuscular injection of these peptides

Tritium-labeled dermorphin fragments Tyr-[3,4-³H]Pro-Ser-NH₂ and Tyr-[3,4-³H]-D-Pro-Ser-NH₂ were synthesized. The kinetics of distribution of these peptides in rat organs was studied. The highest content of the radioactive label upon injection of Tyr-[3,4-³H]Pro-Ser-NH₂ and Tyr-[3,4-³H]-D-Pro-Ser-NH₂ is found in kidneys. With Tyr-[3,4-³H]-D-Pro-Ser-NH₂, the radioactivity uptake by kidneys is greater than with Tyr-[3,4-³H]Pro-Ser-NH₂.     

Buccal bioadhesive delivery system of 5-fluorouracil: optimization and characterization

The objective of this work was to apply the response surface approach in the development of buccal bioadhesive tablets of 5-fluorouracil (5-FU). Experiments were performed according to a 3(2) factorial design to evaluate the effects of two polymers, Gantrez MS-955 (X(1)) and hydroxypropylmethyl cellulose (HPMC) K15M (X(2)) on the bioadhesive force, percentage drug release in 8 h (Rel(8 h)), time taken for 50% drug release (t(50%)), and diffusion coefficient (n). The effect of the two independent variables on the response variables was studied by response surface plots and contour plots generated by the Design Expert software. The compatibility between 5-FU and the tablet excipients was confirmed by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) studies. Both the polymers were found to have synergistic effect on bioadhesion but the effect of Gantrez was more pronounced. A nonlinear twisted relationship was obtained for Rel(8 h) at the intermediate and high levels of the polymers, which indicated an interaction between them at the corresponding factor levels. Kinetic treatment to the dissolution profiles revealed that the drug release ranged from Fickian to anomalous transport, which was mainly dependent on both the independent variables. The desirability function was used to optimize the response variables, and the observed responses were in agreement with the experimental values.     

Nuclear-chemical synthesis of tritium-labeled fluorinated isoquinolinium derivatives

The developed nuclear-chemical method allows direct phenylation of the nitrogen atom in the isoquinoline molecule and one-step synthesis of tritium-labeled biomarkers containing previously unknown N-(p-difluorophenyl)isoquinolinium fragment with high radiochemical yield.     

Nuclear-chemical synthesis of tritium-labeled phenyl-substituted picoline derivatives

Ion-molecule reactions of free phenyl cations with six-membered nitrogen-containing heterocyclic compounds: α-, β-, and γ-picolines, were studied. Phenyl cations were generated by tritium β-decay in double-labeled benzene. The mechanism of competing reactions of electrophilic addition to the nitrogen heteroatom in the ring and electrophilic substitution of the C-H bond in the pyridine ring was examined. The effect of methyl substituent in the pyridine molecule on the reaction pathway was evaluated. A one-step procedure for nuclear-chemical synthesis of tritium-labeled N-phenylpicolinium salts and phenyl-substituted picolines was developed.     

Solid-phase synthesis of deuterium- and tritium-labeled dopamine using carbon nanomaterials

Various procedures for preparing dopamine labeled with deuterium (²H) and tritium (³H) were considered. The labeled dopamine into which the hydrogen isotopes were introduced by solid-phase halogenation contained, on the average, 2.8 ²H (³H) atoms. The labeled dopamine prepared by solid-phase isotope exchange using nanodiamonds as support contained, on the average, 4.8 ²H (³H) atoms. The process was accompanied by the substrate deamination; as a result, the yield of the labeled analog was low (7–10%). Mass spectrometric analysis shows that the phenolic fragments formed by the dopamine deamination undergo dimerization.     

Indomethacin-5-fluorouracil-methyl ester dry emulsion: a potential oral delivery system for 5-fluorouracil

Objective: To produce a combined effect of indomethacin (IDM) and 5-fluorouracil (5FU) for cancer therapy, the side effects of IDM on the gastrointestinal (GI) tract were reduced and the oral adsorption of 5FU was improved. Indomethacin-5-fluorouracil-methyl ester (IFM) dry emulsion was prepared and evaluated as a potential oral delivery system for 5FU. Methods: IFM was synthesized by formation of an ester between IDM and 5FU intermediate and then characterized by structure, melting point, solubility, apparent partition coefficient, and incubation with GI tract contents and plasma. Gum acacia and sodium carboxymethyl cellulose (CMC-Na) were applied as the adsorbent and solid carrier to prepare IFM dry emulsion. IFM dry emulsion was then characterized by reconstitution in water and in situ intestinal perfusion experiment. Results: Physicochemical properties of the new synthesized compound confirmed the formation of IFM. Incubation of IFM in the contents of the GI tract and plasma revealed that IFM was not relatively stable in GI contents during the time period of transit through the GI tract, whereas it was very unstable in plasma and released 5FU rapidly. The IFM dry emulsion could be easily reconstituted in water, and the mean particle size was 2.416 μm. The absorption rate constant (K) for IFM with concentration of 2, 5, and 10 μg/mL in the in situ perfusion experiment were 0.473, 0.423, and 0.433/h, respectively, demonstrating passive diffusion of IFM across the biological membranes. Conclusion: This study indicates that the IFM dry emulsion may represent a potentially useful oral delivery system for 5FU.     

The release of 5-fluorouracil from microspheres of poly(epsilon-caprolactone-co-ethylene oxide)

The purpose of this study was to evaluate the in vitro release of 5-fluorouracil from microspheres prepared using a novel triblock copolymer of ε-caprolactone and ethylene oxide as the encapsulating material. Microspheres of poly(ε-caprolactone-co-ethylene oxide) were prepared by employing the “hot-melt” method of microencapsulation. Microspheres were sized using sieve analysis and scanning electron microscopy (SEM). Release studies were performed using a custom-made rotating paddle dissolution apparatus. Copolymer microspheres, fabricated by the hot melt method were shown by electron microscopy to have smooth, nonporous surfaces. Drug-loaded microspheres were found to have a broad distribution of sizes, which was thought to be a consequence of the wide range of crystal sizes of the encapsulated unmilled drug. Nonlinear release kinetics were observed from microspheres in the size fraction 75-250 μm, with a pronounced “burst release” associated with the presence of drug at the surface of the microspheres. A specific delineation of the drug release mechanism was not possible due to rapid gelation, swelling, and subsequent dissolution of the microspheres that occurred on hydration. This work describes the preparation of microspheres that swell rapidly and coalesce together on hydration, accompanied by rapid drug release and copolymer dissolution over a 2-hr period.     

Preparation of tritium-labeled modified single-walled carbon nanotubes for pharmacokinetic studies

Tritium was introduced by the thermal activation method into samples of single-walled carbon nanotubes modified with diaminotriethylene glycol. Chemical linking of the modifier considerably increased the specific radioactivity of the product. The maximal specific radioactivity was reached when “hot” (2000 K) tritium atoms acted on targets of modified nanotubes kept at 295 K. The main pharmacokinetic parameters of tritium-labeled modified carbon nanotubes upon intravenous administration into mongrel rats chosen as a model were determined.     

A study on the preparation and anti-tumor efficacy of bovine serum albumin nanospheres containing 5-fluorouracil

The therapeutic profile of many anti-cancer drugs has been improved by their modified distribution through a colloidal carrier system. Hence, bovine serum albumin nanospheres containing 5-fluorouracil were prepared by pH-coacervation methods. To select the most suitable cryoprotector for the formulated nanosphere system, a study on the effect of cryoprotectors in the prevention of particle agglomeration was done. Using glucose and mannitol at various concentrations during freeze drying, glucose at a concentration of 5% was observed to be relatively more effective in the prevention of particle agglomeration than the other cryoprotectors. The carrier capacity was determined through the drug-to-albumin ratio. The particle size of all the drug-loaded batches was analyzed before and after freeze drying. The batch of nanospheres with uniform size distribution, and highest drug loading, was used for other subsequent studies. The effect of surfactant in drug loading was estimated through various concentrations of sodium lauryl sulfate, and it was observed that the surfactant has no influence on drug loading at the selected concentrations. The batch of nanospheres with highest drug loading was evaluated for its in-vitro release, and the drug release was found to be in a bi-phasic pattern. To evaluate the efficacy of 5-fluorouracil-loaded nanospheres against cancer cells, an in vitro cytotoxicity study was carried out using HEp-2 cell lines. The nanosphere-bound drug was observed to produce a better cytotoxic effect than the free drug. The anti-tumor efficacy of drug-loaded nanosphere was investigated in DLA tumor-induced mice models, and the percentage tumor inhibition was relatively higher in animals treated with nanosphere-bound drug than with free drug.     

Modulated release of 5-fluorouracil from pH-sensitive and colon targeted pellets: An industrially feasible approach

Pellets, reliant on pH-sensitivity and time-dependency for drug delivery, provide one of the most versatile opportunities for targeting colon. 5-Fluorouracil (5-FU) loaded pellets were prepared by extrusion-spheronization using Avicel^® PH101 as a spheronization aid and hydroxypropylmethylcellulose K4M (HPMC K4M) solution as a binder. A 3² full factorial design was employed to optimize spheronization speed and time. Obtained pellets were evaluated for flow properties, pellet size, roundness and aspect ratio. Optimized batch was coated in a bottom-spray fluidized bed processor (FBP) with an inner coat of sustained release polymer Eudragit NE30D and an outer coat of pH-sensitive polymer Eudragit FS30D. The coating levels were statistically optimized and in vitro drug release was monitored by changing pH media method. Optimized system with 15% inner and outer coating levels revealed t_50% (time required for 50% drug release) to be about 9?h while almost complete drug was released in 24?h (98.71?±?1.33%) with highest dissolution efficiency (DE_24h) of 58.71%. The optimization model was validated; the predicted and experimental/actual values for validation batch (M1) were in close tolerance and the standard error (SE) was also small. Drug release was also studied at pH 7.4. Scanning electron microscopy (SEM) demonstrated average coating thickness to be 32.50?±?3.0 µm. Hence, the present study provides constructive results for colon targeting of 5-FU pellets with industrially feasible processes.     

Preparation and characterization of 5-fluorouracil pH-sensitive niosome and its tumor-targeted evaluation: in vitro and in vivo

The purpose of this study was to investigate preparation, characterization and tumor-targeted effect of pH-sensitive niosomes, composed of a nonionic surfactant mixed with cholesteryl hemisuccinate (CHEMS), a derivative of cholesterol (CHOL), as a pH-sensitive molecule.

CHEMS was synthesized with CHOL and succinic acid, the structure of which was analyzed by Mass spectrometry (MS) and ¹H Nuclear magnetic resonance (¹H NMR) spectrum. Niosomes were prepared via film hydration-probe ultrasound method. Both normal niosomes and pH-sensitive niosomes showed spherical morphology under transmission electron microscope (TEM) with a average particle sizes of 172?±?6.2?nm and 153?±?4.7?nm, respectively. The thermotropic behavior, structure changes and interaction of 5-fluorouracil (5-Fu) with other materials were characterized by differential scanning calorimetry (DSC), and the disappearance of the melting peak of drug revealed the fact that drug was encapsulated in niosomes. Bulk-equilibrium reverse-dialysis method was chosen to investigate the behavior of drug release from normal niosomes and pH-sensitive niosomes in different pH medium, and the results showed that the noisome containing CHEMS had a pH-sensitive property. Tumor-targeted effect was proved by the fact that pH-sensitive niosomes showed a remarkable high concentration in tumor site of the mice transplanted with tumor cell.