α-Alkylation of amino acid derivatives: Synthesis and chiral resolution of [C]β-aminoisobutyric acid

A synthesis of ¹¹C-labeled β-aminoisobutyric acid ([¹¹C]β-AIB) and its enantiomeric resolution by high performance liquid chromatography (HPLC) are reported. β-Alanine ethyl ester 2 was converted to benzaldimine-β-alanine ethyl ester 3 in 87% yield. Treatment of the imine derivative 3 with lithium diisopropylamide (1.1 eq) in tetrahydrofuran at −78 °C, followed by addition of cold iodomethane (1.1 eq) produced the -methylated benzaldimine-β-alanine ethyl ester 4 in 73% chemical yield. Deprotection of the amino group by acidic hydrolysis followed by basic hydrolysis of the ester group produced the desired product 1 in 37% chemical yield. Labeling was accomplished using [¹¹C]methyl iodide. The radiola-beled product was purified by HPLC using a semipreparative reversed-phase C-18 column and 2 mM phosphate buffer (pH 5.9) as the mobile phase. The synthesis time was 35–40 min including HPLC purification, with 20–60% radiochemical yield (decay corrected). Radiochemical purity was >99%, with average specific activity being 450 mCi/μmol. Enantiomers of β-AIB were well separated by analytical HPLC using a chiral column and aqueous perchloric acid as the mobile phase. (S)-β-AIB was eluted at 17.4 min and the (R)-enantiomer was eluted at 20.0 min when the jacketed column was maintained at low temperature by circulation of ice-cold water, and the pH of the mobile phase was 1.05.     

Radiation chemistry in alanine irradiated with γ-rays and ion beams

In order to extend the application of alanine dosimetry, the behavior of free radicals in solid α-alanine irradiated with γ-rays with ions beams was studied by electron spin resonance. Stable neutral radicals are produced through the decomposition of originally generated ion radicals in alanine irradiated at 300 K, while at 77 K the ion radicals are stable, and also do not decompose. The rate of the combination reaction of the neutral radicals and of the iron radicals was studied by measuring the saturation behavior of the radical concentration in γ-radiolysis at 300 and at 77 K. The yield of the neutral radicals was compared between 0.5, 1, 2 and 3 MeV H⁺, 0.5, 1,and 3 MeV He⁺, 175 MeV Ar⁸⁺ and 460 MeV Ar¹³⁺ ion irradiations. Dependence of the radical yield on the radiation quality is understood more in terms of the rate of the combination reaction between the ion radicals that with that between the neutral radicals, and has to do with high local dose within the ion tracks.     

Synthesis of a [C]Methoxy derivative of α-Dihydrotetrabenazine: a radioligand for studying the vesicular monoamine transporter

The synthesis of [¹¹C]TBZOMe, a [¹¹C]methoxy derivative at the 2-hydroxy position of α-dihydrotetrabenazine, was carried out by an O-[¹¹C]methylation reaction. The product [¹¹C]TBZOMe (100–200 mCi) was obtained in 15–40% radiochemical yield (corrected for decay) within 37 min, and in high specific activity (2000–2500 Ci/mmol) and radiochemical purity (>97%). [¹¹C]TBZOMe is a potential new radioligand for studying the vesicular monoamine transporter using positron emission tomography.     

2β-carbomethoxy-3β-(4- and 2-[F]fluoromethylphenyl)tropanes: specific probes for in vivo quantification of central dopamine transporter sites

Dopamine reuptake transporter binding kinetics of 2β-carbomethoxy-3β-(4-[¹⁸F]fluoromethylphenyl)tropane (p-FWIN) and 2β-carbomethoxy-3β-(2-[¹⁸F]fluoromethylphenyl)tropane (o-FWIN) were determined in vervet monkeys using positron emission tomography (PET). Ligand localization was rapid and specific to the striatum with kinetic estimates comparable with those of ¹¹C-labeled WIN 35,428 (CWIN). Binding was more specific with p-FWIN than with CWIN or o-FWIN. The relatively longer half-life of the ¹⁸F radiolabel enabled longer acquisition times with p-FWIN, resulting in less variability in the kinetic estimates.     

Radiosynthesis of 1-[F]fluoroethyl-L-tryptophan as a novel potential amino acid PET tracer

¹⁸F labeled natural amino acids have been introduced as promising tumor imaging agents. A novel [¹⁸F]fluoro amino acid analog 1-[¹⁸F]fluoroethyl-L-tryptophan (1-[¹⁸F]FETrp) was designed and synthesized by a two-pot three-step procedure, including the synthesis of 1-[¹⁸F]fluoro-2- (tosyloxy)ethane, the [¹⁸F]fluoroethylation of the precursor N-Boc-L-tryptophan ethyl ester and following the deprotection of the tert-butoxycarbonyl and ethyl ester protecting groups. 1-[¹⁸F]FETrp was resulted in 0.9±0.2% (n=5) radiochemical yields (no decay corrected) by HPLC purification, within a total synthesis time of 65 min. The radiochemical purity of 1-[¹⁸F]FETrp was 95-97%. The radiosynthetic method needs to be further optimized to get a satisfying radiochemical yield.     

The efficiency variation method for 4πβ−γ coincidence counting by ink-jet printing

In order to vary the counting efficiencies in the 4πβ−γ coincidence extrapolation technique, a radioactive source was coated directly with varying amounts of an electrical conducting pigment using an ink-jet printer. This method can be used to efficiently prepare the multiple sources needed to generate efficiency extrapolation curves, and was successfully applied to the standardization of a ⁵⁴Mn source.     

Standardization of F using the 4π(β+γ) integral counting technique

Α 4π(β+γ) integral counting technique using a 4πβ−4πγ detector configuration was adopted for the standardization of ¹⁸F. In this technique, the β-detector is composed of two thin plastic scintillators sandwiching the source, coupled with a slender photomultiplier tube. The β-detector part with the source was inserted into a large well-type NaI(Tl) scintillation detector for γ-ray detection, making a 4πβ−4πγ coincidence counting system. In this work, positron particles were detected with high efficiency in the β-channel and annihilation quanta were also detected with high efficiency in the 4πγ channel. The very small inefficiency of the 4π(β+γ) integral counter for the β-plus branch has been confirmed by EGS5 Monte Carlo simulation. The result using this technique agreed within the uncertainties with the result obtained by the conventional 4πβ−γ coincidence counting with the efficiency extrapolation technique using the same detector configuration and a conventional 4πβ−γ coincidence counter.     

A new synthesis of [3-C]pyruvic acid using alanine racemase

The synthesis of [3-¹¹C]pyruvic acid was attempted by two reaction systems (A: alanine racemase and -amino acid oxidase, B: alanine racemase and -alanine dehydrogenase) utilizing a new thermostable enzyme, alanine racemase. Conversion rates from , -[3-¹¹C]alanine to [3-¹¹C]pyruvic acid were almost 100% in both methods. Similar results were obtained with immobilized enzymes packed in a single column. Furthermore, the same column could be used repeatedly without a remarkable decrease of the [3-¹¹C]pyruvic acid yield. Various matrices were tested for the immobilizing enzyme, and Aminopropyl-CPG was concluded to be the most suitable since the loss of the enzyme activity was the least in the studied matrices.     

Synthesis and biodistribution of R- and S-isomers of [F]-fluoropropranolol, a lipophilic ligand for the β-adrenergic receptor

The S and R isomers of [¹⁸F]-fluoropropranolol (1-[1-fluoro-2-isopropylamino]-3-naphthalen-1-yloxy-propan-2-ol) have been prepared by reductive alkylation of the appropriate aminoalcohols. The radiosynthesis provides a reasonable yield (25%) to give products of 99% enantiomeric excess and specific activities of 1–3 Ci/μmol. The dissociation constants for the β₂ adrenergic receptor are 0.5 and 2.5 nM for the S and the R isomers, respectively. The biodistribution data in rats show that uptake and egress of the tracer is rapid but that the result of blocking studies and the difference between the R and the S isomers suggest receptor-mediated uptake in receptor-rich tissue.     

Observation of β-ray spectra after penetrating absorbing materials

β-Ray spectra after penetrating absorbing materials of various thicknesses were observed by the use of a scintillation-type β-ray spectrometer equipped with a flat NE-102 plastic scintillator of 5 mm thickness for sources of ⁶⁰Co, ⁹⁰Sr–⁹⁰Y, ¹³⁷Cs, ¹⁴⁷Pm and ²⁰⁴Tl. Although the spectra changed rapidly with increasing absorber thickness, the average β-ray energy was kept nearly constant for a wider range. These results are consistent in that the β-ray absorption curve becomes quasi-linear in a semi-logarithmic plot. Spectra including scattered β-rays from several materials placed behind the source were also measured for ¹³⁷Cs and ²⁰⁴Tl. It may be concluded that mean energy measurements by the use of β-ray spectrometer of this kind is useful for the identification of nuclides in radiation protection purposes even in worse source-conditions.     

Effects of γ-radiation on the fungus Alternaria alternata in artificially inoculated cereal samples

The objective of this study was to evaluate the effects of different γ-radiation doses on the growth of Alternaria alternata in artificially inoculated cereal samples. Seeds and grains were divided into four groups: Control Group (not irradiated), and Groups 1, 2 and 3, inoculated with an A. alternata spore suspension (1×10⁶ spores/mL) and exposed to 2, 5 and 10 kGy, respectively. Serial dilutions of the samples were prepared and seeded on DRBC (dichloran rose bengal chloramphenicol agar) and DCMA (dichloran chloramphenicol malt extract agar) media, after which the number of colony-forming units per gram was determined in each group. In addition, fungal morphology after irradiation was analyzed by scanning electron microscopy (SEM). The results showed that ionizing radiation at a dose of 5 kGy was effective in reducing the growth of A. alternata. However, a dose of 10 kGy was necessary to inhibit fungal growth completely. SEM made it possible to visualize structural alterations induced by the different γ-radiation doses used.     

Enzymatic synthesis of no-carrier-added 6-[F]fluoro- -dopa with β-tyrosinase

An enzymatic synthesis of nca 6-[¹⁸F]fluoro- -dopa has been developed. The process consists of a chemical synthesis of 4-[¹⁸F]fluorocatechol and its enzymatic reaction with β-tyrosinase. The 4-[¹⁸F]fluorocatechol was prepared by nucleophilic aromatic substitution of the NO₂ group on 6-nitroveratoraldehyde with [K/222]⁺¹⁸F⁻, followed by decarbonylation with tris(triphenylphosphine) rhodium(I) chloride and hydrolysis with hydroiodic acid. By C18 Sep-Pak purification, 4-[¹⁸F]fluorocatechol was obtained in ethanol with a radiochemical yield of 9.2%. An enzymatic reaction of 4-[¹⁸F]fluorocatechol, ammonium and pyruvate catalyzed by β-tyrosinase in an ethanolic Tris–HCl buffer (pH 9.0) containing ascorbate gave within 5 min 6-[¹⁸F]fluoro- -dopa with an approximate radiochemical yield of 60% without any isomers. The deproteinized reaction mixture was applied to a preparative reverse phase column, and the radiochemically and enantiomerically pure 6-[¹⁸F]fluoro- -dopa was obtained with a radiochemical yield of 2.0% based on [¹⁸F]F⁻ (decay-corrected). The synthesis time was 150 min from the EOB and the specific activity was >200 GBq/μmol.     

Distribution of estrone sulfatase in rat brain determined by in vitro autoradiography with 16α-[F]fluoroestradiol-3,17β-disulfamate

16α-Fluoroestradiol-3,17β-disulfamate (FESDS) strongly inhibits estrone sulfatase (ES), an enzyme which is also present in the brain. The enzyme is probably involved in important regulatory functions of neurosteroids which may be disturbed in certain brain diseases. In the present study, [¹⁸F]FESDS was used to measure the amount of ES in various rat brain regions using quantitative in vitro autoradiography. The obtained values vary between 0.29 pmol (mg protein)^–1 (pons) and 11.5 pmol (mg protein)^–1 (striatum). They are positively correlated with the enzyme activity measured in homogenates of the corresponding regions. Because this radiotracer binds also to carbonic anhydrase in the brain it is only of limited use for in vivo imaging studies.     

Optimisation study of α-cyclotron production of At-211/Po-211g for high-LET metabolic radiotherapy purposes

The production of no-carrier-added (NCA) α-emitter ²¹¹At/^211gPo radionuclides for high-LET targeted radiotherapy and immunoradiotherapy, through the ²⁰⁹Bi(α,2n) reaction, together with the required wet radiochemistry and radioanalytical quality controls carried out at LASA is described, through dedicated irradiation experiments at the MC-40 cyclotron of JRC-Ispra. The amount of both the γ-emitter ²¹⁰At and its long half-lived α-emitting daughter ²¹⁰Po is optimised and minimised by appropriate choice of energy and energy loss of α particle beam. The measured excitation functions for production of the main radioisotopic impurity ²¹⁰At→²¹⁰Po are compared with theoretical predictions from model calculations performed at ENEA.     

Stereoselective synthesis, in vitro, and initial in vivo evaluation of 1-methylpiperidin-4-yl α-hydroxy-α-(1-iodo-1-propen-3-yl)-α-phenylacetate (IPIP): a novel radioiodinated molecular probe with high affinity for the muscarinic receptor

1-Methylpiperidin-4-yl α-hydroxy-α-(1-iodo-1-propen-3-yl)-α-phenylacetate (IPIP, Fig. 1) was investigated as a potential radioiodinated molecular probe targeted to the muscarinic receptor complex. The IPIP stereoisomers were synthesized via a chiral intermediate in >95% enantiomeric excess. The R-isomers demonstrated a M₁ to M₂ subtype selectivity of approximately 3 to 1 and the S-isomers demonstrated non-subtype selective binding in vitro. IPIP was radiolabeled with iodide-125 with an average radiochemical yield of 74.4% (±14.8, N = 5), specific activities >800 mCi/μmol, and radiochemical purities >97%. In vivo the Z-isomers demonstrated high uniform cerebral uptake suggesting non-subtype selective binding. In contrast, E-R-IPIP, after allowing a low uptake in M₂ rich areas to clear, demonstrated a retention of activity in M₁ and M₄ rich cerebral regions. In addition, the cerebral uptake of E-R-IPIP and Z-S-IPIP were inhibited by 70–90% via pretreatment with R-QNB, an established muscarinic antagonist. An ex vivo metabolism study demonstrated Z-S-IPIP was stable at the receptor site with an absence of radiolabeled metabolites.

Full-size image (6K)

Fig. 1. QNB and various radiolabeled mAChR antagonists.

Synthesis of [131I/123I]-2-{5-(4-iodophenyl)pentyl}oxirane-2-carboxylic acid ethyl ester

A method is described for the synthesis, purification and radiolabelling of [¹²³I/¹³¹I]2-{5-(4-iodophenyl)-pentyl}oxirane-2-carboxylic acid ethyl ester. For the synthesis of this new agent, 5-phenylpentyl bromide (1), synthesized by reacting 5-phenyl-I-pentanol with sodium bromide under acidic conditions, was converted to diethyl 5-phenylpentylmalonate (2), which, on alkaline hydrolysis, yielded ethyl 5-phenyl-pentylmalonate (3). Ethyl 7-phenyl-2-methyleneheptanoate (4), prepared from the monoester (3), was oxidized with m-chloroperbenzoic acid to yield ethyl 2-(5-phenylpentyl)oxirane-2-carboxylate 5. The method of radiolabelling, based on the thallation of compound (5) and the subsequent treatment with radioiodide, resulted in a regioselective radioiodination with a 54% radiochemical yield.     

α-Particle and γ-ray spectrometry of a plutonium solution for impurity determination

A highly enriched ²⁴⁰Pu solution was measured by α-particle and γ-ray spectrometry to determine other radionuclides present in the material as impurities. Low activities of ²³⁸Pu, ²⁴¹Am, ²⁴³Cm and ²⁴⁴Cm were determined by measuring thin sources, made from the original solution, in a high-resolution alpha-particle spectrometer. The sources were prepared by evaporating the plutonium solution on quartz plates in a vacuum chamber. From the ingrowth of ²⁴¹Am in the original solution, the amount of ²⁴¹Pu could be calculated. After radiochemical separation of ²⁴¹Am, the plutonium was measured by high-efficiency alpha-particle spectrometry to determine the amount of ²³⁸Pu. The enriched ²⁴⁰Pu material was also measured by high-resolution gamma-ray spectrometry, using two different HPGe detectors to determine the impurities of ²³⁹Pu and ²⁴¹Am. The preparation of the sources and the measurement methods are described and discussed. The measured impurities, given in % of the ²⁴⁰Pu activity, are compared with the values on the certificate.     

Production of Ho through Dy(n,γ)Dy(n, γ)Dy(β)Ho and separation of Ho

After irradiation with thermal neutrons ¹⁶⁴Dy produces ¹⁶⁶Ho through the nuclear reaction: ¹⁶⁴Dy(n,γ) ¹⁶⁵Dy(n,γ) ¹⁶⁶Dy ¹⁶⁶Ho. ¹⁶⁶Ho has been separated from the bulk dysprosium target with the help of HPLC using Aminex A7 ion exchanger resin and -hydroxyisobutyric acid (-HIBA) as the mobile phase. The separation was quantitative and without any contamination from the dysprosium target. Method has also been developed to produce holmium free of -HIBA ligands. Attempts have been made to produce no-carrier-added recoiled ¹⁶⁶Ho and ¹⁶⁵Dy in water.     

Determination of some antiallergic drugs in human plasma by direct-injection high-performance liquid chromatography-tandem mass spectrometry

A detailed procedure for analysis of four antiallergic drugs, ketotifen, olopatadine, cetirizine, and ibudilast, in human plasma by high-performance liquid chromatography (HPLC)-tandem mass spectrometry (MS-MS) using a new polymer column (MSpak GF), which enables direct injection of crude biological samples, is presented. The protein and/or macromolecule matrix compounds were first eluted from the column, while the drugs were retained on the polymer stationary phase. The analytes retained on the column were then eluted into an acetonitrile-rich mobile phase using a gradient separation technique. All compounds showed base peaks due to [M + H]⁺ ions by HPLC-MS with positive ion electrospray ionization, and the product ions were produced from each [M + H]⁺ ion by HPLC-MS-MS. Quantification was made by selected reaction monitoring. The recoveries of the four antiallergic drugs spiked into plasma were 51.7–95.5%. The regression equations for the four antiallergic drugs showed excellent linearity in the range of 1–100 ng/ml of plasma. The detection limit was 0.5 ng/ml for all compounds. The intraday and interday precisions for the drugs in plasma were not greater than 9.5%. The data obtained from actual determination of the antiallergic drugs in human plasma after their oral administration are also presented for validation of the method.     

Advanced γ ray technology for scanning cargo containers

The shipping industry is striving to increase security for cargo containers without significantly impeding traffic. Three Science Applications International Corporation (SAIC) development programs are supporting this effort. SAIC's ICIS system combines SAIC's VACIS^® γ ray imaging, radiation scanning, OCR, elemental analysis and other technologies to scan containers for nuclear materials and other hazards in normal terminal traffic. SAIC's enhanced γ ray detector improves VACIS image resolution by a factor of three. And SAIC's EmptyView software analyzes VACIS images to automatically verify empty containers.