Synthesis of [¹¹C]uric acid, using [¹¹C]phosgene, as a possible biomarker in PET imaging for diagnosis of gout

The synthesis and in vivo evaluation of (11)C -labeled uric acid ([(11)C]1), a potential imaging agent for the diagnosis of urate-related life-style diseases, was performed using positron emission tomography (PET) image analysis. First, the synthesis of [(11)C]1 was achieved by reacting 5,6-diaminouracil (2) with (11)C-labeled phosgene ([(11)C]COCl(2)). The radiochemical yield of [(11)C]1 was 37±7% (decay-corrected based on [(11)C]COCl(2)) with specific radioactivities of 96-152GBq/μmol at the end of synthesis (n=6). The average time of radiosynthesis from the end of bombardment, including formulation, was about 30min with >98% radiochemical purity. Second, the synthetic approach to [(11)C]1 was optimized using 5,6-diaminouracil sulfate (3) with [(11)C]COCl(2) in the presence of 1,8-bis(dimethylamino)naphthalene. [(11)C]1 was synthesized in 36±6% radiochemical yield, 89-142GBq/μmol of specific radioactivities, and 98% radiochemical purity by this method (n=5). This allowed the synthesis of [(11)C]1 to be carried out repeatedly and the radiochemical yield, specific radioactivities, average time of synthesis, and radiochemical purity of [(11)C]1 were similar to those obtained using 2. PET studies in rats showed large differences in the accumulation of radioligand in the limbs under normal and hyperuricemic conditions. Thus, an efficient and convenient automated synthesis of [(11)C]1 has been developed, and preliminary PET evaluation of [(11)C]1 confirmed the increased accumulation of radioactivity in the limbs of a rat model of hyperuricemia.     

Measurement of methane emission from sheep by the sulphur hexafluoride tracer technique and by the calorimetric chamber: failure and success

The aim of this study was to evaluate the sulphur hexafluoride (SF6) tracer technique for methane (CH4) emission measurement in sheep. Ten cryptorchid Romney sheep were involved in two indoor trials (T1 and T2), where daily CH4 emissions were individually measured both by the SF6 tracer ('tracer CH4') and by the indirect calorimetry chamber ('chamber CH4') techniques while fed on lucerne hay at 1.2 times maintenance requirements. Separate sets of permeation tubes with pre-calibrated permeation rates ('pre-calibrated PRs') were used in the two trials (for tracer CH4) and at the time of T1 and T2 these tubes had been deployed in the rumen for 250 and 30 days, respectively. The tracer CH4 measurements were carried out for 2 (T1) and 5 (T2) days in digestibility crates housed within a building (T1) or a well-ventilated covered yard (T2). Sheep were transferred to calorimetry chambers for 3 days acclimatisation, followed by measurement of CH4 emission for 7 (T1) and 3 (T2) days. In T1 samples from the chamber, outflow and inflow (collected over ～22 h) were analysed for CH4 and SF6 concentrations using the tracer protocol. Thus, PRs of SF6 at the time of the trials ('calculated PRs') could be inferred and the corresponding CH4 emissions are then calculated using either the pre-calibrated PR or calculated PR. Permeation tubes were recovered at the end of the animal trials and their 'post-recovery PR' determined. In trial T1, the tracer CH4 estimates (based on the pre-calibrated PR) were much higher and more variable than the chamber CH4 values. In this trial, the calculated PR and the post-recovery PR were similar from each other but smaller than the pre-calibrated PR, and when the calculated PR was used in place of the pre-calibrated PR the CH4 emission estimates agreed well with the chamber CH4 values. This suggested that the discrepancy was due to a declining PR during the long deployment time of the tubes in T1, an observation reported elsewhere. When the long intra-ruminal deployment was avoided in T2, good agreement between the techniques for CH4 emission measurement was observed.     

Radiosynthesis of [11C]BBAC and [11C]BBPC as potential PET tracers for orexin2 receptors

Radiosynthesis of [N-methyl-(11)C](S)-N-([1,1'-biphenyl]-2-yl)-1-(2-((1-methyl-1H-benzo[d]imidazol-2-yl)thio)acetyl)pyrrolidine-2-carboxamide ([(11)C]BBAC or [(11)C]3) and [N-methyl-(11)C] (S)-N-([1,1'-biphenyl]-2-yl)-1-(3-(1-methyl-1H-benzo[d]imidazol-2-yl)propanoyl)pyrrolidine-2-carboxamide ([(11)C]BBPC or [(11)C]-4), two potential PET tracers for orexin2 receptors are described. Syntheses of non-radioactive standards 3, 4 and corresponding desmethyl precursors 1, 2 were achieved from common intermediate (S)-2-([1,1'-biphenyl]-2-yl)-1-(pyrrolidin-2-yl)ethanone. Methylation using [(11)C]CH(3)OTf in the presence of base in acetone afforded [(11)C]3 and [(11)C]4 in 30±5% yield (EOS) with >99 % radiochemical purities with a specific activity ranged from 2.5±0.5 Ci/μmol (EOB). The logP of [(11)C]3 and [(11)C]4 were determined as 3.4 and 2.8, respectively. The total synthesis time was 30 min from EOB. However, PET scans performed in a rhesus monkey did not show tracer retention or appropriate brain uptake. Hence [(11)C]3 and [(11)C]4 cannot be used as PET tracers for imaging orexin2 receptors.     

(N-succinimidyl 4-pentynoate)hexacarbonyldicobalt: a transition-metal carbonyl complex having similar uses to the Bolton-Hunter reagent

The synthesis of the transition-metal carbonyl complex (N-succinimidyl 4-pentynoate)hexacarbonyldicobalt [[(C4H4O2N)O(CO)CH2CH2C identical to CH]Co2(CO)6] is described. This cobalt carbonyl complex is structurally similar to the Bolton-Hunter conjugation reagent and has been successfully employed as a nonradioactive tracer for labeling the drug carbamazepine. The metal carbonyl tracer can be detected at extremely low concentrations (ca. 1 pmol) by FT-IR spectroscopy in the v(CO) region (2150-1800 cm-1). The cobalt carbonyl labeled carbamazepine retains good recognition for anti-carbamazepine antibodies. This novel labeling procedure, which can be broadly termed carbonylmetalloimmunoassay (CMIA), has considerable potential for assaying a wide range of biological materials.     

5-(5-(6-[(11)C]methyl-3,6-diazabicyclo[3.2.0]heptan-3-yl)pyridin-2-yl)-1H-indole as a potential PET radioligand for imaging cerebral α7-nAChR in mice

The radiosynthesis and in vivo evaluation of 5-(5-(6-[(11)C]methyl-3,6-diazabicyclo[3.2.0]heptan-3-yl)pyridin-2-yl)-1H-indole [(11)C]rac-(1), a potential PET tracer for α7 nicotinic acetylcholine receptors (α7-nAChR), are described. Syntheses of the nonradioactive standard rac-1 and corresponding desmethyl precursor 7 were achieved in several reaction steps. Radiomethylation of 7 with [(11)C]CH(3)I afforded [(11)C]rac-1 in an average radiochemical yield of 30 ± 5% (n=5) with high radiochemical purity and an average specific radioactivity of 444 ± 74 GBq/μmol (n=5). The total synthesis time was 30 min from end-of-bombardment. Biodistribution studies in mice showed that [(11)C]rac-1 penetrates the blood-brain barrier and specifically labels neuronal α7-nAChRs.     

DNA binding and cytotoxicity studies of magnetic nanofluid containing antiviral drug oseltamivir

In this work, the possibility of preparing a nanoparticle with improved treatment properties was investigated. In this regard, synthesis, characterization, in vitro cytotoxicity and DNA binding of Fe₃O₄@oleate/oseltamivir magnetic nanoparticles (MNPs) were investigated. Fe₃O₄ nanoparticles were synthesized via chemical co-precipitation and coated by oleate bilayers. Then, Fe₃O₄@OA MNPs were functionalized with an antiviral drug (oseltamivir), for better biological applications. The MNPs were subsequently characterized by zeta sizer and Zeta potential measurements, Fourier transform infrared (FT-IR) spectroscopy, vibrating sample magnetometer (VSM) and transmission electron microscopy (TEM) analyses. The TEM image demonstrated that average sizes of Fe₃O₄@OA/oseltamivir MNPs were about 8?nm. The in vitro cytotoxicity of Fe₃O₄@OA/oseltamivir MNPs was studied against cancer cell lines (MCF-7 and MDA-MB-231) and compared with oseltamivir drug. The results illustrated that Fe₃O₄@OA/oseltamivir magnetic nanoparticles have better antiproliferative effects on the mentioned cell lines as compared with oseltamivir. Also, in vitro DNA binding studies were done by UV–Vis, circular dichroism, and Fluorescence spectroscopy. The results indicated that Fe₃O₄@OA/oseltamivir MNPs bound to DNA via groove binding. Moreover, this magnetic nanofluid has potential for magnetic hyperthermia therapy due to magnetic core of its nanoparticles.

Communicated by Ramaswamy H. Sarma     

Synthesis, in vitro and in vivo evaluation of [O-methyl-11C] 2-{4-[4-(3-methoxyphenyl)piperazin-1-yl]-butyl}-4-methyl-2H-[1,2,4]-triazine-3,5-dione: a novel agonist 5-HT1A receptor PET ligand

Synthesis and in vivo evaluation of 2-{4-[4-(3-methoxyphenyl)piperazin-1-yl]-butyl}-4-methyl-2H-[1,2,4]triazine-3,5-dione (5 or MMT), a high affinity and selective serotonin 5-HT1AR agonist PET tracer, are described. GTPgammaS assay shows that MMT is an agonist with an EC50 comparable to 5-HT. Radiolabeling of 5 was achieved in 30% yield (EOS) from desmethyl-MMT (4) with >99% chemical and radiochemical purities and a specific activity >1000 Ci/mmol. PET studies in baboon show that [11C]5 penetrates the blood-brain barrier but, because of low specific binding and fast clearance of radioactivity it is not a suitable PET tracer for the in vivo quantification of 5-HT1AR.     

Evaluation of [11C]hemicholinium-15 and [18F]hemicholinium-15 as new potential PET tracers for the high-affinity choline uptake system in the heart

[(11)C]Hemicholinium-15 ([(11)C]HC-15) and [(18)F]hemicholinium-15 ([(18)F]HC-15) have been synthesized as new potential PET tracers for the heart high-affinity choline uptake (HACU) system. [(11)C]HC-15 was prepared by N-[(11)C]methylation of the appropriate precursor, 4-methyl-2-phenyl-morpholin-2-ol, using [(11)C]CH(3)OTf in 55-70% radiochemical yield decay corrected to end of bombardment (EOB) and 2-3Ci/mumol specific activity at end of synthesis (EOS). [(18)F]HC-15 was prepared by N-[(18)F]fluoromethylation of the precursor using [(18)F]FCH(2)OTf in 20-30% radiochemical yield decay corrected to EOB and >1.0Ci/mumol specific activity at EOS. The biodistribution of both compounds was determined in rats at 20min post-intravenous injection, and the results show the heart region uptakes 1.32+/-0.75%ID/g in R-ventricle for [(11)C]HC-15 and 1.28+/-0.81%ID/g in L-ventricle for [(18)F]HC-15, respectively. The dynamic PET imaging studies of [(11)C]HC-15 in rats were acquired 60min post-intravenous injection of the tracer using the IndyPET-II scanner. For the blocking experiments, the rats were intravenously pretreated with 3.0mg/kg of unlabeled HC-15 prior to [(11)C]HC-15 injection. [(11)C]HC-15 rat heart PET studies show rapid heart uptake to give clear heart images. The rat heart PET blocking studies found no significant blocking effect. The dynamic PET studies in normal and ablated dogs were performed using Siemens PET scanner with [(13)N]NH(3), [(11)C]HC-15, and [(18)F]HC-15. PET studies in dogs of both [(11)C]HC-15 and [(18)F]HC-15 also show significant heart uptake and give images of the heart. However, there is no significant change in [(11)C]HC-15 L-ventricle uptake following radiofrequency ablation in the dog. These results suggest that the localization of HC-15 tracers in the heart is mediated by non-specific processes, and the visualization of HC-15 tracers on the heart is related to non-specific binding of HACU.     

Synthesis of an acromelic acid A analog-based 11C-labeled PET tracer for exploration of the site of action of acromelic acid A in allodynia induction

A novel ¹¹C-labeled PET (positron emission tomography) tracer, which was designed based on the (phenylthio)pyrrolidine derivative that can competitively block the acromelic acid A-induced allodynia, was synthesized. A protocol in which methylation by palladium-mediated coupling of the boronate derivative with [¹¹C]CH₃I and deprotection of the protected amino acid moiety are successively performed in one-pot within 5 min was established for the synthesis of the tracer. The tracer is potentially useful as a tool to investigate the mode of action of acromelic acid A in the induction of allodynia.     

Modification of eremomycin by amine groups

Possible modification of eremomycin, a novel glycopeptide antibiotic by the amine groups with acylating agents such as Ac2O/MeOH and CH3(CH2)7COCl/Et3N and alkylating agents such as CH3CHO, NaBH and NaBH3CN was studied. N-Acetyl, N,N'-diacetyl. N-pelargoil, N-ethyl, N,N'-diethyl and N,N',N"-triethyl derivatives of eremomycin were prepared. Their structure was asserted and the order of the substitute introduction was determined. The antimicrobial activity against Bacillus subtilis and Staphylococcus aureus was assayed. It was found that with introduction of the ethyl substitutes to the eremomycin molecule the antibiotic activity lowered insignificantly whereas the acylation resulted in its decreasing by 1-2 orders.     

Effect of release rate of the SF(6) tracer on methane emission estimates based on ruminal and breath gas samples

The release rate (RR) of sulphur hexafluoride (SF(6)) gas from permeation tube in the rumen appears to be positively related with methane (CH(4)) emissions calculated using the SF(6) tracer technique. Gas samples of breath and ruminal headspace were collected simultaneously in order to evaluate the hypothesis that transactions of SF(6) in the rumen are the source for this relationship. Six non-lactating dairy cows fitted with rumen cannulae were subdivided into two groups and randomly assigned to a two-period crossover design to permeation tubes with low RR (LRR = 1.577 mg/day) or two-times higher RR (HRR = 3.147 mg/day) RR. The cows were fed limited amounts of maize silage (80% ad libitum) split into two meals (40% at 0800 h and 60% at 1600 h). Each period consisted of 3-day gas sampling. Immediately before the morning feed and then each hour over 8 h, ruminal gas samples (50 ml) were withdrawn through the cannula fitted with stoppers to prevent opening. Simultaneously, 8-h integrated breath gas samples were collected over the same period. Ratios of concentration of CH(4)/SF(6), CO(2)/SF(6) and CO(2)/CH(4) and emission estimates of CH(4) and CO(2) were calculated for each sample source using the SF(6) tracer technique principles. The LRR treatment yielded higher (P < 0.001) ruminal CH(4)/SF(6) (by 1.79 times) and CO(2)/SF(6) (by 1.90 times) ratios than the HRR treatment; however, these differences were lower than the 2.0 times difference expected from the RR between the LRR and HRR. Consequently, the LRR treatment was associated with lower (P < 0.01) ruminal emissions of CH(4) over the 8-h collection period than with the HRR treatment (+11%), a difference also confirmed by the breath samples (+11%). RR treatments did not differ (P = 0.53) in ruminal or breath CO(2) emissions; however, our results confirm that the SF(6) tracer seems inappropriate for CO(2) emissions estimation in ruminants. Irrespective of the RR treatment, breath samples yielded 8% to 9% higher CH(4) emission estimates than the ruminal samples (P = 0.01). The relationship between rumen and breath sources for CH(4) emissions was better for LRR than for HRR treatment, suggesting that tracer performance decreases with the highest RR of SF(6) tested in our study (3.1 mg/day). A hypothesis is discussed with regard to the mechanism responsible for the relationship between RR and CH(4) emission estimates. The use of permeation tubes with small range in RR is recommended in animal experiments to decrease variability in CH(4) emission estimates using the SF(6) tracer technique.     

Radiosynthesis and in vivo evaluation of [11C]MP-10 as a PET probe for imaging PDE10A in rodent and non-human primate brain

2-((4-(1-[(11)C]Methyl-4-(pyridin-4-yl)-1H-pyrazol-3-yl)phenoxy)methyl)-quinoline (MP-10), a specific PDE10A inhibitor (IC(50)=0.18 nM with 100-fold selectivity over other PDEs), was radiosynthesized by alkylation of the desmethyl precursor with [(11)C]CH(3)I, ～45% yield, >92% radiochemical purity, >370 GBq/μmol specific activity at end of bombardment (EOB). Evaluation in Sprague-Dawley rats revealed that [(11)C]MP-10 had highest brain accumulation in the PDE10A enriched-striatum, the 30 min striatum: cerebellum ratio reached 6.55. MicroPET studies of [(11)C]MP-10 in monkeys displayed selective uptake in striatum. However, a radiolabeled metabolite capable of penetrating the blood-brain-barrier may limit the clinical utility of [(11)C]MP-10 as a PDE10A PET tracer.     

Synthesis and in vitro evaluation of 68Ga-DOTA-4-FBn-TN14003, a novel tracer for the imaging of CXCR4 expression

The expression of the chemokine receptor CXCR4 in tumors is associated with tumor aggressiveness and poor prognosis for the patient and contributes to metastatic seeding. Therefore it is of high interest to find a specific PET tracer for the imaging of CXCR4 expression in tumors. The aim of this study was the synthesis, (68)Ga labeling and first evaluation of DOTA-4-FBn-TN14003 as a potential PET tracer for this purpose. DOTA-4-FBn-TN14003 was synthesized using solid phase peptide synthesis and radiolabeling of this versatile precursor was performed with (68)Ga, which was obtained from a (68)Ge/(68)Ga generator. (68)Ga-DOTA-4-FBn-TN14003 was reproducibly obtained in isolated radiochemical yields of 72.5±4.9% with an excellent radiochemical purity of >99.5%. Specific activities of up to 29.8±3.1 GBq/μmol were achieved. In competition binding assays with SDF-1α, human T cell lymphoma Jurkat cells expressed high levels of CXCR4 whereas human breast cancer MDA-MB-231 cells expressed significantly lower levels of this chemokine receptor. The inhibition constants (IC(50)) of Ga-DOTA-4-FBn-TN14003 and 4-FBn-TN14003 to CXCR4 were determined in a competition assay against (125)I-SDF-1α using Jurkat as well as MDA-MB-231 cells. The IC(50) values of Ga-DOTA-4-FBn-TN14003 (1.99±0.31 nM) and 4-FBn-TN14003 (4.07±1.00 nM) proved to be comparable, indicating negligible influence of the metal complex. These results suggest (68)Ga-DOTA-4-FBn-TN14003 as a promising agent for the imaging of CXCR4 expression in tumors and metastases.     

Synthesis, biological evaluation and radiochemical labeling of a dansylhydrazone derivative as a potential imaging agent for apoptosis

To develop a small molecule-based tracer for in vivo apoptosis imaging, dansylhydrazone (DFNSH) was synthesized in 93% yield in less than 30 min. The biological evaluation showed that DFNSH selectively binds to paclitaxel-induced apoptotic cancer cells. The high magnification fluorescent images demonstrate that DFNSH is localized within the cytoplasm of cells that bound Alexa 488 labeled annexin V on the plasma membrane. [(18)F]-DFNSH ([(18)F]-3) was synthesized and isolated in 50-60% radiochemical yields, based on [K/K(222)](18)F, with a synthesis time of 50 min (EOB). The straightforward preparation of fluorine-18 labeled 3 makes it a promising tracer for PET imaging of apoptosis.     

Efficient sequential synthesis of PET Probes of the COX-2 inhibitor [11C]celecoxib and its major metabolite [11C]SC-62807 and in vivo PET evaluation

Synthesis of [(11)C]celecoxib, a selective COX-2 inhibitor, and [(11)C]SC-62807, a major metabolite of celecoxib, were achieved and the potential of these PET probes for assessing the function of drug transporter in biliary excretion was evaluated. The synthesis of [(11)C]celecoxib was achieved in one-pot by reacting [(11)C]methyl iodide with an excess of the corresponding pinacol borate precursor using Pd(2)(dba)(3), P(o-tolyl)(3), and K(2)CO(3) (1:4:9) in DMF. The radiochemical yield of [(11)C]celecoxib was 63±23% (decay-corrected, based on [(11)C]CH(3)I) (n=7) with a specific radioactivity of 83±23GBq/μmol (n=7). The average time of synthesis from end of bombardment including formulation was 30min with >99% radiochemical purity. [(11)C]SC-62807 was synthesized from [(11)C]celecoxib by further rapid oxidation in the presence of excess KMnO(4) with microwave irradiation. The radiochemical yield of [(11)C]SC-62807 was 55±9% (n=3) (decay-corrected, based on [(11)C]celecoxib) with a specific radioactivity of 39±4GBq/μmol (n=3). The average time of synthesis from [(11)C]celecoxib including formulation was 20min and the radiochemical purity was >99%. PET studies in rats and the metabolite analyzes of [(11)C]celecoxib and [(11)C]SC-62807 showed largely different excretion processes, and consequently, [(11)C]SC-62807 was rapidly excreted via hepatobiliary excretion without further metabolism. [(11)C]SC-62807 was shown to have a high potential as a PET probe for evaluating drug transporter function in biliary excretion.     

The use of positron emission tomography for studies of long-distance transport in plants: uptake and transport of 18F

Abstract. Positron emission tomography (PET) has been utilized to obtain dynamic images of long distance nutrient translocation in plants. Positron emitting ¹⁸F, produced by a Van de Graaff accelerator using the reaction ¹⁸O(p,n)¹⁸F, was fed in solution to excised stems of Glycine max positioned vertically in a large-aperture PET detector system. Images of tracer activity were recorded with a time resolution of 0.5 min and a spatial resolution of 4 mm. Maximum tracer activities at stem sites were obtained within 3 min of the pulse feed. A model is presented enabling evaluation of regional values for tracer flow, tracer binding, flow speed and flow volume. Analysis of data for one stem position yielded a flow volume of 2.1mm³ min⁻¹ and a flow speed of 36cm min⁻¹. Comparison with the distribution of ¹⁴C-inulin, which was simultaneously fed to the cut stems, indicates the ¹⁸F is suitable for use as an apoplastic tracer; 92% of the tracer activity accumulated in the leaves. The fraction of ¹⁸F that remained bound was most concentrated at stem nodal regions, an observation consistent with the existence of transfer cells at these sites. Advantages and limitations of PET applied to plant physiological investigations are discussed.     

Synthesis, enantiomeric resolution, and selective C-11 methylation of a highly selective radioligand for imaging the norepinephrine transporter with positron emission tomography

Reboxetine, 2-[alpha-(2-ethoxyphenoxy)benzyl]morpholine, is a highly selective norepinephrine transporter (NET) blocker that has been used for the treatment of depression. Its methyl analogue, 2-[alpha-(2-methoxyphenoxy)benzyl]morpholine (MRB), has been radiolabeled with C-11 for studies of the NET system with positron emission tomography (PET). The normethyl precursor, 2-[alpha-(2-hydroxyphenoxy)benzyl]morpholine (desethylreboxetine), was synthesized in 6% overall yield via a multi-step regio- and stereo-specific synthesis, starting from a mono-O-protected catechol. The resulting racemic mixture of desethylreboxetine was resolved by chiral HPLC to provide the (2S,3S) and (2R,3R) enantiomers in >98% enantiomeric excess. These enantiomers were then used as precursors for radiosynthesis to prepare enantiomerically pure individual 11C-labeled MRB enantiomers for comparative PET studies in baboons. Selective C-11 methylation at the phenolic oxygen with [11C]CH3I was achieved in the presence of excess base. After HPLC purification, racemic ((2S,3S)/(2R,3R)) or enantiomerically pure ((2S,3S) or (2R,3R)) [11C]MRB was obtained in 61-74% decay-corrected radiochemical yields from [11C]CH3I in a synthesis time of 40 min with a radiochemical purity of >96% and a specific activity of 1.7-2.3 Ci/micromol (63-85 GBq/micromol) corrected from the end of bombardment (EOB).     

Radiosynthesis of [18F]Lu29-024: a potential PET ligand for brain imaging of the serotonergic 5-HT2 receptor

In a previous work, Lu29-024 (2,5-dimethyl-3-(4-fluorophenyl)-1-(1-methyl-4-piperidinyl)-1H-indole), a selective 5-HT2A receptor antagonist with nanomolar affinity and high selectivity, was labeled with carbon-11 to evaluate its behavior as a potential PET ligand for the serotonergic 5-HT2A receptor in the central nervous system. Administration of this tracer to rats was followed by a good brain uptake, no brain labeled metabolites but no specific, regio-selective, binding at 20 and 40 min post injection. Despite this, the data noted at 20 and 40 min suggest that this tracer, if associated with a radioactive emitter with a longer half-life than that of carbon-11, could be useful for the quantification of 5HT2A receptors. For these reasons, we chose to label this compound, bearing a fluorine atom, with [18F]fluoride, in order to perform rat studies over a more prolonged time-scale. The precursor for the radiosynthesis of [18F]Lu29-024 was obtained in an overall yield of 20% by a multi-step synthesis including an acetonylation reaction followed by a Fisher indole reaction. The radiotracer was prepared by an aromatic substitution with activated [18F]fluoride followed by a decarbonylation reaction that employed Wilkinson's catalyst. The radiosynthesis of [18F]Lu29-024 required approximatively 110 min with an overall radiochemical yield of 20-35% and specific activities of 37GBq/micromol. Fluorine-labeled Lu29-024 may thus be envisaged as a potentially useful PET tracer that can be applied to a wide range of neurological and psychiatric diseases.     

Synthesis and in vitro study of novel neuraminidase inhibitors against avian influenza virus

Evidences of oseltamivir resistant influenza patients raised the need of novel neuraminidase inhibitors. In this study, five oseltamivir analogs PMC-31-PMC-36, synthesised according to the outcomes of a rational design analysis aimed to investigate the effects of substitution at the 5-amino and 4-amido groups of oseltamivir on its antiviral activity, were screened for their inhibition against neuraminidase N1 and N3. The enzymes used as models were from the avian influenza A H7N1 and H7N3 viruses. The neuraminidase inhibition assay was carried out by using recombinant species obtained from a baculovirus expression system and the fluorogenic substrate MUNANA. The assay was validated by using oseltamivir carboxylate as a reference inhibitor. Among the tested compounds, PMC-36 showed the highest inhibition on N1 with an IC(50) of 14.6±3.0nM (oseltamivir 25±4nM), while PMC-35 showed a significant inhibitory effect on N3 with an IC(50) of 0.1±0.03nM (oseltamivir 0.2±0.02nM). The analysis of the inhibitory properties of this panel of compounds allowed a preliminary assessment of a structure-activity relationship for the modification of the 4-amido and 5-amino groups of oseltamivir carboxylate. The substitution of the acetamido group in the oseltamivir structure with a 2-butenylamido moiety reduced the observed activity, while the introduction of a propenylamido group was well tolerated. Substitution of the free 5-amino group of oseltamivir carboxylate with an azide, decreased the activity against both N1 and N3. When these structural changes were both introduced, a dramatic reduction of activity was observed for both N1 and N3. The alkylation of the free 5-amino group in oseltamivir carboxylate introducing an isopropyl group seemed to increase the inhibitory effect for both N1 and N3 neuraminidases, displaying a more pronounced effect against N1.     

Synthesis and ex vivo evaluation of carbon-11 labelled N-(4-methoxybenzyl)-N'-(5-nitro-1,3-thiazol-2-yl)urea ([11C]AR-A014418): a radiolabelled glycogen synthase kinase-3beta specific inhibitor for PET studies

N-(4-Methoxybenzyl)-N'-(5-nitro-1,3-thiazol-2-yl)urea (AR-A014418), a highly selective inhibitor of glycogen synthase kinase-3beta (GSK-3beta), was radiolabelled with carbon-11 (half-life=20.4min) for cerebral positron emission tomography (PET) studies. Reaction of desmethyl AR-A014418 with [(11)C]CH(3)I produced [(11)C]AR-A014418 in 17% decay-corrected radiochemical yield, based on [(11)C]CO(2), with 3230mCi/micromol specific activity after a 30min synthesis time. The desmethyl precursor of AR-A014418 was synthesized in 23% yield by a novel one-pot reaction of 2-amino-5-nitrothiazole with in situ generated TMS-protected 4-hydroxybenzylisocyanate, following deprotection with acid. Ex vivo biodistribution studies were conducted after [(11)C]AR-A014418 was administered via tail vein injection into Sprague-Dawley rats. Very low levels of radioactivity were found in all brain regions (0.08% injected dose/gram of tissue) at 5 and 30min post-injection, uncorrected for vascular compartment. Considering the extremely poor brain penetration of [(11)C]AR-A014418 this compound cannot be used to study GSK-3beta in cerebral PET studies. Furthermore, the specific pharmacological mechanism(s) of antidepressant-like activity attributed to AR-A014418 should be investigated.