Hepatic UDP-glucose 13C isotopomers from [U-13C]glucose: a simple analysis by 13C NMR of urinary menthol glucuronide.

Menthol glucuronide was isolated from the urine of a healthy 70-kg female subject following ingestion of 400 mg of peppermint oil and 6 g of 99% [U-(13)C]glucose. Glucuronide (13)C-excess enrichment levels were 4-6% and thus provided high signal-to-noise ratios (SNRs) for confident assignment of (13)C-(13)C spin-coupled multiplet components within each (13)C resonance by (13)C NMR. The [U-(13)C]glucuronide isotopomer derived via direct pathway conversion of [U-(13)C]glucose to [U-(13)C]UDP-glucose was resolved from [1,2,3-(13)C(3)]- and [1,2-(13)C(2)]glucuronide isotopomers derived via Cori cycle or indirect pathway metabolism of [U-(13)C]glucose. In a second study, a group of four overnight-fasted patients (63 +/- 10 kg) with severe heart failure were given peppermint oil and infused with [U-(13)C]glucose for 4 hr (14 mg/kg prime, 0.12 mg/kg/min constant infusion) resulting in a steady-state plasma [U-(13)C]glucose enrichment of 4.6% +/- 0.6%. Menthol glucuronide was harvested and glucuronide (13)C-isotopomers were analyzed by (13)C NMR. [U-(13)C]glucuronide enrichment was 0.6% +/- 0.1%, and the sum of [1,2,3-(13)C(3)] and [1,2-(13)C(2)]glucuronide enrichments was 0.9% +/- 0.2%. From these data, flux of plasma glucose to hepatic UDPG was estimated to be 15% +/- 4% that of endogenous glucose production (EGP), and the Cori cycle accounted for at least 32% +/- 10% of GP.     

Quantitation of erythrocyte pentose pathway flux with [2-13C]glucose and 1H NMR analysis of the lactate methyl signal.

A simple and sensitive NMR method for quantifying excess (13)C-enrichment in positions 2 and 3 of lactate by (1)H NMR spectroscopy of the lactate methyl signal is described. The measurement requires neither signal calibrations nor the addition of a standard and accounts for natural abundance (13)C-contributions. As a demonstration, the measurement was applied to approximately 3 micromol of lactate generated by erythrocyte preparations incubated with [2-(13)C]glucose to determine the fraction of glucose metabolized by the pentose phosphate pathway (PP). PP fluxes were estimated from the ratio of excess (13)C-enrichment in lactate carbon 3 relative to carbon 2 in accordance with established metabolic models. Under baseline conditions, PP flux accounted for 7 +/- 2% of glucose consumption while in the presence of methylene blue, a classical activator of PP activity, its contribution increased to 27 +/- 10% of total glucose consumption (P < 0.01).     

1H‐[13C] NMR spectroscopy of the rat brain during infusion of [2‐13C] acetate at 14.1 T

Full signal intensity ¹H‐[¹³C] NMR spectroscopy, combining a preceding ¹³C‐editing block based on an inversion BISEP (B₁‐insensitive spectral editing pulse) with a spin‐echo coherence–based localization, was developed and implemented at 14.1 T. ¹³C editing of the proposed scheme was achieved by turning on and off the ¹³C adiabatic full passage in the ¹³C‐editing block to prepare inverted and noninverted ¹³C‐coupled ¹H coherences along the longitudinal axis prior to localization. The novel ¹H‐[¹³C] NMR approach was applied in vivo under infusion of the glia‐specific substrate [2‐¹³C] acetate. Besides a ～50% improvement in sensitivity, spectral dispersion was enhanced at 14.1 T, especially for J‐coupled metabolites such as glutamate and glutamine. A more distinct spectral structure at 1.9–2.2 ppm(parts per million) was observed, e.g., glutamate C3 showed a doublet pattern in both simulated ¹H spectrum and in vivo ¹³C‐edited ¹H NMR spectra. Besides ¹³C time courses of glutamate C4 and glutamine C4, the time courses of glutamate C3 and glutamine C3 obtained by ¹H‐[¹³C] NMR spectroscopy were reported for the first time. Such capability should greatly improve the ability to study neuron‐glial metabolism using ¹H‐observed ¹³C‐edited NMR spectroscopy. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Methionine-dependence phenotype of tumors: metabolite profiling in a melanoma model using L-[methyl-13C]methionine and high-resolution magic angle spinning 1H-13C nuclear magnetic resonance spectroscopy.

Tumors frequently have abnormal L-methionine (Met) metabolism, the so-called Met-dependence phenotype that refers to the inability to proliferate in the absence of Met. However, the origin of this phenotype is still unknown and may arise from one of several pathways of Met metabolism. To help characterize the metabolic features of Met-dependent/independent phenotypes, the fate of the methyl carbon of L-[methyl-13C]Met was chased in a murine model of malignant melanoma (B16-F1) in vitro and in vivo. Growth curves under Met restriction showed that melanoma cells in vitro were Met-independent, whereas implanted melanoma tumors in vivo were Met-dependent. Label-assisted high-resolution magic angle spinning 1H-13C NMR spectroscopy metabolite profiling showed that, in vitro, creatine and phosphatidylcholine 13C-enrichments were poor, but S-adenosyl-Met and posttranslationally N-methylated protein signals were strong. In contrast, in vivo, creatine and phosphatidylcholine enrichments were strong but S-adenosyl-Met and N-methylated protein signals were poor. In addition, in vivo, transsulfuration was very efficient, consumed one-carbon units originating from the methyl carbon of Met, and yielded taurine labeling. From these data, the Met-dependent/independent phenotypes appear closely related to the source of one-carbon units. Thus, L-[methyl-13C]Met-assisted NMR spectroscopy metabolite profiling allowed the discrimination between Met-dependence and Met-independence and provided novel mechanistic information on their origin.     

A method for measuring cerebral glucose metabolism in vivo by 13C-NMR spectroscopy.

Current methods for estimating the rate of cerebral glucose utilization (CMR(glc)) typically measure metabolic activity for 40 min or longer subsequent to administration of [(13)C]glucose, 2-[(14)C]deoxyglucose, or 2-[(18)F]deoxyglucose. We report preliminary findings on estimating CMR(glc) for a period of 15 min by use of 2-[6-(13)C]deoxyglucose. After a 24-hr fast, rats were anesthetized, infused with [1-(13)C]glucose for 50 min, and injected with 2-[6-(13)C]deoxyglucose (500 mg/kg). During the subsequent 12.95 min the estimated value of CMR(glc) was 0.6 +/- 0.4 micromol/min/g (mean +/- SD, N = 7), in agreement with values reported for anesthetized rats studied with the 2-[(14)C]deoxyglucose method and other (13)C-NMR methods that measure CMR(glc). In rats injected with bicuculline methiodide (a known stimulant of CMR(glc)), CMR(glc) increased by more than 75% during 12.95 min following injection of bicuculline (Wilcoxon signed rank test, P = 0.042, N = 8).     

1-13C]glucose MRS in chronic hepatic encephalopathy in man.

[1-13C]-labeled glucose was infused intravenously in a single dose of 0.2 g/kg body weight over 15 min in six patients with chronic hepatic encephalopathy, and three controls. Serial 13C MR spectra of the brain were acquired. Patients exhibited the following characteristics relative to normal controls: 1) Cerebral glutamine concentration was increased (12.6 +/- 3.8 vs. 6.5 +/- 1.9 mmol/kg, P < 0.006) and glutamate was reduced (8.2 +/- 1.0 vs. 9.9 +/- 0.6 mmol/kg, P < 0.02). 2) 13C incorporation into glutamate C4 and C2 positions was reduced in patients (80 min after start of infusion C4: 0.43 +/- 0.09 vs. 0.84 +/- 0.15 mmol/kg, P < 0.001; C2: 0.20 +/- 0.03 vs. 0.45 +/- 0.07 mmol/kg, P < 0.0001). 3) 13C incorporation into bicarbonate was delayed (90 +/- 21 vs. 40 +/- 10 min, P < 0.003), and the time interval between detection of glutamate C4 and C2 labeling was longer in patients (22 +/- 8 vs. 12 +/- 3 min, P < 0.03). 4) Glutamate C2 turnover time was reduced in chronic hepatic encephalopathy (17.1 +/- 6.8 vs. 49.6 +/- 8.7 min, P < 0.0002). 5) 13C accumulation into glutamine C2 relative to its substrate glutamate C2 increased progressively with the severity of clinical symptoms (r = 0.96, P < 0.01). These data indicate disturbed neurotransmitter glutamate/glutamine cycling and reduced glucose oxidation in chronic hepatic encephalopathy. [1-13C] glucose MRS provides novel insights into disease progression and the pathophysiology of chronic hepatic encephalopathy.     

13C NMR study of the generation of C2- and C3,-deuterated lactic acid by tumoral pancreatic islet cells exposed to D-[1-13C]-, D-[2-13C]- and D-[6-13C]-Glucose in 2H2O

Tumoral pancreatic islet cells of the RIN5mF line were incubated for 120 min in media prepared in ²H₂O and containing D -[1-¹³C]glucose, and D -[2-¹³C]glucose, and D -[6-¹³C]glucose. The generation of C₂- and C₃- deuterated lactic acid was assessed by ¹³C NMR. The interpretation of experimental results suggests that a) the efficiency of deuteration on the C₁ of D-fructose 6-phosphate does not exceed about 47% and 4% in the phosphoglucoisomerase and phosphomannoisomerase reactions, respectively; b) approximately 38% of the molecules of D -glyceraldehyde 3-phosphate generated from D -glucose escape deuteration in the sequence of reactions catalyzed by triose phosphate isomerase and aldolase; and c) about 41% of the molecules of pyruvate generated by glycolysis are immediately converted to lactate, the remaining 59% of pyruvate molecules undergoing first a single or double back-and-forth interconversion with L -alanine. It is proposed that this methodological approach, based on high resolution ¹³C NMR spectroscopy, may provide novel information on the regulation of back-and-forth interconversion of glycolytic intermediates in intact cells as modulated, for instance, by enzyme-to-enzyme tunneling.     

Methods for metabolic evaluation of prostate cancer cells using proton and 13C HR‐MAS spectroscopy and [3‐13C] pyruvate as a metabolic substrate

Prostate cancer has been shown to undergo unique metabolic changes associated with neoplastic transformation, with associated changes in citrate, alanine, and lactate concentrations. ¹³C high resolution‐magic angle spinning (HR‐MAS) spectroscopy provides an opportunity to simultaneously investigate the metabolic pathways implicated in these changes by using ¹³C‐labeled substrates as metabolic probes. In this work, a method to reproducibly interrogate metabolism in prostate cancer cells in primary culture was developed using HR‐MAS spectroscopy. Optimization of cell culture protocols, labeling parameters, harvesting, storage, and transfer was performed. Using [3‐¹³C] pyruvate as a metabolic probe, ¹H and ¹³C HR‐MAS spectroscopy was used to quantify the net amount and fractional enrichment of several labeled metabolites that evolved in multiple cell samples from each of five different prostate cancers. Average enrichment across all cancers was 32.4 ± 5.4% for [3‐¹³C] alanine, 24.5 ± 5.4% for [4‐¹³C] glutamate, 9.1 ± 2.5% for [3‐¹³C] glutamate, 25.2 ± 5.7% for [3‐¹³C] aspartate, and 4.2 ± 1.0% for [3‐¹³C] lactate. Cell samples from the same parent population demonstrated reproducible fractional enrichments of alanine, glutamate, and aspartate to within 12%, 10%, and 10%, respectively. Furthermore, the cells produced a significant amount of [4‐¹³C] glutamate, which supports the bioenergetic theory for prostate cancer. These methods will allow further characterization of metabolic properties of prostate cancer cells in the future. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

In vivo detection of cortical GABA turnover from intravenously infused [1-13C]D-glucose.

In this study [2-(13)C] gamma-aminobutyric acid (GABA) was spectrally resolved in vivo and detected simultaneously with [4-(13)C]glutamate (Glu) and [4-(13)C]glutamine (Gln) in the proton spectra obtained from a localized 40 microL voxel in rat neocortex with the use of an adiabatic (1)H-observed, (13)C-edited (POCE) spectroscopy method and an 89-mm-bore vertical 11.7 Tesla microimager. The time-resolved kinetics of (13)C label incorporation from intravenously infused [1-(13)C]glucose into [4-(13)C]Glu, [4-(13)C]Gln, and [2-(13)C]GABA were measured after acute administration of gabaculine, a potent and specific inhibitor of GABA-transaminase. In contrast to previous observations of a rapid turnover of [2-(13)C]GABA from [1-(13)C]glucose in intact rat brain, the rate of (13)C incorporation from [1-(13)C]glucose into [2-(13)C]GABA in the gabaculine-treated rats was found to be significantly reduced as a result of the blockade of the GABA shunt.     

IDEAL spiral CSI for dynamic metabolic MR imaging of hyperpolarized [1-13C]pyruvate

Metabolic imaging with hyperpolarized [1-(13)C]pyruvate offers the unique opportunity for a minimally invasive detection of cellular metabolism. Efficient and robust acquisition and reconstruction techniques are required for capturing the wealth of information present for the limited duration of the hyperpolarized state (~1 min). In this study, the Dixon/IDEAL type of water-fat separation is expanded toward spectroscopic imaging of [1-(13) C]pyruvate and its down-stream metabolites. For this purpose, the spectral-spatial encoding is based on single-shot spiral image encoding and echo-time shifting in between excitations for the chemical-shift encoding. In addition, also a free-induction decay spectrum is acquired and the obtained chemical-shift prior knowledge is efficiently used in the reconstruction. The spectral-spatial reconstruction problem is found to efficiently separate into a chemical-shift inversion followed by a spatial reconstruction. The method is successfully demonstrated for dynamic, multislice [1-(13)C]pyruvate metabolic MR imaging in phantom and in vivo rat experiments.     

Preferential labeling of glial and meningial brain tumors with [2-(14)C]acetate.

Acetate is preferentially transported into and metabolized by astrocytes, rather than synaptosomes or neurons, and labeled acetate is used as a glial reporter molecule to assess glial metabolism and glial-neuronal interactions. Because monocarboxylic acid transporter specificity might confer a phenotype to help localize, detect, and characterize brain tumors of glial origin, use of [2-(14)C]acetate and [(14)C]deoxyglucose (a glucose analog metabolized by all brain cells) was compared in rat and human brain tumors. METHODS: Cultured C6 glioma or U-373 glioblastoma/astrocytoma tumor cells were injected into the caudate nucleus of anesthetized CDF Fisher rats; 2--3 wk later, an intravenous pulse of [2-(14)C]acetate or [(14)C]deoxyglucose was given, and timed blood samples were drawn during the 5- or 45-min experiment, respectively. Local (14)C levels in the brain were assayed by quantitative autoradiography, and acetate uptake or glucose use was calculated. Uptake and metabolism of the [(14)C]acetate was also assayed in C6 glioma and human surgical tumor samples in vitro. RESULTS: [(14)C]Acetate uptake into rat brain C6 tumors was 9.9 +/- 2.1 mL/100 g/min, compared with 3.9 +/- 1.0 mL/100 g/min in contralateral tissue (n = 6; P < 0.001), and was much higher than that into other brain structures (e.g., 5:1 for white matter and 2:1 for cortical gray matter). Glucose use in C6 tumors was 111 +/- 34 micromol/100 g/min, versus 81 +/- 5 micromol/100 g/min in contralateral tissue (n = 6; P = 0.08); no left-right differences in glucose use or acetate uptake were seen in other brain structures. The tumor-to-contralateral-tissue ratio for acetate (2.3 +/- 0.3) exceeded that for deoxyglucose (1.4 +/- 0.5) (P < 0.05), indicating that acetate is a sensitive C6 glioma marker. [(14)C]Acetate uptake also demarcated a few 3-wk-old C6 tumors that had unlabeled necrotic cores. U-373 tumors were smaller than C6 tumors in rat brain and were detected equally well with [(14)C]acetate and [(14)C]deoxyglucose. In vitro uptake of [(14)C]acetate into human glioblastoma or meningioma tumors was higher than uptake into pituitary adenoma. Rat C6 and human tumors with high uptake metabolized acetate to acidic compounds and amino acids. CONCLUSION: Tumor imaging with radiolabeled acetate can help to localize and classify brain tumors. Transporter and metabolic substrate specificity are traits that can be exploited further for in vivo imaging of brain glial tumors.     

High molar activity of [11C]TCH346 via [11C]methyl triflate using the "wet" [11C]CO2 reduction method.

[(11)C]TCH346, a compound acting on the glycolytic enzyme, glycerol-aldehyde-3-phosphate dehydrogenase, was produced under optimised conditions by methylation of the desmethyl compound with no-carrier added (n.c.a.) [(11)C]methyl triflate. An i.v. injectable solution of n.c.a. [(11)C]TCH346 containing 4040+/-1550 MBq (n=6) containing a molar activity between 40 and 5700 GBq/micromol and a radiochemical purity of >99% was obtained within 30 min (after EOB) by irradiation of nitrogen gas containing 0.5% oxygen with 16.5 MeV protons at 45 microA for 30 min. The alkylation reagent [(11)C]methyl triflate was prepared via on-line conversion of [(11)C]methyl iodide. For the formation of [(11)C]methyl iodide, [(11)C]carbon dioxide from the target chamber was reduced by a lithium aluminium hydride solution, and the methanol obtained on-line was converted using triphenylphosphine diiodide. The molar activity of [(11)C]TCH346 could be improved from 40 up to nearly 5700GB q/micromol during the optimisation of the synthesis using the same stock solution of lithium aluminium hydride solution in tetrahydrofuran.     

Two routes to [11C-carbonyl]organo-isocyanates utilizing [11C]phosgene ([11C]organo-isocyanates from [11C]phosgene).

Two generic radiosynthetic routes for the preparation of [¹¹C-carbonyl]isocyanates have been developed. Reaction of N-organo-sulfinylamines; RNSO, (R = Me, Et, allyl, cyclohexyl and phenyl) with [¹¹C]phosgene gave the corresponding [¹¹C-carbonyl]isocyanates in good radiochemical yield (53–68%) from [¹¹C]phosgene (decay corrected) in ca 16 min from EOB. Alternatively, the reaction of [¹¹C]phosgene with N,N′-organo-ureas; (RNH)₂CO, (R = Me, Et, Pr and phenyl) also gave the corresponding [¹¹C-carbonyl]isocyanates in moderate radiochemical yield (9–37%) from [¹¹C]phosgene (decay corrected) in ca 16 min from EOB. For identification, the [¹¹C-carbonyl]organo-isocyanates were derivatized with 1-(2-methoxyphenyl)piperazine in situ to [¹¹C-carbonyl]carboxamides and the position of radiolabelling in the carbonyl group confirmed by [^11/13C]co-labeling and subsequent carbon-13 NMR spectroscopy.     

NMR measurement of brain oxidative metabolism in monkeys using 13C-labeled glucose without a 13C radiofrequency channel.

We detected glutamate C4 and C3 labeling in the monkey brain during an infusion of [U-13C6]glucose, using a simple 1H PRESS sequence without 13C editing or decoupling. Point-resolved spectroscopy (PRESS) spectra revealed decreases in 12C-bonded protons, and increases in 13C-bonded protons of glutamate. To take full advantage of the simultaneous detection of 12C- and 13C-bonded protons, we implemented a quantitation procedure to properly measure both glutamate C4 and C3 enrichments. This procedure relies on LCModel analysis with a basis set to account for simultaneous signal changes of protons bound to 12C and 13C. Signal changes were mainly attributed to 12C- and 13C-bonded protons of glutamate. As a result, we were able to measure the tricarboxylic acid (TCA) cycle flux in a 3.9 cm3 voxel centered in the monkey brain on a whole-body 3 Tesla system (VTCA = 0.55 +/- 0.04 micromol x g(-1) x min(-1), N = 4). This work demonstrates that oxidative metabolism can be quantified in deep structures of the brain on clinical MRI systems, without the need for a 13C radiofrequency (RF) channel.     

Synthesis and in vivo evaluation of [11C]zolpidem,an imidazopyridine with agonist properties at central benzodiazepine receptors

The synthesis and evaluation of [(11)C]zolpidem, an imidazopyridine with agonist properties at central benzodiazepine receptors, is reported herein. The reaction of desmethylzolpidem with [(11)C] methyl iodide afforded the title compound [(11)C]zolpidem in a yield of 19.19 +/- 3.23% in 41 +/- 2 min in specific activities of 0.995-1.19 Ci/micromol (1.115 +/- 0.105 Ci/micromol) (n = 3; decay corrected, EOB). The amount of radioactivity in the brain after tail vein injection in male Wistar rats was low, and the regional distribution was homogeneous and not consistent with the known distribution of the central benzodiazepine receptors. The frontal cortex/cerebellum ratio was not significantly greater than one (1.007 +/- 0.266 at 5 min) and did not increase from 5 to 40 min post-injection. A PET brain imaging study in one baboon confirmed the results obtained in rats. Therefore, it can be concluded that [(11)C]zolpidem is not a suitable tracer for in vivo visualization of central benzodiazepine receptors.     

Synthesis and radiolabeling of N-[4-[4-(2-[11C]methoxyphenyl)piperazin-1-yl]butyl]benzo[b]thiophene-2-carboxamide -- a potential radiotracer for D3 receptor imaging with PET

FAUC346 (N-[4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl]benzo[b]thiophene-2-carboxamide), an in vitro D(3)-selective ligand, and its normethyl derivative have been synthesized from commercially available 1-(2-substituted-phenyl)piperazines. FAUC346 has been labeled using [(11)C]methyl triflate in acetone containing aqueous NaOH (5 Eq) at -10 degrees C for 1 min, purified on semipreparative reverse-phase high-performance liquid chromatography (HPLC) and formulated as an intravenous injectable solution using a Sep-Pak Plus C(18) device. Up to 5.5 GBq of [(11)C]FAUC346 (N-[4-[4-(2-[methyl-(11)C]methoxyphenyl)piperazin-1-yl]butyl]benzo[b]thiophene-2-carboxamide), with a specific radioactivity of 45-75 GBq/micromol, could be obtained in 30-35 min, including HPLC purification and formulation starting from 44.4 GBq of [(11)C]carbon dioxide. Preliminary pharmacological evaluation of [(11)C]FAUC346 in rat brain clearly demonstrated in vivo selectivity for D(3) receptors and the absence of radiolabeled metabolite within the brain. These encouraging results, however, could not be confirmed in nonhuman primates; therefore, this radioligand does not appear to have the required pharmacological profile for a positron emission tomography probe for imaging D(3) receptors.     

Selective resonance suppression 1H‐[13C] NMR spectroscopy with asymmetric adiabatic RF pulses

Despite obvious improvements in spectral resolution at high magnetic field, the detection of ¹³C labeling by ¹H‐[¹³C] NMR spectroscopy remains hampered by spectral overlap, such as in the spectral region of ¹H resonances bound to C3 of glutamate (Glu) and glutamine (Gln), and C6 of N‐acetylaspartate (NAA). The aim of this study was to develop, implement, and apply a novel ¹H‐[¹³C] NMR spectroscopic editing scheme, dubbed “selective Resonance suppression by Adiabatic Carbon Editing and Decoupling single‐voxel STimulated Echo Acquisition Mode” (RACED‐STEAM). The sequence is based on the application of two asymmetric narrow‐transition‐band adiabatic RF inversion pulses at the resonance frequency of the ¹³C coupled to the protons that need to be suppressed during the mixing time (TM) period, alternating the inversion band downfield and upfield from the ¹³C resonance on odd and even scans, respectively, thus suppressing the detection of ¹H resonances bound to ¹³C within the transition band of the inversion pulse. The results demonstrate the efficient suppression of ¹H resonances bound to C3 of Glu and Gln, and C4 of Glu, which allows the ¹H resonances bound to C6 of NAA and C4 of Gln to be revealed. The measured time course of the resolved labeling into NAA C6 with the new scheme was consistent with the slow turnover of NAA. Magn Reson Med 61:260–266, 2009. © 2009 Wiley‐Liss, Inc.     

Metabolic imaging in the anesthetized rat brain using hyperpolarized [1‐13C] pyruvate and [1‐13C] ethyl pyruvate

Formulation, polarization, and dissolution conditions were developed to obtain a stable hyperpolarized solution of [1‐¹³C]‐ethyl pyruvate. A maximum tolerated concentration and injection rate were determined, and ¹³C spectroscopic imaging was used to compare the uptake of hyperpolarized [1‐¹³C]‐ethyl pyruvate relative to hyperpolarized [1‐¹³C]‐pyruvate into anesthetized rat brain. Hyperpolarized [1‐¹³C]‐ethyl pyruvate and [1‐¹³C]‐pyruvate metabolic imaging in normal brain is demonstrated and quantified in this feasibility and range‐finding study. Magn Reson Med 63:1137–1143, 2010. © 2010 Wiley‐Liss, Inc.     

Two routes to [C-carbonyl]organo-isocyanates utilizing [C]phosgene ([C]organo-isocyanates from [C]phosgene)

Two generic radiosynthetic routes for the preparation of [¹¹C-carbonyl]isocyanates have been developed. Reaction of N-organo-sulfinylamines; RNSO, (R = Me, Et, allyl, cyclohexyl and phenyl) with [¹¹C]phosgene gave the corresponding [¹¹C-carbonyl]isocyanates in good radiochemical yield (53–68%) from [¹¹C]phosgene (decay corrected) in ca 16 min from EOB. Alternatively, the reaction of [¹¹C]phosgene with N,N′-organo-ureas; (RNH)₂CO, (R = Me, Et, Pr and phenyl) also gave the corresponding [¹¹C-carbonyl]isocyanates in moderate radiochemical yield (9–37%) from [¹¹C]phosgene (decay corrected) in ca 16 min from EOB. For identification, the [¹¹C-carbonyl]organo-isocyanates were derivatized with 1-(2-methoxyphenyl)piperazine in situ to [¹¹C-carbonyl]carboxamides and the position of radiolabelling in the carbonyl group confirmed by [^11/13C]co-labeling and subsequent carbon-13 NMR spectroscopy.     

Synthesis procedure for routine production of [carbonyl-11C]desmethyl-WAY-100635.

An improved one-pot synthesis procedure for routine production of [carbonyl-(11)C]desmethyl-WAY-100635 ([(11)C]DWAY) is described. An efficient purification of the crude product has also been developed and was accomplished by C-18 reversed-phase semi-preparative HPLC using 55/45 EtOH-NaH(2)PO(4) buffer (20 mM, pH=6.5) as the eluent. The desired product fraction was collected in a 2.0-2.5 mL volume and formulated with 11 mL of 0.9% saline. The radioligand was ready for human use in 45 min (EOB). The product was obtained with a radiochemical yield of 11.1+/-1.8% (EOB, n=15) with a radiochemical purity of >99%. Specific activity was 133.2-185.0 GBq/micromol (3.6-5.0 Ci/micromol, EOS, n=2) when ca. 37.0 GBq (ca. 1.0 Ci) of starting [(11)C]CO(2) was used. Unlabeled mass of [(11)C]DWAY was found to be 0.15-0.24 microg/mL and the precursor was present in less than 50 ng/mL in final production solution.