Synthesis of [1-11C]d -glucose and [1-11C]d -mannose from on-line produced [11C]nitromethane

Appl. Radiat. ht. Vol. 42, No. 9, pp. 877-883, Radiat. Appl. Instrum. Part A Printed in Great Britain. All rights reserved

1991

0883-2889/91

[ 1 -l

$3.00 + 0.00 Press plc

Copyright 0 1991Pergamon

Int. J.

Synthesis of [ I-“C]D-Glucose and ‘CID-Mannose from On-line Produced [“ClNitromethane KARL-OLOF SCHOEPS’~‘, SHARON STONE-ELANDER4

BENGT and

LANGSTRoM3,

CHRISTER

HALLDINi*

Departments of ‘Psychiatry and Psychology and 2Neuroradiology, Karolinska Hospital, 10401 Stockholm, Sweden, ‘Department of Organic Chemistry, University of Uppsala, Box 531, 75121 Uppsala, Sweden and 4Karolinska Pharmacy, Box 60024, 10401 Stockholm, Sweden (Received

5

November 1990)

A method for the preparation of [1-“CID-glucose (III) and [1-“CID-mannose (IV) from [“Clnitromethane is described. [“ClNitromethane was produced using the on-line method from [“Clmethyl iodide. The condensation of no-carrier-added or carrier-added [“Clnitromethane with D-arabinose to form the intermediate epimeric [I-“CID-nitro alcohols (I and II) was investigated under various conditions. Compounds I and II were converted to III and IV by the classical Nef reaction with IV as the major product [(IV)/(III) = 3/l-4/1]. The isolated radiochemical yield of III and IV was 25-30% (based on [“Clnitromethane and decay-corrected) and 14-17% (EOB) with a total synthesis time of 50min. including HPLC-purification. Compounds III and IV were isolated using semi-preparative HPLC and the radiochemical purity was > 97%. In a typical run, 1.5-2.0 mCi of III and 6-8 mCi of IV could be isolated (starting from 70-90 mCi [“Clnitromethane).

Introduction Most studies of regional cerebral glucose metabolism with positron emission tomography (PET) have been performed using glucose analogs (Phelps et al., 1979). For example, [I-“C]2-deoxy-D-glucose and [2-‘*F]2fluoro-2-deoxy-D-glucose have been widely used as tracers for quantitative mapping of the first step of the glycolysis. The labelled analogs are trapped in tissue after the phosphorylation step and the rate of phosphorylation can be measured. None of these tracers are naturally occurring substances and there are some disadvantages associated with the use of them. For example, the tracer models involve the which must be determined in “lumped constant”, order to calculate the metabolic rates. Some of the problems encountered from the use of glucose analogs may be solved by use of the natural substance and specific labelling (Hawkins et al., 1985). Carbon-l 1 labelled glucose has been synthesized by biosynthetic methods (Lifton and Welch, 1971; Wolf, 1971). One disadvantage is the lack of specific labelling. The tracer is randomly (but not necessarily uniformly) labelled in all 6 positions which make mathematical modelling difficult. In addition, uncertainties introduced during the handling of plant *Author for correspondence.

materials employed for the biosynthesis, can result in irreproducibility of the synthesis. The general approach for the synthesis of [I-“CID-glucose by a modification of the classical synthesis cyanohydrin using Kiliani-Fischer [“CJcyanide as the labelled precursor has been reported previously (Shiue and Wolf, 1985). This method has been adapted for production of [I-“CID-glucose (Stone-Elander et d., 1989) for PET-measurements of cerebral glucose utilization (Widen et al., 1988; Blomqvist et al., 1990). An alternative approach when diborane was used in the reduction of the intermediates has also been described (Tada et al., 1989). Design of a method for the radiosynthesis of [6-“C]D-glucose has been briefly reported (Grierson et al., 1989) although the potential of the compound and synthetic method has not yet been fully evaluated. The development of a new class of “C-labelled precursors, “C-labelled nitroalkanes, has increased the range of available labelled tools-a necessity for synthetic flexibility in radiochemistry. Nitroalkanes can readily be converted into carbon nucleophiles by the addition of base and may thereafter undergo condensation and nucleophilic substitution reactions [for a review see Mathieu and Weil-Raynal (1973)]. Nitroalkanes can also be converted to other functionalities such as carbonyl compounds (Nef’s reaction)

KARL-OLOFSCHOEPS~~

878

and to amines. The one-pot preparation of [“Clnitromethane from [“Clmethyl iodide has been described (Schoeps er al., 1988). An improved method for producing I-“C-labelled nitroalkanes (nitromethane, nitroethane and nitropropane) on-line from the corresponding “C-1abelled alkyl iodides was recently reported (Schoeps et al., 1989). The condensation of nitromethane with D- or t_-arabinose under basic conditions has been reported to yield the isolated, pure and crystalline forms of the epimeric nitroalcohols. Treatment of the sodium salts of the nitroalcohols with sulphuric acid (Nef’s reaction) yielded the corresponding aldohexoses: D- and L-glucose. D- and L- mannose (Sowden and Fischer, 1947). Carrier-added (CA) [‘%]methyl iodide has also been converted to [?Z]nitromethane and [r4C]methyl nitrite with silver nitrite. The [‘4C]nitromethane was condensed with D-arabinose to give [r4C]1-nitro-1-desoxy-D-sorbitol and [‘4C]1-nitro-ldesoxy-D-mannitol in an overall radiochemical yield of 28%. The epimeric nitroalcohols were separated by fractional crystallization, and were subsequently treated with sulphuric acid to produce [1-‘“CIDglucose and [l-‘4C]D-mannose in good yield [Sowden (1949); for review see Sowden (1951)]. In the present study the preparation of no-carrieradded (NCA) or CA [I-“CID-glucose (III) and [I-“CID-mannose (IV) from [“Clnitromethane is reported (Scheme 1). [“ClNitromethane was produced using the on-line method from [“Clmethyl iodide (Schoeps et al., 1989). The reaction of NCA or CA [“Clnitromethane with D-arabinose in a basic solution to form the intermediate epimeric [I-“CID-nitro alcohols (I and II) was investigated under various conditions. Compounds I and II were converted to III and IV by the classical Nef reaction. A remote-controlled experimental set-up (Fig. 1) was also developed in connection with the permanent [“Clnitroalkane system. To confirm the position of labelling a preparation of [ l-‘3C]D-gluCOse from [‘3C]nitromethane was performed, using similar reaction conditions as in the synthesis of [ l-“CIDglucose. The “C-NMR spectrum of the product was compared with spectra obtained from D-glucose and D-mannose.

“CH,N02 OH-

F”” R

H&OH k

(1)

b )h k

N2 )C

Fig. 1. Principal illustration of the experimental set-up containing valves (a-i), flowmeters (j and k), reaction vessel containing magnetic stirrer (I mL Altech) (I), test tube (4 mL) (m), reaction vessel containing magnetic stirrer (5 mL) (n), basic anion-exchange column (o), solvent tainer (p), NH2 column (q).

+

General

Dimethyl sulphoxide (DMSO) was obtained from Merck and dimethylformamide (DMF) from BDH Chemicals Ltd. Both solvents were distilled and dried over molecular sieves (4A) before use. Nitromethane was obtained from Merck and distilled and kept in refrigerator. [“NlNitromethane was obtained from Aldrich. D-Arabinose, D-mannose and D-glucose were all purchased from Sigma. Other chemicals were obtained from commercial sources and were of analytical grade. The columns used for crude purification were a weakly basic anion exchange resin (AG 4-X4,

HO&H k

(11)

HOAH R=

con-

Experimental

“CH,NO,

“CH2N0, *

nl.

HAOH HAOH

Scheme I

1) OH2)

“CHO H&OH

“CHO +

HO&H

k

k

m

(IV)

[I-“CID-glucose

and

Bio Rad) and an amino-extraction column (Analytithem International). [“C]Carbon dioxide was produced at the Karolinska Hospital with a Scanditronix MC-16 cyclotron using 17 MeV protons in the 14N(p cz)“C reaction. The gas target was irradiated in a batch production. The [“Clcarbon dioxide produced was trapped in a stainless steel coil cooled with liquid nitrogen before being transferred to the “Clabelled nitroalkane system (Schoeps et al., 1989). The radiochemical purity of III and IV and analysis of the intermediate products was performed by analytical HPLC using an Kontron 420 pump, a Rheodyne injector (7125 with a 1OOpL loop) connected to an LDC-Milton Roy 300 U.V. detector (254nm) or an Shimadzu RIDdA refractive index detector coupled in series with a Beckman 170 radioactivity monitor. Three separate analytical systems were used: (a) Waters p-BondapakCl8 column (300 x 7.8 mm, 10 pm), acetonitrile/O.Ol M phosphoric acid (S/95) at a flow rate of 4.0 mL/min. (b) Waters p-Bondapak-NH, column (300 x 3.9 mm, 10 pm), acetonitrile/water (85/15) at a flow rate of 3.5 mL/min (Figs 2 and 4). (c) Bio-Rad Aminex HPX-87P Carbohydrate column (300 x 7.8 mm, 9 pm) with water as the mobile phase with a flow rate of 0.8 mL/min at 75°C (Fig. 4). A Shimadzu C-R2AX two channel data processor was used for integration. Semipreparative HPLC was performed using a Shimadzu LC-6A pump, a Supelco injector (Type VICI with a 3 mL loop), a Bio-Rad Aminex HPX-87P Carbohydrate column (300 x 7.8 mm, 9 pm) coupled in series with a GM tube for radiation detection. Compounds III and IV were both purified using water as the mobile phase with a flow rate of 0.6mL/min at 75°C (Fig. 3). NMR was performed on a Varian XL-300 NMR spectrometer using D,O as solvent at 20°C. The chemical shift values are expressed on a ppm scale downfield relative to sodium 3-(trimethylsilyl)propanesulphonate used as an internal reference. [l

-“c/o

-Glucose

(III)

and [l

-“c]D

-mannose

(IV)

(Fig. 1)

[“ClNitromethane was trapped in a reaction vessel (1 mL mini-vial, Alltech, I) at room temperature, containing DMSO (0.3 mL) and D-arabinose (50 mg, 0.33 mmol) (see Fig. 1). NaOH (125 pL, 1 M) and nitromethane (12 pL, 0.22 mmol) in DMSO (1OOpL) were added subsequently through valve (a). The vessel was sealed and reaction allowed to proceed with magnetic stirring at 40°C for 3 min. The light yellow reaction mixture was transferred by the addition of NaOH (2.0 mL, 0.6 M, a) into a test tube (4mL, m). The combined mixture was transferred dropwise into a pearshaped vessel (5 mL, n) containing vigorously stirred sulphuric acid (0.54 mL, 8 M). The crude product was eluted through a column AR’42,-

[I-“CID-mannose

879

containing a weakly basic anion exchange resin (1 .Og, The resin was rinsed with water (2 mL) added through valve (d). The combined eluates were mixed in a container (p) together with acetonitrile (30 mL) and passed by nitrogen gas pressure through an amino-extraction column (12 cc, q). The first eluate was discarded together with two washing phases: acetonitrile/water (85/15, 20 mL) and water (2 mL, g). The sugars (III and IV) which still retained on the column were eluted with additional water (2 mL) and were finally isolated by semi-preparative HPLC. Using the semi-preparative HPLC column (Bio-Rad Aminex HPX-87P Carbohydrate), III and IV eluted after 14-l 7 min and 18-23 min, respectively, with the same retention times as standard reference samples (Fig. 3). III was filtered through a Millipore filter (0.22 pm), yielding a solution which was sterile and free from pyrogens. 0).

[l -“CID -Glucose

D-Arabinose (50 mg, 0.33 mmol) was dissolved in DMSO (0.3 mL). NaOH (125pL, 1 M) and [‘3C]nitromethane (12 pL, 0.22 mmol) in DMSO (100 pL) were added. The vessel was sealed and the reaction allowed to proceed with magnetic stirring at 40°C for 30min. The reaction mixture was purified using the same procedure as described above for [I-“CID-glucose. Isolation of the product from [l-‘3C]D-mannose and n-arabinose using the same semi-preparative HPLC system as described above and evaporation of the collected fraction yielded 3.8 mg (10%) [l-‘3C]n-glucose. The 13CNMR spectrum shows two peaks at 94.8 and 98.6ppm which are consistent with the c(- and /I-anomers of C-l of D-ghCOSe.

Results and Discussion The number of suitable labelled precursors available for labelling compounds with shortlived radionuclides is limited. The preparation of [I-“CID-glucose, by the modified Kiliani-Fischer utilizes nucleophilic cyanohydrin synthesis, [“Clcyanide as the labelled precursor (Shiue and Wolf, 1985). The electrophilic precursor, [“Clmethyl iodide, is easily prepared by the one-pot reaction set-up from [“Clcarbon dioxide (Langstrom ef al., 1986, 1987; Halldin et al., 1990) and is frequently employed in N-, 0- and C-alkylation reactions. The [“Clmethyl iodide production unit can be adapted in an on-line extension to produce nucleophilic [“C]nitroalkanes (Schoeps et al., 1989). [“C]Nitromethane has already shown its potential as a potent nucleophilic “C-1abelled precursor in condensation reactions to produce [“C]flnitrostyrene (Schoeps et al., 1988), [2-“Clglycine (Halldin et al., 1989; Schoeps et al., 1991) and [“Clranitidine (LeBreton et al., 1991). The methodology used in the preparative synthesis of aldohexoses, (Sowden and Fischer, 1947) and the

880

KARL-OLOF SCHOEPSet al.

Table I, The conversion of [“C]nitrome.thane to I dependency of solvent, temperature and carrier during sation step*

and II as a the conden-

Solvent

Temp. (“C)

I and II (%)** (CA)

I and II (%)** (NCA)

Water Water Water DMSO DMSO DMSO

r.t. 40 60 1.1. 40 60

18 25 35 53 68 64

25 31 65 -

*The reactions were carried out during 10 min for water and 3 min for DMSO. **The conversion was analysed by HPLC.

CA preparation of [l-‘4C]D-glucose and [1-‘“CIDmannose (Sowden, 1949), was applied in the development of the syntheses of [I-“CID-glucose and [I-“CID-mannose from [“Clnitromethane. Because of the short half-life of “C (20.3 min) the development of a fast labelling and purification procedure was unavoidable. In addition, a remote-controlled experimental set-up (Fig. 1) was built-up for connection to the permanent [“Clnitroalkane system. The influence of parameters such as type of solvent, amount and choice of base, temperature and NCA or CA conditions was considered. The following solvents were examined in the condensation step: DMSO, DMF, water, methanol and THF. A higher incorporation of [“Clnitromethane in the condensation step was achieved when the polar aprotic solvents, DMSO and DMF, were used instead of the polar protic solvents water and methanol. A solvent change from water to DMSO increased the radiochemical yield of I and II by a factor of about 5 at similar reaction conditions. By using DMSO, the reaction time as well as the reaction temperature needed were lower thereby decreasing side reactions. Slightly lower yields were obtained for DMF using analogous reaction conditions. If the non-polar

Table 2. The conversion of solvent, concentration

Solvent

H,SO,

Water Water Water Water Water DMSO DMSO DMSO DMSO DMSO

4 6 8 IO 12 4 6 8 IO 12

(M)

of I and II to III and IV as a dependency of sulphuric acid and carrier during the Nef step* III and IV (%)** (CA)

III and IV (%)** (NCA)

32 53 77 70 17 41 75 85 16 89

13 56 71 59 23 21 31

*The reactions were carried out during I min reaction temperature for both water and DMSO. **The conversion was analysed by HPLC.

time at room

aprotic solvent THF was used, no significant yield was obtained. Different bases were tested to optimize the incorporation in the condensation step. Sodium hydroxide was found to be the most suitable base tested, giving high and reproducible radiochemical yields. Other bases for example, sodium methoxide, sodium sulphoxide or the non-nucleophilic 2,2,6,6tetramethylpiperidine (TMP) were all found to be less suitable. The conversion of [“Clnitromethane in water to yield the products I and II was 18% (r.t. for 10 min) (Table 1). The yield was increased to 35% by increasing the temperature to 60°C. In DMSO the conversion was 53% (r.t. for 3 min) with a slight increase (up to 68%) obtained at elevated temperatures. Longer reaction times or NCA reaction conditions did not change the yields significantly either in water or in DMSO. To obtain reproducible yields of III and IV it was necessary to add a sodium hydroxide solution (0.5 M) containing the intermediate epimeric nitrosugars (I and II) dropwise into a vigorously stirred sulphuric acid (8 M). It was not possible to

1 IV

I I, II

IV

III I, II III

LL.

A_ I

0

2 4 Time iminI

1

.

1

.

1

1

’

0246002460

Time (mid

Time (mid

Fig. 2. Analytical HPLC chromatograms, showing radioactivity vs time, using a Waters p-Bondapak-NH, column. Left, condensation step; middle, after Nef’s reaction; right, after anion-exchange and NH, column purification but prior to HPLC. I, II, [I-“CID-nitro alcohols; III, [I-“CID-glucose; IV, [I-“CID-mannose.

[I-“C]D-glucose and

I.

1

0

4

*

1

6

*

1

*

’

*

’

12 16 20 Time (mid

*

’

24

*

’

*

I

26

Fig. 3. Semipreparative HPLC chromatogram, showing radioactivity vs time, using a Bio-Rad Aminex HPX87P Carbohydrate column. III, [I-“C]D-glucose; IV, [I-“C]D-mannose.

enhance the yield by altering the concentration of the sulphuric acid (within the range of 4-12 M). The optimal concentration during CA conditions was between 8-12 M giving 70-77% and 76-89% conversion in water and DMSO, respectively (Table 2). The yields and reproducibility were lower during NCA conditions. As the glucose/mannose ratio is established during the nucleophilic attack of the anionic species of

[I-‘t]D-IIMIlIOSe

881

[“Qtitromethane, it was important to investigate the influence of solvent (water and DMSO) at different temperatures. In general the ratio was lower in water (l/IO) and was not markedly changed by altering the reaction temperature. In DMSO the relative product distribution of III/IV was about l/3-1/4 (Fig. 2). A slightly increased ratio could be obtained at elevated temperatures (III/IV higher than l/3 at > 60°C). This caused, however, also an increased amount of labelled impurities which were difficult to separate during the purification. An approach to reverse the glucose/mannose ratio from l/3 to 3/l by using sodium carbonate in the reaction of D-arabinose with cyanide (Isbell et al., 1952) gave in our case (using [“C]nitromethane instead of cyanide) no effect. A crude purification procedure was performed by use of anion exchange- (0) and NH,-columns (q) (Fig. 1). o was used to desalt and neutralize the reaction mixture and q was used to separate the sugars from DMSO and labelled by-products. Before elution through q, the eluate from o was mixed with acetonitrile in a container p to obtain a mixture of acetonitrile/water (85/15, v/v). The radiochemical purity of the sugars was about 95% prior to HPLC. Compounds III and IV were isolated by semi-preparative HPLC using a Bio-Rad Aminex HPX-87P carbohydrate column with water as the mobile phase. No evaporation of the mobile phase was necessary before sterile filtration. A considerable loss of radioactivity (40-50%) was, however, obtained during the HPLC procedure. III and IV eluted after 14-17 min and 18-23 min, respectively, with the same retention times as standard reference samples (Fig. 3).

P 8

I

0

.

.

*

-

.

2 4 6 Time (mid

,

I.

0

1.1.1.

2

I.

4

I.

6 6 10 Time Iminl

I.

12

I

.,

14

Fig. 4. Analytical HPLC chromatograms, showing radioactivity and refractive index vs time, after HPLC-purification of [I-“Cjo-glucose. Left, a Waters I-Bondapak-NH, column with glucose as a reference; right, a Bio-Rad Aminex HPX-87P Carbohydrate column with glucose and mannose as references. III, [I-“Cjo-glucose; III’, o-glucose; IV’, o-mannose.

KARL-OLOFSCHOEPS~~

882

Three different analytical HPLC-columns used in order to analyse the individual reaction and the radiochemical purity of III and IV: (a) Waters (b) Waters

p-Bondapak p-Bondapak

C-18 column; NH, column;

and

were steps

al.

(c) Bio-Rad Aminex HPX-87P column (Figs 2 and 4).

Carbohydrate

The radiochemical purity of both III and IV was better than 97% (Fig. 4). The isolated radiochemical yield of CA III and IV was 2530% (based on

b)

Fig. 5. “C NMR spectra of (a) o-mannose, (b) [I-“CID-glucose and (c) o-glucose. D,O is used as solvent and sodium 3-(trimethylsilyl)-propanesulphonate is used as an internal reference.

[I-“CID-glucose and [I-“CID-mannose

[“Clnitromethane and decay-corrected) and 14-17% [based on [“Clcarbon dioxide and decay-corrected (EOB)] with a total synthesis time of 50 min (including HPLC purification). In a typical production run, 1.5-2.0mCi of III and 6-8 mCi of IV could be isolated (starting from 70-90 mCi [“Clnitromethane). The 13C NMR spectrum of [l-‘3C]D-glucose was compared with the spectra obtained from D-glucose and D-mannose. Two peaks at 94.8 and 98.6ppm were observed which are consistent with the u- and p-anomers of C-l of D-glucose. In conclusion, the present synthetic method is an alternative approach for the preparation of [ I-“CID-glucose and [ I-“CID-mannose. The method utilizes [“C]nitromethane via [“Clmethyl iodide instead of [“Clcyanide as the labelled precursor. Reaction time, radiochemical yield and radiochemical purity are sufficient enough for the tracers to be used in studies of regional cerebral glucose metabolism with PET. Acknowledgements-The

authors are indebted to Mr Goran Printz and Mr Fredrik Hamnqvist for assistance with the radionuclide production. We also would like to thank Mr Jan-Olov Thorell for valuable discussions and Mr Walter Pulka for technical assistance. This research has been supoorted bv erants from the Swedish Medical Research Council (03560): the Swedish Natural Science Research Council (K-KU 9973-300), the National Institute of Mental Health U.S.A. (NIMH, Grant No. 48414) and the Karolinska Institute which is gratefully acknowledged.

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Isbell H. S., Karabinos J. V., Frush H. L., Holt N. B., Schwebel A. and Galkowski T. T. (1952) Synthesis of

D-glucose-l-W and o-mannose-1-W. J. Res. Nat. Eur. Stand. 48, 163. Lt%ngstrGmB., Antoni G., Gullberg P., Halldin C., N&en K., Rimland A. and Svard H. (1986) The synthesis of I-“C-alkyl iodides and examples of alkylation reactions. Ini. J. Appl. Radial. 37, 1141. LAngstrom B., Antoni G., Gullberg P., Halldin C., Malmborg P., Nagren K., Rimland A. and Svtird H. (1987) Synthesis of L- and o-[methyl-“C]methionine. J. Nucl. Med. 28, 1037.

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Mathieu J. and Weill-Raynal J. (1973) Formation of C-C Bonds, Vol. 1, p. 120. George Thieme Publishers, Stuttgart. Phelps M. E., Huang S. C., Hoffman E. J., Selin C., Sokoloff L. and Kuhl D. E. (1979) Tomographic measurement of local cerebral glucose metabolic rate in human with (F-18)2-fluoro-2-deoxy-o-glucose: Validation of method. Ann. Neurol. 6, 371.

Schoeps K-O., Halldin C., Stone-Elander S., LAngstrom B. and Greitz T. (1988) Preparation of “C-nitromethane and an example of its use as a radio-labeling precursor. J. Lab. Comp. I&diopharm. 25, 749.

-

_

Schoeos K-O.. Stone-Elander S. and Halldin C. (1989) On-iine synthesis of [“Clnitroalkanes. Appl. Rod& Iso;. 40, 261.

Schoeps K-O., Halldin C., Ram S. and Ehrenkaufer R. (1991) The synthesis of [2-“Clglycine from [“Cjnitromethane. Acta Radiologica Proc. (in press). Shiue C.-Y. and Wolf A. P. (1985) The synthesis of l[“Cl-o-Glucose and related compounds for the measurement of brain glucose metabolism. J. Lab. Comp. Radiopharm. 22, 17 1.

Sowden J. C. (1949) The condensation of ‘%-nitromethane with o-arabinose: Preparation of l-‘4C-o-glucose and I-‘4C-o-mannose. J. Biol. Chem. 180, 55. Sowden J. C. (1951) The nitromethane and 2nitroethanol synthesis. Ado. Carbohydrate Chem. 6, 291. Sowden J. C. and Fischer H. 0. L. (1947) The condensation of nitromethane with D- and L-arabinose: Preparation of L-glucose and L-mannose. J. Am. Chem. Sot. 69, 1963. Stone-Elander S., Halldin C., Lilngstriim B., Blomqvist G., Hamnqvist F. and Widen L. (1989) Method for routine production of [I-“Cl-o-glucose from [“C]ammonium cyanide. J. Nucl. Med. 5, 927 (Abstract). Tada M., Oikawa A., Matsuzawa T., Itoh M., Fukuda H., Kubota K., Kawai H., Abe Y., Sugiyama H., Ido T., Ishiwata K., Iwata R., Imahori Y. and Sato T. (1989) A convenient synthesis of D-[l-“C]gh~copyranose and D[I-“Cl-galactopyranose using diborane. J. Lab. Camp. Radiopharm. 27, 2.

Widen L., Blomqvist G., Stone-Elander S., Halldin C., Roland P., Solin O., Lindqvist M., Langstrom B. and Wiesel F-A. (1988) Problems in measurements of cerebral metabolic rate of glucose. Eur. J. Nucl. Med. 14, 224. Wolf A. P. (1971) The preparation of organic radiopharmaceuticals containing isotopes of short half-life. Radioisoropy 12, 499.