The metabotropic glutamate receptor 2 (mGluR2) has emerged as a potential therapeutic target for the treatment of various neurological diseases, prompting substantial interest in the development of mGluR2-targeted drug candidates. As part of our medicinal chemistry program, we synthesized a series of isoindolone derivatives and assessed their potential as mGluR2 positive allosteric modulators (PAMs). Notably, AZ12559322 exhibited high affinity (K i mGluR2 = 1.31 nM) and an excellent in vitro binding specificity of 89% while demonstrating selectivity over other mGluR subtypes (>4000-fold). Autoradiography with the radiolabeled counterpart, [3H]AZ12559322, revealed a heterogeneous accumulation with the highest binding in mGluR2-rich brain regions. Radioligand binding was significantly reduced by pretreatment with nonradioactive mGluR2 PAMs in brains of rats and nonhuman primates. Although positron emission tomography imaging of [11C]AZ12559322 (6a) revealed low brain uptake in a nonhuman primate, this study provides valuable guidance to further design novel isoindolone-based mGluR2 PAMs with improved brain exposure.

In support of a program to develop an alpha 7 agonist as a treatment for Alzheimer's disease, three drug candidates, 1, 2, and 3, were prepared in labeled forms. Compound 1 was prepared in C-14 labeled form by lithiation of [2,6-(14)C2]2-chloropyridine and subsequent coupling with spirooxirane-2,3'-quinuclidine. When this same coupling was attempted using [3,4,5,6-(2)H4]2-chloropyridine, alcohol [(2)H6]-6 was the major product indicating that the primary isotope effect for the lithiation step was significant enough to shift the reaction pathway. Therefore, an alternate site of labeling was used to prepare [(2)H4]-1. [(13)C5]-2 was prepared in five steps from [(13)C5 ]2-furoic acid, but the C-14 labeled compound used [(14)C2]-1 as the starting material instead. [(14)C2]-3 was prepared in two steps from [carbonyl-(14)C]nicotinic acid.

In the liver microsome cyanide (CN)-trapping assays, piperazine-containing compounds formed significant N-methyl piperazine CN adducts. Two pathways for the N-methyl piperazine CN adduct formation were proposed: 1) The α-carbon in the N-methyl piperazine is oxidized to form a reactive iminium ion that can react with cyanide ion; 2) N-dealkylation occurs followed by condensation with formaldehyde and dehydration to produce N-methylenepiperazine iminium ion, which then reacts with cyanide ion to form the N-methyl CN adduct. The CN adduct from the second pathway was believed to be an artifact or metabonate. In the present study, a group of 4'-N-alkyl piperazines and 4'-N-[¹³C]methyl-labeled piperazines were used to determine which pathway was predominant. Following microsomal incubations in the presence of cyanide ions, a significant percentage of 4'-N-[¹³C]methyl group in the CN adduct was replaced by an unlabeled natural methyl group, suggesting that the second pathway was predominant. For 4'-N-alkyl piperazine, the level of 4'-N-methyl piperazine CN adduct formation was limited by the extent of prior 4'-N-dealkylation. In a separate study, when 4'-NH-piperaziens were incubated with potassium cyanide and [¹³C]-labeled formaldehyde, 4'-N-[¹³C]methyl piperazine CN-adduct was formed without NADPH or liver microsome suggesting a direct Mannich reaction is involved. However, when [¹³C]-labeled methanol or potassium carbonate was used as the one-carbon donor, 4'-N-[¹³C]methyl piperazine CN adduct was not detected without liver microsome or NADPH present. The biologic and toxicological implications of bioactivation via the second pathway necessitate further investigation because these one-carbon donors for the formation of reactive iminium ions could be endogenous and readily available in vivo.

In support of a program to develop a treatment for diseases resulting from an imbalance in dopamine levels, two drug candidates, 1 and 2, were prepared in stable isotope and C‐14 labeled forms. Both compounds contained an aminothiazole ring, and the C‐14 label was introduced into the ring using KS14CN. However, the use of KS14CN to form [14C]‐2 gave poor results; therefore, benzoyl [14C]isothiocyanate was used instead, which led to a much improved yield. The stable isotope labeled forms were prepared with the label in the side chain from [2H5]ethyl iodide for [2H5]‐1 and from 1‐[13C]methyl [15N2]pyrazole[13C]carboxaldehyde, which was prepared in turn from [carbonyl‐13C]DMF, [15N2]hydrazine sulfate, and [13C]methyliodide for [13C2, 15N2]‐2. Copyright © 2012 John Wiley & Sons, Ltd.

In support of a program to develop an antipsychotic treatment for schizophrenia, three labeled forms of the NK3 receptor antagonist AZD2624 have been prepared. [3H2]AZD2624 was synthesized by tritiodehalogenation for use in receptor occupancy and autoradiographic studies. [13C6]AZD2624 was prepared for use as an internal standard through the intermediacy of [13C6]isatin, and two C-14 isotopomers of AZD2624 were prepared from [14C]benzoic acid and [14C]isatin for a variety of DMPK studies. Copyright © 2011 John Wiley & Sons, Ltd.

In support of a program to develop a treatment for depression, four labeled forms of a delta opioid agonist were prepared. The [2H4] labeled form was prepared using a relatively straightforward conversion of [2H4]bromoethanol to [2H4]N‐methyl‐2‐hydroxyethylamine. The key step in the synthesis of the [2H6] labeled form involved the Pd‐catalyzed exchange in D2O of 8‐quinolin‐8‐ol to give [2H6] 8‐quinolin‐8‐ol. The C‐14 labeled form was synthesized in one step using [14C]carbonylation, and the C‐11 labeled form was prepared in two steps from 11CH3I. Copyright © 2011 John Wiley & Sons, Ltd.

The inventory of labeled compounds and methods for their preparation are constantly growing, but still more building blocks of biologically relevant compounds need to be developed. Furans are frequently encountered in bioactive molecules, and a good synthesis of labeled furan is found in the literature. We required a relatively uncommon labeled furan, 5-chloro-2-furoic acid, for investigative work labeled with C-13 and C-14. Carboxylation of the lithium anion of [C-13(4)] furan with (CO2)-C-13 followed by chlorination using benzyltrimethylammonium dichloroiodate provided the target compound in modest yield and high purity. The same procedure was then repeated with unlabeled furan and (CO2)-C-14 to give [carbonyl-C-14]-5-chlorofuran-2-carboxylic acid.

Radiotracers suitable for positron emission tomography studies often serve as preclinical tools for in vivo receptor occupancy. The serotonin 1B receptor (5-HT(1B)) subtype is a pharmacological target used to discover treatments for various psychiatric and neurological disorders. In psychiatry, 5-HT(1B) antagonists may provide novel therapeutics for depression and anxiety. We report on the in vitro and in vivo evaluation of tritiated 5-methyl-8-(4-methyl-piperazin-1-yl)-4-oxo-4H-chromene-2-carboxylicacid (4-morpholin-4-yl-phenyl)-amide ([N-methyl-(3)H(3)]AZ10419369), a potent 5-HT(1B) radiotracer. [N-methyl-(3)H(3)]-AZ10419369 showed saturable single-site high-affinity in vitro binding (guinea pig, K(d) = 0.38 and human, K(d) = 0.37) to guinea pig or human 5-HT(1B) receptors in recombinant membranes and high-affinity (K(d) = 1.9 nM) saturable (B(max) = 0.099 pmol/mg protein) binding in membranes from guinea pig striatum. When [N-methyl-(3)H(3)]AZ10419369 was administered to guinea pigs by intravenous bolus, the measured radioactivity was up to 5-fold higher in brain areas containing the 5-HT(1B) receptor (striatum/globus pallidus, midbrain, hypothalamus, and frontal cortex) compared with the cerebellum, the nonspecific binding region. Specific uptake peaked 30 min after injection with slow dissociation from target regions, as suggested by the in vitro binding kinetic profile. Pretreatment with 6-fluoro-8-(4-methyl-piperazin-1-yl)-4-oxo-4H-chromene-2-carboxylic acid [4-(4-propionyl-piperazin-1-yl)-phenyl]-amide (AZD1134) and 2-aminotetralin (AR-A000002), 5-HT(1B)-selective ligands, inhibited [N-methyl-(3)H(3)]AZ10419369-specific binding in a dose-dependent manner. In the guinea pig striatum, AZD1134 (ED(50) = 0.017 mg/kg) occupies a greater percentage of the 5-HT(1B) receptors at a lower administered dose than AR-A000002 (ED(50) = 2.5 mg/kg). In vivo receptor occupancy is an essential component to build binding-efficacy-exposure relationships and compare novel compound pharmacology. [N-methyl-(3)H(3)]AZ10419369 is a useful preclinical tool for investigating 5-HT(1B) receptor occupancy for novel compounds targeting this receptor.

In support of a program to develop a treatment for depression, three isotopically labeled forms of the 5-HT(1B) antagonist AZ12320927 were synthesized. A tritium labeled version was synthesized for autoradiography using Ir-catalyzed hydrogen-tritium exchange. A C-14 labeled version was prepared for use in metabolism studies in four-steps from [u-(14) C]p-nitrophenol. A stable isotope labeled version was synthesized for use as an internal standard for LC/MS/MS quantitation in two steps from chromenone 1.

Journal of Labelled Compounds and RadiopharmaceuticalsVolume 50, Issue 5-6 p. 523-525 Short Research Article Investigation of isotopic exchange reactions using N-heterocyclic iridium (I) complexes† Mark E. Powell, Corresponding Author Mark E. Powell [email protected] CNS Chemistry, AstraZeneca Pharmaceuticals LP, 1800 Concord Pike, Wilmington, DE 19850, USACNS Chemistry, AstraZeneca Pharmaceuticals LP, 1800 Concord Pike, Wilmington, DE 19850, USASearch for more papers by this authorCharles S. Elmore, Charles S. Elmore CNS Chemistry, AstraZeneca Pharmaceuticals LP, 1800 Concord Pike, Wilmington, DE 19850, USASearch for more papers by this authorPeter N. Dorff, Peter N. Dorff CNS Chemistry, AstraZeneca Pharmaceuticals LP, 1800 Concord Pike, Wilmington, DE 19850, USASearch for more papers by this authorJ. Richard Heys, J. Richard Heys CNS Chemistry, AstraZeneca Pharmaceuticals LP, 1800 Concord Pike, Wilmington, DE 19850, USASearch for more papers by this author Mark E. Powell, Corresponding Author Mark E. Powell [email protected] CNS Chemistry, AstraZeneca Pharmaceuticals LP, 1800 Concord Pike, Wilmington, DE 19850, USACNS Chemistry, AstraZeneca Pharmaceuticals LP, 1800 Concord Pike, Wilmington, DE 19850, USASearch for more papers by this authorCharles S. Elmore, Charles S. Elmore CNS Chemistry, AstraZeneca Pharmaceuticals LP, 1800 Concord Pike, Wilmington, DE 19850, USASearch for more papers by this authorPeter N. Dorff, Peter N. Dorff CNS Chemistry, AstraZeneca Pharmaceuticals LP, 1800 Concord Pike, Wilmington, DE 19850, USASearch for more papers by this authorJ. Richard Heys, J. Richard Heys CNS Chemistry, AstraZeneca Pharmaceuticals LP, 1800 Concord Pike, Wilmington, DE 19850, USASearch for more papers by this author First published: 30 July 2007 https://doi.org/10.1002/jlcr.1239Citations: 18 † Proceedings of the Ninth International Symposium on the Synthesis and Applications of Isotopically Compounds, Edinburgh, 16-20 July 2006. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. REFERENCES 1 (a) Heys JR. Chem Commun 1992; 680; (b) Shu AYL, Saunders D, Levinson SH, Landvatter SW, Mahoney A, Senderoff SG, Mokhallalati MK, Heys JR. J Label Compd Radiopharm 1999; 42: 797; (c) Shu AYL, Heys JR. Tetrahedron Lett 2000; 41: 9015; (d) Hesk D, Gignan G, Lee F, Yang J, Voronin K, Magatti D, McNamara P, Koharski D, Hendershot S, Saluja S, Wang S. J Label Compd Radiopharm 2002; 45: 145; (e)Ellames GJ, Gibson JS, Herbert JM, Kerr WJ, McNeill AH. J Label Compd Radiopharm 2004; 47: 1; (f) HickeyMJ, JonesJR, Kingston LP, Lockley WJS, Mather AN, McAuley BM, Wilkinson DJ. Tetrahedron Lett 2003; 44: 3959. 2 (a) Vazquez-Serrano LD, Owens BT, Buriak JM. Chem Commun 2002; 2581; (b) Lee HM, Jian T, Stevens ED, Nolan SP. Organometallics 2001; 20: 1255; (c) Hillier AC, Lee HM, Stevens ED, Nolan SP. Organometallics 2001; 20: 4246; (d) Vazquez-Serrano LD, Owens BT, Buriak JM. Inorg Chim Acta 2006; 359: 2786. 3 (a) Crabtree RH, Felkin H, Morris GE. J Organomet Chem 1977; 141: 205; (b) Crabtree RH. Acc Chem Res 1979; 12: 331. Citing Literature Volume50, Issue5-6Special Issue: Proceedings of the Ninth International Symposium on the Synthesis and Applications of Isotopically Labelled Compounds, Edinburgh, 16–20 July 2006.April ‐ May 2007Pages 523-525 ReferencesRelatedInformation