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. 2011 Oct 5;2(12):882–884. doi: 10.1021/ml200162f

Synthesis and Evaluation of Metabotropic Glutamate Receptor Subtype 5 Antagonists Based on Fenobam

Moses G Gichinga 1, Jeremy P Olson 1, Elizabeth Butala 1, Hernán A Navarro 1, Brian P Gilmour 1, S Wayne Mascarella 1, F Ivy Carroll 1,*
PMCID: PMC3328804  NIHMSID: NIHMS330530  PMID: 22523618

Abstract

graphic file with name ml-2011-00162f_0004.jpg

In an effort to discover potent and selective metabotropic glutamate receptor subtype 5 (mGluR5) antagonists, 15 tetrahydropyrimidinone analogues of 1-(3-chlorophenyl)-3-(1-methyl-4-oxo-4,5-dihydro-1H-imidazol-2-yl)-urea (fenobam) were synthesized. These compounds were evaluated for antagonism of glutamate-mediated mobilization of internal calcium in an mGluR5 in vitro efficacy assay. The IC50 value for 1-(3-chlorophenyl)-3-(1-methyl-4-oxo-1,4,5,6-tetrahydropyridine)urea (4g) was essentially identical to that of fenobam.

Keywords: Fenobam, metabotropic glutamate receptors, drug addiction, mGluR5 antagonist

Metabotropic glutamate receptor subtype 5 has been linked to various central nervous system disorders including addiction, pain, fragile X syndrome, depression, and anxiety.1−5 The discovery of 3-methyl-6-(phenylethynyl)pyridine (MPEP; 1) and (2-methyl-1,3-thiazol-4-yl)ethynylpyridine (MTEP; 2) as potent and selective metabotropic glutamate receptor 5 (mGluR5) antagonists has led to intensive investigations focused on developing new analogues.6−9graphic file with name ml-2011-00162f_0005.jpg

During the 1970s and 1980s, McNeil Laboratories developed fenobam (3) as a potential anxiolytic but with a then unknown molecular target.10−12 Apparently because of mixed results from clinical studies, fenobam's further development was discontinued.10−13 In 2005, fenobam (3) was shown to be a potent and selective mGluR5 antagonist prompting structure–activity relationship studies using fenobam as the lead compound.14−17 Despite considerable progress in the search for mGluR5 antagonists, identification of potent mGluR5 antagonists with better drug-like properties remains a challenge.

In this paper, we describe the synthesis of a novel class of compounds (4a–m) containing a tetrahydropyrimidinone moiety as a replacement of the imidazolinone moiety in fenobam (3). This class of compounds has been proposed to possess anxiolytic properties in patent literature,18 but neither chemical properties nor their activity as mGluR5 antagonists has ever been explored.

The tetrahydropyrimidinone series of compounds 4a–m was synthesized as outlined in Scheme 1. First, 5a–c were prepared as described in literature procedures.19 Condensation of commercially available phenyl isocyanates 6a–f with 5a–c in chloroform provided target compounds 4a–m in moderate to good yields after recrystallization from ethanol. (See Table 1 for % yields.)

Scheme 1. Synthesis of Tetrahydropyrimidinone Series of Compounds 4a–m.

Scheme 1

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Table 1. Inhibition of Human mGluR5-Mediated Intracellular Calcium Mobilization Values for Compounds 3, 4a–m, 8, and 10.

compd yield (%)a IC50 (nM)b
3   43.0 ± 5.20
4a 78 8700 ± 3600
4b 75 9300 ± 1300
4c 71 9200 ± 480
4d 25 3900 ± 2100
4e 70 6000 ± 1400
4f 79 4000 ± 1700
4g 24 50.0 ± 10.0
4h 52 96.0 ± 21.0
4i 38 2400 ± 310
4j 35 870 ± 360
4k 24 1200 ± 280
4l 27 100 ± 30.0
4m 65 250 ± 35.0
8 40 570 ± 100
10 45 850 ± 81.0
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a

Yield for syntheses 4a–m from reaction of 5a–c with 6a–f, synthesis of 8 from reaction of 5b with 7, and synthesis of 10 from reaction of 9 with 6a.

b

The data represent the means ± SEs from at least three independent experiments except 4d and 8 where n = 2.

Alteration of the urea linkage in 4g with thiourea linkage was achieved by reaction of 5b with 3-chlorophenylisothiocyanate 7 to provide 8 (Scheme 2). The reaction of 9 with 3-chlorophenyl isocyanate 6a provided 10 in 45% yield.

Scheme 2. Synthesis of Fenobam Analogues 8 and 10.

Scheme 2

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The 15 tetrahydropyrimidinone analogues of fenobam 4a–m, 8, and 10 were evaluated for antagonism of glutamate-mediated mobilization of internal calcium in an mGluR5 in vitro efficacy assay. Compounds were tested for in vitro efficacy using Chinese hamster ovary (CHO-K1) cells stably transfected with the human mGluR5 complementary DNA (cDNA). Ca2+ was measured using a FlexStation3 (Molecular Devices Corp.). IC50 values were calculated from a four-parameter logistic equation fit to the calcium flux concentration–response data using Prism (GraphPad Software, San Diego, CA). All compounds fully antagonized the action of glutamate and did not display agonist activity at 10 μM. The IC50 values for 4a–m, 8, and 10 along with IC50 value for the standard mGluR5 antagonist fenobam are listed in Table 1. The tetrahydropyrimidinone analogues 4a–f, which do not have an N-methyl, had weak antagonist efficacy at the mGluR5 receptor. The most potent analogue was the 3-methylphenyl substituted analogue 4d, which had an IC50 = 3900 nM. N-Methylation of the tetrahydropyrimidinone ring in 4a–f to give compounds 4g–l, respectively, resulted in increased antagonist efficacy. The 3-chlorophenyl N-methyltetrahydropyrimidinone fenobam analogue 4g with an IC50 = 50 nM had an antagonist efficacy similar to that found for fenobam (IC50 = 43.0 nM). However, changing the chloro group in 4g to other substituents did not improve the potency, although the bromo and cyano analogues (4h and 4l) were in the same potency range (96.0 and 100 nM, respectively). Replacing the N-methyl group in 4g with an N-ethyl group to obtain 4m and alteration of the urea linkage with thiourea to obtain 8 led to a significant reduction in antagonist efficacy. Even adding a double bond to the tetrahydropyrimidinone ring of 4g to give 10 resulted in significant decrease in potency. Because pharmacokinetic (PK) studies in humans have indicated variable plasma levels for fenobam,20 even small changes in the structure of fenobam (3) could lead to a compound with better drug-like properties. While beyond the scope of this letter, future PK and metabolism studies will help reveal the potential of 4g as a useful mGluR5 antagonist.

In summary, 15 tetrahydropyrimidinone fenobam analogues were synthesized and tested for antagonism at mGluR5. The meta-substituted 3-chloro-, 3-bromo-, and 3-cyano-analogues 4g, 4h, and 4l possessed low nanomolar IC50 values in an mGluR5 efficacy assay. Thus, these compounds, particularly 4g, represent new lead structures for the development of pharmacotherapies for treating addiction and other central nervous system disorders.

Glossary

Abbreviations

CHO-K1

Chinese hamster ovary

mGluR5

metabotropic glutamate receptor 5

MPEP

3-methyl-6-(phenylethynyl)pyridine

MTEP

(2-methyl-1,3-thiazol-4-yl)ethynylpyridine

PK

pharmacokinetic

tPSA

total polar surface area

cDNA

complementary DNA

Supporting Information Available

Experimental procedures for the synthesis and elemental analysis data for 4a–m, 8, and 10. This material is available free of charge via the Internet at http://pubs.acs.org.

This research was supported by the National Institute on Drug Abuse, Grant DA05477.

Notes

Part of the research was presented at the 241st National Meeting and Exposition of the American Chemical Society, Anaheim, CA, March 27–31, 2011. Gichinga M. G.; Butala E.; Navarro H. A.; Gilmour B. P.; Carroll F. I.. Synthesis and evaluation of tetrahydropyrimidinone-based fenobam analogues as metabotropic glutamate receptor subtype 5 antagonists. Abstr. Pap. Am. Chem. Soc. 2011, 241.

Funding Statement

National Institutes of Health, United States

Supplementary Material

ml200162f_si_001.pdf (130.2KB, pdf)

References

  1. Bear M. F. Therapeutic implications of the mGluR theory of fragile X mental retardation. Genes Brain Behav. 2005, 4, 393–398. [DOI] [PubMed] [Google Scholar]
  2. Chiamulera C.; Epping-Jordan M. P.; Zocchi A.; Marcon C.; Cottiny C.; Tacconi S.; Corsi M.; Orzi F.; Conquet F. Reinforcing and locomotor stimulant effects of cocaine are absent in mGluR5 null mutant mice. Nat. Neurosci. 2001, 4, 873–874. [DOI] [PubMed] [Google Scholar]
  3. Dolan S.; Kelly J. G.; Monteiro A. M.; Nolan A. M. Up-regulation of metabotropic glutamate receptor subtypes 3 and 5 in spinal cord in a clinical model of persistent inflammation and hyperalgesia. Pain 2003, 106, 501–512. [DOI] [PubMed] [Google Scholar]
  4. Li X.; Need A. B.; Baez M.; Witkin J. M. Metabotropic glutamate 5 receptor antagonism is associated with antidepressant-like effects in mice. J. Pharmacol. Exp. Ther. 2006, 319, 254–259. [DOI] [PubMed] [Google Scholar]
  5. Tatarczynska E.; Klodzinska A.; Chojnacka-Wojcik E.; Palucha A.; Gasparini F.; Kuhn R.; Pilc A. Potential anxiolytic- and antidepressant-like effects of MPEP, a potent, selective and systemically active mGlu5 receptor antagonist. Br. J. Pharmacol. 2001, 132, 1423–1430. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Alagille D.; Baldwin R. M.; Roth B. L.; Wroblewski J. T.; Grajkowska E.; Tamagnan G. D. Synthesis and receptor assay of aromatic-ethynyl-aromatic derivatives with potent mGluR5 antagonist activity. Bioorg. Med. Chem. Lett. 2005, 13, 197–209. [DOI] [PubMed] [Google Scholar]
  7. Carroll F. I.; Kotturi S. V.; Navarro H. A.; Mascarella S. W.; Gilmour B. P.; Smith F. L.; Gabra B. H.; Dewey W. L. Synthesis and pharmacological evaluation of phenylethynyl[1,2,4]methyltriazines as analogues of 3-methyl-6-(phenylethynyl)pyridine. J. Med. Chem. 2007, 50, 3388–3391. [DOI] [PubMed] [Google Scholar]
  8. Chua P. C.; Nagasawa J. Y.; Bleicher L. S.; Munoz B.; Schweiger E. J.; Tehrani L.; Anderson J. J.; Cramer M.; Chung J.; Green M. D.; King C. D.; Reyes-Manalo G.; Cosford N. D. Cyclohexenyl- and dehydropiperidinyl-alkynyl pyridines as potent metabotropic glutamate subtype 5 (mGlu5) receptor antagonists. Bioorg. Med. Chem. Lett. 2005, 15, 4589–4593. [DOI] [PubMed] [Google Scholar]
  9. Iso Y.; Grajkowska E.; Wroblewski J. T.; Davis J.; Goeders N. E.; Johnson K. M.; Sanker S.; Roth B. L.; Tueckmantel W.; Kozikowski A. P. Synthesis and structure-activity relationships of 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine analogues as potent, noncompetitive metabotropic glutamate receptor subtype 5 antagonists; search for cocaine medications. J. Med. Chem. 2006, 49, 1080–1100. [DOI] [PubMed] [Google Scholar]
  10. LaPierre Y. D.; Oyewumi L. K. Fenobam: Another anxiolytic?. Curr. Ther. Res. 1982, 31, 95–101. [Google Scholar]
  11. Pecknold J. C.; McClure D. J.; Appeltauer L. Fenobam in Anxious Outpatients. Curr. Ther. Res. 1980, 27, 119–123. [Google Scholar]
  12. Pecknold J. C.; McClure D. J.; Appeltauer L.; Wrzensinski L.; Allan T. Treatment of anxiety using fenobam (a nonbenzodiazepine) in a double-blind standard (diazepam) placebo-controlled study. J. Clin. Psychopharmacol. 1982, 2, 129–133. [PubMed] [Google Scholar]
  13. Friedmann C. T. H.; Davis L. J.; Ciccone P. E.; Rubin R. T. Phase II double blind controlled study of a new anxiolytic, fenobam. Curr. Ther. Res. 1980, 27, 144–151. [Google Scholar]
  14. Ceccarelli S. M.; Jaeschke G.; Buettelmann B.; Huwyler J.; Kolczewski S.; Peters J. U.; Prinssen E.; Porter R.; Spooren W.; Vieira E. Rational design, synthesis, and structure-activity relationship of benzoxazolones: New potent mglu5 receptor antagonists based on the fenobam structure. Biorg. Med. Chem. Lett. 2007, 17, 1302–1306. [DOI] [PubMed] [Google Scholar]
  15. Jaeschke G.; Porter R.; Buttelmann B.; Ceccarelli S. M.; Guba W.; Kuhn B.; Kolczewski S.; Huwyler J.; Mutel V.; Peters J. U.; Ballard T.; Prinssen E.; Vieira E.; Wichmann J.; Spooren W. Synthesis and biological evaluation of fenobam analogs as mGlu5 receptor antagonists. Bioorg. Med. Chem. Lett. 2007, 17, 1307–1311. [DOI] [PubMed] [Google Scholar]
  16. Porter R. H.; Jaeschke G.; Spooren W.; Ballard T. M.; Buttelmann B.; Kolczewski S.; Peters J. U.; Prinssen E.; Wichmann J.; Vieira E.; Muhlemann A.; Gatti S.; Mutel V.; Malherbe P. Fenobam: a clinically validated nonbenzodiazepine anxiolytic is a potent, selective, and noncompetitive mGlu5 receptor antagonist with inverse agonist activity. J. Pharmacol. Exp. Ther. 2005, 315, 711–721. [DOI] [PubMed] [Google Scholar]
  17. Wallberg A.; Nilsson K.; Osterlund K.; Peterson A.; Elg S.; Raboisson P.; Bauer U.; Hammerland L. G.; Mattsson J. P. Phenyl ureas of creatinine as mGluR5 antagonists. A structure-activity relationship study of fenobam analogues. Bioorg. Med. Chem. Lett. 2006, 16, 1142–1145. [DOI] [PubMed] [Google Scholar]
  18. Rasmussen C. R. McNeil Laboratories, Inc., Fort Washington, PA. 4-Oxo-2-imidazolidinylidene ureas. U.S. Patent 3,983,135, September 28, 1976.
  19. Kim Y. H.; Lee N. J. Facile Synthesis of 2-Amino-Dihydro-4(1h)-Pyrimidinone Derivatives—Cyclization of N-Substituted Guanidines with Alpha,Beta-Unsaturated Esters. Heterocycles 1983, 20, 1769–1772. [Google Scholar]
  20. Berry-Kravis E.; Hessl D.; Coffey S.; Hervey C.; Schneider A.; Yuhas J.; Hutchison J.; Snape M.; Tranfaglia M.; Nguyen D. V. A pilot open-label single-dose trial of fenobam in adults with fragile X syndrome. J. Med. Genet. 2009, 46, 266–271. [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

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Supplementary Materials

ml200162f_si_001.pdf (130.2KB, pdf)

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