S. K. Ahmed et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4358–4362
4361
In sum, the hydantoin group has been shown to be an effective
carboxylic acid isostere in the design of new inhibitors of the vesic-
ular glutamate transporter (VGLUT), but one of questionable value
in the further development of blockers of the obligate exchange
transporter, SxÀc .
H
(i, ii, iii)
HO
N
O
EtO
S
S
NH
O
O
O
6
7
Scheme 3. Synthesis of 5-(2,5-dioxoimidazolidin-4-yl)thiophene-2-carboxylic
acid. Reagents and conditions: (i) hexamethylenetetramine, CF3CO2H, 90 °C, 3 h,
93%; (ii) (NH4)2CO3, KCN, 1:1 EtOH, H2O, 50–60 °C, 3 h, 67%; (iii) LiOH, THF/MeOH
(1:1), rt, 48 h, 53%.
Acknowledgments
This research was supported by NS38248 (CMT), the Core Lab-
oratory for Neuromolecular Production P30 NS055022 (CMT),
NS058229 (ATERIS Technologies LLC), NS30570 (RJB), NS42077
(RJB) and the COBRE Center for Structural and Functional Neurosci-
ence (NIH P20-RR015583).
References and notes
1. Meldrum, B. Epilepsia 1984, 25, S140. suppl. 2.
2. Meldrum, B. S. Neurology 1994, 44, S14.
3. Meldrum, B. S. J. Nutr. 2000, 130, 1007S.
4. Nakanishi, S. Science 1992, 258, 597.
5. Schoepp, D. D.; Conn, P. J. Trends Pharmacol. Sci. 1993, 14, 13.
6. Seeburg, P. H. Trends Neurosci. 1993, 16, 359.
7. Watkins, J. C.; Pook, P. C.; Sunter, D. C.; Davies, J.; Honore, T. Adv. Exp. Med. Biol.
1990, 268, 49.
8. Choi, D. W.; Rothman, S. M. Annu. Rev. Neurosci. 1990, 13, 171.
9. Swanson, G. T.; Sakai, R. Prog. Mol. Subcell. Biol. 2009, 46, 123.
10. Moriyama, Y.; Omote, H. Biol. Pharm. Bull. 2008, 31, 1844.
11. Takamori, S. Neurosci. Res. 2006, 55, 343.
12. Burdo, J.; Dargusch, R.; Schubert, D. J. Histochem. Cytochem. 2006, 54, 549.
13. Domercq, M.; Sanchez-Gomez, M. V.; Sherwin, C.; Etxebarria, E.; Fern, R.;
Matute, C. J. Immunol. 2007, 178, 6549.
14. Bridges, R. J.; Kavanaugh, M. P.; Chamberlin, A. R. Curr. Pharm. Des. 1999, 5, 363.
15. Bridges, R. J.; Lovering, F. E.; Koch, H.; Cotman, C. W.; Chamberlin, A. R.
Neurosci. Lett. 1994, 174, 193.
16. Etoga, J. L.; Ahmed, S. K.; Patel, S.; Bridges, R. J.; Thompson, C. M. Bioorg. Med.
Chem. Lett. 2010, 20, 2680.
17. Patel, S. A.; Rajale, T.; O’Brien, E.; Burkhart, D. J.; Nelson, J. K.; Twamley, B.;
Blumenfeld, A.; Szabon-Watola, M. I.; Gerdes, J. M.; Bridges, R. J.; Natale, N. R.
Bioorg. Med. Chem. 2010, 18, 202.
Figure 2. Inhibition of VGLUT by 2l and 4b.
18. Carrigan, C. N.; Bartlett, R. D.; Esslinger, C. S.; Cybulski, K. A.;
Tongcharoensirikul, P.; Bridges, R. J.; Thompson, C. M. J. Med. Chem. 2002, 45,
2260.
19. Carrigan, C. N.; Esslinger, C. S.; Bartlett, R. D.; Bridges, R. J.; Thompson, C. M.
Bioorg. Med. Chem. Lett. 1999, 9, 2607.
20. Thompson, C. M.; Davis, E.; Carrigan, C. N.; Cox, H. D.; Bridges, R. J.; Gerdes, J. M.
Curr. Med. Chem. 2005, 12, 2041.
21. Barraclough, P.; Bolofo, M. L.; Giles, H.; Gillam, J.; Harris, C. J.; Kelly, M. G.; Leff,
P.; McNeill, A.; Robertson, A. D.; Stepney, R. J.; Whittle, B. J. Bioorg. Med. Chem.
1996, 4, 81.
ing uptake level to 7% of control. This suggests that all or part con-
version of the aldehyde to the corresponding carboxylic acid could
account for the observed activity.
The large difference in VGLUT inhibitory activity between com-
pound 4b and inactive bis-hydantoins 4a and 5a/5b suggests that
the thiophene sulfur atom and/or the angular difference imposed
on the bis-hydantoin substituents by the five-membered ring
may play a role in blocking uptake at VGLUT. Further, compounds
5a/5b lack the acidic imide protons that may be needed for effec-
tive binding to VGLUT. Molecular modeling using previously de-
fined pharmacophore models20 provided no clear insight for
hydantoin-containing VGLUT inhibitors although the addition of
lipophilic groups has not yet been thoroughly explored.
22. Groutas, W. C.; Stanga, M. A.; Castrisos, J. C.; Schatz, E. J. J. Enzyme Inhib. 1990, 3,
237.
23. Meanwell, N. A.; Roth, H. R.; Smith, E. C.; Wedding, D. L.; Wright, J. J.; Fleming, J.
S.; Gillespie, E. J. Med. Chem. 1991, 34, 2906.
24. Sarges, R.; Oates, P. J. Prog. Drug Res. 1993, 40, 99.
25. Li, J. J. Name Reactions; Springer: Berlin Heidelberg, 2009. p 76.
26. Synthesis of compounds 4a–b. To approx. 2.0 g of carbonyl compound
(0.02 mol) dissolved in 50% methanol (50 mL) were added ammonium
carbonate (9.1 g; 0.08 mol) and potassium cyanide (2.6 g; 0.04 mol). The
mixture was warmed to 58–60 °C for 3 h, concentrated to 15 mL, and chilled to
0 °C to produce white-off yellow crystals.
As noted, the majority of the hydantoins tested were essentially
inactive as inhibitors of SxÀc , with none exhibiting inhibitory activ-
ity comparable to cystine, although, compounds 2k, 2l, 2o and 4b
27. Spectral data for selected compounds. Compound 2b: yield 35%; mp >300 °C;
1H NMR (400 MHz, DMSO-d6): d (s, 1H), 7.73 (d, J = 8.25 Hz, 1H), 7.50 (d,
J = 8.25 Hz, 1H), 5.77 (s, 1H); 13C: d 169.5, 158.7, 143.4, 140.5, 136.8, 134.4,
129.7, 128.6, 54.2; ESI MS m/z = 336 (M+1); Anal. Calcd for C9H8N2O8S2: C,
32.14; H, 2.40; N, 8.33. Found: C, 32.33; H, 2.22; N, 8.62. Compound 2l: 1H NMR
(400 MHz, acetone-d6). d. 10.9 (b s, 1H), 9.81 (s, 1H), 7.81 (d, J = 3.9 Hz 1H), 7.71
(d, J = 3.9 Hz, 1H), 5.91 (s, 1H); 13C: d 182.1, 164.6, 164.1, 148.2, 141.4, 138.4,
129.5, 64.2; ESI MS m/z = 211 (M+1); Anal. Calcd for C8H6N2O3S: C, 45.71; H,
2.88; N, 13.33. Found: C, 45.33; H, 2.91; N, 13.67. Compound 2m: yield 75%;
mp 258–261 °C; 1H NMR (400 MHz, DMSO-d6): 12.02 (b s, 1H), 10.58 (b s, 1H),
8.06 (b s, 1H), 7.59 (s, 1H), 7.09 (s, 1H), 4.99 (s, 1H); ESI MS m/z = 167 (M+1); (n
max/cmÀ1): 3414, 3241, 2700, 1729, 1456. Anal. Calcd for C6H6N4O4: C, 43.38;
H, 3.64; N, 33.72. Found: C, 43.33; H, 3.59; N, 33.62. Compound 4a: yield 59%;
mp >300 °C; 1H NMR (400 MHz, DMSO-d6): 10.78 (b s, 1H), 8.39 (b s, 1H), 7.33
(s, 4H), 5.15 (s, 2H); ESI MS m/z = 275 (M+1); (n max/cmÀ1): 3237, 2925, 2721,
1701, 1458, 1377, 722. Anal. Calcd for C12H10N4O4: C, 52.56; H, 3.68; N, 20.43.
Found: C, 52.33; H, 3.44; N, 20.62.
blocked glutamate uptake from 34–51% of control at 500 lM.
Interestingly, each of these compounds contains a thiophene-
linked hydantoin. The only other structure shown to block uptake
at SxÀc to an appreciable amount was benzylhydantoin 2f at 47% of
control. This lack of activity was somewhat surprising, given the
structural similarities between the hydantoins and numerous isox-
azole-based inhibitors.15,26 It remains to be determined if this re-
flects an unfavorable interaction directly between the hydantoin
group and the SxÀc binding site or the moiety’s influence on the
R-group position (or a combination of both). Owing to poor inhibi-
tion of the hydantoins at SxÀc , compounds were not tested as
individual enantiomers although further studies are underway
with stereoisomers to refine and improve the potency as VGLUT
inhibitors.
28. Patel, S. A.; Warren, B. A.; Rhoderick, J. F.; Bridges, R. J. Neuropharmacology
2004, 46, 273.
29. Kish, P. E.; Ueda, T. Methods Enzymol. 1989, 174, 9.