Synthesis and evaluation of 6-methyl-3-phenylcoumarins as potent and selective MAO-B inhibitors

Article abstract of DOI:10.1016/j.bmcl.2009.07.039

A series of 6-methyl-3-phenylcoumarins 3-6 were synthesized and evaluated as monoamine oxidase A and B (MAO-A and MAO-B) inhibitors. A comparative study between the three possible mono methoxy 3-phenyl derivatives and the p-hydroxy analogue is reported. T

Full text of DOI:10.1016/j.bmcl.2009.07.039

Bioorganic & Medicinal Chemistry Letters 19 (2009) 5053–5055
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and evaluation of 6-methyl-3-phenylcoumarins as potent
and selective MAO-B inhibitors
Maria Joao Matos a,b, , Dolores Viña a,c, Carmen Picciau a,b, Francisco Orallo c,
*
Lourdes Santana a, Eugenio Uriarte a
a Departamento de Química Orgánica, Facultad de Farmacia, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain
b Dipartimento Farmaco Chimico Tecnologico, Facoltà di Farmacia, Università di Cagliari, 09124 Cagliari, Italy
c Departamento de Farmacología, Facultad de Farmacia, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 6-methyl-3-phenylcoumarins 3-6 were synthesized and evaluated as monoamine oxidase A
and B (MAO-A and MAO-B) inhibitors. A comparative study between the three possible mono methoxy
3-phenyl derivatives and the p-hydroxy analogue is reported. The synthesis of these new resveratrol-cou-
marin hybrids was carried out by a Perkin reaction between the 5-methylsalicylaldehyde and the corre-
sponding phenylacetic acids. The p-methoxy substituted compound 3 was hydrolyzed to 6 by a
traditional reaction with hydriodic acid. The prepared compounds show high selectivity to the MAO-B
isoenzyme, some of them with IC50 values in the low nanomolar range. Compound 4, with the methoxy
group in meta position, is the most active of this series, with an IC50 against MAO-B of 0.80 nM, and is
several times more potent and MAO-B selective than the R-(ꢀ)-deprenyl (reference compound).
Ó 2009 Elsevier Ltd. All rights reserved.
Received 12 June 2009
Revised 4 July 2009
Accepted 7 July 2009
Available online 10 July 2009
Keywords:
Phenylcoumarins
MAOIs
Monoamino oxidase
Perkin reaction
Coumarin–resveratrol hybrids
Coumarins are present in remarkable amounts in the nature.
They have attracted considerable interest due to their numerous
biological activities depending on their substitution pattern.1
These compounds have been shown to possess antioxidative and
anticarcinogenic properties and to inhibit several enzymes.2–6
Some coumarin derivatives of natural and synthetic origin have
been characterized as monoamine oxidase inhibitors (MAOIs).7–12
Monoamine oxidase (MAO) is an FAD-containing enzyme
bound to the mitochondrial outer membrane of neuronal, glial,
and other cells.10,13 This enzyme regulates levels of biogenic
amines (including neurotransmitters) in the brain and the periph-
eral tissues by catalyzing their deamination.11 MAO exists as two
distinct enzymatic isoforms, MAO-A and MAO-B, based on their
substrate and inhibitor specificities.14,15
species, produced in response to an exterior or interior damage.18
Resveratrol shows a large number of pharmacological activities,
including antiinflammatory, antioxidant, anticancer, and cardio-
protective properties and enzyme inhibition.19–23 cis and trans-res-
veratrol proved to be MAO activity inhibitors, the trans isomer
being more effective than the cis.24
Because of their similar characteristics, it was interesting to de-
sign and synthesize hybrids that incorporate the nucleus of the
coumarins and resveratrol molecules.19,25 In previous work, our re-
search group had reported a comparative study of the importance
to the MAOI activity of the different number of methoxy groups on
the phenyl ring in the 3 position of coumarin. This study contrib-
uted to establish a relationship between them and with the non-
substituted analogue.8 Based on this, and with the aim of helping
to better understand a structure/activity relationship for the
MAO inhibitory activity and selectivity, in this paper we report
the synthesis and evaluation of a new series. Maintaining the 6-
methyl-3-phenylcoumarin structure, the three possible different
positions of one methoxy group in 3-phenyl ring were explored.
We also explored the importance of the hydrolysis of this methoxy
group.
MAO-A preferentially deaminates serotonin, adrenaline and
noradrenaline. That isoenzyme is irreversibly inhibited by low con-
centrations of clorgyline. MAO-B preferentially deaminates b-
phenylethylamine and benzylamine and is irreversibly inhibited
by R-(ꢀ)-deprenyl.16 The MAOIs have been used for several years
in the treatment of depression and anxiety diseases (MAO-A inhib-
itors) and in Parkinson’s disease (MAO-B inhibitors).17
Resveratrol, structurally 3,40,5-trihydroxystilbene, is a natural
phenolic component of Vitis vinifera L. and other spermatophyte
The synthesis of the 6-methyl-3-phenylcoumarins was carried
out via the classical Perkin reaction.26 This reaction is performed
by condensation of the 5-methylsalicylaldehyde 1 and the appro-
priately substituted phenylacetic acids 2, with N,N0-dicyclohexyl-
carbodiimide (DCC) as dehydrating agent, in DMSO, at 110 °C, for
* Corresponding author. Tel.: +34 1918523676.
E-mail address: mariacmatos@gmail.com (M.J. Matos).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.07.039

5054
M. J. Matos et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5053–5055
24 h (Scheme 1). Compounds 3,8 427 and 528 were obtained in
yields of 61%, 53%, and 59%, respectively. The reaction mixture
was purified by flash chromatography, using hexane/ethyl acetate,
in a proportion of 9:1, as eluent.
The p-methoxy derivative 3 was hydrolyzed with hydriodic
acid, in the presence of acetic acid and acetic anhydride, at
110 °C, for 5 h (Scheme 1). The residue was purified by crystalliza-
tion of acetonitrile, and the phenol derivative 629 was obtained
with a yield of 63%.
of them present activity in the low nanomolar range. The introduc-
tion of one meta methoxy group in the 3-phenyl ring improves sev-
eral times the MAO-B inhibitory activity in respect to ortho and
para positions. Compound 4 is about 24 times more active that
R-(ꢀ)-deprenyl, and several times more selective than this drug.
The hydrolysis of methoxy groups is not a strategy to get better
MAOI activity. These studied modifications can interestingly im-
prove the pharmacologic potential of the 3-phenylcoumarins in
the treatment of Parkinson’s disease.
MAO inhibiting activity of compounds 3-6 was evaluated
in vitro by the measurement of the enzymatic activity of human re-
combinant MAO isoforms in BTI insect cells infected with baculo-
virus.8 Then, the IC50 values and MAO-B selectivity ratio [IC50
(MAO-A)]/[IC50 (MAO-B)] for inhibitory effects of both new com-
pounds and reference inhibitors were calculated (Table 1).30
Acknowledgments
Thanks to the Spanish Ministerio de Sanidad y Consumo
(PI061457 and PI061537) and to Xunta da Galicia (BTF20303PR,
PXIB203022PR, and CSA019203PR) and Fondazione Banco Sarde-
gna (Italy) for financial support. M.J.M. also thanks MIUR for a
PhD grant.
The resveratrol–coumarin hybrid compounds 3, 4, and
6
showed high selectivity for the MAO-B isoenzyme and inhibitory
activity in the nano to picomolar range. Compound 4 was the most
active compound of this series, making the meta methoxy position
the most interesting position at which to improve the MAO-B-
inhibiting activity. Compound 5 has no MAOI activity up to the
highest tested concentration, proving that the methoxy group in
the ortho position is not favorable to the measured enzymatic inhi-
bition. Changes on the methoxy substituent position on the phenyl
ring in coumarin’s 3 position can modulate the pharmacologic po-
tential of the synthesized coumarins.
Comparing compound 3 with its hydroxyl derivative 6, it was
shown that the hydrolysis of methoxy groups is not, in this case,
a strategy to improve the MAOI activity. The IC50 of compound 6
for inhibition of MAO-B activity is approximately 10 times bigger
than compound 3. However, this value is also in the nanomolar
range, and the molecule is also a potent MAOI, selective for the
MAO-B isoenzyme.
References and notes
1. Borges, F.; Roleira, F.; Milhazes, N.; Santana, L.; Uriarte, E. Curr. Med. Chem.
2005, 12, 887.
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4. Kabeya, L.; Marchi, A.; Kanashiro, A.; Lopes, N.; Silva, C.; Pupo, M.; Lucisano-
Valim, Y. Bioorg. Med. Chem. 2007, 15, 1516.
5. Carotti, A.; Altomare, C.; Catto, M.; Gnerre, C.; Summo, L.; De Marco, A.; Rose, S.;
Jenner, P.; Testa, B. Chem. Biod. 2006, 3, 134.
6. Chilin, A.; Battistutta, R.; Bortolato, A.; Cozza, G.; Zanatta, S.; Poletto, G.;
Mazzorana, M.; Zagotto, G.; Uriarte, E.; Guiotto, A.; Pinna, L.; Meggio, F.; Moro,
S. J. Med. Chem. 2008, 51, 752.
7. Santana, L.; Uriarte, E.; González-Díaz, H.; Zagotto, G.; Soto-Otero, R.; Méndez-
Álvarez, E. J. Med. Chem. 2006, 49, 1118.
8. Matos, M. J.; Viña, D.; Quezada, E.; Picciau, C.; Delogu, G.; Orallo, F.; Santana, L.;
Uriarte, E. Bioorg. Med. Chem. Lett. 2009, 19, 3268.
9. Santana, L.; González-Díaz, H.; Quezada, E.; Uriarte, E.; Yáñez, M.; Viña, D.;
Orallo, F. J. Med. Chem. 2008, 51, 6740.
10. Gnerre, C.; Catto, M.; Leonetti, F.; Weber, P.; Carrupt, P.; Altomare, C.; Carotti,
A.; Testa, B. J. Med. Chem. 2000, 43, 4747.
11. Catto, M.; Nicolotti, O.; Leonetti, F.; Carotti, A.; Favia, A.; Soto-Otero, R.;
Méndez-Álvarez, E.; Carotti, A. J. Med. Chem. 2006, 49, 4912.
12. Chimenti, F.; Secci, D.; Bolasco, A.; Chimenti, P.; Bizzarri, B.; Granese, A.;
Carradori, S.; Yanez, M.; Orallo, F.; Ortuso, F.; Alcaro, S. J. Med. Chem. 2009, 52,
1935.
13. Chimenti, F.; Secci, D.; Bolasco, A.; Chimenti, P.; Granese, A.; Befani, O.; Turini,
P.; Alacaro, S.; Ortuso, F. Bioorg. Med. Chem. Lett. 2004, 14, 3697.
14. Geha, R. M.; Rebrin, I.; Chen, K.; Shih, J. C. J. Biol. Chem. 2001, 276, 9877.
15. Johnston, J. P. Biochem. Pharmacol. 1968, 17, 1285.
16. Grimsby, J.; Lan, N. C.; Neve, R.; Chen, K.; Shih, J. C. J. Neurochem. 1990, 55,
1166.
17. Harfenist, H.; Heuseur, D. J.; Joyner, C. T.; Batchelor, J. F.; White, H. L. J. Med.
Chem. 1996, 39, 1857.
18. Frémont, L. Life Sci. 2000, 66, 663.
19. Vilar, S.; Quezada, E.; Santana, L.; Uriarte, E.; Yánez, M.; Fraiz, N.; Alcaide, C.;
Cano, E.; Orallo, F. Bioorg. Med. Chem. Lett. 2006, 16, 257.
20. Orallo, F. In Resveratrol in Health and Disease; Aggarwal, B. B., Shishodia, S., Eds.;
CRC Press: USA, 2005; p 577.
21. Leiro, J.; Álvarez, E.; Arranz, J.; Laguna, R.; Uriarte, E.; Orallo, F. J. Leukocyte Biol.
2004, 75, 1156.
In conclusion, the synthesized resveratrol–coumarin hybrid
compounds show high selectivity for the MAO-B isoenzyme. Most
R
HO
O
Me
CHO
OH
Me
a
O
O
OMe
1
2
3: R = p-OMe
4: R = m-OMe
5: R = o-OMe
b
6: R = p-OH
Scheme 1. Reagents and conditions: (a) DCC, DMSO, 110 °C, 24 h; (b) HI, AcOH,
Ac2O, 110 °C, 5 h.
22. Orallo, F. Curr. Med. Chem. 2008, 15, 1887.
23. De Colibus, L.; Li, M.; Binda, C.; Lustig, A.; Edmondson, D. E.; Mattevi, A. Proc.
Natl. Acad. Sci. U.S.A. 2005, 102, 12684.
Table 1
24. Yánez, M.; Fraiz, N.; Cano, E.; Orallo, F. Biochem. Biophys. Res. Commun. 2006,
344, 688.
MAO-A and MAO-B inhibition by the prepared compounds 3–6 and for the reference
compounds
25. Vilar, S.; Quezada, E.; Alcaide, C.; Orallo, F.; Santana, L.; Uriarte, E. Qsar Comb.
Sci. 2007, 26, 317.
Compounds
MAO-A IC50
MAO-B IC50
Ratio
´
26. Kamat, S. P.; DSouza, A. M.; Paknikar, S. K.; Beaucahmp, P. S. J. Chem. Res. (S)
*
*
*
*
3
4
5
6
13.05 0.90 nM
>7663b
2002, 242.
802.60 53.75 pM
>124,595b
27. 3-(30-Methoxy)phenyl-6-methylcumarin (4): It was obtained with a yield of 53%.
Mp 84–85 °C. 1H NMR (CDCl3) d (ppm), J (Hz): 2.44 (s, 3H, –CH3), 3.88 (s, 1H, –
OCH3), 6.97 (m, 1H, H-40), 7.26–7.42 (m, 6H, H-5, H-7, H-8, H-20, H-50 and H-60)
7.78 (s, 1H, H-4). 13C NMR (CDCl3) d (ppm): 20.77, 55.37, 114.15, 114.38,
116.10, 119.28, 120.86, 127.70, 129.43, 132.48, 134.12, 136.12, 139.91, 140.10,
151.60, 159.45 160.66. MS m/z (%): 267 (48), 266 (M+, 100), 239 (16), 238 (70),
237 (20), 195 (48), 194 (16), 166 (10), 165 (29), 152 (23). Anal. Calcd for
C17H14O3: C, 76.68; H, 5.30. Found: C, 76.76; H, 5.21.
*
155.59 17.09 nM
19.60 0.86 nM
7.54 0.36 lM
>643b
3431
0.87
R-(ꢀ)-Deprenyl
67.25 1.02 l
Ma
6.56 0.76
Iproniazid
lM
*
Inactive at 100 lM (highest concentration tested). At higher concentrations the
compounds precipitate.
a
28. 3-(20-Methoxy)phenyl-6-methylcumarin (5): It was obtained with a yield of 59%.
Mp 177–178 °C. 1H NMR (CDCl3) d (ppm), J (Hz): 2.41 (s, 3H, –CH3), 3.82 (s, 1H,
–OCH3), 7.02 (m, 2H, H-30, H-40), 7.24–7.41 (m, 5H, H-5, H-7, H-8, H-50 and H-
60) 7.69 (s, 1H, H-4). 13C NMR (CDCl3) d (ppm): 20.80, 55.81, 111.31, 116.21,
P
<0.01 versus the corresponding IC50 values obtained against MAO-B, as
determined by ANOVA/Dunnett’s.
b
Values obtained under the assumption that the corresponding IC50 against
MAO-A is the highest concentration tested (100 lM).

M. J. Matos et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5053–5055
5055
119.24, 120.57, 124.20, 126.36, 127.58, 130.14, 130.80, 132.21, 133.89, 141.84,
151.82, 157.22 160.55. MS m/z (%): 267 (22), 266 (M+, 100), 265 (10), 249 (29),
237 (22), 235 (14), 223 (22), 220 (12), 195 (29), 173 (26), 165 (25), 152 (17),
145 (19), 118 (19). Anal. Calcd for C17H14O3: C, 76.68; H, 5.30. Found: C, 76.76;
H, 5.22.
8.4), 7.56 (m, 3H, H-20, H-60 and H-5), 8.06 (s, 1H, H-4). 13C NMR (CDCl3) d
(ppm): 20.31, 115.04, 115.52, 119.45, 125.29, 126.66, 127.92, 129.83, 132.00,
133.67, 138.46, 150.79, 157.95, 160.04. MS m/z (%): 253 (13), 252 (M+, 75), 224
(58), 223 (26), 165 (12) 152 (15), 143 (23), 99 (37), 98 (25), 83 (12), 70 (20), 56
(100), 55 (27). Anal. Calcd for C16H12O3: C, 76.18; H, 4.79. Found: C, 75.99; H,
4.69.
29. 3-(40-Hydroxy)phenyl-6-methylcumarin (6): It was obtained with a yield of 63%.
Mp 217–218 °C. 1H NMR (CDCl3) d (ppm), J (Hz): 2.37 (s, 3H, –CH3), 6.84 (d, 2H,
H-30 and H-50, J = 8.8), 7.31 (d, 1H, H-8, J = 8.4), 7.40 (dd, 1H, H-7, J = 1.9 and
30. All IC50 values shown in the table are expressed as means SEM from five
experiments.