Synthesis of N-propargylphenelzine and analogues as neuroprotective agents

Article abstract of DOI:10.1016/S0960-894X(01)00549-2

A series of N¹- and N²-propargylphenelzine derivatives and analogues (1-7) was synthesized. In addition to their activity as monoamine oxidase inhibitors, two of the compounds, N¹- and N²-propargylphenelzines (3 and 6), were found to be potent at preventing DSP-4-induced noradrenaline (NA) depletion in mouse hippocampus, suggesting that they have neuroprotective properties.

Full text of DOI:10.1016/S0960-894X(01)00549-2

Bioorganic & Medicinal Chemistry Letters 11 (2001) 2715–2717
Synthesis of N-Propargylphenelzine and Analogues as
Neuroprotective Agents
Lei Ling,a,* Liana J. Urichuk,a B. Duff Sloley,a Ronald T. Coutts,b Glen B. Baker,b
Jacqueline J. Shana,* and Peter K. T. Panga
aCV Technologies Inc., Edmonton Research Park, 9411-20 Ave., Edmonton, Alberta, Canada T6N 1E5
bNeurochemical Research Unit, Department of Psychiatry, University of Alberta, Edmonton, Canada T6G 2R7
Received 26 September 2000; accepted 3 August 2001
Abstract—A series of N1- and N2-propargylphenelzine derivatives and analogues (1–7) was synthesized. In addition to their activity
as monoamine oxidase inhibitors, two of the compounds, N1- and N2-propargylphenelzines (3 and 6), were found to be potent at
preventing DSP-4-induced noradrenaline (NA) depletion in mouse hippocampus, suggesting that they have neuroprotective prop-
erties. # 2001 Elsevier Science Ltd. All rights reserved.
Monoamine oxidase (MAO, EC 1.4.3.4) is an enzyme
that oxidizes many monoamines, including important
neurotransmitter amines, such as noradrenaline (NA),
dopamine, and 5-hydroxytryptamine (5-HT).1 Numer-
ous MAO inhibitors have been synthesized and eval-
uated, and some of them have proven to be useful for
treatment of psychiatric disorders such as depression,
panic disorder, and social phobia.2,3 Phenelzine, a non-
selective MAO inhibitor that inhibits both the A and B
isozymes of MAO, has been used clinically for such
purposes for many years.4 R-(À)-Deprenyl (N-methyl-
N-propargylamphetamine), a selective MAO-B inhi-
bitor, has proven to be effective in alleviating symptoms
of Parkinson’s disease5 and has also been shown to be
capable of protecting animals from DSP-4 [N-(2-chloro-
ethyl)-N-ethyl-2-bromobenzylamine]-induced neuronal
degeneration.5 Pargyline, another MAO inhibitor that
also contains an N-propargyl group, is also capable of
protecting against DSP-4-induced neurotoxicity.6
Because both deprenyl and pargyline inhibit MAO and
apparently have neuroprotective activity, many other
potential MAO inhibitors with the propargyl group
have been synthesized and evaluated as neuroprotective
agents.5b,7 In order to study structure–activity relation-
ships and to discover new potent neuroprotective
agents, we have recently synthesized a series of N1- and
N2-propargylphenelzine derivatives and analogues of
these compounds that contain different spacer groups
between the aromatic ring and the hydrazine moiety.
The compounds synthesized are shown in Scheme 1.
The effects of these propargylated phenelzine derivatives
and their analogues on protection from DSP-4-induced
Scheme 1.
*Corresponding author. Fax: +1-780-433-8964; e-mail: linglei@cvtechnologies.com
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00549-2

2716
L. Ling et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2715–2717
depletion of NA in mouse hippocampus were investi-
gated in preliminary studies. The chemical syntheses
and preliminary experimental results are reported here.
same conditions as in Scheme 2 to give products 2 and 4
(40 and 28% yields, respectively). The final products 1–
4 were converted to their HCl salts by treatment with
anhydrous hydrogen chloride (1 N, in ether). The pre-
cipitates formed were collected and washed with ether
to produce the final products.8
The syntheses of compounds 1 and 3 are shown in
Scheme 2. The corresponding starting materials, phe-
nylhydrazine (8) and phenelzine, were subjected to
direct propargylation with propargyl bromide in a bi-
phasic system of acetonitrile and a saturated aqueous
potassium carbonate solution. The reaction was carried
out overnight at room temperature. Because of the
electron-donating property of the alkyl group, the N1
atom of each starting material was selectively pro-
pargylated to give products N1-propargylphenylhy-
drazine (1) and N1-propargylphenelzine (3). These
products (1 and 3) were isolated from the organic layer
by silica gel chromatography in yields of 44 and 84%,
respectively.8
The syntheses of the N2-propargyl compounds (5–7) are
shown in Scheme 4. Starting material 14 was prepared
from phenelzine by reacting with di-tert-butyl-dicarbo-
nate. Introduction of the propargyl group to 10, 11, and
14 was carried out in the presence of sodium hydride.
All reactions proceeded smoothly to give the products
15, 16, and 17 in high yields. Removal of the protective
group with HCl (4 N in dioxane) gave the final products
N1-benzyl-N2-propargylhydrazine (5), N2-propargyl-
phenelzine (6), and N1-trans-cinnamyl-N2-propargyl-
hydrazine (7) as their HCl salts.9
Due to the lack of availability of the direct starting
materials, N1-propargyl-N1-benzylhydrazine (2) and N1-
propargyl-N1-trans-cinnamylhydrazine (4) were synthe-
sized from hydrazine. The synthesis is shown in Scheme 3.
Both of the N-atoms of hydrazine were protected by
reacting with di-tert-butyl-dicarbonate [(BOC)2O] in
methanol at room temperature to produce compound 9
(96% yield). Benzyl or trans-cinnamyl groups were
introduced onto the protected hydrazine in the presence
of sodium hydride in anhydrous THF to give com-
pounds 10 and 11 in yields of 99 and 76%, respectively.
Removal of the protective group of 10 and 11 by anhy-
drous HCl (in dioxane) produced the intermediates 12
and 13 as their HCl salts (96 and 61% yields, respec-
tively). The precipitates of 12 and 13 were isolated by
filtration and subjected to propargylation under the
Compounds 1–7 were examined for their effect on DSP-
4-induced depletion of NA in mouse hippocampus ex
vivo and for their ability to inhibit MAO activity in rat
whole brain in vitro according to reported literature
methods.7b,10 The effect of the propargylated phenelzine
derivatives and their analogues (10 mg/kg, ip) on DSP-
4-induced NA depletion is expressed as percentage of
NA restoration by comparing mice that received drug
prior to DSP-4 administration with mice that received
only vehicle prior to the DSP-4. Higher percentages of
restoration indicate higher levels of neuroprotection.
The results are shown in Table 1 and are compared with
those obtained with the same doses of phenelzine and
deprenyl. All of the synthesized compounds were rela-
tively potent inhibitors of MAO-A and -B. More
importantly, both N1- and N2-propargylphenelzine
Scheme 2.
Scheme 3.
Scheme 4. (a) NaH, propargyl bromide; (b) 4 N HCl in dioxane.

L. Ling et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2715–2717
2717
Table 1. Effect of the synthesized compounds on prevention of DSP-
4-induced NA depletion ex vivo and on MAO activity in vitro
during this work. The expert technical assistance of
Richard Strel is gratefully acknowledged.
Compd
DSP-4
(% NA restoration)a
IC50 for
inhibition
IC50 for
inhibition
of MAO-A (M)a of MAO-B (M)a
References and Notes
Phenelzine
43.48Æ9.13
79.71Æ7.89
À49.82Æ5.39
33.58Æ6.57
56.38Æ8.80
À39.20Æ7.68
31.74Æ7.31
76.83Æ8.49
À7.21Æ5.17
3.31Â10À8b
5.16Â10À7b
1.13Â10À5
1.56Â10À6
2.04Â10À6
1.17Â10À6
3.62Â10À7
1.85Â10À6
7.90Â10À6
7.63Â10À8b
b
(À)-Deprenyl
2.76Â10À9
1. Tipton, K. F., Dostert, P., Benedetti, M. S., Eds.; Mono-
amine Oxidase and Disease; Academic: London, 1984.
2. Dowson, J. H. J. Neural Transm. 1987, 23, 121.
1
2
3
4
5
6
7
1.01Â10À6
1.21Â10À7
7.65Â10À8
3.53Â10À6
2.84Â10À6
3.18 Â10À6
1.02Â10À5
3. Krishnan, K. R. R. In The American Psychiatric Associa-
tion Textbook of Psychopharmacology; Schatzberg, A. F.,
Nemeroff, C. B., Eds.; APA: Washington, D.C., 1998; p 239.
4. (a) Nies, A.; Robinson, D. S. In Monoamine Oxidase Inhi-
bitors; Youdim, M. B. H., Paykel, E. S., Eds.; John Wiley &
Sons: New York, 1981; p 141. (b) Tyrer, P.; Gardner, M.;
Lambourn, J.; Whitford, M. In Monoamine Oxidase Inhibi-
tors; Youdim, M. B. H., Paykel, E. S., Eds.; John Wiley &
Sons: New York, 1981; p 149. (c) Baker, G. B.; Urichuk, L. J.;
McKenna, K. F.; Kennedy, S. H. Cell. Mol. Neurobiol. 1999,
19, 411.
5. (a) Knoll, J.; Ecsery, Z.; Nievel, J. B.; Kelemen, K.; Knoll,
B. Arch. Int. Pharmacodyn. Ther. 1965, 155, 154. (b) Knoll, J.
In Monoamine Oxidase: Structure, Function, and Altered
Functions; Singer, T. P., Korff, R. W. V., Murphy, D. L., Eds.;
Academic: New York, 1979; pp 431–446.
aData represent meansÆSEM (n=5) unless otherwise indicated.
bData represent meansÆSEM of seven experiments.
(3 and 6), compounds with two-carbon chain spacer
between aromatic ring and hydrazine moiety, showed
considerable activity at preventing DSP-4-induced NA
depletion. Compound 3 was similar in neuroprotective
potency to phenelzine, while compound 6 provided
substantially more protection from DSP-4-induced
neurodegeneration, similar to the activity of (À)-depre-
nyl. This suggests that compounds 3 and 6 may be
effective neuroprotective agents.
6. Hallman, H.; Jonsson, G. Eur. J. Pharmacol. 1984, 103,
269.
7. (a) Yu, P. H.; Davis, B. A.; Boulton, A. A. J. Med. Chem.
1992, 35, 3705. (b) Yu, P. H.; Davis, B. A.; Fang, J.; Boulton,
A. A. J. Neurochem. 1994, 63, 1820. (c) Yu, P. H.; Davis, B. A.;
Boulton, A. A. Biochem. Pharmacol. 1993, 46, 753. (d) Yu,
P. H.; Zhang, X.; Zuo, D. M.; Lai, C. F.; Tien, K.; Davis,
B. A.; Boulton, A. A. Restorat. Neurol. Neurosci. 1998, 12,
113. (e) Avila, M.; Balsa, M. D.; Fernandez-Alvarez, E.; Tip-
ton, K. F.; Unzeta, M. Biochem. Pharmacol. 1993, 45, 2231.
8. 1H NMR of compound 3 in CDCl3: d 2.30 (t, 1H, J=2.45
Hz, CH), 2.85 (m, 4H, CH2Â2), 3.20 (brs, 2H, NH2), 3.59 (d,
2H, J=2.45 Hz, CH2 of propargyl group), 7.18–7.33 (m, 5H,
aromatic); HCl salt in D2O: d 2.95 (m, 3H, CH2 and CH), 3.37
(t, 2H, J=7.02 Hz, CH2), 3.97 (m, 2H, CH2 of propargyl
group), 7.28–7.39 (m, 5H, aromatic).
In summary, a series of N1- and N2-propargylphenelzine
derivatives and analogues was synthesized. Both N1-
and N2-propargylphenelzine were relatively potent in
preventing DSP-4-induced NA depletion. These findings
suggest that some of these analogues should undergo fur-
ther screening to evaluate their potential use as anti-
depressant agents and/or for use in prevention or
treatment of neurodegenerative disorders.
Acknowledgements
9. 1H NMR of compound 6 (HCl salt in D2O): d 2.81 (m, 1H,
CH), 3.04 (m, 2H, CH2), 3.45 (m, 2H, CH2), 3.82 (m, 2H, CH2
of propargyl group), 7.33–7.39 (m, 5H, aromatic).
10. Lyles, G. A.; Callingham, B. A. Biochem. Pharmacol.
1982, 31, 1417.
Dr. Lei Ling and Dr. Liana J. Urichuk were supported
by Industrial Research Fellowships from the Natural
Sciences and Engineering Research Council of Canada