Influence of ring size on the cognition-enhancing activity of DM235 and MN19, two potent nootropic drugs

Article abstract of DOI:10.1016/j.bmcl.2012.01.045

A series of analogs of DM235 and MN19, characterized by rings with different size, have been prepared and evaluated for their nootropic activity in the mouse passive-avoidance test. It was found that the optimal ring size for the analogs of DM235, showing endocyclic both amidic groups, is 6 or 7 atoms. For the compounds structurally related to MN19, carrying an exocyclic amide group, the piperidine ring is the moiety which gives the most interesting compounds.

Full text of DOI:10.1016/j.bmcl.2012.01.045

Bioorganic & Medicinal Chemistry Letters 22 (2012) 1936–1939
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Influence of ring size on the cognition-enhancing activity of DM235
and MN19, two potent nootropic drugs
L. Guandalini a, E. Martini a, L. Di Cesare Mannelli b, S. Dei a, D. Manetti a, S. Scapecchi a, E. Teodori a,
C. Ghelardini b, M.N. Romanelli a,
⇑
a Department of Pharmaceutical Sciences, University of Florence, Via Ugo Schiff 6, 50019 Sesto Fiorentino, Italy
b Department of Preclinical and Clinical Pharmacology, University of Florence, Viale Pieraccini 6, 50139 Firenze, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of analogs of DM235 and MN19, characterized by rings with different size, have been prepared
and evaluated for their nootropic activity in the mouse passive-avoidance test. It was found that the opti-
mal ring size for the analogs of DM235, showing endocyclic both amidic groups, is 6 or 7 atoms. For the
compounds structurally related to MN19, carrying an exocyclic amide group, the piperidine ring is the
moiety which gives the most interesting compounds.
Received 22 December 2011
Revised 12 January 2012
Accepted 13 January 2012
Available online 25 January 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Cognition-enhancers
Piracetam-like compounds
Mouse passive-avoidance test
DM235
MN19
Nootropic drugs are compounds able to improve learning and
memory, by acting through many different mechanisms which
may involve neurotransmitter receptors or enzymes.1–4 These com-
pounds are potentially useful in pathologies where cognitive func-
tions are attenuated, such as Alzheimer’s disease, ADHD,
schizophrenia, or to counteract the cognitive decline connected to
age. Among nootropics, piracetam and piracetam-like compounds
have been reported to improve cognitive performance in several
different conditions. This class of compounds lacks a common
mechanism of action, although for some members the modulation
of the cholinergic and glutamatergic systems has been disclosed.5,6
Somehow related to piracetam is DM232 (Unifiram, 1, Chart 1).
This compound shares with piracetam the 2-oxopirrolidine ring,
but differs from the lead for its nootropic potency, being some or-
ders of magnitude more potent in several behavioral tests.7 Struc-
tural modification of 1 led to DM2358 (sunifiram, 2, Chart 1) and
MN199 (sapunifiram, 3) which showed a nootropic potency similar
to 1. These compounds have been reported to stimulate cholinergic
and glutamatergic systems,9,10 but the precise biological target has
not been clarified yet.
azepane moiety produced compounds with potency similar to 2,
while the contraction to imidazolidine decreased activity.12 As a
continuation of this research, we wanted to check the effect of fur-
ther ring expansion on the diazacyclic moiety, synthesizing the
corresponding diazocanes (Chart 1, general formula A). Moreover,
in order to check the optimal ring size also in analogs showing
an exocyclic amide group, the piperidine ring of MN19 was substi-
tuted with nitrogen-containing saturated heterocycles with 4–8
atoms (general formulas B–E). The acyl and sulfonyl groups which
decorate the structures were chosen among those giving, in the
previous series, the most interesting compounds.
The general procedure for the synthesis of compounds 7–10 is
reported in Scheme 1. 1-Benzyl-1,5-diazocane 4 was prepared
according to Ref. 13 and treated with the suitable acyl chloride
to give amides 5a,b. The protecting group was removed by cata-
lytic hydrogenation to give secondary amines 6a,b which were
R1
N
R1
N
R1
N
H
N
iii
ii
i
Structural manipulation on leads 1–3 allowed to derive some
structure–activity relationships, showing that a diamidic structure
is important for activity.11 In addition, it was previously reported
that the enlargement of the piperazine ring of DM235 into an
N
N
H
N
N
R2
Ph
Ph
5a,b
7-10
4
6a,b
Scheme 1. Reagents and conditions: (i) R1Cl, Et3N, CHCl3; (ii) H2/Pd/C; (iii) R2Cl,
⇑
Corresponding author.
E-mail address: novella.romanelli@unifi.it (M.N. Romanelli).
Et3N, CHCl3. (a) R1 = COCH3; (b) R1 = COC2H5.
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2012.01.045

L. Guandalini et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1936–1939
1937
O
NHR1
(CH2)m
NH2
NHR1
n(H2C)
N
O
n(H2C)
N
O
O
i
n(H2C)
HN
N
ii
(CH2)m
Ph
N
N
N
Ph
HN (CH2)m
11: m, n = 1
O
15a,b: m, n = 1
19b: m, n = 1
N
S
O
N
12
: m = 1, n = 2
16a-d
iii
: m = 1, n = 2
20a-d
: m = 1, n = 2
O
O
S
NH2
13: m = 2, n = 3
14 m, n = 3
17a-d: m = 2, n = 3
18a,b m, n = 3
21a-d: m = 2, n = 3
22a,b m, n = 3
O
O
NHR1
(CH2)m
F
F
n(H2C)
piracetam
1
2
3
DM232 ( )
DM235 ( )
MN19 ( )
23-44
N
R2
N
NHR2
R2
NHR2
NHR2
NHR2
Scheme 2. Reagents and conditions: (i) R1Cl, Et3N, CHCl3; (ii) H2/Pd/C; (iii) R2Cl,
Et3N, CHCl3. Compound 12 and its enantiomers were commercially-available. (a)
R1 = COCH3; (b) R1 = COC2H5; (c) R1 = COPh; (d) R1 = SO2C6H4-pF.
N
N
N
N
N
R1
R1
R1
R1
R1
A
B
C
D
E
O
N
O
NH2
( )n
Chart 1. Reference molecules and general formulas of the new compounds
reported in this Letter.
i
ii, iii
( )n
N
N
Ph
Ph
Ph
their diazepane analogs (compounds F1 and F2, Table 1) were ac-
tive at doses below 1.0 mg/kg.12 Apparently, further expansion of
the seven-membered ring abolished activity. Previous work has
shown12 that the contraction of the piperazine moiety into the
imidazolidine ring, or the shift of the two amidic functions from
piperazines to hexahydropyrimidines gave compounds showing
MED between 1 and 10 mg/kg. Therefore, from these studies we
can conclude that in the diazacyclic derivatives, the optimal ring
size is six or seven atoms, with at least two carbon units between
the two amidic functions; one unit decrease or increase in the
number of atoms within the ring reduced or abolished, respec-
tively, the nootropic activity.
The influence of ring size on activity was checked also for the
exocyclic amide derivatives, structurally related to MN19. To this
aim, the piperidine ring of 3 was contracted to azetidine (23, 24)
and pyrrolidine (25–32) or enlarged to azepane (33–40) and azo-
cane (41–44). One atom contraction to pyrrolidines, or enlarge-
ment to azepanes gave a general decrease of potency; a further
variation to azetidine or azocanes is even more detrimental,
although the azocane sulfonyl derivatives maintain some activity.
In the whole set of compounds, only pyrrolidine 28 shows a MED
comparable to MN19 (0.1 mg/kg); this compound shows some
enantioselectivity in its ability to revert scopolamine-induced
amnesia, the S isomer being 10 times more active than the R form.
A similar enantioselectivity ratio was found for the enantiomers of
DM232,20 while for some bicyclic analogs of MN19 no enantiose-
lectivity was observed in the passive-avoidance test.21
13
45
: n = 1
: n = 1
46: n = 2
14: n = 2
Scheme 3. Reagents and conditions: (i) N-methyl-N-nitrosourea (Ref. 17). (ii)
NH2OH.HCl, base: (iii) LiAlH4, THF.
transformed into the desired compounds by treatment with the
suitable acyl or sulfonyl chloride.
The same pathway was used to prepare compounds 23–44
starting from amines 11–14 (Scheme 2). Amine 1114 was prepared
from 1-benzylazetidin-3-ol mesylate15 by reaction with aqueous
ammonia. Amine 12 and its enantiomers were commercially avail-
able. Amine 1316 and 14 were prepared from N-benzylazepan-4-
one 4517 and 1-benzylazocan-5-one 46,18 respectively, by reaction
with hydroxylamine and reduction of the resulting oximes with
lithium aluminium hydride (Scheme 3).
Compound 46 was obtained in low yield as byproduct in the
preparation of 45 starting from benzylpiperidone and N-methyl-
N-nitrosourea according to Ref. 18 (Scheme 3): differently from
what reported by Blizzard16 for the CBZ-protected 4-azepanone,
the ring expansion of 45 gave only the symmetric ketone 46, while
the isomeric N-benzyl-4-azocanone was not detected in the com-
plex reaction mixture. Attempts to improve the yield by changing
the reaction conditions were not successful; therefore 46 was
prepared in higher yields as reported in Ref. 18.
Regarding the azetidin-3-amine series, only the propionamide
derivatives 23 and 24 were synthesized, since compound 15a
proved to be unstable. Therefore, due also to the low potency of
23 and 24, the synthesis of their N-acetyl analogs was abandoned.
The mouse passive-avoidance test of Jarvik and Kopp,19 slightly
modified by us (see Supplementary data and Ref. 12) was used to
measure the nootropic activity of the synthesized compounds.
The substances were dissolved in saline and tested i.p. up to the
dose of 10 mg/kg; the results are expressed as the Minimal Effec-
tive Dose (MED, mg/kg) and are reported in Table 1, in comparison
with previously-synthesized analogs with different ring size. Com-
pounds were considered inactive if they did not show activity up to
the dose of 10 mg/kg, which is three and four orders of magnitude
higher than the MED of the lead compounds MN19 and DM235,
respectively.
As it happened also for other analogs, a particular combination
of substituent does not produce the same effect in all the series
synthesized so far. For instance, the combination between 4-F-ben-
zenesulfonyl and acetyl groups gave the most interesting com-
pound (3, MN19) in the 4-aminopiperidine series, but the same
pattern gave in the 4-aminoazepane series an inactive compound
(34); homologation of the acetyl residue to propionyl decreased
activity in the 4-aminopiperidine series,9 while activity increased
in the aminopyrrolidine series and did not change in the 3-amin-
opiperidine derivatives.22 These differences can be explained by
the fact that the biological activity measured in vivo is affected
by both pharmacokinetic and pharmacodynamic factors, on which
structural modifications may produce different effects. Unfortu-
nately, the lack of knowledge about the biological target makes it
impossible to perform in vitro studies, where pharmacodynamic
factors should be largely predominant. Following the same reason-
ing, it may be possible that the different activity of the enantiomers
Unexpectedly, diazocanes 7–10 were completely devoid of
activity when tested up to the highest dose. This is surprising since

1938
L. Guandalini et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1936–1939
Table 1
Minimal Effective Dose (MED) of the compounds against scopolamine-induced amnesia in the mouse passive avoidance test, in comparison with reference substancesa
NHR1
R1
N
R1
NHR1
N
NHR1
NHR1
N
N
N
N
N
N
R2
B
R2
R2
R2
R2
C
R2
E
D
F
A
Treatment
Structure
R1
R2
Dose (mg/kg)
Training session (s)
Retention session (s)
D
Saline
S
7 + S
8 + S
9 + S
16.5 2.9
18.1 3.0
—
—
—
108.2 7.1
43.8 4.1
—
—
—
91.7
25.7
—
—
—
—
44.1
—
70.3
51.0
45.4
48.8
56.6
69.4
48.1
—
—
—
—
—
b
A
A
A
A
B
B
C
C
C
C
C
C
C
C
C
C
D
D
D
D
D
D
D
D
E
COCH3
COCH3
COC2H5
COC2H5
COC2H5
COC2H5
COCH3
COCH3
COC2H5
COC2H5
COC2H5
COC2H5
COPh
COPh
SO2C6H4F
COPh
SO2C6H4F
SO2C6H4F
COPh
COPh
SO2C6H4F
COPh
SO2C6H4F
SO2C6H4F
SO2C6H4F
COCH3
COC2H5
COCH3
COC2H5
COPh
n.a.
n.a.
n.a.
n.a.
10
n.a.
10
1.0
1.0
0.1
1.0
10
1.0
n.a.
n.a.
n.a.
b
b
b
10 + S
23 + S
24 + S
25 + S
26 + S
27 + S
28 + S
(S)-28 + S
(R)-28 + S
29 + S
30 + S
31 + S
32 + S
33 + S
34 + S
35 + S
36 + S
37 + S
38 + S
39 + S
40 + S
41 + S
42 + S
43 + S
44 + S
Piracetam + Sc
2 + Sd
3 + Se
—
—
18.5 3.1
—
62.6 8.5^
—
b
15.8 3.2
17.9 2.6
16.4 2.5
17.1 3.4
16.7 2.6
15.7 2.8
13.5 2.8
—
—
—
—
—
15.6 2.7
16.7 3.2
16.8 3.2
15.8 2.9
19.1 3.0
14.8 3.9
—
86.1 8.3*
68.9 6.1*
61.8 7.0^
65.9 5.3^
73.3 7.5*
85.1 9.1*
61.6 7.7^
—
b
COPh
b
SO2C6H4F
SO2C6H4F
COCH3
COCH3
COC2H5
COC2H5
COPh
—
—
—
—
b
b
n.a.
n.a.
b
SO2C6H4F
COPh
1.0
10
1.0
1.0
1.0
10
n.a.
1.0
n.a.
10
78.3 8.1*
63.5 8.1^
87.2 9.1*
85.2 9.1*
64.9 7.6*
96.2 9.8*
—
62.7
46.8
70.4
69.4
45.8
81.4
—
SO2C6H4F
COCH3
COC2H5
COCH3
COC2H5
COPh
SO2C6H4F
COPh
SO2C6H4F
—
COPh
SO2C6H4F
SO2C6H4F
COCH3
COCH3
COC2H5
COC2H5
—
b
E
E
E
—
—
—
F
19.1 3.2
—
63.9 7.9^
—
44.8
—
b
14.9 2.7
15.2 3.5
20.5 3.4
14.5 3.8
17.3 3.6
16.2 2.6
87.1 8.2*
97.6. 9.1*
91.5 8.0*
90.6 12.5*
77.2 8.4*
88.1 7.3*
72.2
82.4
71.0
76.1
59.9
71.9
30
—
—
—
—
COPh
COPh
0.001
0.01
0.01
0.1
F1 + Sf
F2 + Sf
COCH3
COC2H5
F
*
P <0.01 in comparison with scopolamine-treated mice.
All compounds were dissolved in saline and injected i.p. 20 min before training session. Each value represents the mean of 8–18 mice. Scopolamine (S) was injected
a
immediately after punishment.
^
P <0.05.
b
This compound did not revert scopolamine-induced amnesia at doses up to 10 mg/kg i.p.
From Ref. 21.
c
d
From Ref. 8.
From Ref. 9.
e
Compounds F1 and F2 have been previously characterized,12 and their activity is reported here, together with that of the new analogs, for comparative purposes.
f
of 28 is mainly due to pharmacodynamic or to pharmacokinetic
reasons, or it is a combination of both properties. Obviously other
explanations cannot be ruled out, such as a different binding mode
for the various series, or the interaction with a different biological
target.
continuing to elucidate the biological target of this class of cogni-
tion-enhancers.
Acknowledgments
In conclusion, a series of derivatives of DM235 and MN19 were
synthesized which show cognition-enhancing activity, with po-
tency similar to piracetam. The new compounds allowed to derive
further structure–activity relationships; in particular it was found
that for the diazacyclic series the optimal ring size is six atoms
with at least two carbon atoms between the two amidic functions,
and also the seven-member diazepane ring is well tolerated. For
the derivatives carrying one exocyclic amide group, the 4-aminopi-
peridine moiety is the one giving the best results. Work is
This work was supported by grants from MUR (Ministero
dell’Università e della Ricerca) and the University of Florence (ex
60%).
Supplementary data
Supplementary data (synthetic procedures and biological tests)
associated with this article can be found, in the online version, at
doi:10.1016/j.bmcl.2012.01.045.

L. Guandalini et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1936–1939
1939
12. Martini, E.; Salvicchi, A.; Ghelardini, C.; Manetti, D.; Dei, S.; Guandalini, L.;
Martelli, C.; Melchiorre, M.; Cellai, C.; Scapecchi, S.; Teodori, E.; Romanelli, M.
N. Bioorg. Med. Chem. 2009, 17, 7606.
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