Synthesis of new l-proline amides with anticonvulsive effect

Article abstract of DOI:10.1135/cccc19961085

Series of heterocyclic L-proline amides were prepared from BOC-L-proline and heterocyclic amines (mostly substituted piperazines and morpholines) via active ester with hydroxysuccinimide. 4-(4-Fluorobenzoyl)piperidine afforded L-proline 4-(4-(4-(4-fluorobenzoyl)piperidin-1-yl)benzoyl)piperidine (7b) simultaneously with expected L-proline 4-(4-fluorobenzoyl)piperidide (7a). D-Proline N-(3-(4-(3-chlorophenyl)piperazin-1-yl)propyl)amide (2) was prepared starting from D-proline. The amides were tested by methods of biochemical and behavioural pharmacology.

Full text of DOI:10.1135/cccc19961085

Synthesis of New L-Proline Amides
1085
SYNTHESIS OF NEW L-PROLINE AMIDES WITH ANTICONVULSIVE
EFFECT
Alexandra SILHANKOVA, Karel SINDELAR, Karel DOBROVSKY, Ivan KREJCI,
1,
Jarmila HODKOVA and Zdenek POLIVKA *
Research Institute for Pharmacy and Biochemistry, 130 60 Prague 3, Czech Republic;
e-mail: 1 zpvufb@mbox.vol.cz
Received February 20, 1996
Accepted April 29, 1996
Series of heterocyclic L-proline amides were prepared from BOC-L-proline and heterocyclic amines
(mostly substituted piperazines and morpholines) via active ester with hydroxysuccinimide. 4-(4-
Fluorobenzoyl)piperidine afforded L-proline 4-(4-(4-(4-fluorobenzoyl)piperidin-1-yl)benzoyl)pipe-
ridine (7b) simultaneously with expected L-proline 4-(4-fluorobenzoyl)piperidide (7a). D-Proline
N-(3-(4-(3-chlorophenyl)piperazin-1-yl)propyl)amide (2) was prepared starting from D-proline. The
amides were tested by methods of biochemical and behavioural pharmacology.
Key words: Amides preparation; Amino acids reaction; Amines reaction; Anticonvulsive effect.
In a recent paper1 we described a series of basic amides of racemic proline for which
neuroprotective effects and positive influence on learning and memory were expected.
The object of the present paper is the synthesis of heterocyclic L-proline amides by a
different method. Proline N-(3-(4-(3-chlorophenyl)piperazin-1-yl)propyl)amide, pre-
pared formerly in the racemic form has now been obtained in the form of the L- and
D-enantiomers (1b and 2).
Reaction of BOC-L-proline2,3 with N-hydroxysuccinimide in dichloromethane in
presence of N,N′-dicyclohexylcarbodiimide gave active ester (for method cf. ref.4)
which was treated with the following heterocyclic amines: 1-(3-aminopropyl)-4-(2-
chlorophenyl)piperazine5, 1-(3-aminopropyl)-4-(3-chlorophenyl)piperazine6, 1-(3-amino-
propyl)-4-(4-chlorophenyl)piperazine5, 4-(2-aminoethyl)morpholine, 4-(4-aminobutyl)-
morpholine7, 1-(2-aminoethyl)-4-(3-trifluoromethylphenyl)piperazine8, 1-(4-amino-
butyl)-4-(3-trifluoromethylphenyl)piperazine9, 1-(2-fluorophenyl)piperazine, 1-(3-fluoro-
phenyl)piperazine10, 1-(4-fluorophenyl)piperazine, 1-(3-chlorophenyl)piperazine, 1-(3-
trifluoromethylphenyl)piperazine and 1-(4-trifluoromethylphenyl)piperazine11: the ob-
tained N-protected intermediates (in several cases there were purified and
* The author to whom correspondence should be addressed.
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

1086
Silhankova et al.:
characterized) were processed in crude state by deprotection (removal of BOC) with
ethanolic solutions of hydrogen chloride12. The resulting L-prolinamides 1a–1c, 3a, 3b,
4a, 4b and 5a–5f were partly isolated directly in the form of crystalline hydrochlorides.
In some cases, it was necessary to release the bases from the crude hydrochlorides and
transform them to hydrogen oxalates for characterization and biological testing. The
active ester which was similarly obtained from BOC-D-proline, gave by treatment with
1-(3-aminopropyl)-4-(3-chlorophenyl)piperazine6 compound 2, the mentioned enantio-
mer of 1b.
H
H
CONH(CH2)3
N
N
CONH(CH2)n
R
N
H
N
H
R
n
R
1
2
4
3
4
2-Cl
3-Cl
4-Cl
a
b
c
R
3, 4
a
b
N
O
N
CONH(CH2)3
H
N
N
CF3
N
H
Cl
N
2
O
R
N
H
H
N
N
R1
C
C
N
H
N
R
O
O
R
5
R
2-F
3-F
4-F
3-Cl
a
b
c
d
e
f
COOC(CH3)3
H
6
7
R1
6, 7
3-CF3
4-CF3
F
a
b
F
N
O
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

Synthesis of New L-Proline Amides
1087
A similar sequence starting from the same activated BOC-L-proline ester and 4-(4-
fluorobenzoyl)piperidine13 was complicated by the simultaneously proceeding substitu-
tion reaction between two molecules of the starting piperidine derivative (the fluorine
atom is strongly activated by the para carbonyl group) which resulted in 4-(4-(4-(4-flu-
orobenzoyl)piperidin-1-yl)benzoyl)piperidine: this by-product was not isolated but it
participated in the coupling reaction. The crude product was thus separated to 6a and 6b.
Usual deprotection of these products gave the desired compound 7a and the unexpected 7b.
The compounds prepared were tested by methods of biochemical pharmacology in
the following tests: inhibition of binding of [3H]glycine (rat brain cortex membranes),
[3H]5,7-dichlorokynurenic acid (rat brain cortical membranes), [3H]CGP-39653 (rat
brain membranes), [3H]AMPA (3-hydroxy-5-methylisoxazol-4-ylalanine) (membrane
fraction from rat brain cortex) and [3H]MK-801. In these tests, the compounds were
practically inactive (some indications of effect in the inhibition of [3H]glycine and
[3H]5,7-dichlorokynurenic acid binding).
Some of the products showed in behavioural tests antiischemic effects. Protection
from acute anoxia induced by intravenous administration of KCN (i.p. dose of 20 mg/kg of
the tested compound, time of survival in s): 2, 31.4; 5a, 30.3 (control, 25 s). Anticon-
vulsant effect in the electroshock test in female mice (i.p. dose of 20 mg/kg, effect in
the number of animals out of the group given): 1c, 5/6; 2, 8/10; 5b, 5/8; 5c, 4/5. More
detailed results of the testing (especially behavioural pharmacology) will be published
in a separate paper.
EXPERIMENTAL
Melting points of analytical samples were determined in the Kofler block and they are not corrected;
the samples were dried in vacuo of about 40 Pa at room temperature or at a suitably elevated tem-
perature. IR spectra (ν in cm–1) were recorded mostly in Nujol with Unicam SP 2000 or Perkin–
Elmer 298 spectrophotometers; NMR spectra (bases in deuteriochloroform, salts in
hexadeuteriodimethyl sulfoxide) on a Tesla BS 567A instrument (1H at 100 MHz, 13C at 25.14 MHz;
chemical shifts are given in ppm ( δ-scale), coupling constants (J) in MHz); mass spectra were
measured on a Varian-MAT 44S (GC-MS) spectrometer. The homogeneity of the products and com-
position of the mixtures were checked by thin-layer chromatography (TLC) on silica gel (Silufol
UV254). Preparative chromatographic separations were carried out on a columns of silica gel (Fluka
60, 0.063–0.20 mm).
General Procedure for Preparation of the L-Proline Amides 1a–1c, 3a, 3b, 4a, 4b and 5a–5f
A stirred solution of BOC-L-proline2,3 (3.4 g, 0.016 mol) in dichloromethane (60 ml) was treated at
–10 °C with N-hydroxysuccinimide (1.8 g, 0.016 mol) and then at the same temperature dropwise
with a solution of the N,N′-cyclohexylcarbodiimide (3.24 g, 0.016 mol) in dichloromethane (20 ml).
The mixture was stirred for 1 h at –10 °C and then treated dropwise at –5 to 10 °C with a solution
of the corresponding amine (0.016 mol) in dichloromethane (20 ml). After 1 h stirring, the cooling
was discontinued and the mixture was allowed to stand overnight at room temperature. The separated
N,N′-dicyclohexylurea was filtered off, washed with dichloromethane, the filtrate was washed three
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

1088
Silhankova et al.:
times with 10% KHSO4 solution, then with water, two times with 5% NaHCO3 solution and finaly 2 ×
with water, dried with MgSO4, and evaporated in vacuo. The crude BOC-protected intermediate
(mostly oily) was dissolved in ethanol (25 ml), the solution was treated with ethanol which was satu-
rated with HCl (11 ml) and the mixture was stirred for 1.5 h at room temperature. In some cases,
homogeneous hydrochlorides separated by standing were used. In cases of inhomogeneous or hygros-
copic hydrochlorides, the bases were released, sometimes used for measurement of spectra, and trans-
formed by neutralization with oxalic acid to crystalline hydrogen oxalates.
L-Proline N-(3-(4-(2-chlorophenyl)piperazin-1-yl)propyl)amide (1a). The general procedure ap-
plied to 1-(3-aminopropyl)-4-(2-chlorophenyl)piperazine5 (3.98 g, 0.016 mol) afforded 6.5 g (91%) of
the oily BOC-1a. This compound (5.4 g) was deprotected using the general procedure which resulted
in a hygroscopic hydrochloride. This was decomposed in chloroform by saturation with NH3. The
separated NH4Cl was filtered off (a layer of celite), the filtrate was evaporated and the oily base 1a
(2.9 g, 51%) was transformed to the bis(hydrogen oxalate), m.p. 180–182.5 °C (methanol), [α]2D0 –16.8°
(c 0.5, water). 13C NMR spectrum: 168.44 s (CO), 164.78 s (oxalic acid), 147.82 s (C-1"), 130.42 d
(C-3"), 128.25 d (C-5"), 127.58 s (C-2"), 124.59 d (C-6"), 121.00 d (C-4"), 58.93 d (C-1), 53.63 t
(C-7), 51.47 t (C-2′, C-6′), 48.33 t (C-3′, C-5′), 45.34 t (C-4), 36.45 t (C-5), 29.43 t (C-6), 23.98 t
(C-3), 23.68 t (C-2). For C22H31ClN4O9 (531.0) calculated: 49.77% C, 5.88% H, 6.67% Cl, 10.55% N;
found: 49.59% C, 6.04% H, 6.99% Cl, 10.34% N.
L-Proline N-(3-(4-(3-chlorophenyl)piperazin-1-yl)propyl)amide (1b). The use of 1-(3-aminopro-
pyl)-4-(3-chlorophenyl)piperazine6 (7.6 g, 0.03 mol) led (without deprotection) to 12.6 g of mixture
which was separated by chromatography on silica gel. There were obtained first 2.28 g of unreacted
N-BOC-L-proline N-hydroxysuccinimide ester, m.p. 136–138 °C (ref.12 gave the m.p. 135–136 °C).
This was followed by 9.56 g (76%) of homogeneous oily BOC-1b. 13C NMR spectrum: 172.02 s
(CO of BOC), 154.77 s (CO), 151.86 s (C-1"), 134.45 s (C-3"), 129.60 d (C-5"), 118.69 d (C-4"),
115.26 d (C-2"), 113.39 d (C-6"), 79.70 s (O–C– of BOC), 60.20 d (C-1), 56.02 t (C-7), 52.59 t
(C-2′and C-6′), 48.10 t (C-3′and C-5′), 46.76 t (C-4), 37.87 t (C-5), 29.35 t (C-2), 28.01 q (CH3 of
BOC), 25.69 t (C-3), 23.75 t (C-6). Oily BOC-1b was deprotected by stirring for 1.5 h with ethanol
saturated with HCl (23 ml). After the addition of ether, the separated product was isolated by decan-
tation, stirred with propanol (10 ml) and filtered after standing overnight in a refrigerator. Yield 5.75 g
(41%) of 1b trihydrochloride, m.p. 137–140 °C (2-propanol–ethanol), [α]2D0 –20.0° (c 1, water). IR spec-
trum: 950, 1 255, 1 455 (CH2); 1 568 (amide); 1 598 (arom.); 1 685 (C=O amide); 2 210–3 080
(NH+); 2 935, 2 980 (aliph. C–H); 3 080 (arom.); 3 230 (NH). 13C NMR spectrum: 167.99 s (CO),
163.81 s (oxalic acid), 151.18 s (C-1"), 133.71 s (C-3"), 130.19 d (C-5"), 118.47 d (C-4"), 114.73 d
(C-2"), 113.69 d (C-6"), 58.93 d (C-1), 53.78 t (C-7), 50.94 t (C-2′and C-6′), 45.71 t (C-3′and C-5′),
45.27 t (C-4), 36.53 t (C-5), 29.06 t (C-2), 24.05 t (C-6), 23.23 t (C-3). For C18H30Cl4N4O (460.2)
calculated: 46.96% C, 6.57% H, 30.82% Cl, 12.17% N; found: 47.09% C, 6.63% H, 30.55% Cl,
12.03 % N.
L-Proline N-(3-(4-(4-chlorophenyl)piperazin-1-yl)propyl)amide (1c). The use of 1-(3-aminopro-
pyl)-4-(4-chlorophenyl)piperazine5 (6.3 g, 0.025 mol) resulted in 8.2 g (72%) of crystalline BOC-1c,
1
m.p.134–136 °C (cyclohexane), [α]2D0 –30.43° (c 0.5, ethanol). H NMR spectrum: 7.20 d, 2 H, J = 8.5
(H-3", H-5"); 6.85 d, 2 H, J = 8.5 (H-2", H-6"); 4.10 bm, 1 H (H-1); 3.40 bm, 4 H (2 × H-4, 2 × H-5);
3.18 bt, 4 H (2 × H-3′ and 2 × H-5′); 2.58 bt, 4 H (2 × H-2′ and 2 × H-6′); 2.46 t, 2 H (2 × H-7); 1.46 s,
9 H ((CH3)3CO). For C23H35ClN4O3 (451.0) calculated: 61.25% C, 7.82% H, 7.86% Cl, 12.42% N;
found: 61.37% C, 8.05% H, 7.95% Cl, 12.10% N. Deprotection of BOC-1c (5.5 g) with ethanolic
HCl gave 6.l g (53%) 1c trihydrochloride, m.p. 154–158 °C (ethanol–methanol), [α]2D0 –20.12° (c 1,
water). For C18H30Cl4N4O (460.2) calculated: 46.96% C, 6.57% H, 30.82% Cl, 12.17% N; found:
46.87% C, 6.68% H, 30.65% Cl, 12.08% N.
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

Synthesis of New L-Proline Amides
1089
D-Proline N-(3-(4-(3-chlorophenyl)piperazin-1-yl)propyl)amide (2). BOC-D-Proline (2.97 g, 0.014 mol)
and 1-(3-aminopropyl)-4-(3-chlorophenyl)piperazine6 (3.5 g, 0.014 mol) gave similarly 5.3 g of oily
BOC-2, which was purified by chromatography on silica gel: 2.95 g (47%) of homogenous oily
BOC-2 whose 13C NMR spectrum was identical with that of BOC-1b. Treatment of 2.75 g BOC-2
with ethanolic HCl (6.2 ml) gave l.7 g of 2 trihydrochloride, m.p. 138–142 °C (2-propanol–ethanol).
[α]2D0 +19.27° (c 1, water). IR spectrum: 950, 1 255, 1 455 (CH2); 1 568 (amide); 1 598 (arom.); 1 685
(C=O of amide); 2 210–3 230 (NH+); 2 935, 2 980 (aliph. C–H); 3 080 (arom.); 3 230 (NH). 13C NMR
spectrum: 168.21 s (C=O), 150.87 s (C-1"), 134.00 s (C-3"), 130.72 d (C-5"), 119.40 d (C-4"),
115.33 d (C-2"), 114 .28 d (C-6"), 58.93 d (C-1), 53.26 t (C-7), 50.42 t (C-2′, C-6′), 45.34 t (C-3′,
C-5′), 44.82 t (C-4), 36.47 t (C-5), 29.58 t (C-6), 23.60 t (C-2), 23.30 t (C-3). Mass spectrum, m/z
(%): 350 (M+, C18H27ClN4O, 0.3), 335 (1), 280 (1.8), 209 (5), 198 (6), 184 (31), 167 (10), 113 (8),
86 (9), 84 (13), 70 (100), 36 (HCl). For C18H30Cl4N4O (460.2) calculated: 46.96% C, 6.57% H,
30.82% Cl, 12.17% N; found: 46.86% C, 6.55 % H, 30.55% Cl, 12.08% N.
L-Proline N-(2-(morpholin-4-yl)ethyl)amide (3a). From 4-(2-aminoethyl)morpholine (3.84 g, 0.03 mol),
8.16 g (83%) of crude BOC-3a was obtained and the deprotection with releasing the base gave 4.28 g
1
(73%) of oily 3a. Bis(hydrogen oxalate), m.p. 127–129 °C (ethanol), [α]2D0 –10.68° (c 1, water). H NMR
spectrum: 9.45 bs, 5 H (NH and oxalate); 8.65 bt, 1 H (CONH); 4.20 bt, l H (H-1); 3.70 bt, 4 H
(2 × H-2′ and 2 × H-3′); 3.33 m, 4 H and 2.77 m, 6 H (2 × H-4, 2 × H-5, 2 × H-6, 2 × H-1′ and 2 × H-4′);
2.41–1.78 bm, 4 H (2 × H-2 and 2 × H-3). For C15H25N3O10 (407.4) calculated: 44.22% C, 6.18% H,
10.31% N; found: 43.94% C, 6.13% H, 10.30% N.
L-Proline N-(2-(4-(3-(trifluoromethyl)phenyl)piperazin-1-yl)ethyl)amide (3b). The use of 1-(2-
8
aminoethyl)-4-((3-trifluoromethyl)phenyl)piperazine (4.1 g, 0.015 mol) led to 7.02 g of crude BOC-3b
which was subjected to treatment with ethanolic HCl. The hydrochloride obtained was hygroscopic,
the base (3.88 g, 73 %) was released and transformed to the tris(hydrogen oxalate), m.p. 149–151 °C
(ethanol); [α]2D0 –9.52° (water). 1H NMR spectrum: 8.85 bs (oxalic acid, CONH); 7.56–7.04 m, 4 H
(H-arom.); 4.21 m, 1 H (H-1); 3.60–1.76 m, 18 H (CH2). Mass spectrum, m/z (%): 370 (M+,
C18H25F3N4O), 355, 301, 300, 256, 243, 229, 200, 170, 145, 113, 70, 45. For C24H31FN4O13 (640.5)
calculated: 45.00% C, 4.88% H, 8.90% F, 8.75% N; found: 44.65% C, 4.88% H, 8.82% F, 8.44% N.
L-Proline N-(4-(morpholin-4-yl)butyl)amide (4a). 4-(4-Aminobutyl)morpholine7 (4.68 g, 0.03 mol)
gives similarly 10.48 g (98%) of BOC-4a which was treated with ethanolic HCl and afforded with
NH3 in chloroform 7.6 g (97%) of crude 4a. Bis(hydrogen oxalate) hemihydrate, m.p. 142–143 °C
1
(ethanol), [α]2D0 –23.5° (c 1, water). H NMR spectrum: 8.53 bt, 1 H, J = 6.6 (CONH); 4.17 bt, 1 H
(H-1); 3.77 bt, 4 H (2 × H-2′and 2 × H-3′); 3.37–2.71 m, 10 H (2 × H-4, 2 × H-5, 2 × H-8, 2 × H-1′,
2 × H-4′); 1.91 m, 4 H (2 × H-2, 2 × H-3); 1.56 m, 4 H ( 2 × H-6, 2 × H-7). For C17H29N3O10 . 0.5 H2O
(444.4) calculated: 45.94% C, 6.80% H, 9.45% N; found: 45.92% C, 6.77% H, 9.37% N.
L-Proline N-(4-(4-(3-(trifluoromethyl)phenyl)piperazin-1-yl)butyl)amide (4b). 1-(4-Aminobutyl)-4-
9
((3-trifluoromethyl)phenyl)piperazine (6.03 g, 0.02 mol) gave similarly 9.35 g (96%) of crude BOC-4b
which afforded by the deprotection procedure a hygroscopic hydrochloride. The released base 4b was
transformed to the bis(hydrogen oxalate), m.p. 149–150.5 °C (ethanol), [α]2D0 –18.14° (c 1, water). 1H NMR
spectrum: 8.51 bt, 1 H (CONH); 7.79 bs, 4 H (oxalic acid); 7.60–7.04 m, 4 H (H-arom.); 4.18 bt, 1 H
(H-1); 3.59–1.42 m, 22 H (11 × CH2). For C24H33F3N4O9 (578.6) calculated: 49.82% C, 5.75% H,
9.85% F, 9.68% N; found: 49.88% C, 5.77% H, 9.83% F, 9.64% N.
L-Proline 4-(2-fluorophenyl)piperazide (5a). From 1-(2-fluorophenyl)piperazine (5.40 g, 0.03 mol),
12.06 g of crude BOC-5a (partly crystallizing yellow oil) was obtained which was subjected to the
action of ethanolic HCl. The obtained 5a hydrochloride proved inhomogeneous and the base, there-
1
fore, was released: homogeneous oil (TLC). H NMR spectrum: 7.00 m, 4 H (H arom.); 3.60–4.05 bm,
5 H (H-1, 2 × H-1′, 2 × H-4′); 2.75–3.30 bm and 2.78 bs, 7 H (N-H, 2 × H-4, 2 × H-2′ and 2 × H-3′);
1.60–2.30 bm, 4 H (2 × H-2, 2 × H-3).
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Silhankova et al.:
Hydrogen oxalate: m.p. 137.5–139 °C (2-propanol), [α]2D0 –59.3° (c 1, water). For C17H22FN3O5
(367.4) calculated: 55.58 % C, 6.04% H, 5.17% F, 11.44% N; found: 55.42% C, 6.08% H, 5.31% F,
11.37% N.
L-Proline 4-(3-fluorophenyl)piperazide (5b). 1-(3-Fluorophenyl)piperazine10 (5.4 g, 0.03 mol) gave
similarly 10.8 g (95%) of BOC-5b which was subjected to deprotection with ethanolic HCl. From the
unstable hydrochloride, the oily base (6.55 g, 78%) was released. 1H NMR spectrum: 7.18 m, 1 H
(H-2"); 6.62 m, 3 H (H-4", H-5", H-6"); 2.92 m and 2.84 s, 2 H (H-1, N-H); 2.27–1.53 bm, 4 H (2 × H-2,
2 × H-3); 4.08–3.51 bm and 3.18 bt, 10 H (H of piperazine ring and 2 × H-4).
Hydrogen oxalate, m.p. 192–193.5 °C (ethanol–methanol), [α]2D0 –63.06° (c 1, water). Mass spec-
trum, m/z (%): 277 (M+, C15H20FN3O, 0.7), 165 (2), 152 (1), 138 (2.3), 122 (2), 70 (100). For
C17H22FN3O5 (367.4) calculated: 55.58% C, 6.04% H, 5.17% F, 11.44% N; found: 55.48% C, 6.22% H,
5.36% F, 11.39% N.
L-Proline 4-(4-fluorophenyl)piperazide (5c). 1-(4-Fluorophenyl)piperazine (3.6 g, 0.02 mol) gave
similarly 7.70 g of BOC-5c which afforded by treatment with ethanolic HCl an ustable 5c hydro-
chloride. The released base 5c was transformed to the hydrogen oxalate, m.p. 205–207 °C (ethanol–
methanol), [α]2D0 –59.88° (c 1, water). Mass spectrum, m/z (%): 277 (M+, C15H20FN3, 0.2), 165 (3),
152 (2.5), 138 (3), 122 (2.5), 70 (100). For C17H22FN3O5 (367.4) calculated: 55.58% C, 6.04% H,
5.17% F, 11.44% N; found: 55.40% C, 6.13% H, 5.27% F, 11.27% N.
The homogeneous base 5c, released from the oxalate, crystallized and melted at 109–112 °C
(cyclohexane), [α]2D0 –77.24° (methanol). 1H NMR spectrum: 6.95 m, 4 H (H-arom.); 3.50–4.00 nm,
5 H (H-1, 2 × H-1′, 2 × H-4′); 3.08 bt, 4 H (2 × H-2′, 2 × H-3′); 2.56 s, 1 H (N-H); 1.50–1.90 nm,
4 H (2 × H-2, 2 × H-3); 2.70–3.40 bm and 1.90–2.30 bm, 2 H (2 × H-4). For C15H20FN3O (277.3)
calculated: 64.96% C, 7.27% H, 6.85% F, 15.15% N; found: 64.90% C, 7.37% H, 6.91% F, 14.93% N.
L-Proline 4-(3-chlorophenyl)piperazide (5d). l-(3-Chlorophenyl)piperazine (3.1 g, 0.016 mol) gave
similarly 6.0 g of crude BOC-5d which was cleaved by treatment with ethanolic HCl. From the hy-
groscopic hydrochloride obtained, the base 5d was released and transformed to the hydrogen oxalate,
1
m.p. 189–190 °C (2-propanol–ethanol), [α]D20 –60.93° (c 1, water). H NMR spectrum: 6.80–7.40 m,
4 H (H-arom.); 4.65 bt, 1 H (H-1); 3.63 m and 3.25 bt, 8 H (H of piperazine); 2.20–2.40 bm, 2 H (2 × H-4);
1.90 m, 4 H (2 × H-2, 2 × H-3). For C17H22ClN3O5 (383.8) calculated: 53.20% C, 5.78% H, 9.28% Cl,
10.95% N; found: 53.01% C, 5.86% H, 9.36% Cl, 11.04 % N.
L-Proline 4-(3-(trifluoromethyl)phenyl)piperazide (5e). From 1-(3-(trifluoromethyl)phenyl)pipe-
razine (4.6 g, 0.02 mol), 7.5 g (87%) of crude BOC-5e were obtained which was transformed by
treatment with ethanolic HCl to the crude 5e hydrochloride. The released base 5e crystallized on
standing, m.p. 105.5–108 °C (cyclohexane), [α]2D0 –59.88° (c 1, water). 1H NMR spectrum: 6.95–7.43 m, 4 H
(H-arom.); 3.80 m, 6 H (2 × H-4, 2 × H-1′, 2 × H-4′); 3.25 bt, 4 H (2 × H-2′, 2 × H-3′); 2.90 m,
1 H (H-1); 2.56 s, 1 H (N-H); 1.80–2.30 m, 4 H (2 × H-2, 2 × H-3). For C16H20F3N3O (327.4)
calculated: 58.70% C, 6.16% H, 17.41% F, 12.84% N; found: 58.73% C, 6.31% H, 17.16% F,
12.57% N.
Hydrogen oxalate, m.p. 180–181 °C (ethanol), [α]2D0 –56.1° (c 1, water). Mass spectrum, m/z (%):
327 (M+, C16H20F3N3O, 0.4), 288 (0.3), 215 (0.9), 200 (0.8), 188 (1.9), 172 (1.2), 145 (1.4), 70
(100). For C18H22F3N3O5 (417.4) calculated: 51.80 % C, 5.31% H, 13.66% F, 10.07% N; found:
51.29% C, 5.33 % H, 13.51% F, 9.89% N.
L-Proline 4-(4-(trifluoromethyl)phenyl)piperazide (5f). From 1-(4-trifluoromethyl)phenyl)pipe-
razine11 (2.99 g, 0.013 mol) 5.56 g of oily BOC-5f were obtained which was subjected to the action
of ethanolic HCl and from the crude 5f hydrochloride, the base 5f (3.08 g, 72%) was released, m.p.
1
127–130 °C (cyclohexane). H NMR spectrum: 7.51 d, 2 H, J = 8.5 (H-3", H-5"); 6.93 d, 2 H, J = 8.5
(H-2", H-6"); 3.40–4.04 bm, 4 H (2 × H-1′, 2 × H-4′); 3.02–3.40 bm, 4 H (2 × H-2′, 2 × H-3′); 2.66 bs,
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Synthesis of New L-Proline Amides
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1 H (N-H); 2.70–3.00 bm and 1.50–2.30 bm, 7 H (H of pyrrolidine). For C16H20F3N3O (327.4) cal-
culated: 58.70% C, 6.16% H, 17.41% F, 12.84% N; found: 58.55% C, 6.09% H, 17.18% F, 12.66% N.
Hydrogen oxalate, m.p. 173–176 °C (2-propanol–ethanol), [α]2D0 –55.7° (c 1, water). 1H NMR
spectrum: 7.53 d, 2 H, J = 8.9 (H-3", H-5"); 7.09 d, 2 H, J = 8.9 (H-2", H-6"); 4.67 bt, 1 H (H-1);
3.64 m and 3.37 m, 8 H ( H of piperazine); 2.40–1.72 bm, 6 H (2 × H-2, 2 × H-3, 2 × H-4). For
C18H22F3N3O5 (417.4) calculated: 51.80% C, 5.31% H, 13.66% F, 10.07% N; found: 51.47% C,
5.25% H, 13.54% F, 9.78% N.
1-(tert-Butyloxycarbonyl)-L-proline 4-(4-fluorobenzoyl)piperidide (6a). A similar sequence starting
from 4-(4-fluorobenzoyl)piperidine13 (4.7 g, 0.024 mol) resulted in a mixture which was separated by
chromatography on silica gel (130 g). The first to be eluted with chloroform was the crystalline 6a
1
(3.8 g, 39%), m.p. 116.5–118 °C (ether–cyclohexane). H NMR spectrum: 7.97 dd, 2 H, J = 8.5 (H-2
and H-6 of aryl); 7.15 t, 2 H, J = 8.5 (H-3 and H-5 of aryl); 1.44 s, 9 H ((CH3)3C). Mass spectrum,
m/z (%): 404 (M+, C22H29FN2O4, 1), 331 (3), 303 (1.2), 234 (3), 206 (3.2), 191 (2), 190 (2.4), 170
(21), 123 (21), 114 (88), 95 (8), 70 (100), 57 (70). For C22H29FN2O4 (404.5) calculated: 65.33% C,
7.23% H, 4.70% F, 6.93% N; found: 65.53% C, 7.30% H, 4.81% F, 6.83 % N.
Continued elution with a mixture of chloroform and ethanol (20 : 1) gave 2.4 g (17%) of crystal-
line 1-(tert-butyloxycarbonyl)-L-proline 4-(4-(4-(4-fluorobenzoyl)piperidin-1-yl)benzoyl)piperidide
(6b), m.p. 201–205 °C (benzene–cyclohexane). For C34H42FN3O5 (591.7) calculated: 69.01% C,
7.15% H, 3.21% F, 7.10% N; found: 68.72% C, 7.15% H, 2.80% F, 7.01% N.
L-Proline 4-(4-fluorobenzoyl)piperidide (7a). A solution of 6a (2.3 g, 0.0056 mol) in ethanol (100 ml)
was treated with 10% solution of HCl in ether (10 ml) and the mixture was allowed to stand for 3 days
at room temperature. It was then evaporated in vacuo. The residue was made alkaline with 5% NaOH
and the product was extracted with ether. After drying with K2CO3, the solution was evaporated giv-
ing 1.05 g (62%) of crude 7a which was transformed to the hydrogen succinate, m.p. 111–114 °C
(water). Mass spectrum, m/z (%): 305 (M + 1), 304 (M+, C17H21FN2O2, chemical ionization), 303,
234, 206, 170, 123, 114, 95, 70, 57. For C21H27FN2O6 (422.5) calculated: 59.70% C, 6.44% H,
4.50% F, 6.63% N; found: 60.50% C, 6.11% H, 4.60% F, 6.78% N.
L-Proline 4-(4-(4-(4-fluorobenzoyl)piperidin-1-yl)benzoyl)piperidide (7b). A solution of 6b (0.9 g,
0.0015 mol) in ethanol (100 ml) was treated with 10% solution of HCl in ether (2 ml), after standing
for 2 days the mixture was evaporated in vacuo, and the residue was distributed by shaking between
benzene and 5% NaOH. The organic layer was dried and evaporated in vacuo. Crystallization of the
residue from a mixture of benzene and cyclohexane gave 0.69 g (90%) of 7b, m.p. 163–167.5 °C.
For C21H27FN2O6 (422.5) calculated: 71,55% C, 6.81% H, 3.77% F, 8.34% N; found: 71.06% C,
6.83% H, 3.60% F, 8.37% N.
The authors thank the following colleagues at the Research Institute for Pharmacy and Biochemistry
for co-operation: Mr M. Cech, Mrs R. Svatosova and Mrs A. Svatonova (elemental analyses), Dr J.
Holubek (NMR spectra), Dr M. Ryska (mass spectra), Dr E. Svatek and Mrs R. Hanusova (IR spectra),
Dr Lapka, Mrs B. Moserova, Dr J. Sedlackova, Mrs M. Pribylova (biochemical pharmacology). This
work was supported by the Grant Agency of the Czech Republic (Grant No. 307/93) and by Galena,
Komarov near Opava.
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