Designing Nootropic Dipeptides
21
1
ne methyl ester in 10 ml of methanol saturated with gaseous
ammonia was allowed to stand overnight at 20°C. Then, the
solution volume was reduced by half through evaporation,
and the white precipitate was separated by filtration, washed
with ether, and dried over P2O5 in a vacuum desiccator to ob-
tain 120 mg (60%) of the target product; m.p., 182 – 183°C;
[a]2D0, –5.8° (c, 1; water); Rf, 0.29 (isopropanol – ammonia,
0.5; ethanol); H NMR spectrum in DMSO-d6 (d, ppm):
1.76, 2.21 (2m, 2H, CbH2 pGlu), 2.07 (m, 2H, CgH2 pGlu),
2.80, 2.93 (2dd, 2H, CbH2 His), 4.00 (dd, 1H, CaH pGlu),
4.40 (ddd, 1H, CaH His), 6.76, 7.10 (2s, 2H, NH2 His), 7.37
(s, 1H, C4kH His), 7.51 (s, 1H, NH pGlu), 7.97 (s, 1H, C2kH,
His), 8.12 (d, 1H, NH His), 11.80 (bs, 1H, NkH His);
C11H15N5O3. Reported [15]: m.p., 216°C; [a]2D6, –20.0° (c, 1;
1
7 : 3); 0.34 (dioxane – water, 10 : 1); H NMR spectrum in
acetic acid).
DMSO-d6 (d, ppm): 1.90, 2.24 (2m, 2H, CbH2 pGlu), 2.12
(m, 2H, CgH2 pGlu), 3.58 (m, 2H, CbH2 Ser), 4.08 (dd, 1H,
CaH pGlu), 4.20 (m, 1H, CaH Ser), 4.92 (m, 1H, OH), 7.12,
7.32 (2s, 2H, NH2), 7.82 (s, 1H, NH pGlu), 7.87 (d, 1H, NH
Ser); C8H13N3O4.
L-Pyroglutamyl-L-aspartic acid di-tert-butyl ester
(L-pGlu-L-Asp(OBut)2). To a solution of 0.25 g (0.9 mmole)
of L-aspartic acid di-tert-butyl ester hydrochloride (Serva)
and 0.375 g (1.0 mmole) of L-pGlu-OPcp in 10 ml DMF was
added on cooling (ice-cold water) 0.12 ml (0.9 mmole) of
ethylmorpholine and the mixture was stirred for 1 h at room
temperature. Then, the solvent volume was reduced by evap-
oration in vacuum. The residue was chromatographed on a
silica gel column eluted with a chloroform – methanol mix-
ture. The solvent was evaporated to obtain L-pGlu-L-
Asp(OBut)2 in the form of transparent oil; Rf, 0.30 (chloro-
L-Histidine
methyl
ester
dihydrochloride
(L-His-OMe · 2HCl). This salt was obtained using the con-
ventional method [14] with a yield of 85.8%; m.p.,
195 – 200°C; Rf, 0.42 (isopropanol – ammonia, 7 : 3); 0.55
(dioxane – water, 10 : 1); 0.26 (butanol – acetic acid – water,
4 : 1 : 1); 1H NMR spectrum in DMSO-d6 (d, ppm): 3.32 (d,
2H, CbH2), 3.73 (s, 3H, OCH3), 4.47 (t, 1H, CaH), 7.53 (s,
20
1
form – methanol, 9 : 1); [a]D , –11.20° (c, 1; ethanol); H
1H, C4kH), 9.09 (s, 1H, C2kH), 14.5 (bs, 3H, NH3 ). Reported
+
NMR spectrum in DMSO-d6 (d, ppm): 1.35, 1.40 (2s, 18H,
COOC(CH3)3), 2.00 – 2.55 (m, 4H, CbH2 – CgH2 pGlu),
2.65 – 2.85 (m, 2H, CbH2 Asp), 4.10 – 4.15 (m, 1H, CaH
pGlu), 4.60 – 4.65 (m, 1H, CaH Asp), 6.45 (1H, c, NH
pGLu), 7.05 (d, 1H, NH pGlu); C17H28N2O6.
[14]: m.p., 200 – 201°C.
L-Pyroglutamyl-L-histidine
methyl
ester
(L-pGlu-L-His-OMe). To a solution of 0.76 g (2 mmole) of
L-pyroglutamic acid pentachlorophenyl ester in 10 ml DMF
was added 0.58 g (2.41 mmole) of L-histidine methyl ester
hydrochloride (Fluka) and 0.67 ml (4.82 mmole) of TEA.
The mixture was stirred for 5 h at room temperature and al-
lowed to stand overnight. Then, the precipitated TEA hydro-
chloride was separated by filtration and the solvent volume
was reduced by evaporation in vacuum. The residue was
chromatographed on a silica gel column eluted with a chloro-
form – ethanol (40 : 1) mixture. The solvent was evaporated
and the solid residue was recrystallized from methanol. The
target compound was obtained in the form of a white crystal-
line powder; yield, 160 mg (29%); m.p., 178 – 180°C (with
decomp.); [a]2D0, –3.9° (c, 1; ethanol); Rf, 0.30 (dioxane –
L-Pyroglutamyl-L-serine di-tert-butyl ester (L-pGlu-
L-Ser(OBut)2). To a solution of 500 mg (1.32 mmole) of
L-pyroglutamic acid pentachlorophenyl ester in 6 ml DMF
was added 360 mg (1.4 mmole) of O-tert-butylserine-tert-
butyl ester hydrochloride (Reanal) and 0.2 ml (1.4 mmole) of
TEA. The mixture was stirred for 5 h at room temperature
and allowed to stand overnight. Then, the precipitated TEA
hydrochloride was separated by filtration and the solvent
volume was reduced by evaporation in vacuum. The residue
was chromatographed on a silica gel column eluted with a
chloroform – ethanol (48 : 2) mixture. Finally, the solvent
was evaporated to yield 210 mg (44%) of a chromato-
graphically homogeneous product with m.p., 103°C; Rf, 0.38
(chloroform – ethanol, 9 : 1), 0.31 (dioxane – water, 10 : 1);
water, 10 : 1), 0.23 (butanol – acetic acid – water, 4 : 1 : 1);
1
0.47 (isopropanol – ammonia, 7 : 3); H NMR spectrum in
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1
DMSO-d6 (d, ppm): 1.80, 2.22 (2m, 2H, CbH2 pGlu), 2.06
(m, 2H, CgH2 pGlu), 2.88, 2.95 (dd, 2H, CbH2 His), 3.60 (s,
3H, OCH3), 4.02 (dd, 1H, CaH pGlu), 4.48 (ddd, 1H, CaH
His), 6.84 (s, 1H, C4kH His), 7.59 (s, 1H, NH pGlu), 7.89 (s,
1H, C2kH His), 8.39 (d, 1H, NH His).
[a]D , –1.7° (c, 1; ethanol); H NMR spectrum in DMSO-d6
(d, ppm): 1.42 (s, 9H, (CH3)3), 1.40 (bs, 9H, (CH3)3), 1.88,
2.24 (2m, 2H, CbH2 pGlu), 2.08 (m, 2H, CgH2 pGlu), 3.43,
3.64 (2dd, 2H, CbH2 Ser), 4.15 (dd, 1H, CaH pGlu), 4.33
(ddd, 1H, CaH Ser), 7.83 (s, 1H, NH pGlu), 8.08 (d, 1H, NH
Ser); C16H28N2O5.
L-Pyroglutamyl-L-histidine amide (L-pGlu-L-His-
NH2). A solution of 80 mg L-pyroglutamyl-L-histidine
methyl ester in 10 ml of methanol saturated with gaseous
ammonia was allowed to stand overnight at 20°C. Then, the
solution volume was slightly reduced through evaporation,
and the white precipitate was separated by filtration, washed
with ether, and dried to obtain 70 mg (82%) of the target
product in the form of a white crystalline powder; m.p.,
211°C (with decomp.); Rf, 0.22 (dioxane – water, 10 : 1),
0.17 (butanol – acetic acid – water, 4 : 1 : 1); [a]2D0, +2.6° (c,
EXPERIMENTAL PHARMACOLOGICAL PART
The biological experiments were performed on white
mongrel male rats weighing 180 – 240 g (Kryukovo nursery,
Moscow Oblast). The effect of the synthesized dipeptides on
learning and memory was studied on a PACR model with
MES as the amnesic agent. The test compounds were intro-
duced by intraperitoneal injections with 0.9% aqueous NaCl