Studies on Tetrapeptide Mimetics
FULL PAPER
(2R)-[(4S)-4-Amino-3-oxo-1,3,4,5-tetrahydro-benz[c]azepin-2-yl]pro-
304.1667. [α]2D0 = +32.5 (c = 0.6, EtOH). 1H NMR (CDCl3,
3
pionic Acid (19) [(S)-Aba–(R)-Ala–OH]: Phth–(S)-Aba–(R)-Ala– 500 MHz, 298 K): δ = 1.26 (d, J = 7.1 Hz, 3 H, CH3 Ala), 2.10 (s,
OH (18, 169 mg, 0.448 mmol) was dissolved in EtOH (5 mL). After 3 H, CH3 Ac), 2.83 (d, 3J = 4.8 Hz, 3 H, NH–CH3), 2.95 [dd,
3
the addition of NH2NH2·H2O (130 µL, 2.68 mmol) the mixture
was refluxed for 1.5 h. The solvent was then removed under re-
duced pressure and the residue was suspended in H2O (2.5 mL).
The pH was adjusted with AcOH until pH 5. After 1 h stirring
at room temperature the precipitate was filtered. The filtrate was
evaporated and the product was further purified by preparative
HPLC. A white powder that rapidly became a transparent paste
2J(Hβ,HβЈ) = 16.9 Hz, J(Hα,HβЈ) = 13.0 Hz, 1 H, HβЈ], 3.45 [dd,
2J(Hβ,HβЈ) = 16.9 Hz, 3J(Hα,Hβ) = 4.2 Hz, 1 H, Hβ], 4.18 [dЈ,
2
2J(Hε,HεЈ) = 17.2 Hz, 1 H, Hε], 4.97 [d, J(Hε,HεЈ) = 17.2 Hz, 1
H, Hε], 5.16 (q, 3J = 7.1 Hz, 1 H, Hα Ala), 5.45 (m, 1 H, Hα
3
3
benzazepine), 6.41 (q, J = 4.8 Hz, 1 H, NH–CH3), 6.99 (d, J =
6.3 Hz, 1 H, NH–Ac), 7.08–7.22 (m, 4 H, H arom.) ppm. 1H NMR
([D6]DMSO, 500 MHz, 298 K): δ = 1.10 (d, 3J = 7.4 Hz, 3 H, CH3
3
was obtained. Yield 93 mg (84%). HPLC tret = 11.4 min; Rf = 0.65 Ala), 1.94 (s, 3 H, CH3 Ac), 2.61 (d, J = 4.5 Hz, 3 H, NH–CH3),
3
(EtOAc/BuOH/AcOH/H2O, 1:1:1:1). HRMS calcd. 249.1239,
found 249.1243. [α]2D0 = +40.7 (c = 0.786, dioxane/H2O, 9:1). 1H
NMR (CD3OD, 250 MHz): δ = 1.35 (d, 3J = 7.4 Hz, 3 H, CH3
2.85 [dd, 2J(Hβ,HβЈ) = 17.3 Hz, J(Hα,HβЈ) = 13.1 Hz, 1 H, HβЈ],
3.17 [dd, 2J(Hβ,HβЈ) = 17.3 Hz, 3J(Hα,Hβ) = 4.1 Hz, 1 H, Hβ],
2
3
4.16 [d, J(Hε,HεЈ) = 17.5 Hz, 1 H, HεЈ], 5.02 (q, J = 7.4 Hz, 1
2
2
Ala), 3.18–3.44 (m, 2 H, 2 Hβ), 4.24 [d, J(Hε,HεЈ) = 17.5 Hz, 1
H, Hα Ala), 5.06 [d, J(Hε,HεЈ) = 17.5 Hz, 1 H, Hε], 5.40 (m, 1
H, Hε], 5.07–5.23 (m, 3 H, HεЈ, Hα Ala, Hα benzazepine), 7.17–
7.32 (m, 4 H, H arom.) ppm. 13C NMR (CD3OD, 63 MHz): δ =
20.11 (CH3 Ala), 39.26 (CH2 β), 53.35 (CH2 ε), 55.29 (CH α benza-
zepine, CH α Ala), 132.54, 132.65, 134.27, 135.99 (CH arom.),
138.84, 139.88 (Cq arom.), 174.91, 178.87 (C=O) ppm.
H, Hα benzazepine), 7.12–7.27 (m, 4 H, H arom.), 7.86 (q, 3J =
3
4.5 Hz, 1 H, NH–CH3), 8.09 (d, J = 7.0 Hz, 1 H, NH–Ac) ppm.
13C NMR (CDCl3, 126 MHz, 298 K): δ = 14.4 (CH3 Ala), 22.8
(CH3 Ac), 26.3 (NH–CH3), 36.1 (CH2 β), 47.5 (CH2 ε), 48.6 (CH
α benzazepine), 52.7 (CH α Ala), 126.4, 127.9, 128.2, 130.6 (CH
arom.), 133.2, 134.7 (Cq arom.), 170.1 (C=O Ac), 170.9 (C=O
benzazepine), 172.0 (C=O Ala) ppm. 13C NMR ([D6]DMSO,
126 MHz, 298 K): δ = 15.7 (CH3 Ala), 22.5 (CH3 Ac), 25.8 (NH–
CH3), 36.1 (CH2 β), 47.0 (CH2 ε), 47.9 (CH α benzazepine), 52.3
(CH α Ala), 126.1, 127.3, 128.4, 130.4 (CH arom.), 135.1, 135.4
(Cq arom.), 168.5 (C=O Ac), 170.7 (C=O Ala), 171.6 (C=O benz-
azepine) ppm.
(2R)-[(4S)-4-Acetylamino-3-oxo-1,3,4,5-tetrahydro-benz[c]azepin-2-
yl]propionic Acid (20) [Ac–(S)-Aba–(R)-Ala–OH]: (S)-Aba–(R)-
Ala–OH (19, 70 mg, 0.282 mmol) was dissolved in water (3 mL).
The pH was adjusted to 6 with NEt3, and Ac2O (133 µL,
1.41 mmol) was added in three portions. Meanwhile the pH was
kept at 6 with NEt3. After 2 h stirring at room temperature HPLC
analysis demonstrated completion of the reaction. The reaction
mixture was evaporated, and the product was further purified by
preparative HPLC. A white powder that rapidly became a trans-
Characterisation of 6: HPLC tret = 12.0 min; Rf = 0.70 (EtOAc/
BuOH/AcOH/H2O, 1:1:1:1). HRMS calcd. 304.1661, found
1
304.1656. H NMR (CDCl3, 500 MHz, 298 K): δ = 1.41 (d, 3J =
parent paste was obtained. Yield 49 mg (60 %). HPLC tret
=
7.0 Hz, 3 H, CH3 Ala), 2.09 (s, 3 H, CH3 Ac), 2.33 (d, 3J = 5.0 Hz,
3 H, NH–CH3), 2.93 [dd, 2J(Hβ,HβЈ) = 17.0 Hz, 3J(Hα,HβЈ) =
13.8 min; Rf = 0.24 (EtOAc/MeOH, 2:1). HRMS calcd. 291.1345,
1
found 291.1348. [α]2D0 = +65.4 (c = 1, MeOH). H NMR (CDCl3,
2
3
3
12.7 Hz, 1 H, HβЈ], 3.56 [dd, J(Hβ,HβЈ) = 17.0 Hz, J(Hα,Hβ) =
250 MHz): δ = 1.34 (d, J = 7.4 Hz, 3 H, CH3 Ala), 2.14 (s, 3 H,
2
3
CH3 Ac), 2.96 [dd, 2J(Hβ,HβЈ) = 16.8 Hz, J(Hα,Hβ) = 12.8 Hz, 1
5.0 Hz, 1 H, Hβ], 4.12 [dЈ, J(Hε,HεЈ) = 16.7 Hz, 1 H, Hε], 4.92
2
3
H, Hβ], 3.49 [dd, 2J(Hβ,HβЈ) = 16.9 Hz, 3J(Hα,HβЈ) = 4.0 Hz, 1
H, HβЈ], 4.00 [d, 2J(Hε,HεЈ) = 17.3 Hz, 1 H, Hε], 5.13 [d,
2J(Hε,HεЈ) = 17.1 Hz, 1 H, HεЈ], 5.30 (q, 3J = 7.3 Hz, 1 H, Hα
Ala), 5.52 (m, 1 H, Hα benzazepine), 5.80 (br. s, 1 H, NH amide),
7.04–7.30 (m, 4 H, H arom.) ppm. 13C NMR (CDCl3, 63 MHz): δ
= 15.73 (CH3 Ala), 23.26 (CH3 Ac), 36.58 (CH2 β), 49.29 (CH2 ε),
53.32 (CH α benzazepine, CH α Ala), 127.05, 128.60, 128.66,
131.33 (CH arom.), 133.76, 135.45 (Cq arom.), 171.71, 172.44,
174.93 (C=O) ppm.
[d, J(Hε,HεЈ) = 16.7 Hz, 1 H, Hε], 5.16 (q, J = 7.0 Hz, 1 H, Hα
Ala), 5.40 (m, 1 H, Hα benzazepine), 5.45 (q, 3J = 5.0 Hz, 1 H,
3
NH–CH3), 6.92 (d, J = 6.4 Hz, 1 H, NH–Ac), 7.05–7.21 (m, 4 H,
H arom.) ppm. H NMR ([D6]DMSO, 500 MHz, 298 K): δ = 1.20
1
3
3
(d, J = 7.0 Hz, 3 H, CH3 Ala), 1.92 (s, 3 H, CH3 Ac), 2.29 (d, J
= 4.5 Hz, 3 H, NH–CH3), 2.99 [dd, 2J(Hβ,HβЈ) = 17.0 Hz,
3J(Hα,HβЈ) = 13.2 Hz, 1 H, HβЈ], 3.11 [dd, J(Hβ,HβЈ) = 17.3 Hz,
2
3J(Hα,Hβ) = 4.3 Hz, 1 H, Hβ], 4.18 [d, 2J(Hε,HεЈ) = 16.7 Hz, 1
3
2
H, HεЈ], 4.80 (q, J = 7.0 Hz, 1 H, Hα Ala), 4.95 [d, J(Hε,HεЈ) =
16.7 Hz, 1 H, Hε], 5.19 (m, 1 H, Hα benzazepine), 7.05–7.18 (m,
3
3
(2R)-[(4S)-4-Acetylamino-3-oxo-1,3,4,5-tetrahydro-benz[c]azepin-2-
yl]-N-methylpropionamide (5) [Ac–(S)-Aba–(R)-Ala–NHMe]: Ac–
(S)-Aba–(R)-Ala–OH (20, 104 mg, 0.358 mmol) was dissolved in
CH2Cl2 (6.5 mL). NEt3 (50 µL, 0.358 mmol) and TBTU (138 mg,
0.430 mmol) were added, and the reaction mixture was stirred for
5 min, followed by the addition of CH3NH2·HCl (26.6 mg,
0.394 mmol) and NEt3 (150 µL, 1.07 mmol). The coupling was con-
tinued overnight. HPLC analysis indicated that the starting mate-
rial had been completely consumed. The reaction mixture was di-
luted with CH2Cl2 (50 mL) and washed with 1 HCl (1×25 mL)
in order to remove most of the HOBt. The product was dried
(MgSO4), filtered and the solvents evaporated. LC/MS demon-
strated that 30% racemisation had occurred with formation of Ac–
(S)-Aba–(S)-Ala–NHMe (6). The product was further purified by
preparative HPLC (both diastereomers were collected) until suf-
ficient material for the NMR study was obtained (21 mg of 5, 9 mg
of 6).
4 H, H arom.), 7.55 (q, J = 4.5 Hz, 1 H, NH–CH3), 8.12 (d, J =
7.0 Hz, 1 H, NH–Ac) ppm. 13C NMR (CDCl3, 126 MHz, 298 K):
δ = 13.7 (CH3 Ala), 23.0 (CH3 Ac), 25.7 (NH-CH3), 36.1 (CH2 β),
47.0 (CH2 ε), 48.8 (CH α benzazepine), 52.4 (CH α Ala), 126.1,
127.9, 128.9, 130.4 (CH arom.), 132.7, 134.4 (Cq arom.), 169.5
(C=O Ac), 170.0 (C=O Ala), 171.7 (C=O benzazepine) ppm. 13C
NMR ([D6]DMSO, 126 MHz, 298 K): δ = 14.8 (CH3 Ala), 22.6
(CH3 Ac), 25.5 (NH-CH3), 35.8 (CH2 β), 47.4 (CH2 ε), 48.4 (CH
α benzazepine), 53.3 (CH α Ala), 125.6, 127.2, 128.7, 130.2 (CH
arom.), 134.7, 135.6 (Cq arom.), 168.8 (C=O Ac), 170.1 (C=O Ala),
171.0 (C=O benzazepine) ppm.
[(4S)-4-Acetylamino-3-oxo-1,3,4,5-tetrahydro-benz[c]azepin-2-yl]-
acetic Acid (22) [Ac–(S)-Aba–Gly–OH]: (S)-Aba–Gly–OH (21,
300 mg, 1.11 mmol) was dissolved in water (15 mL). The pH was
adjusted to 6 with NEt3, and Ac2O (1.1 mL, 11.5 mmol) was
added. Meanwhile the pH was kept at 6 with NEt3. After overnight
stirring at room temperature HPLC analysis demonstrated comple-
tion of the reaction. The reaction mixture was acidified with 1
Characterisation of 5: HPLC tret = 12.9 min; Rf = 0.64 (EtOAc/
BuOH/AcOH/H2O, 1:1:1:1). HRMS calcd. 304.1661, found HCl to pH 2 and extracted with EtOAc (4×10 mL). The organic
Eur. J. Org. Chem. 2006, 2899–2911
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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