Journal of Medicinal Chemistry
ARTICLE
(m, 1H), 3.37 (m, 1H), 3.56 (s, 2H), 4.24 (t, J = 6.8 Hz, 1H), 7.28ꢀ7.33
(m, 5H), 8.28 (s, 1H); 13C NMR (100 MHz, CDCl3) δ 24.8, 27.6, 29.2,
38.3, 41.2, 48.4, 60.9, 80.9, 127.0, 128.5, 128.8, 133.7, 159.5, 168.9, 172.0.
HRMS m/z calcd for C19H28N3O4 [M + H]+ 362.2074, found 362.2074.
Representative Protocol for Azapeptide Benzyl Ester
Synthesis. Phenylacetyl-aza-propargylglycinyl-(2S)-prolyl-
(2S)-3-pyridylalaninyl-(3S)-β-homophenylalanine Benzyl
Ester (23a). Phenylacetyl-aza-propargylglycinyl-(2S)-proline tert-butyl
ester (21a, 85 mg, 0.22 mmol) was treated with a solution of 9:1 TFA in
dichloromethane and stirred for 1 h at room temperature until complete
disappearance of starting material. The mixture was then evaporated and
coevaporated 3 times with dichloromethane, then dissolved in EtOAc.
The organic phase was extracted with saturated NaHCO3, and the basic
aqueous phase was acidified with 1 N HCl and then back-extracted with
5 ꢁ 10 mL of EtOAc. After evaporation of the volatiles, crude acid 22a
was dissolved in THF (7 mL), cooled to ꢀ15 °C, treated sequentially
with isobutyl chloroformate (31 μL, 0.242 mmol) and N-methylmor-
pholine (36 μL, 0.33 mmol), stirred for 15 min, and treated with a
solution of (3-pyridyl)alaninyl-β-homophenylalanine benzyl ester hy-
drochloride (14, 111 mg, 0.27 mmol) in ethyl acetate (5 mL). After the
mixture was stirred at ꢀ15 °C for 1 h, the volatiles were removed under
reduced pressure and the crude material was purified by chromatogra-
phy on silica gel using ethyl acetate as eluant to afford benzyl ester 23a
(64 mg, 40% yield) as a pale yellow foam. Rf = 0.42 (10% MeOH/
CH2Cl2); [R]2D5 14.7° (c 1.5, CHCl3); 1H NMR (400 MHz, CDCl3) δ
1.13ꢀ1.28 (m, 1H), 1.61ꢀ1.69 (m, 2H), 2.17 (m, 1H), 2.32 (s, 1H),
2.59ꢀ2.71 (m, 2H), 2.81ꢀ2.84 (m, 2H), 2.85ꢀ2.99 (m, 2H), 3.26 (d,
J = 12.8 Hz, 1H), 3.36 (t, J = 8 Hz, 1H), 3.64ꢀ3.76 (m, 2H), 3.82 (d, J =
17.2 Hz, 1H), 4.24ꢀ4.28 (dd, J = 7.2, 10.4 Hz, 1H), 4.41 (d, J = 16.8 Hz,
1H), 4.55 (m, 2H), 5.09 (dd, J = 12.4, 17.6 Hz, 2H), 7.16 (m, 6H),
7.25ꢀ7.35 (m, 11H), 7.41 (d, J = 7.6 Hz, 1H), 7.57 (d, J = 8.4 Hz, 1H),
8.42 (s, 2H), 9.98 (s, 1H); 13C NMR (100 MHz, CDCl3) δ 26.1, 30.0,
30.1, 34.4, 38.9, 40.7, 41.2, 48.5, 50.4, 54.8, 63.4, 66.8, 74.5, 78.3, 123.8,
126.9, 128.0, 128.6, 128.7, 129.4, 129.7, 130.1, 134.2, 134.5, 136.1, 136.3,
136.8, 138.1, 148.1, 150.6, 160.3, 171.0, 171.1, 171.2, 172.1. HRMS m/z
calcd for C42H45N6O6 [M + H]+ 729.3395, found 729.3382.
160.7, 170.6, 170.7, 171.2, 172.1. HRMS m/z calcd for C42H47N6O6
[M + H]+ 731.5552, found 731.3541.
Phenylacetyl-aza-alaninyl-(2S)-prolyl-(2S)-3-pyridylalan-
inyl-(3S)-β-homophenylalanine Benzyl Ester (23d). 23d was
obtained from ester 21d (65 mg, 0.18 mmol) as described above in 40%
yield as a pale yellow foam. Rf = 0.32 (10% MeOH/CH2Cl2); [R]D25
ꢀ19.6° (c 2.8, CHCl3); 1H NMR (400 MHz, CDCl3) δ 1.27 (m, 1H),
1.67ꢀ1.70 (m, 2H), 2.15ꢀ2.17 (m, 1H), 2.63ꢀ2.71 (m, 2H),
2.81ꢀ2.84 (m, 2H), 2.86ꢀ2.97 (m, 5H), 3.22ꢀ3.32 (m, 2H), 3.67
(s, 2H), 4.25ꢀ4.29 (dd, J = 6.8, 10.4 Hz, 1H), 4.52ꢀ4.60 (m, 2H), 5.09
(d, J = 12.4 Hz, 1H), 5.13 (d, J = 12.4 Hz, 1H), 7.17ꢀ7.19 (m, 6H),
7.27ꢀ7.42 (m, 13H), 7.58 (d, J = 8.8 Hz, 1H), 8.35ꢀ8.43 (s, 1H), 9.27
(s, 1H); 13C NMR (100 MHz, CDCl3) δ 26.2, 29.9, 34.4, 39.2, 41.0,
41.4, 48.6, 50.3, 54.8, 63.4, 66.8, 126.8, 128.0, 128.5, 128.7, 128.9, 129.4,
129.5, 130.1, 136.4, 136.9, 138.4, 147.9, 161.4, 170.6, 171.3, 172.4.
HRMS m/z calcd for C40H45N6O6 [M + H]+ 705.3395, found 705.3392.
Phenylacetyl-aza-propargylglycinyl-(2S)-prolyl-(2S)-3-
(pyridyl)-alaninyl-(3S)-β-homophenylalanine (7). Phenylacetyl-
aza-propargylglycinyl-(2S)-prolyl-(2S)-3-pyridylalaninyl-(3S)-β-homo-
phenylalanine benzyl ester (23a, 25 mg, 0.034 mmol) was dissolved in a
minimum amount of dioxane, cooled to 0 °C, treated with a 2 N LiOH
(5 mL), and stirred for 30 min, and the volatiles were evaporated under
reduce pressure. The aqueous residue was acidifiedto pH 5 using 1 N HCl
and extracted with ethyl acetate. The organic extractions were combined,
dried with sodium sulfate, and concentrated under vacuum. The residue
was purified by preparative HPLC on a C18 reverse-phase column, using
methanol in water as eluant. Freeze-drying of the collected fractions gave
acid 7 (14.6 mg, 67%) as a pale yellow oil: Rf = 0.24 (10% MeOH/
CH2Cl2); [R]2D5 9.5° (c 1.05, CH3OH); 1H NMR (700 MHz, CH3OD) δ
1.20 (m, 1H), 1.79ꢀ1.81 (m, 2H), 2.17 (m, 1H), 2.57 (d, J = 6.9 Hz, 1H),
2.72ꢀ2.78 (dd, J = 8.3, 13.6 Hz, 1H), 2.79 (t, J = 2.5 Hz, 1H), 2.81 (m,
1H), 2.98ꢀ3.01 (dd, J = 4.9, 13.7 Hz, 1H), 3.06ꢀ3.09 (dd, J = 4.1, 14.3
Hz, 1H), 3.16 (m, 1H), 3.47ꢀ3.49 (m, 1H), 3.72 (d, J = 14.5 Hz, 1H),
3.76 (d, J = 14.5Hz, 1H), 3.82ꢀ3.89 (m, 1H), 4.22ꢀ4.25 (dd, J = 6.9, 10.4
Hz, 1H), 4.37ꢀ4.39 (dd, J = 4.0, 11.3 Hz, 1H), 4.47ꢀ4.49 (m, 2H), 7.14
(m, 3H), 7.22 (m, 2H), 7.28 (t, J = 7.4 Hz, 1H), 7.34 (m, 3H), 7.42 (m,
2H), 7.53 (d, J = 7.2 Hz, 1H), 8.25 (s, 1H), 8.40 (d, J = 4.8 Hz, 1H), 8.47
(s, 1H); 13C NMR (175 MHz, CH3OD) δ 25.1, 29.5, 33.6, 38.6, 39.8,
39.9, 47.3, 48.3, 49.8, 54.6, 62.7, 73.7, 77.4, 123.8, 126.0, 127.1, 127.9,
128.5, 129.1, 129.5, 134.4, 134.5, 137.3, 137.9, 146.9, 149.2, 160.0, 170.7,
171.0, 173.1, 173.8. HRMS m/z calcd for C35H39N6O6 [M + H]+
639.2926, found 639.2942. RP-HPLC system 1: 98.9%, tR= 7.96 min.
RP-HPLC system 3: 98.5%, tR= 11.86 min.
Phenylacetyl-aza-phenylalaninyl-(2S)-prolyl-(2S)-(3-pyridyl)-
alaninyl-(3S)-β-homophenylalanine (8). 8 was obtained from
23b (31 mg, 0.039 mmol) as described above in 66% yield: Rf = 0.32
(10% MeOH/CH2Cl2); [R]2D5 12.4° (c 2.5, CH3OH); 1H NMR
(700 MHz, CH3OD) δ 1.16ꢀ1.23 (m, 1H), 1.79ꢀ1.83 (m, 2H),
2.18ꢀ2.20 (m, 1H), 2.61 (m, 2H), 2.79ꢀ2.82 (dd, J = 8.7, 13.1 Hz,
1H), 2.86ꢀ2.90 (m, 1H), 3.02 (d, J = 10.9 Hz, 1H), 3.12 (d, J = 12.7 Hz,
1H), 3.17ꢀ3.21 (dd, J = 9.8, 17.1 Hz, 1H), 3.48 (m, 1H), 3.61 (s, 2H),
3.93 (m, 1H), 4.28ꢀ4.31 (dd, J = 6.9, 10.6 Hz, 1H), 4.41 (d, J = 7.9 Hz,
1H), 4.52 (m, 1H), 5.11 (m, 1H), 7.17ꢀ7.18 (m, 3H), 7.21 (m, 2H),
7.28ꢀ7.37 (m, 11H), 7.59 (s, 1H), 8.31 (s, 1H), 8.42 (s, 1H); 13C NMR
(175 MHz, CH3OD) δ 25.2, 29.4, 29.5, 33.6, 39.8, 40.0, 48.4, 50.0,
54.0, 54.6, 62.9, 126.1, 127.1, 127.5, 128.0, 128.3, 128.5, 129.1,
129.2, 129.5, 134.4, 135.9, 138.1, 161.0, 170.7, 170.8, 173.3. HRMS
m/z calcd for C39H43N6O6 [M + H]+ 691.3238, found 691.3231.
RP-HPLC system 1: 97.4%, tR= 8.84 min. RP-HPLC system 3: 98.9%,
tR= 13.99 min.
Phenylacetyl-aza-phenylalaninyl-(2S)-prolyl-(2S)-3-pyri-
dylalaninyl-(3S)-β-homophenylalanine Benzyl Ester (23b).
23b was obtained from ester 21b (42 mg, 96 μmol) as described above in
48% yield as a pale yellow foam. Rf = 0.35 (10% MeOH/CH2Cl2); [R]D25
1
9.3° (c 1.4, CHCl3); H NMR (400 MHz, CDCl3) δ 1.28 (m, 1H),
1.69ꢀ1.74 (m, 2H), 2.19ꢀ2.21 (m, 1H), 2.64ꢀ2.67 (m, 2H), 2.87ꢀ
3.01 (m, 3H), 3.07 (m, 1H), 3.22 (d, J = 12.4 Hz, 1H), 3.38 (t, J = 8 Hz,
1H), 3.61 (s, 2H), 3.89 (d, J = 13.6 Hz, 1H), 4.30ꢀ4.34 (dd, J = 6.8, 10.2
Hz, 1H), 4.55ꢀ4.59 (m, 2H), 5.03ꢀ5.14 (m, 3H), 7.12ꢀ7.35 (m, 22H),
7.51 (d, J = 7.2 Hz, 1H), 7.60 (d, J = 8.8 Hz, 1H), 8.34 (br, 2H), 8.72
(s, 1H); 13C NMR (100 MHz, CDCl3) δ 25.4, 29.4, 33.5, 38.3, 40.0,
40.7, 47.7, 49.8, 53.7, 53.9, 62.7, 66.0, 126.0, 127.4, 127.7, 127.8, 127.9,
128.0, 128.1, 128.4, 128.7, 128.8, 128.9, 129.3, 132.9, 135.1, 135.6, 137.6,
160.3, 169.8, 169.9, 170.5, 171.3. HRMS m/z calcd for C46H49N6O6
[M + H]+ 781.3708, found 781.3727.
Phenylacetyl-aza-allylglycinyl-(2S)-prolyl-(2S)-3-pyridyla-
laninyl-(3S)-β-homophenylalanine Benzyl Ester (23c). 23c
was obtained from ester 21c (66 mg, 0.17 mmol) as described above
in 55% yield as a yellow foam. Rf = 0.40 (10% MeOH/CH2Cl2); [R]D25
ꢀ10.6° (c 1.8, CHCl3); 1H NMR (400 MHz, CDCl3) δ 1.27 (m, 1H),
1.67ꢀ1.74 (m, 2H), 2.16ꢀ2.21 (m, 1H), 2.59ꢀ2.70 (m, 2H), 2.82ꢀ
2.96 (m, 3H), 3.02ꢀ3.08 (m, 1H), 3.27ꢀ3.37 (m, 2H), 3.54ꢀ3.59 (dd,
J = 8.8, 14.4 Hz, 1H), 3.68 (s, 2H), 4.28ꢀ4.32 (m, 2H), 4.54ꢀ4.59 (m,
2H), 5.05ꢀ5.15 (m, 4H), 5.68ꢀ5.77 (m, 1H), 7.19ꢀ7.21 (m, 6H),
7.28ꢀ7.36 (m, 11H), 7.52 (d, J = 8 Hz, 1H), 7.58 (d, J = 8 Hz, 1H), 8.43
(br, 2H), 8.69 (s, 1H); 13C NMR (100 MHz, CDCl3) δ 26.1, 30.1, 34.3,
39.0, 40.8, 41.6, 48.5, 50.4, 53.7, 54.7, 63.3, 66.8, 120.7, 126.8, 128.2,
128.5, 128.7, 128.8, 128.9, 129.5, 129.6, 130.0, 132.7, 133.9, 136.4, 138.4,
Phenylacetyl-aza-allylglycinyl-(2S)-prolyl-(2S)-(3-pyridyl)
alaninyl-(3S)-β-homophenylalanine (9). 9 was obtained from
23c (18 mg, 0.025 mmol) as described above in 72% yield: Rf = 0.28
(10% MeOH/CH2Cl2); [R]2D5 ꢀ54.2° (c 1.2, CH3OH); 1H NMR
6094
dx.doi.org/10.1021/jm200608k |J. Med. Chem. 2011, 54, 6085–6097