tripeptide as a white solid. Purification was done by silica gel
column (100–200 mesh size) and ethyl acetate and hexane (1 : 2)
as eluent.
and evaporated under vacuum to yield compound 7 as a white
solid. Purification was done by silica gel column (100–200 mesh
size) and ethyl acetate and hexane (1 : 3) as eluent.
ꢁ
Yield: 3.04 g (7.077 mmol, 65.68%); mp: 114 C.
Yield: 1.51 g (2.61 mmol, 46.19%).
1H NMR (CDCl3, 500 MHz, d ppm): 6.66 [s, 1H, Aib(3) NH],
6.60–6.58 [d, 1H, J ¼ 8.5 Hz, Val(2) NH], 4.87 [b, 1H, Leu(1)
NH], 4.19–4.16 [m, 1H, Leu(1) CaH], 4.07–4.06 [m, 1H, Val(2)
CaH], 3.71 [s, 3H, –OCH3], 2.27–2.21 [m, 1H, Val(2) CbH], 1.65–
1.65 [m, 3H, Leu(1) CbH & CgH], 1.52 [s, 6H, Aib(3) CH3], 1.44
[s, 9H, Boc CH3], 0.953–0.919 [m, 12H, Leu(1) CdH and Val(2)
CgH]. 13C NMR (CDCl3, 125 MHz, d ppm): 174.61, 172.55,
170.04, 155.74, 79.87, 58.27, 56.31, 52.41, 40.76, 31.20, 28.26,
24.77, 19.10, 17.47, 15.48. FT-IR (KBr): 3328, 2959, 2932, 2870,
1749, 1690, 1648, 1542, 1388, 1367, 1290, 1243, 1172, 1045,
1H NMR (500 MHz, CDCl3, d ppm): 7.27–7.20 [m, 5H,
aromatic ring protons], 7.16–7.14 [d, 1H, J ¼ 7 Hz, Phe(4) NH],
6.74 [s, 1H, Aib(3) NH], 6.59–6.57 [d, 1H, J ¼ 7.5 Hz, Val(2)
NH], 4.88–4.87 [d, 1H, J ¼ 8 Hz, Leu(1) NH], 4.80–4.76 [m, 1H,
Phe(4) CaH], 4.10–4.07 [m, 1H, Leu(1) CaH], 4.05–4.03 [m, 1H,
Val(2) CaH], 3.69 [s, 3H, –OCH3], 3.18–3.05 [m, 2H, Phe(4)
CbH], 2.31–2.21 [m, 1H, Val(2) CbH], 1.71–1.65 [m, 2H, Leu(1)
CbH], 1.63 [s, 3H, Aib(3) CH3], 1.48 [s, 3H, Aib(3) CH3], 1.44 [s,
9H, Boc CH3], 1.41[m, 1H, Leu(1) CgH], 0.95–0.88 [m, 12H,
Leu(1) CdH Val(2) CgH]. 13C NMR (125 MHz, CDCl3, d ppm):
173.88, 172.95, 171.92, 170.34, 155.86, 136.75, 129.33, 128.37,
126.86, 80.67, 59.14, 57.30, 55.83, 53.57, 52.20, 40.41, 37.82,
29.77, 28.23, 25.51, 24.80, 24.70, 22.93, 21.77, 19.32, 17.41. FT-
IR (KBr): 3332, 2961, 2927, 2872, 2346, 1747, 1651, 1524, 1455,
1024 cmꢀ1
.
Anal calcd for C21H39N3O6 (429.55): C, 58.72; H, 9.16; N,
9.78. Found: C, 58.75; H, 9.18; N, 9.76%.
(e) Boc-Leu-Val-Aib-OH (6). To 3.0
g
(7.0 mmol) of
1391, 1366, 1245, 1172, 1118, 1046, 1024 cmꢀ1
.
compound 4, 25 mL MeOH and 2 M 15 mL NaOH were added
and the progress of saponification was monitored by thin layer
chromatography (TLC). The reaction mixture was stirred. After
10 h, methanol was removed under vacuum; the residue was
dissolved in 50 mL of water, and washed with diethyl ether (2 ꢂ
50 mL). Then the pH of the aqueous layer was adjusted to 2 using
1 M HCl and it was extracted with ethyl acetate (3 ꢂ 50 mL). The
extracts were pooled, dried over anhydrous sodium sulfate, and
evaporated under vacuum to obtain the compound as a waxy
solid.
Anal calcd for C30H48N4O7 (576.72): C, 62.48; H, 8.39; N,
9.71. Found: C, 62.52; H, 8.45; N, 9.76%.
(g) Boc-Leu-Val-Aib-Phe-OH (8). To 1.5 g (2.61 mmol) of
compound 7, 25 mL MeOH and 2 M 15 mL NaOH were added
and the progress of saponification was monitored by thin layer
chromatography (TLC). The reaction mixture was stirred. After
10 h, methanol was removed under vacuum; the residue was
dissolved in 50 mL of water, and washed with diethyl ether (2 ꢂ
50 mL). Then the pH of the aqueous layer was adjusted to 2 using
1 M HCl and it was extracted with ethyl acetate (3 ꢂ 50 mL). The
extracts were pooled, dried over anhydrous sodium sulfate, and
evaporated under vacuum to obtain the compound as a waxy
solid.
Yield: 2.35 g (5.65 mmol, 79.83%).
1H NMR (DMSO-d6, 500 MHz, d ppm): 12.19 [s, 1H,
–COOH], 8.18 [s, 1H, Aib(3) NH], 7.47–7.45 [d, 1H, J ¼ 9 Hz,
Val(2) NH], 7.13–7.12 [d, 1H, J ¼ 8.5 Hz, Leu(1) NH], 4.19–4.16
[m, 1H, CaH Leu(1)], 3.95–3.92 [m, 1H, Val(2) CaH], 1.94–1.90
[m, 1H, Val(2) CbH], 1.59–1.56 [m, 2H, Leu(1) CbH], 1.43–1.40
[m, 1H, Leu(1) CgH], 1.40 [s, 6H, Aib(3) CH3], 1.31 [s, 9H, Boc
CH3], 0.87–0.83 [m, 12H, Leu(1) CdH and Val(2) CgH]. 13C
NMR (DMSO-d6, 125 MHz, d ppm) 175.25, 169.88, 155.84,
78.12, 56.66, 54.67, 53.15, 31.33, 28.13, 24.95, 24.54, 24.26, 22.89,
21.58, 18.96, 17.73. FT-IR (KBr): 3298, 2963, 2936, 2870, 1718,
1654, 1535, 1387, 1367, 1281, 1248, 1170, 1046, 1021, 937, 875,
Yield: 1.46 g (2.59 mmol, 99.2%).
1H NMR (DMSO-d6, 500 MHz, d ppm): 12.75 [br, 1H,
–COOH], 7.98 [s, 1H, Aib(3) NH], 7.61–7.59 [d, 1H, J ¼ 8 Hz,
Phe(4) NH], 7.39–7.38 [d, 1H, J ¼ 8 Hz, Val(2) NH], 7.26–7.15
[m, 5H aromatic ring protons], 7.05–7.03 [d, 1H, J ¼ 8.5 Hz,
Leu(1) NH], 4.40–4.35 [m, 1H, Phe(4) CaH], 4.10–4.07 [m, 1H,
Leu(1) CaH], 3.96–3.95 [m, 1H, Val(2) CaH], 3.01–2.90
[m, 2H, Phe(4) CbH], 1.95–1.89 [m, 1H, Val(2) CbH], 1.55–1.53
[m, 2H, Leu(1) CbH], 1.39–1.36 [m, 1H, Leu(1) CgH], 1.34 [s,
9H, Boc CH3], 1.32 [s, 6H, Aib(3) CH3], 0.81–0.78 [m, 12H,
Leu(1) CdH, Val(2) CgH]. 13C NMR (DMSO-d6, 125 MHz,
d ppm): 129.18, 128.07, 126.36, 78.04, 56.00, 53.46, 40.09, 36.77,
28.12, 25.00, 24.20, 23.12, 21.79, 19.13, 17.89. FT-IR (KBr):
3422, 2959, 2928, 2855, 1657, 1532, 1385, 1261, 1169, 1169, 1047,
781, 610 cmꢀ1
.
Anal calcd for C20H37N3O6 (415.52): C, 57.81; H, 8.98; N,
10.11. Found: C, 57.91; H, 9.04; N, 10.0%.
(f) Boc-Leu-Val-Aib-Phe-OMe (7). 2.32 g (5.6 mmol) of
compound 5 was dissolved in 25 mL dry DCM in an ice-water
bath. H-Phe-OMe was isolated from 2.41 g (11.2 mmol) of the
corresponding methyl ester hydrochloride by neutralization,
subsequent extraction with ethyl acetate and the ethyl acetate
extract was concentrated to 10 mL and then added to the reac-
tion mixture, followed immediately by 1.155 g (5.6 mmol) dicy-
clohexylcarbodiimide (DCC) and 0.857 g (5.6 mmol) of HOBt.
The reaction mixture was allowed to come to room temperature
and stirred for 72 h. DCM was evaporated and the residue was
dissolved in ethyl acetate (60 mL) and dicyclohexylurea (DCU)
was filtered off. The organic layer was washed with 2 M HCl (3 ꢂ
50 mL), brine (2 ꢂ 50 mL), 1 M sodium carbonate (3 ꢂ 50 mL)
and brine (2 ꢂ 50 mL) and dried over anhydrous sodium sulfate,
1024, 800 cmꢀ1
.
Anal calcd for C29H46N4O7 (562.7): C, 61.90; H, 8.24; N, 9.96.
Found: C, 62.00; H, 8.25; N, 9.86%.
(h) Boc-Leu-Val-Aib-Phe-Aib-OMe (1). 1.15 g (2.57 mmol) of
compound 7 was dissolved in 25 mL DCM in an ice-water bath.
H-Aib-OMe was isolated from 1.38 g (9.0 mmol) of the corre-
sponding methyl ester hydrochloride by neutralization, subse-
quent extraction with ethyl acetate and the ethyl acetate extract
was concentrated to 10 mL. It was then added to the reaction
mixture, followed immediately by 0.530 g (2.57 mmol) dicyclo-
hexylcarbodiimide (DCC) and 0.393 g (2.57 mmol) of HOBt. The
This journal is ª The Royal Society of Chemistry 2011
CrystEngComm, 2011, 13, 3064–3071 | 3069