Acyl Groups as Prospective Protection for Imidazole
FULL PAPER
4.50 (dd, JЈ ϭ 8.6, JЈЈ ϭ 4.9 Hz, 1 H, CαValϪH), 4.58Ϫ4.63 (br. m, (509 mg, 70%). RP-HPLC (gradient 3): tR ϭ 46.7 min. TLC
1
1 H, CαHisϪH), 6.65 (d, J ϭ 8.5 Hz, 2 H, ArϪH), 6.69 (d, J ϭ (system A): Rf ϭ 0.53. H NMR (400 MHz, CDCl3): δ ϭ 0.87 (d,
7.2 Hz, 1 H, NH), 7.27 (br. s, 1 H, im), 7.32 (br. t, J ϭ 7.4 Hz, 2
J ϭ 6.9 Hz, 3 H, CγValϪH), 0.92 (d, J ϭ 7.0 Hz, 3 H, CγValϪH),
H, Fmoc), 7.42 (br. t, J ϭ 7.4 Hz, 2 H, Fmoc), 7.45 (t, J ϭ 8.5 Hz, 2.16Ϫ2.20 (m, 1 H, CβValϪH), 3.03 (dd, JЈ ϭ 15.0, JЈЈ ϭ 6.4 Hz, 1
1 H, ArϪH), 7.57Ϫ7.64 (br. m, 3 H, Fmoc ϩ NH), 7.78 (d, J ϭ H, CβHisϪH), 3.11 (dd, JЈ ϭ 14.9, JЈЈ ϭ 5.1 Hz, 1 H, CβHisϪH),
7.4 Hz, 2 H, Fmoc), 7.87 (br. s, 1 H, im) ppm. 13C NMR
3.68 (s, 3 H, COOCH3), 4.25Ϫ4.26 (br. m, 1 H, OCH2CH),
(100 MHz, CDCl3): δ ϭ 18.0, 19.2, 30.8, 31.4, 47.5, 52.5, 54.9, 56.4, 4.32Ϫ4.36 (br. m, 2 H, OCH2CH), 4.55 (dd, JЈ ϭ 8.6, JЈЈ ϭ 4.9 Hz,
57.8, 67.7, 104.4, 111.7, 114.8, 120.4, 125.6, 127.5, 128.1, 133.4, 1 H, CαValϪH), 4.59Ϫ4.62 (m, 1 H, CαHisϪH), 6.71 (s, 1 H, im),
137.6, 140.1, 141.7, 144.2, 156.6, 158.1, 163.3, 171.4, 172.4 ppm.
6.86 (br. d, J ϭ 5.0 Hz, 1 H, NH), 7.11Ϫ7.14 (m, 6 H, Trt),
HRMS (ES-TOF): m/z calcd. for C36H39N4O8 [M
ϩ
H]ϩ: 7.30Ϫ7.34 (m, 11 H, Trt ϩ Fmoc), 7.40 (t, J ϭ 7.4 Hz, 2 H, Fmoc),
7.45 (s, 1 H, im), 7.63 (br. d, J ϭ 7.1 Hz, 2 H, Fmoc), 7.77 (d ϩ
br., J ϭ 7.5 Hz, 3 H, Fmoc ϩ NH) ppm. 13C NMR (100 MHz,
655.2768; found 655.2771.
Fmoc-His(π-2,6-Dmbz)-Val-OMe (5): White solid (295 mg, 90%).
RP-HPLC (gradient 1): tR ϭ 23.9 min. TLC (system A): Rf ϭ 0.57.
1H NMR (400 MHz, CDCl3): δ ϭ 0.93Ϫ0.97 (m, 6 H, CγValϪH),
2.15Ϫ2.25 (m, 1 H, CβValϪH), 3.23 (dd, JЈ ϭ 14.9, JЈЈ ϭ 9.6 Hz, 1
H, CβHisϪH), 3.68 (dd, JЈ ϭ 15.1, JЈЈ ϭ 3.6 Hz, 1 H, CβHisϪH),
3.74 (s, 3 H, COOCH3), 3.78 (s, 6 H, OCH3), 4.21 (t, J ϭ 7.3 Hz,
CDCl3): δ ϭ 18.2, 19.4, 31.0, 31.7, 47.5, 52.5, 55.5, 57.7, 67.6, 75.8,
119.9, 120.4, 125.7, 127.5, 128.1, 128.5, 130.2, 137.1, 138.8, 141.7,
142.7, 144.3, 156.7, 171.7, 172.5 ppm. HRMS (ES-TOF): m/z calcd.
for C46H45N4O5 [M ϩ H]ϩ: 733.3390; found 733.3383.
Fmoc-D-His-L-Val-OMe (8): Dipeptide 7 (220 mg, 0.3 mmol) was
1 H, OCHCH2), 4.27Ϫ4.32 (m, 2 H, OCHCH2), 4.54 (dd, JЈ ϭ 8.5, dissolved in TFA/H2O (95:5, v/v; 2.0 mL) and stirred at room tem-
JЈЈ ϭ 5.0 Hz, 1 H, CαValϪH), 4.65Ϫ4.70 (m, 1 H, CαHisϪH), 5.73
perature for 1 h. The solvents were evaporated under a flow of ni-
(d, J ϭ 8.2 Hz, 1 H, NH), 6.63 (d, J ϭ 8.4 Hz, 2 H, ArϪH), 6.80 trogen, and the residual oil was partitioned between EtOAc
(d, J ϭ 8.6 Hz, 1 H, NH), 6.93 (s, 1 H, im), 7.26Ϫ7.31 (br. m, 2 (10 mL) and 5% NaHCO3 (15 mL), the aqueous layer was ex-
H, Fmoc), 7.39 (t, J ϭ 7.5 Hz, 2 H, Fmoc), 7.44 (t, J ϭ 8.5 Hz, 1 H,
ArϪH), 7.54Ϫ7.57 (br. m, 3 H, Fmoc ϩ im), 7.76 (d, J ϭ 7.5 Hz, 1
tracted with EtOAc (2 ϫ 10 mL) and the organic layers were
pooled and dried over Na2SO4. After filtration, the organic phase
H, Fmoc) ppm. 13C NMR (100 MHz, CDCl3): δ ϭ 18.2, 19.4, 31.5, was concentrated in vacuo until pure compound 8 separated as a
32.0, 47.4, 52.6, 54.7, 56.5, 57.8, 67.6, 104.4, 112.8, 120.3, 125.6,
127.5, 128.1, 128.6, 131.9, 133.3, 141.0, 141.6, 144.2, 156.5, 158.0,
165.9, 171.6, 172.4 ppm. HRMS (ES-TOF): m/z calcd. for
C36H39N4O8 [M ϩ H]ϩ: 655.2768; found 655.2769.
crystalline material, which was collected by filtration. White pow-
der (134 mg, 91%). TLC (system A): Rf ϭ 0.19. 1H NMR
(400 MHz, [D6]DMSO): δ ϭ 0.79 (d, J ϭ 6.7 Hz, 3 H, CγValϪH),
0.80 (d, J ϭ 6.7 Hz, 3 H, CγValϪH), 1.96Ϫ2.04 (m, 1 H, CβValϪH),
2.81 (dd, JЈ ϭ 14.7, JЈЈ ϭ 8.9 Hz, 1 H, CβHisϪH), 2.91 (dd, JЈ ϭ
14.7, JЈЈ ϭ 5.4 Hz, 1 H, CβHisϪH), 3.63 (s, 3 H, COOCH3),
4.17Ϫ4.27 (m, 4 H, OCH2CH ϩ CαValϪH), 4.39Ϫ4.42 (m, 1 H,
CαHisϪH), 6.83 (s, 1 H, im), 7.32 (t, J ϭ 7.4 Hz, 2 H, Fmoc), 7.42
(t, J ϭ 7.5 Hz, 2 H, Fmoc), 7.57 (d, J ϭ 8.5 Hz, 1 H, NH), 7.61
(s, 1 H, im), 7.67Ϫ7.70 (m, 2 H, Fmoc), 7.89 (d, J ϭ 7.5 Hz, 2 H,
Fmoc), 8.18 (d, J ϭ 8.5 Hz, 2 H, NH) ppm. 13C NMR (100 MHz,
[D6]DMSO): δ ϭ 18.9, 19.7, 31.0, 47.4, 52.6, 55.3, 58.0, 66.6, 121.0,
126.1, 126.2, 128.0, 128.5, 135.5, 141.5, 144.6, 156.5, 172.5,
172.8 ppm. HRMS (ES-TOF): m/z calcd. for C27H31N4O5 [M ϩ
H]ϩ: 491.2294; found 491.2299.
Fmoc-His(τ-Trt)-Val-OMe (6): White solid (348 mg, 92%). RP-
HPLC (gradient 1): tR ϭ 29.5 min. RP-HPLC (gradient 3): tR
ϭ
48.0 min. TLC (system A): Rf ϭ 0.55. 1H NMR (400 MHz,
CDCl3): δ ϭ 0.88 (d, J ϭ 6.6 Hz, 6 H, CγValϪH), 2.14Ϫ2.19 (m, 1
H, CβValϪH), 3.03 (dd, JЈ ϭ 15.0, JЈЈ ϭ 6.3 Hz, 1 H, CβHisϪH),
3.13 (dd, JЈ ϭ 15.0, JЈЈ ϭ 4.9 Hz, 1 H, CβHisϪH), 3.68 (s, 3 H,
COOCH3), 4.24Ϫ4.28 (br. m, 1 H, OCH2CH), 4.33Ϫ4.41 (m, 2 H,
OCH2CH), 4.51 (dd, JЈ ϭ 8.3, JЈЈ ϭ 4.9 Hz, 1 H, CαValϪH), 4.61
(dd, JЈ ϭ 11.9, JЈЈ ϭ 6.3 Hz, 1 H, CαHisϪH), 6.72 (br. s, 1 H, im),
6.90 (br. s, J ϭ 6.6 Hz, 1 H, NH), 7.11Ϫ7.13 (m, 6 H, Trt),
7.28Ϫ7.35 (m, 11 H, Trt ϩ Fmoc), 7.39Ϫ7.43 (m, 3 H, Fmoc ϩ
im), 7.64 (br. d, J ϭ 7.0 Hz, 2 H, Fmoc), 7.78 (d, J ϭ 7.5 Hz, 2 H, Fmoc-
Fmoc), 7.84 (br. d, J ϭ 8.0 Hz, 1 H, NH) ppm. 13C NMR Dmbz)-
(100 MHz, CDCl3): δ ϭ 18.3, 19.5, 31.0, 31.5, 47.5, 52.4, 55.3, 57.9, pended in dry CH2Cl2 (3 mL) in the presence of DIEA (38 µL,
D-His(τ-2,6-Dmbz)-L-Val-OMe (9) and Fmoc-D-His(π-2,6-
L-Val-OMe (10): Compound 8 (98 mg, 0.20 mmol) was sus-
67.7, 75.8, 119.9, 120.3, 125.7, 127.5, 128.1, 128.5, 130.2, 137.4,
138.8, 141.6, 142.7, 144.3, 144.4, 156.7, 171.8, 172.5 ppm. HRMS
0.22 mmol). 2,6-Dimethoxybenzoyl chloride (44 mg, 0.22 mmol)
was added and the mixture was stirred at room temperature for
(ES-TOF): m/z calcd. for C46H45N4O5 [M ϩ H]ϩ: 733.3390; 1 h, during which time the residual solid dissolved. The solution
found 733.3391.
was diluted with CH2Cl2 (2 mL) and washed with 10% citric acid
(5 mL), 5% NaHCO3 (5 mL), and brine (5 mL). After standing
over Na2SO4, the organic phase was filtered and the solvents were
evaporated to dryness. The resulting white foam (119 mg) con-
tained a mixture of 9 and 10 in approximately 7:2 molar ratio,
according to RP-HPLC analysis. The residue was chromato-
graphed on a silica-gel column (120 ϫ 23 mm) with the mobile
phase being EtOAc/n-hexane, 2:1 (v/v). The fractions containing 9
(46 mg) and the fractions containing a mixture of 9 and 10 (ca. 1:6
molar ratio; 44 mg) were collected and concentrated to yield white
solid materials.
Fmoc- -His(τ-Trt)-
D
L-Val-OMe
(7):
Fmoc--His(τ-Trt)-OH
(620 mg, 1.0 mmol) and HBTU (380 mg, 1.0 mmol) were weighed
in a vial bearing a septum and then DMF (2.5 mL) was added.
DIEA (190 µL, 1.1 mmol) was injected and the mixture was reacted
for 1 min at room temperature. The solution was taken up with a
syringe and transferred into a sealed vial containing HCl·H--Val-
OMe (183 mg, 1.1 mmol) and DIEA (190 µL, 1.1 mmol) in DMF
(1.0 mL). The coupling reaction was carried out at room tempera-
ture for 2 h. DMF was evaporated in vacuo and the oily residue
was partitioned between EtOAc (12 mL) and 10% citric acid
(10 mL). The organic phase was washed with H2O (10 mL), brine
(10 mL), 5% NaHCO3 (15 mL), H2O (15 mL), and brine (15 mL),
dried with Na2SO4 and the solvents evaporated to dryness. The oily
Fmoc-D-His(τ-2,6-Dmbz)-L-Val-OMe (9): RP-HPLC (gradient 3):
1
tR ϭ 36.9 min. TLC (system A): Rf ϭ 0.61. H NMR (400 MHz,
CDCl3): δ ϭ 0.85 (d, J ϭ 7.2 Hz, 3 H, CγValϪH), 0.89 (d, J ϭ
residue was chromatographed on a silica-gel column (75 ϫ 30 mm) 6.6 Hz, 3 H, CγValϪH), 2.12Ϫ2.16 (br. m, 1 H, CβValϪH),
with a mobile phase of EtOAc/n-hexane, 1:1 (v/v). The fractions
containing the product were concentrated to yield a white powder
3.01Ϫ3.14 (br. m, 2 H, CβHisϪH), 3.71 (s, 3 H, COOCH3), 3.77 (s,
6 H, OCH3), 4.25 (t, J ϭ 7.2 Hz, 1 H, OCH2CH), 4.38 (d, J ϭ
Eur. J. Org. Chem. 2003, 2454Ϫ2461
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2459