Journal of Medicinal Chemistry
Article
The solvent was removed by evaporation, and the residue was purified
by flash chromatography using hexane:AcOEt (1:2 v/v) to yield the
purified and lyophilized to yield 20 mg (82%) of 22 as a white powder.
1H NMR (300 MHz, D2O): δ 1.11 (d, J = 6.6 Hz, 3H), 1.15 (d, J = 6.6
Hz, 3H), 1.20−1.23 (m, 2H), 1.47−1.66 (m, 4H), 1.55 (t, J = 7.5 Hz,
3H), 1.56 (t, J = 7.5 Hz, 3H), 1.61 (d, J = 7.2 Hz, 3H), 1.80−1.98 (m,
7H), 2.28 (s, 3H), 2.30−2.33 (m, 1H), 3.01 (q, J = 7.5 Hz, 2H), 3.03
(q, J = 7.5 Hz, 2H), 3.32 (dd, J = 15.3 Hz, 10.8 Hz, 1H), 3.58 (dd, J =
15.3 Hz, 3.6 Hz, 1H), 4.32 (d, J = 4.8 Hz, 1H), 4.37 (d, J = 7.5 Hz,
1H), 4.57−4.64 (m, 2H), 4.71−4.75 (m, 1H), 7.55 (s, 1H), 8,84 (s,
1H). 13C NMR: δ 14.18, 14.34, 16.99, 17.84, 18.79, 22.10, 25.98,
26.06, 26.15, 26.25, 26.44, 27.04, 30.69, 32.46, 33.36, 33.87, 39.33,
49.99, 51.67, 52.43, 54.88, 59.26, 117.30, 130.23, 133.66, 172.63,
173.72, 173.75, 174.88. MALDI-TOF MS. Calcd, 633.324 for
C29H50N6O4S2Na; found, 633.299 for [M + Na]+. Peptide thioacetals
23−27 were similarly prepared as above.
26
desired product as an oil. Yield, 0.50 g (42%); [α]D +18.2 (c 0.6,
1
CHCl3). H NMR (300 MHz, CDCl3): δ 3.05 (dd, J = 15.0 Hz, 5.4
Hz, 1H), 3.16 (dd, J = 15.0 Hz, 5.4 Hz, 1H), 4.22 (t, J = 7.5 Hz, 1H),
4.97 (d, J = 7.5 Hz, 2H), 4.46 (dd, J = 6.9 Hz, 5.4 Hz, 1H), 6.45 (brd,
J = 6.9 Hz, 1H), 6.62 (s, 1H), 7.08−7.77 (m, 24H), 9.68 (brs). 13C
NMR: δ 27.24, 47.21, 59.89, 67.20, 75.37, 119.70, 119.85, 119.96,
125.24, 127.08, 127.54, 127.69, 128.02, 128.09, 128.13, 129.71, 135.88,
138.82, 141.29, 142,27, 142,47, 143.89, 156.39, 200.31.
Fmoc-His(Trt)-al 1-Octanol-ethylene Acetal [Fmoc-His(Trt)-
acetal] (19). To a stirred solution of Fmoc-His(Trt)-al (0.59 g, 0.98
mmol) and decane-1, 2, 10-triol 18 (0.19 g, 0.98 mmol) in CH2Cl2
(10 mL) was added BF3-Et2O (0.2 mL), and the mixture was stirred at
25 °C for 30 min. H2O (10 mL) was added, and the organic phase was
washed with H2O and dried on MgSO4. The solvent was evaporated to
yield 0.57 g (75%) of a white amorphous powder, and the product was
Ac-Asn-Val-Cha-His-(SEt)2 (23). Yield, 74%. 1H NMR (300
MHz, D2O): δ 0.99 (d, J = 6.9 Hz, 3H), 1.01 (d, J = 6.9 Hz, 3H),
1.00−1.12 (m, 2H), 1.33−1.56 (m, 4H), 1.43 (t, J = 7.5 Hz, 3H), 1.44
(t, J = 7.5 Hz, 3H), 1.67−1.92 (m, 7H), 2.18 (s, 3H), 2.18−2.22 (m,
1H), 2.78−2.96 (m, 4H), 3.31 (dd, J = 15.6 Hz, 10.8 Hz, 1H), 3.46
(dd, J = 15.3 Hz, 3.3 Hz, 1H), 4.21 (d, J = 5.1 Hz, 1H), 4.28 (d, J = 6.9
Hz, 1H), 4.45−4.50 (m, 1H), 4.60−4.65 (m, 1H), 4.86 (brt, J = 6.9
Hz, 1H), 7.43 (s, 1H), 8,74 (s, 1H). 13C NMR: δ 14.05, 14.23, 17.47,
18.65, 22.05, 25.85, 25.95, 26.02, 26.14, 26.32, 26.88, 30.60, 32.34,
33.18, 33.69, 36.44, 39.00, 50.67, 51.65, 52.25, 54.65, 59.17, 114.88,
130.00, 133.51, 172.53, 172.54, 173.80, 173.81, 174.36. MALDI-TOF
MS. Calcd, 654.347 for C30H52N7O5S2; found, 654.442 for [M + H]+.
Ac-Ser-Val-Cha-His-(SEt)2 (24). Yield, 21%. 1H NMR (300 MHz,
D2O): δ 0.84 (d, J = 6.9 Hz, 3H), 0.89 (d, J = 6.9 Hz, 3H), 0.90−1.00
(m, 2H), 1.15−1.36 (m, 4H), 1.27 (t, J = 7.5 Hz, 3H), 1.29 (t, J = 7.5
Hz, 3H), 1.54−1.69 (m, 7H), 2.03−2.10 (m, 1H), 2.06 (s, 3H), 2.746
(q, J = 7.5 Hz, 2H), 2.753 (q, J = 7.5 Hz, 2H), 3.07 (dd, J = 15.6 Hz,
11.1 Hz, 1H), 3.31 (dd, J = 15.6 Hz, 3.0 Hz, 1H), 3.81 (d, J = 6.3 Hz,
1H), 4.08 (d, J = 4.8 Hz, 1H), 4.13 (d, J = 7.2 Hz, 1H), 4.34 (dd, J =
9.0 Hz, 6.3 Hz, 1H), 4.43−4.53 (m, 2H), 7.26 (s, 1H), 8,55 (s, 1H).
13C NMR: δ 13.82, 14.01, 17.49, 18.44, 21.84, 25.72, 25.80, 25.86,
26.06, 26.20, 26.86, 30.17, 32.05, 32.94, 33.51, 38.90, 51.52, 52.23,
54.34, 55.62, 59.23, 61.20, 116.93, 130.04, 133.43, 171.97, 172.61,
174.05, 174.35. MALDI-TOF MS. Calcd, 627.336 for C29H51N6O5S2;
found, 627.332 for [M + H]+.
27
used for the next reaction without further purification: [α]D −6.3
(c 0.8, CHCl3). 1H NMR (300 MHz, CDCl3): δ 1.26−1.30 (m, 12H),
1.49−1.56 (m, 2H), 2.81−2.89 (m, 2H), 3.41−3.51 (m, 1H), 3.57−
3.63 (m, 2H), 3.92−4.06 (m, 2H), 4.11−4.29 (m, 4H), 4.98−5.04
(m, 1H), 5.43−5.57 (m, 1H), 6.68 (s, 1H), 7.06−7.75 (m, 24H).
13C NMR: δ 25.71, 25.84, 28.68, 29.35, 29.44, 29.52, 32.88, 33.25,
47.42, 53.42, 62.86, 67.09, 70.27, 75.38, 103.98, 120.02, 125.44,
127.19, 127.74, 128.00, 128.15, 128.87, 129.92, 137.77, 138.49, 141.38,
142.59, 144.20, 156.52, 162.49.
Solid-Phase Synthesis of the Peptide Thioacetal [Ac-Ala-Val-
Cha-His-(SEt)2] (22). To a stirred solution of 19 (0.37 g, 0.48 mmol)
in acetone (5 mL) was added Jones reagent (0.3 mL; 2.67 M solution)
at 0 °C, and the mixture was stirred for 40 min at 25 °C. 2-Propanol
(0.1 mL) was then added, and the mixture was filtered through a
Celite pad. The solvent was removed by evaporation, and the residue
was extracted with CHCl3. The organic layer was washed with H2O,
dried over MgSO4, and evaporated to yield 0.30 g (80%) of the
27
corresponding carboxylic acid 20 as an amorphous powder: [α]D
−
1
13.1 (c 0.8, CHCl3). H NMR (300 MHz, CDCl3): δ 1.26−1.58 (m,
12H), 2.31−2.41 (m, 2H), 2.86−2.95 (m, 2H), 3.45−3.52 (m, 1H),
3.95 (t, J = 6.9 Hz, 1H), 4.06−4.38 (m, 6H), 5.06 (d, J = 7.2 Hz, 1H),
6.69 (s, 1H), 6.99−7.74 (m, 24H). 13C NMR: δ 24.80, 28.93, 29.24,
34.32, 46.58, 47.15, 53.77, 66.85, 119.91, 125.29, 127.06, 127.66,
128.11, 128.23, 128.32, 128.47, 129.63, 141.20, 143.78, 155.60, 181.82.
The product was used without further purification.
Ac-Ser(Ac)-Val-Cha-His-(SEt)2 (28). 1H NMR (300 MHz, D2O):
δ 0.82 (d, J = 6.6 Hz, 3H), 0.89 (d, J = 6.6 Hz, 3H), 0.91−0.96 (m,
2H), 1.18−1.35 (m, 4H), 1.27 (t, J = 7.5 Hz, 3H), 1.29 (t, J = 7.5 Hz,
3H), 1.55−1.69 (m, 7H), 2.04−2.10 (m, 1H), 2.07 (s, 3H), 2.10 (s,
3H), 2.746 (q, J = 7.5 Hz, 2H), 2.755 (q, J = 7.5 Hz, 2H), 3.09 (dd, J =
15.3 Hz, 10.8 Hz, 1H), 3.32 (dd, J = 15.3 Hz, 3.3 Hz, 1H), 4.09 (d, J =
4.5 Hz, 1H), 4.11 (d, J = 7.5 Hz, 1H), 4.27−4.42 (m, 3H), 4.50−4.54
(m, 1H), 7.28 (s, 1H), 8,60 (s, 1H). 13C NMR: δ 13.82, 14.02, 17.73,
18.46, 20.28, 21.81, 25.74, 25.80, 25.85, 26.06, 26.20, 26.80, 30.36,
32.10, 32.95, 33.53, 38.99, 51.51, 52.18, 52.73, 54.37, 59.28, 63.44,
116.94, 129.89, 130.05, 133.33, 170.68, 172.31, 173.47, 173.99, 174.27.
MALDI-TOF MS. Calcd, 669.347 for C31H53N6O6S2; found, 669.348
for [M + H]+.
Piperidine (20%) in DMF (3 mL) was added to a DMF-swelled
Rink amide resin [4-(2,4-dimethoxyphenyl-Fmoc-aminomethyl)-phe-
noxy resin] (140 mg, 89 μmol), and the mixture was agitated at 25 °C
for 20 min. The resin was washed with DMF, the above carboxylic acid
20 (0.28 g, 0.35 mmol), HOBt (54 mg, 0.35 mmol), DIEA (170 μL,
1.1 mmol), and DIPCDI (62 μL, 0.35 mmol) in DMF (2 mL) were
added, and the mixture was agitated at 25 °C for 10 h. Deprotection of
the Nα-Fmoc group by treatment with 20% piperidine in DMF and
coupling with Nα-Fmoc-β-cyclohexyl-L-alanin (Fmoc-Cha-OH) (170 mg,
0.44 mmol) using DIPCDI/HOBt were carried out as above. An
aliquot of the resulting resin [Fmoc-Cha-His(Trt)-acetal resin] (0.10 g,
40 μmol) was then used for coupling with Fmoc-Val-OH (68 mg, 0.20
mmol) and Fmoc-Ala-OH (62 mg, 0.20 mmol) and acetylation using
Ac2O (76 μL, 0.80 mmol) and DIEA (130 μL, 0.80 mmol) to afford
the Ac-Ala-Val-Cha-His(Trt)-acetal resin. To the dried resin were
added anisole (87 μL, 0.80 mmol) and TFA (1.5 mL), and the mixture
was agitated at 25 °C for 4 h. The mixture was filtered, and the solvent
was removed by evaporation. Ether and H2O were added to the
residue, and the aqueous phase was washed with ether. The solvent
was removed by lyophilization to afford 21 as a powder: MALDI-TOF
MS. Calcd, 690.456 for C35H60N7O7; found, 690.302 for [M + H]+.
To the crude product in AcOH (1 mL) were added ethanethiol
(0.13 mL, 1.8 mmol) and BF3-Et2O (100 μL). The mixture was stirred
at 25 °C for 2 h, and H2O (400 μL) was added. Then, 150 μL of the
solution was applied to a semipreparative HPLC column (Cosmosil
5C18, 10 mm × 250 mm) and eluted with a gradient of CH3CN (10−
60%, 60 min) in 0.1% aqueous TFA at 3 mL/min. The desired
thioacetal 22 eluted at 43.60 min. The rest of the solution was similarly
Ac-Thr-Val-Cha-His-(SEt)2 (25). Yield, 31%. 1H NMR (300
MHz, D2O): δ 0.75 (d, J = 6.6 Hz, 3H), 0.85 (d, J = 6.6 Hz, 3H),
0.84−0.95 (m, 2H), 1.11−1.30 (m, 4H), 1.13 (d, J = 6.6 Hz, 3H), 1.22
(t, J = 7.5 Hz, 3H), 1.23 (t, J = 7.5 Hz, 3H), 1.48−1.60 (m, 7H), 1.98−
2.02 (m, 1H), 2.02 (s, 3H), 2.69 (q, J = 7.5 Hz, 2H), 2.70 (q, J = 7.5
Hz, 2H), 3.03 (dd, J = 15.3 Hz, 11.1 Hz, 1H), 3.26 (dd, J = 15.3 Hz,
3.0 Hz, 1H), 4.01−4.08 (m, 3H), 4.22 (d, J = 5.7 Hz, 1H), 4.28−4.32
(m, 1H), 4.43−4.50 (m, 1H), 7.22 (s, 1H), 8,54 (s, 1H). 13C NMR: δ
13.76, 13.94, 17.73, 18.37, 18.88, 21.76, 25.67, 25.76, 25.80, 26.00,
26.16, 26.74, 38.91, 51.35, 52.12, 54.27, 59.23, 59.49, 67.04, 119.88,
129.79, 133.23, 171.74, 172,45, 174.02, 174.38. MALDI-TOF MS.
Calcd, 641.352 for C30H53N6O5S2; found, 641.283 for [M + H]+.
1
Ac-Ser-Ala-Val-Phe-His-(SEt)2 (26). Yield, 18%. H NMR (300
MHz, D2O): δ 0.65 (d, J = 6.6 Hz, 3H), 0.76 (d, J = 6.6 Hz, 3H), 1.15
(t, J = 7.5 Hz, 3H), 1.20 (t, J = 7.5 Hz, 3H), 1.26 (d, J = 7.2 Hz, 3H),
1.77−1.86 (m, 1H), 2.00 (s, 3H), 2.55 (q, J J = 7.5 Hz, 2H), 2.64 (q,
J = 7.5 Hz, 2H), 2.85−2.95 (m, 2H), 3.01 (dd, J = 15.3 Hz, 7.5 Hz,
1H), 3.21 (dd, J = 15.3 Hz, 3.0 Hz, 1H), 3.67 (d, J = 4.2 Hz, 1H),
7970
dx.doi.org/10.1021/jm200870n|J. Med. Chem. 2011, 54, 7962−7973