10.1002/asia.201700203
Chemistry - An Asian Journal
FULL PAPER
give pure 11 (8.0 mg) as a colorless solid. m.p. 140–142 °C; 1H NMR
(500 MHz, CDCl3, 300 K): δ = 9.49 (s, 1H), 9.41 (s, 1H), 7.96 (dd, J = 7.8,
1.4 Hz, 1H), 7.93 (dd, J = 7.8, 1.0 Hz, 1H), 7.89 (d, J = 7.8 Hz, 2H), 7.72
(d, J = 7.6 Hz, 2H), 7.47 (d, J = 7.5 Hz, 2H), 7.41 (d, J = 7.5 Hz, 2H),
7.37–7.29 (m, 8H), 7.24 (m, 2H), 6.29 (d, J = 7.4 Hz, 1H), 5.19 (d, J = 7.8
Hz, 1H), 5.14 (d, J = 12.0 Hz, 1H), 5.08 (d, J = 12.4 Hz, 1H), 4.69 (q, J =
7.0 Hz, 1H), 4.22 (s, 1H), 3.90 (s, 3H), 3.87 (s, 3H), 1.62–1.57 (m, 3H),
1.52 (s, 9H), 1.41–1.30 (m, 2H), 1.26 (t, J = 7.1 Hz, 1H), 0.91 (dd, J = 9.8,
6.5 Hz, 6H), 0.83 ppm (dd, J = 10.1, 6.1 Hz, 6H); 13C NMR (126 MHz,
CDCl3, 300 K): δ = 170.3, 169.4, 167.43, 167.35, 166.6, 165.5, 156.0
(carbonyl), 144.2, 143.2, 138.6, 137.9, 136.4, 135.0, 134.64, 134.50,
134.3, 132.5, 130.47, 130.43, 130.24, 130.19, 129.6, 128.8, 128.5, 128.1,
128.1, 127.2, 126.01, 125.84, 125.6, 125.0 (aromatic), 81.1, 67.0, 54.1,
52.58, 52.45, 40.9, 28.2, 24.81, 24.64, 23.0, 22.8, 22.2, 21.6 ppm
(aliphatic); IR (ATR): ν = 2359, 2342, 1708, 1498, 1456, 1283, 1254,
1201, 1151, 1118, 751, 721, 696, 670, 635, 619 cm–1; MS (ESI-TOF):
m/z calcd for C54H60N4O11 + Na+: 963.4 [11 + Na+]; found: 963.4;
elemental analysis calcd (%) for C54H60N4O11 + 1.5H2O: C 67.00, H 6.56,
N 5.79; found: C 67.05, H 6.63, N 5.47.
127.21, 126.04, 125.98, 125.7, 125.1 (aromatic), 81.0, 66.9, 54.2, 52.8,
52.54, 52.51, 40.8, 40.3, 28.2, 24.9, 24.59, 24.54, 22.88, 22.85, 22.6,
22.34, 22.14, 21.6 ppm (aliphatic) (One of the aromatic signals appears
to be overlapped with other signals.); IR (ATR): ν = 2362, 1709, 1498,
1283, 1254, 1150, 1117, 1066, 971, 838, 794, 751, 695, 679, 669, 650,
628, 606 cm–1; MS (ESI-TOF): m/z calcd for C75H82N6O15 + H+: 1307.6
[12 + H+]; found: 1307.6; elemental analysis calcd (%) for C75H82N6O15
+
H2O: C 67.96, H 6.39, N 6.34; found: C 67.69, H 6.53, N 6.23.
cyclo-(L-Leu-Zbp(Me))3 (1a). The crude product of the former reaction
(nearly pure 12, 354 mg, ~0.271 mmol) was placed in an eggplant flask.
To the flask was added CH2Cl2 (16.5 mL) and trifluoroacetic acid (16.5
mL) consecutively and the compound was completely dissolved. The
mixture was stirred for 30 min at room temperature. The solvent was
removed under reduced pressure to give brown oil. The residue was
dissolved in CHCl3 and washed with water three times. The organic layer
was concentrated under reduced pressure to give nearly pure Cbz-(L-
Leu-Zbp(Me))3-OH (353.0 mg, ~0.282 mmol, ~104%) as a colorless solid.
Although this crude contained a small amount of impurity, this was used
for the next reaction without further purification to avoid loss. The
complete removal of trifluoroacetic acid was confirmed by 19F NMR
analysis. This crude (nearly pure Cbz-(L-Leu-Zbp(Me))3-OH, 353 mg,
~0.282 mmol) was placed in a two-necked flask under an N2 atmosphere.
Dry CH3OH (35 mL) was added to the flask to dissolve the compound
completely. To the solution was added 10% Pd(OH)2/C (67.6 mg, 20
wt%) which was suspended in dry CH3OH (7 mL). The atmosphere in the
flask was replaced with H2, and the mixture was then stirred for 50 min at
room temperature. After the reaction, Pd(OH)2/C was filtered off, and the
filtrate was then concentrated under reduced pressure to give nearly pure
H-(L-Leu-Zbp(Me))3-OH (290 mg, ~0.260 mmol, ~96% in two steps) as
colorless solid. Although this crude contained a small amount of impurity,
this was used for the next reaction without further purification to avoid
loss. This crude product (nearly pure H-(L-Leu-Zbp(Me))3-OH, 290 mg,
~0.260 mmol) and N-HBTU (104 mg, 0.273 mmol, 1 equiv) were placed
in a two-necked flask consecutively under an N2 atmosphere. Dry DMF
(23.0 mL) was added to the flask to dissolve the compounds completely.
After the addition of DIEA (50.0 µl, 0.287 mmol, 1 equiv), the mixture was
stirred for 40 min at room temperature. The solution was then diluted with
AcOEt (100 mL) and washed with water (500 mL), brine (500 mL),
saturated Na2CO3 aq (500 mL), and water (500 mL). The organic layer
was concentrated under reduced pressure to give a crude product.
Purification was performed by short column chromatography (SiO2, φ =
1.6 cm, h = 2 cm for 47.3 mg of the crude material, φ = 3.2 cm, h = 2 cm
for 189 mg of the crude material, CHCl3/AcOEt = 1/1) and GPC (CHCl3)
to give pure 1a (82.9 mg, 0.0754 mmol, 28% from compound 12) as a
colorless solid. The yield from monomer 8 is 22%. m.p. 180–183 °C; 1H
NMR (500 MHz, CDCl3, 300 K): δ = 9.26 (s, 3H, NH), 7.98 (dd, J = 7.9,
1.5 Hz, 3H, ArH), 7.67 (d, J = 8.2 Hz, 6H, ArH), 7.50 (dd, J = 7.7, 1.4 Hz,
3H, ArH), 7.40 (d, J = 8.2 Hz, 6H, ArH), 7.36 (t, J = 7.8 Hz, 3H, ArH),
6.72 (d, J = 8.0 Hz, 3H, NH), 4.66 (td, J = 8.9, 4.7 Hz, 3H, Leu αH), 3.96
(s, 9H, OCH3), 1.65–1.57 (m, 6H, Leu βH, Leu γH), 1.32–1.26 (m, 3H,
Leu βH), 0.91 (d, J = 6.2 Hz, 9H, Leu δH), 0.87 ppm (d, J = 6.4 Hz, 9H,
Leu δH); 13C NMR (126 MHz, CDCl3, 300 K): δ = 170.1 (Leu C=O), 167.7
(ζ-amino acid C=O), 167.4 (methyl ester C=O), 143.0 (Cq), 138.7 (Cq),
134.9 (Cq), 134.7 (CH), 133.5 (Cq), 130.3 (CH), 128.8 (CH), 127.1 (CH),
126.1 (CH), 125.1 (Cq), 52.70 (CH3), 52.61 (Leu αC), 41.7 (Leu βC), 24.9
(Leu γC), 23.1 (Leu δC), 21.9 ppm (Leu δC); IR (ATR): ν = 2360, 1646,
1498, 1455, 1281, 1147, 750, 668, 606, 588 cm–1; UV/vis (CHCl3, 298 K,
[1a] = 10 µM): λmax (ε) = 310 (0.811 × 104), 250 nm (8.69 × 104 M–1 cm–1);
fluorescence (CHCl3, 298 K, [1a] = 10 µM): λex = 268 nm; λem = 398 nm;
HRMS (ESI-TOF): m/z calcd for C63H66N6O12 + Na+: 1121.4636 [1a +
Na+]; found: 1121.4614.
Cbz-(L-Leu-Zbp(Me))3-OtBu (12). Compound 11 (378 mg, 0.401 mmol)
was placed in an eggplant flask. To the flask was added CH2Cl2 (26 mL)
and trifluoroacetic acid (26 mL) consecutively and the compound was
completely dissolved. The mixture was stirred for 30 min at room
temperature. The solvent was removed under reduced pressure to give
brown oil. The residue was dissolved in CHCl3 and washed with water
three times. The organic layer was concentrated under reduced pressure
to give Cbz-(L-Leu-Zbp(Me))2-OH (363 mg, 0.410 mmol, 102%) as a
colorless solid. The complete removal of trifluoroacetic acid was
confirmed by 19F NMR analysis. Cbz-(L-Leu-Zbp(Me))2-OH (351 mg,
0.397 mmol, 1 equiv), compound 9 (176 mg, 0.400 mmol, 1 equiv), and
N-HBTU (152 mg, 0.401 mmol, 1 equiv) were placed in a two-necked
flask consecutively under an N2 atmosphere. Dry DMF (3.0 mL) was
added to the flask to dissolve the compounds completely. After the
addition of DIEA (70 µL, 0.40 mmol, 1 equiv), the mixture was stirred for
50 min at room temperature. Then the solution was diluted with AcOEt
(30 mL) and washed with water (30 mL), brine (30 mL), saturated
Na2CO3 aq (30 mL), and water (30 mL). The organic layer was
concentrated under reduced pressure to give nearly pure 12 (460 mg,
~0.352 mmol, ~88% from compound 11) as a colorless powder. Although
this crude contained a small amount of impurity, this was used for the
next reaction without further purification to avoid loss. Purification for
obtaining the physical data was performed by reprecipitation (crude 27.1
mg, CHCl3/n-hexane = 1/10), column chromatography (SiO2, φ = 1 cm, h
= 10 cm, CHCl3/CH3OH = 20/1), GPC (CHCl3), and reprecipitation
(CHCl3/n-hexane = 1/10) to give pure 12 (2.6 mg) as a colorless solid.
Another purification for 13C NMR data was also performed by short
column chromatography (crude 71.2 mg, SiO2, φ = 1 cm, h = 1 cm,
CHCl3/CH3OH = 20/1) and GPC (CHCl3) to give pure 12 (31.0 mg). m.p.
204–206 °C; 1H NMR (500 MHz, CDCl3, 300 K): δ = 9.73 (s, 1H), 9.52 (s,
1H), 9.35 (s, 1H), 7.95 (d, J = 8.5 Hz, 1H), 7.93 (dd, J = 8.3 Hz, 1.5 Hz,
1H), 7.87 (d, J = 7.0 Hz, 1H), 7.87 (d, J = 8.0 Hz, 2H), 7.72 (d, J = 7.0 Hz,
2H), 7.58 (d, J = 7.4 Hz, 2H), 7.49 (d, J = 8.0 Hz, 1H), 7.43–7.40 (m, 4H),
7.35–7.32 (m, 5H), 7.31–7.26 (m, 6H), 7.22–7.19 (m, 1H), 6.96 (d, J =
6.3 Hz, 1H), 6.34 (d, J = 8.9 Hz, 1H), 5.33 (d, J = 5.1 Hz, 1H), 5.11 (d, J =
12.3 Hz, 1H), 4.98 (d, J = 12.2 Hz, 1H), 4.76–4.68 (m, 1H), 4.51–4.44 (m,
1H), 4.20–4.14 (m, 1H), 3.91 (s, 3H), 3.89 (s, 3H), 3.79 (s, 3H), 1.70–
1.64 (m, 2H), 1.53 (s, 9H), 1.45–1.37 (m, 3H), 1.35–1.27 (m, 4H), 0.92 (d,
J = 6.4 Hz, 3H), 0.87 (d, J = 6.3 Hz, 3H), 0.73 ppm (dd, J = 9.2, 5.8 Hz,
12H); 13C NMR (126 MHz, CDCl3, 300 K): δ = 170.3, 169.6, 169.4,
167.38, 167.28, 167.24, 166.76, 166.56, 165.5, 156.0 (carbonyl), 144.1,
143.4, 143.1, 138.9, 138.4, 137.98, 137.97, 136.47, 136.46, 135.0,
134.73, 134.64, 134.54, 134.3, 134.1, 132.4, 132.2, 130.5, 130.27,
130.19, 130.08, 129.5, 128.54, 128.45, 128.28, 128.01, 127.97, 127.37,
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