Amamistatin B and Analogs
EtOAc (30 mL), washed with H2O (15 mL) and brine (20 mL),
dried over Na2SO4, filtered, and concentrated to a white residue
(305 mg). Purification by flash chromatography (SiO2, 9:1 CH2-
Cl2/EtOAc) gave 12 as a colorless oil (61 mg, 0.074 mmol, 21%)
along with recovered 11 (73 mg, 49%): 1H NMR (500 MHz,
CDCl3) δ 8.15 (s, 1H), 7.55-7.51 (m, 1H), 7.46-7.25 (m, 15H),
6.28-6.21 (m, 1H), 5.17-5.00 (m, 2H), 4.88-4.79 (m, 2H), 4.78-
4.75 (m, 2H), 4.71-4.69 (m, 1H), 4.41-4.31 (m, 2H), 3.62-3.46
(m, 4H), 2.06-1.35 (m, 12H), 1.33-1.14 (m, 14H), 1.17 (s, 3H),
0.86-0.81 (m, 3H); 13C NMR (125 MHz, CDCl) δ 174.2, 171.7,
170.3, 163.1, 156.4, 136.5, 135.0, 134.3, 129.6, 129.5, 129.2, 129.0,
128.8, 128.6, 128.5, 128.2, 128.1, 79.7, 77.7, 66.8, 54.6, 52.9, 52.1,
46.2, 46.1, 43.9, 31.9, 31.7, 31.0, 30.2, 29.3, 29.1, 27.6, 26.3, 26.2,
25.9, 24.9, 23.5, 23.0, 14.1; HRMS (FAB) m/z calcd for C47H65N4O9
[M + H]+ 829.4746, found 829.4745; [R]20D +0.9 (c 2.95, CHCl3).
(FAB) m/z calcd for C18H35N2O5 [M + H]+ 327.2642, found
327.2621. [R]20 +9.6 (c 0.70, CHCl3).
D
((S)-2,2-Dimethyl-1-oxo-1-((S)-2-oxoazepan-3-ylamino)decan-
3-yl) (2S)-2-(Benzyloxycarbonylamino)-6-(N-(benzyloxy)forma-
mido)hexanoate 21. To a solution of S-3 (90 mg, 0.22 mmol) and
20 (60 mg, 0.18 mmol) in dry CH2Cl2 (2 mL) was added DCC (61
mg, 0.29 mmol) followed by 4-pyrrolidinopyridine (5 mg, 0.04
mmol). The reaction was stirred at room temperature for 2 days.
The solution was diluted with CH2Cl2 (5 mL) and filtered to remove
the white solid. The filtrate was diluted with CH2Cl2 (50 mL),
washed with H2O and brine, dried over Na2SO4, filtered, and
concentrated. The crude material was purified by flash chroma-
tography (SiO2, 2:1 EtOAc/CH2Cl2) to give 21 as a colorless oil
(73 mg, 0.10 mmol, 55%): 1H NMR (300 MHz, CDCl3) δ 8.16 (s,
1H), 7.56-7.51 (m, 1H), 7.37-7.28 (m, 10H), 6.47-6.41 (m, 1H),
5.98 (d, 1H, J ) 8.7 Hz), 5.11-4.97 (m, 2H), 4.80 (s, 2H), 4.51-
4.45 (m, 1H), 4.39-4.31 (m, 1H), 3.57-3.40 (m, 1H), 3.25-3.07
(m, 4H), 2.09-1.40 (m, 12H), 1.31-1.09 (m, 12H), 1.22 (s, 3H),
1.15 (s, 3H), 0.90-0.81 (m, 3H); HRMS (FAB) m/z calcd for
C40H59N4O8 [M + H]+ 723.4327, found 723.4348.
((S)-1-((S)-1-(Hydroxy)-2-oxoazepan-3-ylamino)-2,2-dimethyl-
1-oxodecan-3-yl) 6-(N-(Hydroxy)formamido)-(2R)-2-(2-(2-hy-
droxyphenyl)-5-methyloxazole-4-carboxamido)hexanoate 15
(amamistatin B). A solution of 12 (20.5 mg, 0.025 mmol) in MeOH
(3 mL) was purged with Ar for 5 min, 10 wt % Pd on carbon (7.8
mg) was added, and the solution was purged again for 3 min. The
reaction was bubbled with H2 for 30 s and stirred under 1 atm H2
for 1.25 h. The catalyst was removed by gravity filtration and rinsed
with MeOH (15 mL). The solution was concentrated to give 13 as
a colorless residue (13.2 mg). 2,5-Dioxopyrrolidin-1-yl 2-(2-
hydroxyphenyl)-5-methyl oxazole-4-carboxylate 14 (9.6 mg, 0.030
mmol), 13, and NaHCO3 (17.1 mg, 0.204 mmol) were dissolved
in H2O (0.6 mL) and THF (0.6 mL). More NaHCO3 (5.5 mg) was
added to bring the pH to 8. The reaction was stirred overnight at
room temperature and then concentrated under reduced pressure
to a clumpy white residue. The crude material was dissolved in
CH3CN/H2O and purified by reversed-phase prep TLC (25:75 H2O/
CH3CN, 1.5 plates used) to give 15 as a white residue (4.5 mg,
0.006 mmol, 25%): (many peaks doubled due to formamide
((S)-2,2-Dimethyl-1-oxo-1-((S)-2-oxoazepan-3-ylamino)decan-
3-yl) 6-(N-(Benzyloxy)formamido)-(2S)-2-(5-methyl-2-phenylox-
azole-4-carboxamido)hexanoate 23. To a solution of 21 (67 mg,
0.093 mmol) in CH2Cl2 (0.7 mL) was added 33 wt % HBr in acetic
acid (0.7 mL), and the reaction was stirred for 30 min at room
temperature. Volatiles were removed under reduced pressure. The
resulting orange oil was dissolved in saturated NaHCO3 (10 mL)
and extracted with CH2Cl2 (3 × 7 mL). The organic solution was
dried over Na2SO4, filtered, and concentrated under reduced pressure
to a colorless residue (45 mg, 0.77 mmol, 83%). The residue was
dissolved in dry CH2Cl2 (1.0 mL) along with 5-methyl-2-pheny-
loxazole-4-carboxylic acid 2 (17 mg, 0.084 mmol). HOBt (10 mg,
0.076 mmol) was added, and the solution was cooled in an ice
bath. EDC (18 mg, 0.092 mmol) was added, and the reaction
mixture was stirred in an ice bath for 20 min and at room
temperature for 40 h. The solution was diluted with EtOAc (15
mL), washed with H2O (10 mL), saturated NaHCO3, 5% citric acid,
and brine, dried over Na2SO4, filtered, and concentrated under
reduced pressure. The crude material was purified by flash
chromatography (SiO2, 5:1 EtOAc/CH2Cl2) to give 23 as a colorless
oil (12 mg, 0.016 mmol, 20%): 1H NMR (600 MHz, CDCl3) δ
8.16 (s, 1H), 8.01 (s, 1H), 7.46-7.44 (m, 4H), 7.38-7.29 (m, 6H),
6.28-6.21 (m, 1H), 4.80 (s, 2H), 4.51-4.49 (m, 1H), 4.44-4.40
(m, 1H), 3.58-3.52 (m, 1H), 3.33-3.12 (m, 4H), 2.68 (s, 3H),
2.13-1.94 (m, 4H), 1.84-1.71 (m, 4H), 1.51-1.38 (m, 4H), 1.36-
1
rotamers) H NMR (600 MHz, DMSO) δ 10.29 (s, 1H), 9.88 (s,
0.5H), 9.71 (s, 1H), 9.44 (s, 0.5H), 8.88-8.81 (m, 1H), 8.20 (s,
0.5H), 7.87 (s, 0.5H), 7.78 (dd, 1H, J ) 1.8 Hz, 6 Hz), 7.46-7.43
(m, 1H), 7.41-7.38 (m, 1H), 7.04 (d, 1H, J ) 8.4 Hz), 6.99-6.96
(m, 1H), 5.08-5.06 (m, 1H), 4.49-4.42 (m, 1H), 4.41-4.36 (m,
1H), 3.87-3.82 (m, 1H), 3.46-3.36 (m, 3H), 2.63 (s, 3H), 1.87-
1.84 (m, 3H), 1.76-1.67 (m, 1H), 1.62-1.46 (m, 5H), 1.41-1.05
(m, 15H), 1.04 (s, 3H), 1.03 (s, 3H), 0.81-0.75 (m, 3H); 13C NMR
(150 MHz, DMSO) δ 173.3, 171.7, 168.6, 160.8, 157.2, 157.0,
155.9, 152.4, 150.6, 137.0(imp.), 134.3(imp.), 132.6, 128.5, 126.8-
(imp.), 126.5, 123.7(imp.), 119.7, 117.2, 110.4, 78.0, 52.3, 52.0,
50.9, 45.6, 34.3(imp.), 31.2, 31.0, 30.8, 30.0, 29.7, 28.9, 28.6, 28.4,
27.7, 27.0, 25.6, 25.5, 24.4, 22.8, 22.0, 15.8, 13.8, 11.3; HRMS
(FAB) m/z calcd for C36H54N5O10 [M + H]+ 716.3865, found
716.3866; LC/MS (5-80% CH3CN/10 mM ammonium acetate) tR
10.63, m/z for [M + H]+ 716.5, 769.5 (+Fe).
1.11 (m, 12H), 1.18 (s, 3H), 1.16 (s, 3H), 0.86-0.80 (m, 3H); 13
C
NMR (150 MHz, CDCl3) δ 177.9, 175.6, 174.4, 171.8, 163.1, 162.1,
153.6, 130.8, 130.1, 129.7, 129.3, 129.0, 128.8, 128.6, 127.0, 126.6,
78.0, 77.7, 52.5, 52.4, 46.4, 46.1, 42.4, 32.4, 32.0, 31.5, 31.3, 29.8,
29.5, 29.3, 29.1, 28.1, 26.9, 26.4, 23.9, 22.8, 14.3, 12.0; HRMS
(FAB) m/z calcd for C43H60N5O8 [M + H]+ 774.4436, found
774.4426; LC/MS (5%-80% CH3CN/10 mM ammonium acetate)
tR 11.55, m/z for [M + H]+ 774.5.
(S)-3-Hydroxy-2,2-dimethyl-N-((S)-2-oxoazepan-3-yl)decana-
mide 20. To a solution of 4 (150 mg, 0.69 mmol) and (S)-3-
aminoazepan-2-one hydrochloride 19 (113 mg, 0.69 mmol) in
CH3CN (4.5 mL) were added Et3N (97 µL, 0.69 mmol), HOBt (93
mg, 0.69 mmol) and EDC (145 mg, 0.76 mmol) sequentially. The
solution was stirred at room temperature overnight. The reaction
mixture was diluted with EtOAc (75 mL), washed with H2O (30
mL), saturated NaHCO3 (2 × 40 mL), H2O (30 mL), 5% citric
acid (2 × 40 mL), and brine (40 mL), dried over Na2O4, filtered,
and concentrated to a colorless oil. Purification by flash chroma-
tography (SiO2, 1:1-1:2 hexanes/EtOAc) gave 20 as a colorless
oil (126 mg, 0.39 mmol, 56%): 1H NMR (300 MHz, CDCl3) δ
7.27 (d, 1H, J ) 6.9 Hz), 6.73 (t, 1H, J ) 6.0 Hz), 4.53-4.43 (m,
1H), 3.62 (br s, 1H), 3.48-3.41 (m, 1H), 3.27-3.21 (m, 2H), 2.04-
1.96 (m, 2H), 1.86-1.69 (m, 2H), 1.58-1.37 (m, 2H), 1.34-1.21
(m, 12H), 1.20 (s, 3H), 1.14 (s, 3H), 0.86-0.81 (m, 3H); 13C NMR
(75 MHz, CDCl3) δ 177.6, 175.9, 77.4, 52.2, 46.0, 42.1, 31.9, 31.6,
31.0, 29.6, 29.3, 28.9, 28.0, 26.7, 23.5, 22.7, 20.4, 14.1; HRMS
((S)-2,2-Dimethyl-1-oxo-1-((S)-2-oxoazepan-3-ylamino)decan-
3-yl) 6-(N-(Hydroxy)formamido)-(2S)-2-(5-methyl-2-phenylox-
azole-4-carboxamido)hexanoate 24. A solution of 23 (6.8 mg,
0.009 mmol) in MeOH (1 mL) was purged with Ar for 5 min, 10
wt % Pd on carbon (1.5 mg) was added, and the solution was purged
again for 2 min. The reaction was bubbled with H2 for 30 s, stirred
under 1 atm H2 for 5.5 h, and bubbled with H2 again for 15 min.
The catalyst was removed by gravity filtration and rinsed well with
MeOH. LCMS showed starting material remaining in the filtrate.
The solution was concentrated under reduced pressure to a volume
of 1 mL and purged with Ar. Pd on carbon (1 mg, 10 wt %) was
added, and the solution was purged again. The reaction was stirred
under 1 atm H2 for 2.5 h, filtered, and concentrated. Purification
by reversed phase prep TLC (75% CH3CN/H2O, 1/2 plate) to
remove residual starting material gave 24 as a white residue (2
mg, 0.003 mmol, 33%): (many peaks doubled due to formamide
J. Org. Chem, Vol. 73, No. 3, 2008 1023