556 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 4
Schiller et al.
Gen er a lized Cyclic Hexa p ep tid e Syn th esis. Assembly
of the peptides started with either 0.1 or 0.25 mmol of Fmoc-
L-Pro-2-chlorotrityl polystyrene resin and sequential addition
of the approriately protected N-R-Fmoc amino acids.27 Peptides
were removed from the resin using a solution of 0.40% TFA
in CH2Cl2. After 30 min, the slurry was filtered and washed
with additional TFA solution. The filtrate was concentrated,
azeotroped with benzene, and dried. Cyclization occurred by
suspending the peptide (1 equiv) in anhydrous DMF, along
with NaHCO3 (15 equiv) and DPPA (1.5 equiv).28 This solution
was stirred for at least 18 h at 0 °C and monitored by HPLC.
Once complete, the DMF was removed and the peptide was
subjected to silica gel chromatography. The protecting groups
were removed from the cyclic peptides using TFA:CH2Cl2:EDT:
H2O (50:45:3:2), followed by precipitation with ethyl ether:
hexane. The crude peptide was filtered, dried, subjected to
HPLC purification, and lyophilized as an amorphous solid.
dimethylphenol (24.4 g, 0.20 mol) in MeOH (406 mL) and concd
HCl (162 mL) was added a mixture of KI (22.4 g, 0.14 mol)
and KIO3 (13.8 g, 4.5 mmol). The mixture was initially cooled
in an ice bath and allowed to warm to room temperature
overnight. The precipitated product was collected by filtration
and washed with MeOH/H2O (1:1). The crude product was
dissolved in toluene, filtered through Celite, and precipitated
with pentane to give 9 (12.2 g, 24%): mp 133-135 °C (lit.29
131 °C); TLC Rf 0.85 (I).
3,5-Dim eth yl-4-iod op h en yl Aceta te (10).45 To a solution
of 9 (12.0 g, 48.8 mmol), in pyridine (12.0 mL) was added acetic
anhydride (6.9 mL, 72.6 mmol). The reaction was heated to
50 °C for 30 min, cooled to room temperature and diluted with
0.5 N HCl (200 mL) to effect crystallization. The product was
washed with 120 mL 0.5 N HCl followed by 60 mL portions of
H2O until the final wash reached a pH of 5. Vacuum drying
yielded 13.4 g (95%) of crystalline 10: mp 46-47 °C (lit.45 51
°C); TLC Rf 0.9 (II).
Meth yl 3-(2′,6′-Dim eth yl-4′-acetoxyph en yl)acr ylate (11).
To a solution of 10 (5.0 g, 17.24 mmol), methylacrylate (1.63
mL, 18.08 mmol), tri-o-tolylphosphine (0.27 g, 0.91 mmol), and
NEt3 (4.77 mL, 34.0 mmol) was added Pd(AcO)2 (71.6 mg, 0.32
mmol) in MeCN (24.3 mL). The solution was heated to reflux
for 28 h prior to cooling to room temperature. The catalyst
was filtered through Celite, and the solvent removed in vacuo.
The crude product was dissolved in H2O (30 mL) and extracted
with EtOAc (3 × 40 mL). The combined EtOAc extracts were
washed with brine (3 × 30-mL), treated with activated carbon
and dried over MgSO4. Solvent removal in vacuo yielded a red
oil which crystallized upon standing at 5 °C for 18 h. Recrys-
tallization from ethyl acetate/hexane afforded 3.80 g (89%) of
11: mp 59-60 °C; TLC Rf 0.48 (II); 1H NMR (500 MHz, CDCl3)
δ 2.26 (s, 3H, COCH3), 2.36 (s, 6H, Ar-CH3), 3.80 (s, COOCH3),
6.03 (d, 1H, J ) 16.4 Hz), 6.78 (s, 2H, Ar), 7.76 (d, 1H, J )
16.4 Hz).
Cyclo(1-Na l-D-Tr p -Tyr -Th r -P h e-P r o) (2): [R]25 -0.70°
D
1
(c 0.19, MeOH); H NMR (500 MHz, CD3OD) δ 0.78 (m, 2H),
0.86, (m, 1H), 1.15 (d, 3H, J ) 6.4 Hz), 1.37 (m, 1H), 1.73 (m,
1H), 2.49 (dd, 1H, J ) 5.4, 13.9 Hz), 2.56 (dd, 1H, J ) 5.0,
14.2 Hz), 2.78 (m, 2H), 2.88 (m, 1H), 3.03 (m, 2H), 3.18 (m,
1H), 3.41 (dd, 1H, J ) 7.7, 15.6 Hz), 3.52 (dd, 1H, J ) 7.4,
13.6 Hz), 3.61 (d, 1H), 4.11 (dd, 1H, J ) 4.7, 6.4 Hz), 4.15 (dd,
1H, J ) 5.1, 8.0 Hz), 4.30 (dd, 1H, J ) 5.6, 10.8 Hz), 4.38 (d,
1H, J ) 4.6 Hz), 4.44 (dd, 1H, J ) 5.5, 9.9 Hz), 4.82 (d, 1H, J
) 7.6 Hz), 6.56 (s, 4H), 6.80 (s, 1H), 7.06 (t, 1H, J ) 7.5), 7.14
(t, 1H, J ) 10.0 Hz), 7.18 (m, 2H), 7.25 (m, 6H), 7.37 (d, 1H,
J ) 8.2 Hz), 7.42 (d, 1H, J ) 7.9 Hz), 7.44 (m, 1H), 7.73 (d,
1H, J ) 8.1 Hz), 7.83 (d, 1H, J ) 7.8 Hz), 8.22 (d, 1H, J ) 8.4
Hz); 13C NMR (125 MHz, CD3OD) δ 18.9, 22.2, 28.4, 31.6, 36.4,
36.6, 38.6, 47.3, 55.3, 55.8, 56.2, 57.3, 57.9, 62.5, 68.6, 110.3,
112.6, 116.4, 119.3, 119.9, 122.6, 124.4, 124.9, 126.4, 126.8,
128.1, 128.4, 128.6, 128.7, 128.9, 129.8, 130.0, 130.6, 130.9,
133.6, 134.3, 135.4, 136.8, 138.0, 157.2, 171.4, 171.9, 172.6,
173.1, 173.7, 174.2; HRMS (ESI) m/z calcd for C51H53N7O8
+
Meth yl 3-(2′,6′-Dim eth yl-4′-a cetoxyp h en yl)p r op ion a te
(12). To a solution of 11 (3.72 g, 15 mmol) in MeOH/AcOH
(1:1) (50 mL) was added 10% Pd-C (2.42 g). The reaction
vessel was purged with argon and pressurized to 60 psi with
H2. The reaction mixture was stirred vigorously and the
temperature raised to 60 °C. When the pressure dropped to 0
psi, the mixture was cooled to 10 °C, vented with argon and
repressurized to 60 psi with H2. This procedure was repeated
10 times until TLC analysis (III) indicated complete reduction.
The mixture was filtered through Celite and the solvents
removed in vacuo to yield 3.05 g (81.3%) of 12 as an oil: TLC
Rf 0.36 (II), Rf 0.76 (III); 1H NMR (400 MHz, CDCl3) δ 2.28 (s
3H, OCH3), 2.32 (s, 6H, CH3 Ar), 2.44 (t, 2H, CH2), 2.94 (t,
2H, CH2), 3.71 (s, 3H, COOCH3), 6.74 (s, 2H, Ar).
Na 914.3853, found 914.3830 [(M + Na)+].
Cyclo(2-Na l-D-Tr p -Tyr -Th r -P h e-P r o) (3): [R]25 -2.01°
D
1
(c 0.17, MeOH); H NMR (500 MHz, CD3OD) δ 0.80 (m, 2H),
1.12 (d, 3H, J ) 6.4 Hz), 1.25 (m, 1H), 1.68 (m, 1H), 2.65 (dd,
1H, J ) 5.0, 14.2 Hz), 2.70 (dd, 1H, J ) 6.4, 14.0 Hz), 2.78
(dd, 1H, J ) 8.3, 14.2 Hz), 2.90 (m, 2H), 3.06 (m, 3H), 3.20 (m,
2H), 3.60 (d, 1H, J ) 7.6 Hz), 4.09 (dd, 1H, J ) 4.5, 6.4 Hz),
4.20 (dd, 1H, J ) 5.0, 8.3 Hz), 4.37 (m, 1H), 4.44 (dd, 1H, J )
6.5, 9.0 Hz), 4.76 (dd, 1H, J ) 6.7, 7.7 Hz), 6.57 (d, 2H, J )
6.0 Hz), 6.64 (d, 2H, J ) 6.5 Hz), 6.89 (s, 1H), 7.05 (t, 1H, J )
7.5 Hz), 7.13 (m, 1H), 7.25 (m, 6H), 7.37 (m, 4H), 7.44 (s, 1H),
7.64 (m, 2H), 7.74 (m, 1H); 13C NMR (125 MHz, CD3OD) δ 17.5,
20.6, 26.9, 30.1, 35.3, 37.3, 38.3, 45.9, 53.9, 54.5, 54.6, 55.9,
56.4, 61.1, 67.1, 109.1, 111.2, 115.0, 117.9, 118.5, 121.2, 123.1,
125.3, 125.7, 126.9, 127.0, 127.1, 127.2, 127.3, 127.6, 127.7,
128.6, 129.2, 129.5, 132.5, 133.4, 134.1, 135.5, 136.7, 155.9,
170.0, 170.6, 171.1, 171.8, 172.3, 173.0; HRMS (ESI) m/z calcd
for C51H53N7O8 + Na 914.3853, found 914.3853 [(M + Na)+].
3-(2′,6′-Dim eth yl-4′-h ydr oxyph en yl)pr opion ic Acid (Dh p)
(13). A mixture of 12 (3.05 g, 12.2 mmol) and 12 N HCl (14
mL) was heated to reflux for 7.5 h, followed by a cooling to 4
°C overnight. The solid product was collected and recrystallized
from boiling water to give 13 (2.06 g, 87%): mp 123-124 °C;
1
TLC Rf 0.18 (II), Rf 0.77 (III); H NMR (400 MHz, CDCl3) δ
CHO-Dm t-cyclo(D-Or n -2-Na l-D-P r o-Gly) (5). To a solu-
tion of peptide 7 (15 mg, 0.02 mmol) at 0 °C were added DIPEA
(0.005 mL, 0.029 mmol) and p-nitrophenyl formate (0.304 mL,
0.029 mmol). The reaction was stirred for 2 h and allowed to
warm to room temperature. Solvent was removed and the
2.32 (s, 6H, CH3 Ar), 2.44 (t, 2H, CH2), 2.94 (t, 2H, CH2), 6.81
(s, 2H, ar); FAB-MS m/e 195.
O-Boc Der iva tive of 3-(2′,6′-Dim eth yl-4′-h yd r oxyp h en -
yl)p r op ion ic Acid [Dh p (OBoc)] (14). To a solution of 13
(2.06 g, 10.61 mmol) in THF/H2O (1:1) (24 mL) at 0 °C were
added DMAP (0.288 g, 2.35 mmol), NEt3 (3.86 mL, 27.56 mmol)
and Boc2O (2.67 g, 11.67 mmol) in the THF/H2O (1:1) (10 mL).
The reaction stirred for 1.5 h before the THF was removed in
vacuo. Ethyl acetate (30 mL) was added, followed by addition
of a 5% aqueous solution of KHSO4 until a pH of 6 was reached.
The organic phase was separated, dried over MgSO4, and
evaporated to yield the crude product as an oil. Crystallization
from ethyl acetate/hexane afforded crystalline 14 (2.35 g,
peptide was directly purified by HPLC (12.2 mg, 92.4%): [R]25
D
-1.02° (c 0.26, MeOH); 1H NMR (500 MHz, CD3OD) δ 1.03
(m, 1H), 1.28 (m 3H), 1.54 (m, 3H), 1.67 (m, 1H), 2.26 (s, 6H),
2.30 (m, 1H), 2.82 (d, 1H, J ) 13.2 Hz), 2.96 (dd, 1H, J ) 4.8,
13.8 Hz), 3.10 (m, 2H), 3.43 (m, 3H), 3.53 (m, 1H), 4.10 (dd,
1H, J ) 4.5, 8.0 Hz), 4.28 (m, 2H), 4.32 (dd, 1H, J ) 5.4, 11.0
Hz), 4.43 (dd, 1H, 4.3, 10.9 Hz), 6.50 (s, 2H), 7.36 (dd, 1H, J )
1.7, 8.4 Hz), 7.48 (m, 2H), 7.69 (s, 1H), 7.83 (m, 3H), 8.09 (d,
1H, J ) 1.0 Hz); 13C NMR (125 MHz, CD3OD) δ 20.3, 23.5,
25.0, 27.2, 29.9, 31.9, 37.9, 38.8, 43.2, 48.3, 54.2, 54.7, 56.2,
62.9, 116.2, 125.2, 127.2, 127.6, 128.6, 128.7, 129.1, 129.4,
134.1, 134.4, 134.9, 139.9, 157.1, 163.6, 171.8, 174.0, 174.1,
174.3, 174.5; HRMS (ESI) m/z calcd for C37H44N6O7 + Na
707.3169, found 707.3169 [(M + Na)+].
1
80%): mp 108-110 °C; TLC Rf 0.87 (I); H NMR (400 MHz,
CDCl3): δ 1.55 (s, 9H, C(CH3)3), 2.31 (s, 6H, CH3 Ar), 2.45 (t,
2H, CH2), 2.95 (t, 2H, CH2), 6.82 (s, 2H, Ar); FAB-MS m/e 295.
Dh p -D-Or n -2-Na l-D-P r o-Gly-OH (15). Peptide synthesis
was performed by the manual solid-phase technique using a
Merrifield Boc-Gly-OH resin (1% cross-linked, 100-200 mesh,
3,5-Dim eth yl-4-iod op h en ol (9).29 To a solution of 3,5-