Constraints and Steric Bulk in Philanthotoxins
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 1 65
(1H, s, H-j), 7.49-7.36 (3H, m, H-b, H-f, and H-g), 4.59 (1H,
dd, J ) 8.4 and 7.0 Hz, H-R), 3.33-3.01 (10H, m, H-1, H-3,
H-8, H-10, and H-â), 2.90-2.75 (4H, m, H-4 and H-7), 2.17
(2H, t, J ) 7.4 Hz, H-2′), 2.09 (2H, m, H-9), 1.84-1.69 (6H, m,
H-2, H-5, and H-6), 1.51 (2H, sx, J ) 7.4 Hz, H-3′), 0.80 (3H,
t, J ) 7.4 Hz, H-4′). 13C NMR (75 MHz, CD3OD): δ 176.2
(C-1′), 174.8 (CdO, amino acid), 135.9, 134.9, 133.9 (C-a, C-d,
and C-i), 129.2, 128.9, 128.7 and 128.6 (C-c, C-e, C-h, and C-j),
128.4 (C-b), 127.2 and 126.8 (C-f and C-g), 56.9 (C-R), 48.5 and
48.3 (C-4 and C-7), 46.4 (C-3), 46.1 (C-8), 39.1 (C-2′), 38.9
(C-10), 38.1 (C-1), 37.1 (C-â), 27.7 (C-2), 25.7 (C-9), 24.6 (2C,
C-5 and C-6), 20.6 (C-3′), 14.2 (C-4′). HRMS: calcd for
C27H44N5O2 [M + H]+ 470.34895, found 470.34851.
Pentafluorophenyl DL-2-[(9H-Fluoren-9-ylmethoxycar-
bonyl)amino]-3,3-diphenylpropanoate (11c). The Fmoc
group was attached to DL-â,â-diphenylalanine (15a, 500 mg,
2.07 mmol) using general procedure B, which afforded 11b (937
mg, 98%) as a foam. TLC: Rf 0.28 (hexanes-EtOAc-AcOH
20:10:1). The latter compound (779 mg, 1.68 mmol) was
esterified using general procedure C to give 11c (855 mg, 81%).
TLC: Rf 0.18 (hexanes-EtOAc 7:1). 1H NMR (300 MHz,
CDCl3): δ 7.68 (2H, d, J ) 7.2 Hz, H-y), 7.41 (2H, d, J ) 7.2
Hz, H-v), 7.35-7.15 (14H, m, H-w, H-x, and 2 × Ph), 5.47 (1H,
t, J ) 8.5 Hz, NH), 5.10 (1H, d, J ) 8.5 Hz, H-R), 4.53 (1H, d,
J ) 8.5 Hz, H-â), 4.52-4.36 (2H, m, Fmoc-CH2), 4.21 (1H, t, J
) 6.9 Hz, Fmoc-CH). 13C NMR (100 MHz, CDCl3): δ 168.0
(CdO, amino acid), 155.7 (CdO, Fmoc), 143.7 (2C, C-u), 141.5
(2C, C-z), 141.0 (2C, C-2′/C-6′, Pfp), 139.5 (C-4′, Pfp), 139.3
and 138.8 (2C, C-a), 137.5 (2C, C-3′/C-5′, Pfp), 129.3 and 129.1
(each 4C, C-b and C-c), 128.6 and 128.2 (2C, C-x), 127.9 and
127.8 (2C, C-d), 127.2 (2C, C-w), 125.2 (2C, C-v), 125.1 (C-1′
Pfp), 120.1 (2C, C-y), 67.7 (Fmoc-CH2), 57.2 (C-R), 53.2 (C-â),
47.1 (Fmoc-CH). HRMS: calcd for C36H25F5NO4Na [M + Na]+
652.15177, found 652.15103.
DL-N-[3-[[4-[(3-Aminopropyl)amino]butyl]amino]pro-
pyl]-3,3-diphenyl-2-[(1-oxobutyl)amino]propanamide Tris-
(trifluoroacetate) (11). Using general procedure H, resin
loaded with 3a (250 mg, loading approximately 0.80 mmol/g,
0.20 mmol) was elongated successively with 11c and with
pentafluorophenyl butyrate to give, after deprotection and
cleavage, philanthotoxin 11 (71 mg, 42%) as a syrup. 1H NMR
(300 MHz, CD3OD): δ 7.39-7.12 (10H, m, Ph-H), 5.24 (1H,
d, J ) 12.0 Hz, H-R), 4.37 (1H, d, J ) 12.0 Hz, H-â), 3.20-
2.96 (8H, m, H-1, H-7, H-8, and H-10), 2.87-2.73 (2H, m, H-4),
2.90-2.75 (1H, m, HA-3), 2.37-2.25 (1H, m, HB-3), 2.10 (2H,
p, J ) 7.7 Hz, H-9), 2.01 (2H, t, J ) 7.3 Hz, H-2′), 1.87-1.67
(4H, m, H-5 and H-6), 1.67-1.52 (2H, m, H-2), 1.45-132 (2H,
sx, J ) 7.3 Hz, H-3′), 0.70 (3H, t, J ) 7.3 Hz, H-4′). 13C NMR
(75 MHz, CD3OD): δ 175.3 (C-1′), 173.6 (CdO, amino acid),
142.3 and 141.7 (2C, C-a), 129.5, 129.3 and 129.0 (8C, C-b and
C-c), 127.9 (2C, C-d), 57.6 (C-R), 54.5 (C-â), 48.2 and 47.1 (C-7
and C-4), 45.8 (2C, C-3 and C-8), 39.6 (C-2′), 37.8 (C-10), 36.5
(C-1), 27.2 (C-2), 25.4 (C-9), 24.3 (2 C, C-5 and C-6), 20.3
(C-3′), 13.8 (C-4′). HRMS: calcd for C29H46N5O2 [M + H]+
496.36460, found 496.36428.
65.84; H, 3.56; F, 16.80; N, 2.51. Found: C, 65.91; H, 3.44; F,
16.93; N, 2.39.
L-N-[3-[[4-[(3-Aminopropyl)amino]butyl]amino]propyl]-
2-(1-oxobutyl)isoquinoline-3-carboxylamide Tris(trifluo-
roacetate) (12). Pfp ester 12b (346 mg, 0.435 mmol) and
compound 3b (199 mg, 0.386 mmol) were dissolved in dry CH2-
Cl2 (2.0 mL), Et3N (55 µL, 0.40 mmol) was added, and the
mixture was stirred for 2 h at room temperature, when it was
diluted with CH2Cl2 (20 mL) and washed with water (2 × 15
mL). The organic phase was dried (Na2SO4), filtered, and
concentrated. The crude product (0.398 mmol) was dissolved
in dry THF (3.5 mL), DBU (79 µL, 0.079 mmol) and 1-oc-
tanethiol (10 equiv) were added, and then the mixture was
stirred for 2 h at room temperature. The reaction mixture was
concentrated, and the Fmoc-deprotected compound was iso-
lated in quantitative yield by VLC. TLC: Rf 0.20 (CH2Cl2-
MeOH-32% aqueous NH3 200:10:1). The N-butyryl group was
attached to the latter product (255 mg, 0.386 mmol) using
general procedure F to yield the Boc-protected intermediate
(267 mg, 95%). Deprotection of the latter (221 mg, 0.302 mmol)
was performed according to general procedure G to give 12
1
(221 mg, 95%; overall yield: 90%) as a syrup. H NMR (400
MHz, CD3OD, T ) 328 K): δ 7.29-7.18 (4H, m, 4 Ar-H), 4.56
(1H, t, J ) 5.5 Hz, H-R), 4.72 (2H, br s, H-γ), 3.30-3.13 (6H,
m, H-1, H-3, and H-8), 3.09 (4H, t, J ) 7.5 Hz, H-4 and H-7),
2.88 (2H, t, J ) 7.5 Hz, H-10), 2.75 (2H, m, H-â), 2.78-2.18
(2H, t, J ) 7.4 Hz, H-2′), 2.27-2.04 (2H, p, J ) 7.5 Hz, H-9),
1.88-1.63 (8H, m, H-2, H-5, H-6, and H-3′), 1.06-0.95 (3H, t,
J ) 7.4 Hz, H-4′). 13C NMR (100 MHz, CD3OD): δ 176.1
(C-1′), 175.4 (CdO, amino acid), 135.2-127.4 (6C, Ph-C, one
major and several minor rotamers), 56.4 (C-R), 48.3 and 48.2
(C-4 and C-7), 47.4 (C-γ), 45.9 and 45.8 (C-3 and C-8), 37.8
(C-10), 36.7 (C-2′), 36.4 (C-1), 32.9 (C-â), 27.5 (C-2), 25.4
(C-9), 24.3 and 24.2 (C-5 and C-6), 19.3 (C-3′), 14.2 (C-4′); only
signals for the major rotamer have been assigned. HRMS:
calcd for C23H42N5O2 [M + H]+ 432.33330, found 432.33308.
Pentafluorophenyl 2-[(9H-Fluoren-9-ylmethoxycar-
bonyl)amino]indan-2-carboxylate (13c). The Fmoc group
was introduced to 13a (hydrochloride; 255 mg, 1.19 mmol)
using general procedure B to give 13b (82 mg, 17%). TLC: Rf
0.09 (hexanes-EtOAc-AcOH 20:10:1). The carboxylic acid 13b
(131 mg, 0.33 mmol) was esterified using general procedure
C to give 13c (147 mg, 79%). TLC: Rf 0.64 (hexanes-EtOAc
2:1). 1H NMR (300 MHz, CDCl3): δ 7.74 (2H, br d, J ) 7.4 Hz,
H-y), 7.56 (2H, br d, J ) 7.4 Hz, H-v), 7.38 (2H, br t, J ) 7.4
Hz, H-x), 7.29 (2H, br t, J ) 7.4 Hz, H-w), 7.26-7.24 (4H, m,
H-b and H-c), 5.49 (1H, s, NH), 4.60 (2H, d, J ) 6.3 Hz, Fmoc-
CH2) 4.21 (1H, t, J ) 6.3 Hz, Fmoc-CH), 3.85 (2H, d, J ) 16.5
Hz, HA-â), 3.40 (2H, d, J ) 16.5 Hz, HB-â). 13C NMR (75 MHz,
CDCl3): δ 169.1 (CdO, amino acid), 155.4 (CdO, Fmoc), 143.5
(2C, C-u), 141.2 (2C, C-z), 140.7 (2C, C-2′/C-6′, Pfp), 139.5
(C-4′, Pfp), 138.7 (2C, C-a), 137.8 (2C, C-3′/C-5′, Pfp), 127.7
and 127.0 (2C, C-x and C-w), 127.4 (2C, C-b), 124.9 (2C, C-v),
124.7 (2C, C-c), 124.5 (C-1′, Pfp), 120.0 (2C, C-y), 67.4 (Fmoc-
CH2), 66.3 (C-R), 47.3 (Fmoc-CH), 44.1 (2C, C-â). HRMS: calcd
for C31H20F5NO4Na [M + Na]+ 588.12047, found 588.12006.
Pentafluorophenyl L-2-(9H-Fluoren-9-ylmethoxycar-
bonyl)-1,2,3,4-tetrahydroisoquinoline-3-carboxylate (12).
Compound 6a (507 mg, 1.27 mmol) was esterified using
general procedure C to give 6b (544 mg, 76%) as a white foam.
TLC: Rf 0.56 (hexanes-EtOAc 2:1). [R] 25: 0° (c 0.68, CHCl3).
1H NMR (400 MHz, CDCl3): δ 7.77*, 7.7D6 (each 2H, d, J ) 7.5
Hz, H-y), 7.62, 7.57* (each 2H, t, J ) 7.8 Hz, H-v), 7.44-7.37
(2H, m, H-x), 7.34-7.12 (6H, m, H-w, H-b, H-c, H-d, and H-e),
5.42 (1H, dd, J ) 5.8 and 3.6 Hz, H-R), 5.22* (1H, t, J ) 4.9
Hz, H-R), 4.82-4.45 (4H, m, Fmoc-CH2, H-γ), 4.35, 4.28* (each
1H, t, J ) 6.8 Hz, Fmoc-CH), 3.43-3.29 (2H, m, H-â). 13C NMR
(100 MHz, CDCl3): δ 168.3 (CdO, amino acid), 143.8 (2C, C-u),
141.5 (2C, C-z), 133.0, 132.4, 131.2, 128.6, 128.1, 127.9, 127.7,
127.5, 127.3, 126.7, 126.5, 125.1 and 120.2 (C-v, C-w, C-x, C-y,
C-b. C-c, C-d, C-e, mixture of rotamers), 68.5* and 68.3 (Fmoc-
CH2), 54.1* and 53.7 (C-R), 47.3 (Fmoc-CH), 44.8* and 44.7
(C-γ), 32.5* and 31.7 (C-â); (*) denotes signals arising from a
minor amide bond rotamer. Anal. Calcd for C31H20F5NO4: C,
DL-N-[3-[[4-[(3-Aminopropyl)amino]butyl]amino]pro-
pyl]-2-[(1-oxobutyl)amino]indan-2-carboxylamide Tris-
(trifluoroacetate) (13). Pfp ester 13c (100 mg, 0.177 mmol)
and compound 3b (89 mg, 0.177 mmol) were coupled using
general procedure D to yield the conjugate (159 mg, 100%) as
a foam. TLC: Rf 0.13 (hexanes-EtOAc 1:1). Fmoc deprotection
of the conjugate (127 mg, 0.141 mmol) was performed using
general procedure E to give the amine intermediate (92 mg,
96%) as an oil. TLC: Rf 0.21 (CH2Cl2-MeOH-32% aqueous
NH3 200:10:1). The N-butyryl group was introduced to the
latter (76 mg, 0.112 mmol) according to general procedure F
to give the Boc-protected product (62 mg, 44%) as an oil. TLC:
Rf 0.25 (hexanes-EtOAc 1:4). Deprotection of the latter (36
mg, 0.048 mmol) as described in general procedure G yielded
13 (40 mg, 100%; overall yield: 71%) as a syrup. 1H NMR (300
MHz, CDCl3): δ 7.74 (2H, d, J ) 7.3 Hz, H-y), 7.55 (2H, d, J
) 7.3 Hz, H-v), 7.38 (2H, t, J ) 7.3 Hz, H-x), 7.29 (2H, t, J )
7.3 Hz, H-w), 7.24-7.18 (4H, m, H-b and H-c), 5.36 (1H, s,