454
G. Breckle et al. · Synthesis of Sventrin
115.68 (NCCHN), 79.50 (C(CH3)3), 74.26 (CPh3),
42.70 (NCH2), 28.44 (3C, C(CH3)3). Ð MS (ESI):
alkaloids has hardly been explored [18]. Due to its
N-methylation, cyclizations of sventrin (1) would
at most involve the pyrrole carbon atom, leading,
e. g., to analogs of N-methylisophakellin [19]. The
triple bond of dehydrooroidin (3) is designed to
prevent intramolecular cyclization and, instead, fa-
vor the formation of dimers.
m/z (%)
= Ð HRESIMS
481 (100) [M+].
C30H33N4O2 [M + H+]: calcd. 481.2603; found
481.2576. Ð C30H32N4O2 (480.6): calcd. C 74.97, H
6.71, N 11.66; found C 74.69, H 6.60, N 11.61.
4-(3-Amino-propenyl)-1-trityl-1H-imidazol-2-
ylamine (6)
Experimental Section
To a solution of the alkenylaminoimidazole 5
(100 mg, 0.2 mmol) in THF (7 ml) was added p-
toluenesulfonic acid monohydrate (2.5 g) in small
portions over a period of 7 h. After addition of
saturated Na2CO3 (5 ml) and brine (5 ml) the re-
action mixture was extracted with THF (3 ¥ 5 ml),
dried (MgSO4) and concentrated in vacuo. Flash
chromatography (silica gel, CHCl3-MeOH-aq.
NH3 (70:10:1)) afforded 6 (61 mg, 78%) as a pale
yellow solid: M.p. 170 ∞C (decomp.) Ð UV/vis
(MeOH): λmax (lg ε) = 276 nm (4.03). Ð IR (KBr):
General
Unless otherwise noted, reagents were pur-
chased from commercial suppliers and used with-
out further purification. Reactions were controlled
by thin-layer chromatography (precoated silica gel
plate Merck F254). Flash chromatography was car-
ried out on silica gel (Merck, silica gel 60 (40Ð
63 µm)). Melting points are uncorrected. NMR
spectra were recorded on Varian 200 or 400 MHz
spectrometers. Chemical shifts refer to residual
solvent signals based on δTMS = 0. Mass spectra
were taken in EI, FAB (nitrobenzyl alcohol as ma-
trix), or ESI modes. Yields refer to purified com-
pounds.
ν = 3439, 3058, 1968, 1621, 1535, 1446, 1326, 965,
˜
748, 702 cmÐ1. Ð 1H NMR (399.92 MHz, CD3OD):
δ = 7.41Ð7.29 (m, 9H, phenyl-CH), 7.26Ð7.12 (m,
6H, phenyl-CH), 6.37 (s, 1H, NCCHN), 6.15 (d,
3
3J = 15.7 Hz, 1H, CH2CHCH), 6.10 (dt, J = 15.7,
4.5 Hz, 1H, CH2CH), 3.28 (d, 3J = 4.5 Hz, 2H,
NHCH2C). Ð 13C NMR (100.57, CD3OD): δ =
150.40 (NCNH2N), 141.45 (3C, phenyl-C), 133.31
(NCCHN), 129.68 (6C, phenyl-o-CH), 127.89 (6C,
phenyl-m-CH), 127.81 (3C, phenyl-p-CH), 126.52
(CH2CH), 121.51 (CH2CHCH), 114.60 (NCCHN),
74.20 (CPh3), 43.04 (NHCH2). Ð MS (FAB+): m/z
[3-(2-Amino-1-trityl-1H-imidazol-4-yl)-allyl]-
carbamic acid tert-butyl ester (5)
To a solution of the azidoalkynylimidazole 4 ([7],
1.10 g, 2.2 mmol) in dry THF (50 ml) at 0 ∞C was
added Red-Al (2.5 equiv., 65% wt in toluene) un-
der an argon atmosphere. After 30 min the reac-
tion mixture was quenched with saturated Na2CO3
(5 ml), followed by addition of brine (5 ml). The
mixture was extracted with EtOAc (3 ¥ 20 ml).
The combined organic layers were dried (MgSO4)
and concentrated in vacuo. The resulting residue
was purified by flash chromatography (silica gel,
EtOAc) to yield 5 (809 mg, 76%) as a pale yellow
solid. Crystallization from EtOAc afforded color-
less crystals: M.p. 160 ∞C (decomp.). Ð UV/vis
+
(%) = 381 (2) [M + H+], 243 (100) [CPh3 ]. Ð
HRFABMS C25H25N4 [M + H+]: calcd. 381.2058;
found 381.2079.
4,5-Dibromo-1-methyl-1H-pyrrole-2-carboxylic
acid [3-(2-amino-1-trityl-1H-imidazol-4-yl)-
allyl]-amide (8)
(4,5-Dibromo-1-methyl-1H-pyrrole-2-yl)-tri-chlo-
(CHCl3): λmax (lg ε) = 269 nm (4.17). Ð IR (KBr): romethylketone 7 ([14], 227 mg, 0.60 mmol) was
ν = 3444, 3059, 2976, 1713, 1617, 1534, 1493, 1447, added to a solution of 6 (150 mg, 0.40 mmol) in
˜
1365, 1248, 1170, 962, 747, 702 cmÐ1. Ð H NMR dry THF (15 ml). After 96 h the mixture was con-
1
(199.98 MHz, CDCl3): δ = 7.50Ð7.25 (m, 9H, phe- centrated in vacuo and purified by flash chroma-
nyl-CH), 7.26Ð7.15 (m, 6H, phenyl-CH), 6.28 (s, tography (silica gel, CHCl3-MeOH (10:1)) to yield
1H, NCCHN), 6.15 (d, 3J
= 15.4 Hz, 1H, 8 as a pale yellow solid (254 mg, 99%). M.p.
CH2CHCH), 5.98 (dt, 3J = 15.4, 5.5 Hz, 1H, 140 ∞C (decomp.) Ð UV/vis (CHCl3): λmax (lg ε) =
3
CH2CH), 4.58 (br. s, 1H, NH), 3.76 (dd, J = 5.5, 281 nm (4.34). Ð IR (KBr): ν = 3436, 1639, 1533,
˜
1
5.1 Hz, 2H, NHCH2C), 3.60 (s, 2H, NH2), 1.42 (s, 1492, 1447, 1254, 957, 747, 701 cmÐ1. Ð H NMR
9H, C(CH3)3). Ð 13C NMR (100.57, CDCl3): δ = (399.92 MHz, CDCl3): δ = 7.41Ð7.30 (m, 9H, phe-
155.70 (C = O), 149.57 (CNH2), 141.45 (3C, phe- nyl-CH), 7.21Ð7.14 (m, 6H, phenyl-CH), 6.57 (s,
3
nyl-C), 133.24 (NCCHN), 129.99 (6C, phenyl-o- 1H, BrCCH), 6.33 (s, 1H, NCCHN), 6.27 (d, J =
3
CH), 128.17 (6C, phenyl-m-CH), 128.07 (3C, phe- 15.4 Hz, 1H, CH2CHCH), 6.16 (dt, J = 15.4 Hz,
nyl-p-CH), 123.46 (CH2CH), 122.87 (CH2CHCH), 3J = 6.3 Hz, 1H, CH2CH), 5.95 (t, J = 5.2 Hz, 1H,
3
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