U. Diederichsen, H. W. Schmitt
FULL PAPER
20
[α]589 ϭ 38.5 (c ϭ 0.8, DMSO). Ϫ ESI MS; m/z (%): 336.1 (100) H, 8-H), 7.19 (d, J ϭ 3 Hz, 1 H, 8-H), 7.23 (d, J ϭ 3 Hz, 1 H, 8-
[M ϩ H]ϩ. Ϫ IR (KBr): ν˜ ϭ 3420 cmϪ1, 2983, 1699, 1680, 1565, H), 7.35 (d, J ϭ 3 Hz, 1 H, 8-H), 8.13 (s, 1 H, 2-H), 8.14 (s, 1 H,
1512, 1394, 1368, 1281, 1247, 1166. Ϫ 1H NMR (500 MHz, 2-H), 8.15 (m, 2 H, 2-H), 8.17 (m, 2 H, 2-H).
[D6]DMSO): δ ϭ 1.05 (s, br., 1.5 H, Boc-rotamer), 1.25 (s, br., 7.5
H-[(R)-β-Hal7CA]6-(S)-Lys-NH2 (ent-18): The synthesis fol-
H, Boc), 2.28Ϫ2.45 (m, 2 H, α-H), 4.00Ϫ4.15 (m, 2 H, γ-H),
4.18Ϫ4.29 (m, 1 H, β-H), 6.32Ϫ6.40 (m, 0.16 H, 7-H rotamer),
6.50 (d, J ϭ 3 Hz, 0.84 H, 7-H), 6.81 (d, J ϭ 8 Hz, 0.84 H,
BocNH), 6.90 (s, br., 2 H, NH2), 6.93Ϫ6.98 (m, 0.16 H, 8-H rot-
lowed the general method for SPPS and the spectroscopic data are
in agreement with those for enantiomer 18.
H-[(S)-β-Hal7CA]5-(R)-Lys-NH2 (19): The synthesis followed
amer), 7.00 (d, J ϭ 3 Hz, 0.84 H, 8-H), 8.01 (s, 1 H, 2-H). Ϫ 13C
NMR (125 MHz, [D6]DMSO): δ ϭ 28.1, 36.9, 46.9, 48.1, 77.7,
98.4, 102.3, 124.4, 149.8, 151.4, 154.7, 157.3, 172.0. Ϫ C15H21N5O4
(335.4): calcd. C 53.72, H 6.31, N 20.88; found C 53.77, H 6.34,
N 20.44.
the general method for SPPS. Ϫ ESI MS; m/z (%): 1231.6 (100) [M
ϩ H]ϩ, 616.6 (95) [M ϩ 2 H]2ϩ. Ϫ HPLC: 25.2 min, gradient
1
5Ϫ20% acetonitrile in 30 min. Ϫ H NMR (500 MHz, D2O): δ ϭ
1.32Ϫ1.49 (m, 2 H, H-Lys), 1.60Ϫ1.72 (m, 3 H, H-Lys), 1.73Ϫ1.82
(m, 1 H, H-Lys), 2.13Ϫ2.45 (m, 7 H, α-H), 2.48Ϫ2.59 (m, 2 H, α-
H), 2.70Ϫ2.79 (m, 1 H, α-H), 2.95 (t, J ϭ 8 Hz, 2 H, ε-H-Lys),
3.20 (m, 2 H, β-H, γ-H), 3.49 (m, 1 H, β-H, γ-H), 3.56 (m, 1 H, β-
H, γ-H), 3.67 (m, 1 H, β-H, γ-H), 3.70Ϫ3.82 (m, 2 H, β-H, γ-H),
3.88 (m, 1 H, β-H, γ-H), 4.03Ϫ4.11 (m, 1 H, γ-H), 4.18 (m, 1
H, α-H-Lys), 4.23Ϫ4.33 (m, 1 H, γ-H), 4.35Ϫ4.45 (m, 2 H, γ-H),
4.45Ϫ4.53 (m, 1 H, γ-H), 4.53Ϫ4.62 (m, 1 H, γ-H), 4.78Ϫ4.88 (m,
1 H, γ-H), 6.58Ϫ6.62 (m, 2 H, 7-H), 6.63 (d, J ϭ 3 Hz, 1 H, 7-H),
6.64 (d, J ϭ 3 Hz, 1 H, 7-H), 6.76 (d, J ϭ 3 Hz, 1 H, 7-H), 7.06
(m, 2 H, 8-H), 7.13 (d, J ϭ 3 Hz, 1 H, 8-H), 7.21 (d, J ϭ 4 Hz, 1
H, 8-H), 7.35 (d, J ϭ 4 Hz, 1 H, 8-H), 8.12 (m, 2 H, 2-H), 8.16
(m, 3 H, 2-H).
H-[(R)-β-Hal7CA]4-(S)-Lys-NH2 (20): The synthesis followed
the general method for SPPS. Ϫ ESI MS; m/z (%): 1036.6 (5) [M
ϩ Na]ϩ, 508.1 (23) [M ϩ 2 H]2ϩ, 339.2 (100) [M ϩ 3 H]3ϩ. Ϫ
HPLC: 22.1 min, gradient 5Ϫ25% acetonitrile in 30 min. Ϫ 1H
NMR (500 MHz, D2O): δ ϭ 1.29Ϫ1.50 (m, 2 H, H-Lys),
1.55Ϫ1.88 (m, 4 H, H-Lys), 2.13Ϫ2.25 (m, 1 H, α-H), 2.25Ϫ2.45
(m, 4 H, α-H), 2.48Ϫ2.65 (m, 2 H, α-H), 2.68Ϫ2.80 (m, 1 H, α-H),
2.95 (t, J ϭ 7 Hz, 2 H, ε-H-Lys), 3.41 (m, 1 H, β-H), 3.52 (m, 1
H, β-H), 3.66 (m, 1 H, β-H), 3.77 (m, 1 H, β-H), 3.80Ϫ3.95 (m, 3
H, γ-H), 4.05Ϫ4.21 (m, 2 H, α-H-Lys, γ-H), 4.22Ϫ4.32 (m, 1 H, γ-
H), 4.32Ϫ4.49 (m, 2 H, H-γ), 4.50Ϫ4.60 (m, 1 H, γ-H), 4.77Ϫ4.95
(m, 1 H, γ-H), 6.60Ϫ6.75 (m, 3 H, 7-H), 6.80 (d, J ϭ 3 Hz, 1 H,
7-H), 7.11 (d, J ϭ 3 Hz, 1 H, 8-H), 7.15 (d, J ϭ 3 Hz, 1 H, 8-H),
7.22 (d, J ϭ 3 Hz, 1 H, 8-H), 7.56 (d, J ϭ 3 Hz, 1 H, 8-H), 8.17
(s, 1 H, 2-H), 8.19 (s, 1 H, 2-H), 8.20 (s, 1 H, 2-H), 8.21 (s, 1 H,
2-H).
H-[(S)-β-HalA-(S)-β-Hal7CA]3-(R)-Lys-NH2 (21): The syn-
thesis followed the general method for SPPS. Ϫ ESI MS; m/z (%):
1451.6 (34) [M ϩ H]ϩ, 726.7 (100) [M ϩ 2 H]2ϩ. Ϫ HPLC: 12.3
min, gradient 10Ϫ20% acetonitrile in 30 min. Ϫ 1H NMR (500
MHz, D2O): δ ϭ 1.33Ϫ1.50 (m, 2 H, H-Lys), 1.59Ϫ1.82 (m, 4 H,
H-Lys), 2.16Ϫ2.49 (m, 8 H, α-H), 2.50Ϫ2.60 (m, 2 H, α-H),
2.68Ϫ2.80 (m, 2 H, α-H), 2.95 (t, J ϭ 7 Hz, 2 H, ε-H-Lys), 3.58
(m, 1 H, β-H, γ-H), 3.62Ϫ3.80 (m, 3 H, β-H, γ-H), 3.81Ϫ4.10 (m,
6 H, β-H, γ-H), 4.17 (m, α-H-Lys), 4.19Ϫ4.32 (m, 2 H, β-H, γ-H),
4.33Ϫ4.70 (m, 7 H, β-H, γ-H), 6.60Ϫ6.71 (m, 3 H, 7-H 7CA), 7.09
(d, J ϭ 3 Hz, 1 H, 8-H 7CA), 7.19 (d, J ϭ 3 Hz, 1 H, 8-H 7CA),
7.31 (d, J ϭ 3 Hz, 1 H, 8-H, 7CA), 8.05 (s, 2 H, 2-H, 2-H 7CA, 8-
H), 8.11 (s, 2 H, 2-H, 2-H 7CA, 8-H), 8.14 (s, 1 H, 2-H, 2-H 7CA,
8-H), 8.16 (s, 1 H, 2-H, 2-H 7CA, 8-H), 8.21 (s, 3 H, 2-H, 2-H 7CA,
8-H).
(R)-N-tert-Butoxycarbonyl-γ-(7-carba-9-adeninyl)-β-homoala-
nine (ent-2): (R)-N-Boc-γ-(6-azido-7-carba-9-purinyl)-β-homoala-
nine benzyl ester (ent-12) (1.17 g, 2.59 mmol) was dissolved in a
mixture of dioxane (40 ml), water (25 ml), and acetic acid (2 ml)
and reduced by Pd on charcoal (225 mg, 5% Pd on charcoal con-
taining 50.5% water) within 2 d. The precipitated nucleo amino
acid was separated from the charcoal by dissolving in acetonitrile/
methanol (3:2) and subsequent filtration. The solvent was evapo-
rated and the product isolated from the brown residue by crystalli-
zation with water/acetonitrile as a white solid giving 661 mg (76%,
> 99% e.e.). The analytical data of ent-2 and 2 were identical except
20
for [α]589 ϭ Ϫ38.8 (c ϭ 0.9, DMSO).
General Method for SPPS of β-PNA: Oligomerization was per-
formed as a solid-phase peptide synthesis on a 4-methylbenzhydryl-
amine-(MBHA-)polystyrene resin (50 mg, 15.45 mmol) loaded with
(R)-lysine(Z)-OH (Z ϭ benzyloxycarbonyl; 0.309 mmol/g) in a
small column. For each coupling step an excess of four equivalents
of N-tert-butoxycarbonyl-γ-(9-purinyl)-β-homoalanine (77.25
mmol) was used and activated by O-(7-azabenzotriazol-1-yl)-
1,1,3,3-tetramethyluronium hexafluorophosphate (HATU; 26.40
mg, 69.53 mmol) and N,N-diisopropylethylamine (26.3 µl, 154.5
mmol) in DMF (600 µl). After swelling of the resin for 20 min the
following procedure was repeated for every nucleo amino acid unit:
(1) deprotection twice, for 3 min with trifluoracetic acid/m-cresol
(95:5; 2 ml); (2) washing five times each with CH2Cl2/DMF (1:1; 2
ml) and pyridine (2 ml); (3) coupling step, 40Ϫ50 min gentle mov-
ing of the reaction column; (4) washing three times each with
CH2Cl2/DMF (1:1; 2 ml), DMF/piperidine (95:5; 2 ml), and
CH2Cl2/DMF (1:1; 2 ml). Finally, the β-PNA was washed twice
with TFA (2 ml) and cleaved from the solid support within 1 h
using 1.6 ml trifluoracetic acid/trifluormethanesulfonic acid/m-cre-
sol (8:1:1). The dark brown solution was concentrated to 400 µl,
and the β-PNA precipitated with diethyl ether (5 ml) as a white
solid. The β-PNA was separated using a centrifuge, followed by
purification with HPLC (RP-C18). The yield of each coupling step
was estimated from HPLC to be higher than 97%.
H-[(S)-β-Hal7CA]6-(R)-Lys-NH2 (18): The synthesis followed
the general method for SPPS. Ϫ ESI MS; m/z (%): 1470.6 (12) [M
ϩ Na]ϩ, 725.1 (100) [M ϩ 2 H]2ϩ. Ϫ HPLC: 27.0 min, gradient
1
5Ϫ20% acetonitrile in 30 min. Ϫ H NMR (500 MHz, D2O): δ ϭ
1.32Ϫ1.49 (m, 2 H, H-Lys), 1.58Ϫ1.83 (m, 4 H, H-Lys), 2.12Ϫ2.25
(m, 2 H, α-H), 2.26Ϫ2.46 (m, 7 H, α-H), 2.47Ϫ2.59 (m, 2 H, α-H),
General Method for UV Melting Curves and CD Spectroscopy:
2.69Ϫ2.79 (m, 1 H, α-H), 2.95 (t, J ϭ 8 Hz, 2 H, ε-H-Lys), The oligomers (2Ϫ5 µ) were dissolved in an Na2HPO4/H3PO4
3.28Ϫ3.43 (m, 3 H, β-H, γ-H), 3.54Ϫ3.62 (m, 1 H, β-H, γ-H), 3.60 buffer (pH ϭ 7.0, 0.01 ) containing NaCl (0.1 ) and placed in a
(m, 3 H, β-H, γ-H), 3.78Ϫ3.87 (m, 2 H, β-H, γ-H), 3.88Ϫ3.96 (m, UV cell (10 mm). For UV melting curves the following temperature
1 H, β-H, γ-H), 4.10Ϫ4.19 (m, 1 H, γ-H), 4.19 (m, 1 H, α-H-Lys), program was used to control the heating block: 90°C Ǟ Ϫ2°C (90
4.23Ϫ4.35 (m, 1 H, γ-H), 4.36Ϫ4.55 (m, 4 H, γ-H), 4.55Ϫ4.62 (1 min) Ǟ Ϫ2°C (10 min) Ǟ 90°C (190 min) Ǟ Ϫ2°C (190 min) Ǟ
H, γ-H), 4.78Ϫ4.89 (m, 1 H, γ-H), 6.60Ϫ6.75 (m, 5 H, 7-H), 6.89 Ϫ2°C (10 min) Ǟ 90°C (190 min) Ǟ Ϫ2°C (190 min). The tem-
(d, J ϭ 4 Hz, 1 H, 7-H), 7.09 (m, 2 H, 8-H), 7.12 (d , J ϭ 3 Hz, 1 perature for UV spectra was measured directly in the solution and
834
Eur. J. Org. Chem. 1998, 827Ϫ835