A. Weiß, U. Diederichsen
FULL PAPER
H80, RP-C18; 250ϫ20 mm, 4 µm, 80 Å with a flow rate of
10 mLmin–1 and J’sphere column ODS-H80, RP-C18;
150ϫ10 mm, 4 µm, 80 Å with a flow rate of 3 mL of min–1 were
used. Mass spectra were recorded with a Finnigan LCQ spectrome-
ter. High-resolution mass spectra were recorded with a Bruker
APEX-IV FT-ICR mass spectrometer. CD spectra were recorded
with a JASCO J-810 spectrometer equipped with a JASCO ETC-
505S/PTC-423S temperature controller. All CD-measurements
were carried out in Tris·HCl buffer (pH 7.5) or 100 mmol NaCl,
80 mmol Tris acetate buffer (pH 4.5) in a quartz cell of 1 cm path
length. Spectra represent the average of four scans after baseline
correction. Temperature-dependent UV spectra were measured
with a JASCO V-550 UV/Vis spectrometer equipped with a JASCO
ETC-505S/ETC-505T temperature controller. All measurements
were carried out in Tris·HCl buffer at pH 7.5 or 100 mmol NaCl,
80 mmol Tris acetate buffer at pH 4.5. The data were collected at
260 nm at a heating rate of 0.5 °Cmin–1 in a quartz cell of 1 cm
path length. The oligomer concentrations were determined based
on the absorption at 260 nm. The extinction coefficients of the
oligomers were calculated as the sum of the extinction coefficients
of the contained nucleobases.[24]
m/z (%) = 967.6 (100) [M + 2H]2+. HRMS (ESI): calcd. for
C91H148N30O17: 967.58921; found 967.58894 [M + 2H]2+
.
H-(β-HLys-β-HalT-ACHC)4-β-HGly)-NH2 (4): Analytical PR-
HPLC: tR = 18.9 min (gradient: 23–55% B in 30 min). MS (ESI):
m/z (%) = 997.6 (100) [M + 2H]2+. HRMS (ESI): calcd. for
C95H152N26O21: 997.58854; found 997.58811 [M + 2H]2+
.
H-(β-HLys-β-HalY-ACHC)4-β-HGly)-NH2 (5): Analytical PR-
HPLC: tR = 19.3 min (gradient: 45–90% B in 30 min). MS (ESI):
m/z (%) = 933.8 (100) [M + 2H]2+. HRMS (ESI): calcd. for
C99H152N18O17: 622.72670; found 622.72678 [M + 3H]3+
.
Supporting Information (see also the footnote on the first page of
this article): CD spectra of oligomers 1, 5, 1+2, and 2+3. UV and
CD spectra of the β-peptide with sequence TGGG. HR mass spec-
tra of all oligomers; Mass spectra of self-aggregating oligomers 1,
2, 3 and of dimer complex of 1+4.
Acknowledgments
Support by the Deutsche Forschungsgemeinschaft (DFG) and the
Fonds der Chemischen Industrie is gratefully acknowledged.
General Procedure for Solid-Phase β-Peptide Synthesis: β-Peptide
oligomers were synthesized by manual solid-phase peptide synthe-
sis in a small fritted glass column (ø = 1.5 cm). 4-Methylbenzhy-
drylamine-polystyrene (MBHA-PS) resin was used preloaded with
Boc-β-HGly-OH. Oligomers were synthesized on a 16.75 µmol
scale using N-Boc-β-HGly-MBHA-PS resin (25.0 mg, 0.67 mmol/g
loading); peptide coupling was performed at 50 °C. For each coup-
ling reaction an excess of 5.0 equiv. amino acid (83.75 µmol) was
used, preactivated with 1-[bis(dimethylamino)methyliumyl]-1H-
1,2,3-triazolo[4,5-b]pyridine 3-oxide hexafluorophosphate (HATU)
(4.5 equiv.), 1-hydroxy-7-azabenzotriazole (HOAt) (5.0 equiv. of a
0.5 solution in DMF), and DIEA (14 equiv.) in dry DMF
(400 µL). After swelling the loaded resin for 2 h in CH2Cl2 (2 mL),
the following procedure was applied for each coupling step: i. de-
protection twice for 3 min with TFA/m-cresol (95:5, 2 mL); ii.
washing three times with CH2Cl2/DMF (1:1, 2 mL), then five times
with pyridine (2 mL); iii. coupling steps, 2 h gentle movement at
50 °C; iv. washing with CH2Cl2/DMF (1:1, 3ϫ2 mL), DMF/piperi-
dine (95:5, 3ϫ2 mL), and then CH2Cl2/DMF (1:1, 3ϫ2 mL); v.
capping twice for 3 min with DMF/Ac2O/DIEA (8:1:1, 2 mL). Af-
ter the final coupling step the resin was washed with TFA
(3ϫ2 mL) and CH2Cl2 (5 ϫ2 mL), and dried overnight in vacuo.
The resin was transferred into a small glass vessel and suspended
in m-cresol/thioanisole/ethanedithiol (2:2:1, 500 µL). After stirring
for 30 min at room temperature, TFA (2 mL) was added and the
mixture cooled to –20 °C. Trifluoromethanesulfonic acid (TFMSA)
(200 µL) was added dropwise with vigorous stirring. The mixture
was warmed to room temperature over 1.5 h and stirring continued
for another 2 h. The mixture was filtered through a fritted glass
funnel and TFA was removed under reduced pressure. The crude
oligomer was isolated by precipitation from cold diethyl ether
(–15 °C) and dried in vacuo. The crude peptide was dissolved in
water/CH3CN, filtered and purified by HPLC. The synthesis of gu-
aninyl oligomer H-(β-HLys-β-HalG-ACHC)4-β-HGly-NH2 (2) has
already been described.[10]
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H-(β-HLys-β-HalA-ACHC)4-β-HGly)-NH2 (1): Analytical PR-
HPLC: tR = 20.1 min (gradient: 20–43% B in 30 min). MS (ESI):
m/z (%) = 1015.6 (100) [M + 2H]2+. HRMS (ESI): calcd. for
C95H148N38O13: 1015.61168; found 1015.41001 [M + 2H]2+
.
H-(β-HLys-β-HalC-ACHC)4-β-HGly)-NH2 (3): Analytical PR-
HPLC: tR = 20.2 min (gradient: 15–50% B in 30 min). MS (ESI):
[12] L. A. Carpino, A. El-Faham, F. Albericio, Tetrahedron Lett.
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