KIRILLOVA et al.
1774
the mixture was stirred for 20 min at room tempera-
ture. The solvent was removed, the residue was
dissolved/evaporated with toluene (3×2 mL) and with
diethyl ether (3×2 mL) and ground with anhydrous
diethyl ether, and the solid was filtered off and washed
with anhydrous diethyl ether; the resulting white
crystals were dried in a high vacuum and used in
the next step without structure determination. Yield
19.3 mg (87%).
of DMF, 17.4 μL (0.10 mmol) of ethyl(diisopropyl)-
amine, and 15.3 mg (47.5 μmol) of O-(benzotriazol-1-
yl)-N,N,N′,N′-tetramethyluronium hexafluorophos-
phate in 0.6 mL of DMF. Yield of VI 14.4 mg (82%),
1
Rf 0.67 (A), mp 209°C. H NMR spectrum, δ, ppm:
1.41 s (9H, t-Bu), 1.70 s (9H, CH3, thymine), 1.90 m
(2H) and 2.24 m (4H) (β-CH2, glutamic acid), 2.35 m
(6H, γ-CH2, glutamic acid), 3.10 m and 3.29 m (6H
each, HNCH2CH2N), 4.37 m (3H, α-CH, glutamic
acid), 4.64 s [6H, NCH2(C=O)], 5.15 s (6H, CH2Ph),
7.23 m (1H, NH-Boc), 7.35 s (3H, CH. thymine),
7.39 m (15H, Ph), 7.41 s and 7.58 s (1H each, CONH2),
11.22 s (3H, NH, thymine). Found, %: C 58.18;
H 6.00; N 12.94. m/z 1402.5 [M]+. C68H83N13O20. Cal-
culated, %: C 58.24; H 5.97; N 12.98. M 1401.6.
Trifluoroacetate V. Monomer II, 49.0 mg
(89.6 μmol), was dissolved in 1 mL of DMF, 31.2 μL
(0.18 mmol) of ethyl(diisopropyl)amine was added,
and a solution of 26.0 mg (80.6 μmol) of O-(benzo-
triazol-1-yl)-N,N,N′,N′-tetramethyluronium hexa-
fluorophosphate in 0.8 mL of DMF was then added.
The mixture was stirred for 2 min and added to a mix-
ture of 25.0 mg (44.8 μmol) of trifluoroacetate IV and
11.7 μL (0.07 mmol) of ethyl(diisopropyl)amine in
0.5 mL of DMF. The mixture was stirred for 30 min at
room temperature, the solvent was removed, and the
residue was treated with 5 mL of water and 5 mL of
ethyl acetate. The aqueous layer was separated and
extracted with ethyl acetate (2×5 mL), the extracts
were combined with the organic phase, washed with
a saturated solution of NaHCO3 (2 mL), 0.1 M solution
of KHSO4 (2 mL), and brine (2 mL), and dried over
Na2SO4, the solvent was removed, and the product was
isolated by column chromatography (gradient elution
with ethyl acetate–methanol, 0 to 20% of the latter).
The solvent was removed, and the product was dried in
a high vacuum. Yield of Boc/Bzl-protected amide
33.2 mg (76%), Rf 0.45 (A), mp 201°C. 1H NMR spec-
trum, δ, ppm: 1.35 s (9H, t-Bu), 1.72 s (6H, CH3,
thymine), 1.89 m (1H) and 2.20 m (3H) (β-CH2,
glutamic acid), 2.40 m (4H, γ-CH2, glutamic acid),
3.11 m and 3.30 m (4H each, HNCH2CH2N), 4.42 m
(2H, α-CH, glutamic acid), 4.65 s [4H, NCH2C(O)N],
5.10 s (4H, CH2Ph), 7.19 m (1H, NH-Boc), 7.33 s (2H,
CH, thymine), 7.35 m (10H, Ph), 7.41 s and 7.58 s (1H
each, CONH2), 11.25 s (2H, NH, thymine). Found, %:
C 57.91; H 6.15; N 12.89. m/z 974.2 [M]+.
C47H59N9O14. Calculated, %: C 57.96; H 6.11; N 12.94.
M 973.4.
The Boc-protection was removed as described
above using 30.0 mg (21.4 μmol) of the Boc/Bzl-
protected amide and 1.6 mL of TFA in 2 mL of
methylene chloride. Yield of the Bzl-protected amide
trifluoroacetate 29.9 mg (99%). A 15-mg (10.5-μmol)
portion of this product was dissolved in 0.42 mL of
methanol–acetic acid–water (6 : 1 : 1 by volume),
4.5 mg of 10% Pd/C was added, and hydrogen was
passed through the mixture over a period of 1.5 h
under vigorous stirring at room temperature. The cata-
lyst was filtered off and washed with 0.2 mL of water,
the filtrate was evaporated at 40°C under reduced pres-
sure (oil pump), the residue was ground with anhy-
drous diethyl ether, and the white crystalline solid was
filtered off, washed with anhydrous diethyl ether, dried
in a high vacuum, and analyzed by LC/MS. Yield
15.7 mg, Rf 0.87 (B). Found: m/z 1032.0 [M + H]+.
C42H57N13O18. Calculated: M + H 1031.4.
Solid-phase synthesis of PNA oligomers. The
polymer support was prepared as follows. Cross-linked
polystyrene resin modified with 4-[amino(4-methyl-
phenyl)methyl]phenyl groups was kept for 30 min in
methylene chloride and washed in a separatory funnel
with methylene chloride (20 mL per gram of the resin)
until the phase boundary was clearly seen, the solvent
was removed by filtration, and the resin was dried
under reduced pressure (oil pump). It was then washed
on a filter in succession with a 5% solution of ethyl-
(diisopropyl)amine in methylene chloride (2×20 mL
per gram of the resin) and methylene chloride (2×
20 mL per gram of the resin), the solvent was re-
moved, and the resin was dried under reduced pressure
(oil pump) and analyzed for amino groups by the
quantitative Kaiser test (0.6 mmol NH2 per gram of
The Boc-protection was removed as described
above for compound IV using 11.2 mg (11.5 μmol) of
the Boc/Bzl-protected amide and 0.6 mL of TFA in
1 mL of methylene chloride. Yield 11.3 mg (99%).
Trifluoroacetate I. The third monomer unit was
attached as described above for compound V using
27.3 mg (50.0 μmol) of Boc-protected amide in 0.5 mL the resin).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 12 2013