PAPER
Laboratory Scale Synthesis of 3 -C-Ethynylcytidine
2391
1H NMR (250 MHz, DMSO-d6): = 0.07, 0.12 (s, 3 H each,
SiCH3), 0.88 [s, 9 H, SiC(CH3)3], 3.13 (m, 1 H, H-5 ), 3.57 (m, 1 H,
H-5 ), 3.78 (s, 3 H, OCH3), 4.63–4.77 (m, 3 H, H-2 , H-3 , H-4 ),
6.27 (d, J = 5.26 Hz, 1 H, H-1 ), 6.89 (d, J = 7.40 Hz, 1 H, H-5),
7.23–8.07 (m, 19 Harom), 8.35 (d, J = 7.51 Hz, 1 H, H-6), 11.45 (br
s, 1 H, NH).
mixture was brought to r.t. under stirring and diluted by the addition
of H2O (2 L) and filtered. The filtrate was extracted three times with
EtOAc (600 mL). The combined organic layers were concentrated
to a syrup that was dissolved in Et2O (600 mL) and flash chromato-
graphed on silica gel (25 10 cm), using Et2O (8 L) as the eluent.
The fractions containing the desired product were collected, pooled,
concentrated and dried to a foam, yielding 68.6 g (85%) of 6;
Rf 0.57 (CHCl3–acetone, 8:2).
1H NMR (250 MHz, DMSO-d6): = –0.02, 0.04 (s, 3 H each,
SiCH3), 0.10 [s, 9 H, Si(CH3)3], 0.85 [s, 9 H, SiC(CH3)3], 3.75–3.82
(m, 2 H, H-5 , H-5 ), 4.03 (t, J = 4.43 Hz, 1 H, H-4 ), 4.37 (d,
J = 5.63 Hz, 1 H, H-2 ), 5.10 (t, J = 4.75 Hz, 1 H, 5 -OH), 5.88 (s, 1
13C NMR (68 MHz, DMSO-d6):
= –4.95(CH3Si), 17.87
[SiC(CH3)3], 25.38 [SiC(CH3)3], 55.03 (CH3O), 63.91 (C-5 ), 75.69
(C-2 ), 82.65 (C-4 ), 86.16 [C(C6H5)3], 88.31 (C-1 ), 97.25 (C-5),
113.28, 126.99, 127.89, 128.46, 128.55, 130.01, 132.86, 134.47,
137.59, 143.89, 144.01, 158.35 (arom-C), 145.90 (C-4), 154.74 (C-
2), 163.66 (C-4), 167.50 (COC6H5), 207.46 (C-3 ).
H, 3 -OH), 5.93 (d, J = 5.63 Hz, 1 H, H-1 ), 7.38–8.01 (m, 6 Harom
H-5), 8.43 (d, J = 7.58 Hz, 1 H, H-6), 11.29 (br s, 1 H, NH).
,
MS: m/z = 732.3 [M]+.
Anal. Calcd for C42H45N3O7Si: C, 68.92; H, 6.20; N, 5.74. Found:
C, 68.82; H, 6.23; N 5.78.
13C NMR (68 MHz, DMSO-d6): = –5.03, –4.41 (CH3Si), –0.60
[Si(CH3)2], 17.79 [SiC(CH3)3], 25.63 [SiC(CH3)3], 61.50 (C-5 ),
72.90 (C-3 ), 74.78 (C CTMS), 80.35 (C-2 ), 86.90 (C-4 ), 88.51
(C-1 ), 91.21 (C CTMS), 96.55 (C-5), 128.45, 132.78, 133.07
(arom-C), 145.76 (C-6), 154.79 (C-2), 163.18 (C-4), 167.37
(COC6H5).
N4-Benzoyl-2 -O-(tert-butyldimethylsilyl)-3 -ketocytidine (5)
To a solution of 4 (140 g, 192 mmol) in CHCl3 (1.4 L) was added a
methanolic solution of p-toluenesulfonic acid (4%, 1.4 L) and the
resulting mixture was stirred for 5 min. The reaction mixture was
then poured into a half sat. aq solution (2 L) of NaHCO3. The organ-
ic layer was separated and concentrated (bath temperature <40 °C)
to a syrup which was dissolved in acetone (600 mL). The precipitate
was collected by filtration and discarded. The filtrate was concen-
trated (bath temperature <40 °C) to a syrup that was dissolved in
CHCl3 (600 mL) and flash chromatographed on a silica gel column
(20 10 cm) using a two step CHCl3–acetone gradient; first: 100:0
(6 L); second: 80:20 (6 L). The fractions containing the desired
product were pooled, concentrated and crystallized from Et2O (700
mL) at –25 °C. The precipitate was collected by filtration, washed
with ice cold Et2O (200 mL, –25 °C) and dried (CaCl2), yielding
66.6 g (76%) of 5 as colorless crystals; mp 205 °C; Rf 0.46 (CHCl3–
acetone, 8:2).
1H NMR (250 MHz, DMSO-d6): = –0.04, 0.01 (s, 3 H each,
SiCH3), 0.85 [s, 9 H, SiC(CH3)3], 3.75 (br s, 2 H, H-5 , H-5 ), 4.42–
4.44 (m, 1 H, H-4 ), 4.55 (d, J = 7.46 Hz, 1 H, H-2 ), 5.36 (br s, 1 H,
5 -OH), 6.33 (d, J = 7.46 Hz, 1 H, H-1 ), 7.48–8.08 (m, 6 Harom, H-
5), 8.48 (d, J = 7.57 Hz, 1 H, H-6), 11.43 (br s, 1 H, NH).
13C NMR (68 MHz, DMSO-d6): = –5.40, –4.94 (CH3Si), 17.82
[SiC(CH3)3], 25.33 [SiC(CH3)3], 60.67 (C-5 ), 76.73 (C-2 ), 82.56
(C-4 ), 86.43 (C-1 ), 97.37 (C-5), 128.45, 128.53, 132.86 (arom-C),
145.72 (C-6), 154.71 (C-2), 163.45 (C-4), 167.40 (COC6H5),
208.99 (C-3 ).
MS: m/z = 558.6 [M + H]+, 500.3 [M – C4H9]+.
Anal. Calcd for C27H39N3O6Si2: C, 58.14; H, 7.05; N, 7.53. Found:
C, 57.92; H, 6.87; N 7.38.
3 -C-Ethynylcytidine (7)
Compound 6 (68.6 g, 123 mmol) was suspended in methanolic am-
monia (1.2 L) and the resulting solution kept sealed at r.t. for 24 h
and then concentrated to a syrup that was coevaporated twice with
toluene (400 mL). This syrup was dissolved in anhyd THF (700
mL) and the TBAF solution (240 mL) was added under exclusion
of moisture. The reaction mixture was stirred for 4 h followed by
concentration to a syrup that was dissolved in CHCl3 (200 mL) and
flash chromatographical purification on a silica gel column (16
9
cm) using a three step CHCl3–MeOH gradient. First: 95:5 (4 L);
second: 80:20 (4 L) and third: 60:40 (3 L). The fractions containing
the desired product were pooled, concentrated to a syrup which was
crystallized from MeOH–H2O (8:2), yielding 24.6 g (75%) of 3 -C-
ethynylcytidine (7) as colorless crystals; mp 233–235 °C; Rf 0.39
(CHCl3–MeOH, 7:3); [ ]D20 +68 (c = 1.0, H2O).
1H NMR (250 MHz, DMSO-d6): = 3.52 (s, 1 H, C CH), 3.67–
3.75 (m, 2 H, H-5 , H-5 ), 3.85–3.88 (m, 1 H, H-4 ), 4.12 (t, J = 6.55
Hz, H-2 ), 5.05 (t, J = 4.76 Hz, 1 H, 5 -OH), 5.74–5.83 (m, 3 H, 3 -
OH, 2 -OH, H-5), 5.89 (d, J = 6.40 Hz, 1 H, H-1 ), 7.26 (br s, 2 H,
NH2), 7.83 (d, J = 7.49 Hz, 1 H, H-6).
MS: m/z = 460.2 [M + H]+, 402.3 [M – C4H9]+, 214.8 [N4 – benzoyl-
cytosine – H]+, 187.0 [M – N4 – benzoylcytosine – C4H9]+.
13C NMR (68 MHz, DMSO-d6): = 61.57 (C-5 ), 72.56 (C-3 ),
77.05 (C CH), 78.35 (C-2 ), 83.03 (C CH), 86.08 (C-4 ), 87.64 (C-
1 ), 94.28 (C-5), 141.80 (C-6), 155.56 (C-2), 165.49 (C-4).
Anal. Calcd for C22H29N3O6Si: C, 57.50; H, 6.36; N, 9.14. Found:
C, 57.38; H, 6.02; N 8.92.
MS: m/z = 267.9 [M]+.
N4-Benzoyl-2 -O-(tert-butyldimethylsilyl)-3 -C-(trimethylsilyl-
ethynyl)cytidine (6)
Anal. Calcd for C11H14N3O5: C, 49.25; H, 5.26; N, 15.66. Found: C,
49.03; H, 4.98; N, 15.48.
First a suspension of anhydrous cerium(III) chloride in THF was
prepared as follows: Cerium(III) chloride heptahydrate (324 g,
869 mmol) was dried under stirring in vacuum (oil pump) at 140 °C
for 3 h. The dry cerium(III) chloride was then suspended in anhyd
THF (1 L) and stirred overnight under argon. The reaction was car-
ried out under argon at –78 °C unless otherwise indicated. To a
stirred solution of ethynyltrimethylsilane (120.6 mL, 869 mmol) in
anhyd THF (300 mL) was added a solution of BuLi in hexane (544
mL, 869 mmol) keeping the temperature of the reaction mixture be-
low –50 °C. After stirring for 30 min, the precooled (< –50 °C) sus-
pension of cerium(III) chloride (214 g, 869 mmol) in anhyd THF (1
L) was added and the mixture was stirred for 2 h, and then a pre-
cooled solution (< –50 °C) of 5 (66.6 g, 145 mmol) in anhyd THF
(260 mL) was added. After stirring at –65 °C for 3 h, the mixture
was then quenched with an 1 M aq solution of NH4Cl (900 mL). The
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Synthesis 2002, No. 16, 2387–2392 ISSN 0039-7881 © Thieme Stuttgart · New York