Synthesis of ansa1-cytidines

Article abstract of DOI:10.1080/15257770903109896

The synthesis of new ansa1-N45-ethylene cytidines such as 3-ss-D-ribofuranosyl-3,5,6,7-tetrahydro-2H-pyrrolo[2,3-d]pyrimidin-2-one is described and the problems connected with the ring closure to the desired tetrahydro-2H-pyrrolo[2,3-d]pyrimidine base dis

Full text of DOI:10.1080/15257770903109896

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Synthesis of Ansa1-Cytidines
Konrad Krolikiewicz a , Martina Schäfer a & Helmut Vorbrüggen a
a Medicinal Chemistry , The former Schering AG, now Bayer Schering
Pharma AG , Berlin , Germany
Published online: 29 Jul 2009.
To cite this article: Konrad Krolikiewicz , Martina Schäfer & Helmut Vorbrüggen (2009)
Synthesis of Ansa1-Cytidines, Nucleosides, Nucleotides and Nucleic Acids, 28:5-7, 695-712, DOI:
10.1080/15257770903109896
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Nucleosides, Nucleotides and Nucleic Acids, 28:695–712, 2009
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770903109896
SYNTHESIS OF ANSA1-CYTIDINES
Konrad Krolikiewicz, Martina Scha¨fer, and Helmut Vorbru¨ ggen
Medicinal Chemistry, The former Schering AG, now Bayer Schering Pharma AG, Berlin,
Germany
The synthesis of new ansa1-N45-ethylene cytidines such as 3-ß-D-ribofuranosyl-3,5,6,7-
2
tetrahydro-2H-pyrrolo[2,3-d]pyrimidin-2-one is described and the problems connected with the ring
closure to the desired tetrahydro-2H-pyrrolo[2,3-d]pyrimidine base discussed. The lack of biological
activities of the new ansa1− cytidines is furthermore commented on.
Keywords Synthesis of bicyclic ansa1-cytidines; stereochemistry; cytidine-deaminases
INTRODUCTION
This work on the synthesis of the new ansa[1]-ara-cytidine 23 was
patented in 1995[2] and first presented at the 4th Swedish-German Nucleo-
side Meeting, Reisensburg Castle, Germany, November 23–26 (1996).[3]
Ara-cytidine 1 is an important cytostatic drug for the therapy of acute
myeloid leukemia.[4] But its therapeutic application is hampered by its
rather rapid enzymatic deamination in vivo by ubiquitous cytidine deam-
inases, which react via addition of the deaminases to the 6-position of
1 to give via 2 the biologically inactive ara-uridine 3.[5] Consequently,
substituents in 5-position such as in 5-methyl-ara cytidine 4 decrease the rate
of deamination by monkey plasma and mouse kidney cytidine deaminase
Received 20 May 2009; accepted 10 June 2009.
Dedicated to Professor Morris Robins on the occasion of his 70th birthday.
The authors are indebted to Professor M. Schneider and Drs. M. Schirner and H. Wiesinger for
the biological data as well as to Dr. G. Michl for the spectroscopic data. The authors thank furthermore
Professor K.A. Watanabe (formerly Sloan-Kettering-Institute, New York, USA) for a gift of 2-fluoro sugar
31 and in particular Professor J. Mulzer and Dr. M. Czibowski (University of Vienna, Austria) for the
preparation of 2,2-difluoro sugar 35.
Present address for H.V.: Institut fu¨r Chemie und Biochemie, Freie Universita¨t, Berlin, Germany.
Address correspondence to Helmut Vorbruggen, Institut fu¨r Chemie und Biochemie, Freie
Universita¨t, Takustr.314195, Berlin, Germany. E-mail: helvor@chemie.fu-berlin.de
695

696
K. Krolokiewicz et al.
from a relative value (cytidine = 1) of ara-C 1 = 0.7 to a value for 5-methyl-
ara-cytidine 4 = 0.10[6] (Scheme 1).
O
NH2
NH2
H2N
OH
Me
N-H
NH
N
N
O
N
-NH3
HO
N
O
O
N
N
O
O
O
O
O
HO
HO
HO
2
HO
OH
3
HO
OH
4
1
HO
OH
HO
OH
SCHEME 1 Deamination of ara-cytidine.
We thus wondered, whether a five membered ansa1-ring connecting
the 5-position with the 4-amino group such as in ansa1-cytosine 5a or
in ansa1-ara-cytidine 23, which induces a minimal steric distortion of the
cytosine-ring, might not prevent all degradations by cytidine deaminases
as well as by acids. In contrast to cytosine or cytidine the acid catalyzed
addition of the elements of water to ansa1-cytosine 5a or ansa1-cytidines
5b would lead to a rather strained, high energy bicyclic intermediates, 7,
whose subsequent ring opening would afford 8. We thus assumed that the
known 5-aminoethyl-uracil 8a[7] would vice versa not be cyclized by acid
catalyzed silylation-amination[8] via 10 and 9 into ansa1-cytosine 5a, because
the 5-aminoethyl group cannot attack the 4-position of the aromatic silylated
uracil 10a from above (or below) the aromatic plane to the strained interme-
diate 9a. The intermediate 9a would supposedly lose trimethylsilanol as the
leaving group to form the desired ansa1-cytosine 5a. Most importantly, ansa1-
cytosine 5a, prepared by a subsequently discussed different route, remained
unchanged on 6 hours heating with 1 N HCl to 100◦ and could thus not
be hydrolyzed under mild acidic reaction conditions to 5-aminoethyl-uracil
8a! (Scheme 2).
H
O
H N
O 2
H
H
N
N
HN
HO
HN
H
O
?
H3O+
N
HN
N
?
H+
N
N
O
N
R
O
O
N
R
5
7
6
8
R
R
(HMDS)
(Me3Si)2NH
a. R = H; b. R = furanoses
?
(NH4)2SO4
1 N HCl/ 6 h/ 100°
H N
Me3SiO 2
H
HN
N
?
Me3SiO
- Me3SiOH
+
H
H
N
N
N
O
N
H
Me3SiO
N
Me3SiO
N
10a
5a
9a
SCHEME 2 Potential mechanisms of deaminations.

Synthesis of Ansa1-Cytidines
SYNTHESIS OF ANSA1-CYTOSINE
697
It was thus obvious that only cyclization of a cytosine with a leaving
group connected to a 5-ethyl group would afford ansa1-cytosine 5a. A
suitable starting material for such a cyclization is the known 5-hydroxyethyl-
cytosine 15,[9,10] which we prepared, however, by a slightly modified route:
Condensation of the sodium salt of 2-formyl-butyrolactone 11 with thiourea
afforded 5-hydroxyethyl-2-thiouracil 12, which was O-acetylated and subse-
quently transformed by heating with P4S10 in pyridine into 5-acetoxyethyl-
2,4-dithio-uracil 13. Heating of 13 with ammonia under pressure afforded 5-
hydroxyethyl-2-thio-cytosine 14, which gave on desulfurization with alkaline
H2O2 5-hydroxyethyl-cytosine 15 albeit in only moderate yield. Yet heating
of 14 with chloroacetic acid furnished 15 likewise in only moderate yield.
Cyclization[11] of 15 with in situ generated Ph3PBr2/EtN(i-Pr)2 in DMF
afforded the desired ansa1-cytosine 5a in 77% yield, part of which was
N-acetylated to 16 (Scheme 3).
OAc
OH
OH
S
NH2
O
O
O
NH
N
NH
NH3
H2NCSNH2
1.Ac2O/Pyr.
Na
2. P4S10/Pyr.
S
O
N
H
S
N
S
N
H
11
12
13
14
H
NaOH
H2O2
OH
NH
NH2
NAc
Ph3PBr2
Ac2O
Pyr
N
N
N
EtN(i-Pr)2
O
DMF
N
H
N
O
N
O
15
16
H
H
5a
SCHEME 3 Synthesis of ansa1-cytosine.
An alternative approach to ansa1-cytosine 5a starting with 3-formylation
of N-Boc-butyrolactam and subsequent ring-closure with thiourea was aban-
doned after the biological investigation of ansa1-ara-cytidine 23, of ansa1-
ara-cytidine-hydrochloride 24 and other ansa1-cytidines demonstrated that
none of these ansa1-cytidines showed any cytostatic or cytotoxic activity.
SYNTHESIS OF ANSA-CYTIDINES
Silylation of ansa1-cytosine 5a with hexamethyldisilazane (HMDS)/
pyridine to 17 followed by reaction with the standard sugar 1-O-acetyl-2,3,5-
tri-O-benzoyl-ß-D-ribofuranose 18 in 1,2-dichloroethane in the presence of
trimethylsilyl triflate (TMSOTf)[12] afforded the protected crystalline ansa1-

698
K. Krolokiewicz et al.
cytidine 19 in 80% yield, which gave on saponification with methanolic
ammonia the free crystalline ansa1-cytidine 20 in 89% yield (Scheme 4).
NSiMe3
N
NH
N
NH
N
CF3SO3SiMe3
(TMSOTf)
Cl(CH2)2Cl
NH3
N
N
17
MeOH
N
OSiMe3
O
O
O
+
O
O
OAc
HO
BzO
BzO
19
20
BzO
18
OBz
HO
OH
BzO
OBz
SCHEME 4 Synthesis of ansa1-uridine 20.
Reaction of free ansa1-cytidine 20 with 2-acetoxy-isobutyryl chloride
21[13] in acetonitrile provided in 79% yield the crystalline hydrochlo-
ride of the corresponding 2,2ꢁ-anhydro-nucleoside 22. Subsequent con-
version of the crude hydrochloride 22 with methanolic ammonia gave
crystalline ansa1-ara-cytidine 23 in 64% yield, whose structural assignment
was confirmed by x-ray structure analysis. (Figure 1) Treatment of 23 with
methanolic HCl afforded crystalline ansa1-ara cytidine hydrochloride 24.
Phosphorylation of 23 with POCl3 in triethylphosphate[14] provided the
5ꢁ-O-phosphate 25a in 92% yield, which gave with NaOH the corresponding
sodium salt 25b (Scheme 5).
NH
ClH
N
N
NH
Me
N
Me
COCl
21
1.
N
MeOH/NH3
HO
OAc
N
O
N
O
N
O
2. MeOH/HCl
HO
O
O
O
HO
23
22
20
HO
OH
HO
HO
OH
Cl3PO
(EtO)3PO
MeOH HCl
.HCl
N
NH
NH
N
N
O
O
N
O
O
O
24
25
OH
HO
O
ROP
OH
HO
OH
HO
a. R = H; b. R = ONa
SCHEME 5 Syntheses of ansa1-ara-cytidines.

Synthesis of Ansa1-Cytidines
699
FIGURE 1 X-ray structure of ansa1-ara-cytidine 23.
Reaction of silylated 7-N-acetyl-ansa1-cytosine 26 with crystalline 1-α-
chloro-2-deoxy-3,5-di-O-toluoyl-ribofuranose 27[15] in the presence of TM-
SOTf in 1,2-dichloroethane afforded 28% of the desired protected crys-
talline ß-anomer 28 as well as the protected crystalline α-anomer 29.
Saponification of the protected ß-anomer 28 gave 63% of the crystalline
free ß-anomer 30 (Scheme 6).
Reaction of silylated 7-N-acetyl-ansa1-cytosine 26 with 3-O-acetyl-5-O-
benzoyl-2-ß-fluoro-α-D-furanosyl chloride 31[16] afforded ca. 36% of the
corresponding protected ß-anomer 32 as well as some α-anomer 33. The
NAc
TMSOTf
NAc
+
NAc
N
Cl(CH2)2Cl
O
O
26
OSiMe3
N
N
N
N
N
TolO
TolO
29
28
+
O
O
O
TolO
TolO
Cl
MeOH/NH3 48h/22°C
TolO
27
TolO
NH
30
O
N
N
HO
O
HO
SCHEME 6 Synthesis of 2ꢁ-deoxy-ansa1-cytidine 30.

700
K. Krolokiewicz et al.
NH
NAc
NAc
N
N
N
MeOH/NH3
20h/22°C
14h/∆
Cl(CH2)2Cl
26
O
N
F
N
OSiMe3
O
N
O
O
32
34
+
O
F
HO
BzO
F
BzO
HO
AcO
Br
+ α-anomer 33
AcO
31
SCHEME 7 Synthesis of 2ꢁ-deoxy-2ꢁ-β-fluoro-ansa1-cytidine 34.
ß-anomer 32 gave on saponification the free crystalline ß-anomer 34 in 72%
yield (Scheme 7).
Finally, treatment of silylated 7-N-acetyl-ansa1-cytosine 26 with the mix-
ture of anomeric protected 1-O-mesyl-2-deoxy-2,2-difluoro-D-ribofuranose-
3,5-di-O-benzoates 35[17] in the presence of TMSOTf in boiling 1,2-
dichloroethane gave rise to 20% of the α-anomer 37 as well as to 21% of
the desired crystalline ß-anomer 36, which furnished on saponification the
free crystalline ß-anomer of 2ꢁ-deoxy-2ꢁ,2ꢁ-difluoro-ansa1-cytidine 38 in 63%
yield (Scheme 8).
Starting from 5-(2-chloroethyl)-3ꢁ,5ꢁ-di(O-p-toluoyl)-2ꢁ-deoxyuridine[18]
39, D.M.Brown et al.[19] described in 1999 an alternative synthesis of
protected 2ꢁ-deoxy-ansa1-cytidine. Reaction of 39 with 1,2,4-triazole/OPCl3
to 40, followed by treatment with 1-N-methyl-1-N-carbo-benzyloxy-hydrazine
41 gave via 42 the protected N-substituted ansa1-cytidine 43, which afforded
on hydrogenation 2ꢁ-deoxy-3ꢁ,5ꢁ-di(O-p-toluoyl)-ansa1-cytidine 44 (Scheme
9).
NAc
NAc
NH
N
MeOH/NH3
HO
TMSOTf
N
N
N
Cl(CH2)2Cl
OSiMe3
N
O
N
O
26
O
36
O
38
+
F
O
OMs
F
F
F
BzO
BzO
F
BzO
HO
+ α
37
F
35
BzO
-anomer
SCHEME 8 Synthesis of 2ꢁ-deoxy-2ꢁ,2ꢁ-difluoro-ansa1-cytidine 38.

Synthesis of Ansa1-Cytidines
701
Z
N
N
N
N
H
Cl
O
N
N
N
Me
O
Cl
Cl
H2NN(Me)Z 41
NH
N
1,2,4-triazole
OPCl3/MeCN
Z = PhCH2OCO-
O
O
N
O
O
O
42
39
40
TolO
TolO
TolO
TolO
Z
TolO
TolO
Me
N
N
NH
N
N
H2/PtO2/AcOH
TolO
N
O
O
N
O
O
44
43
TolO
TolO
TolO
SCHEME 9 Alternative synthesis of protected 2ꢁ-deoxy-ansa1-cytidine 44.
BIOLOGICAL SCREENING
In the biological studies, in particular compounds 20 (ZK 182306), 22
(ZK 182308), and 24 (ZK 182307) were investigated in detail:
1. In vitro studies: All tested ansa-cytidines were inactive in cell lines of
human prostate carcinoma as well as in cell lines of human large cell
lung cancer.
2. In vivo studies: Likewise all tested ansa-cytidines were inactive in L 1210
mouse leukemia. The mean survival time (MST) of ca. 11 days was not
enhancedby any of the tested compounds. In comparison, fludara (2-
fluoro-ara-C-5ꢁ-O-phosphate) in doses of 5.250 mg/Kg as well as ara-C
enhanced MST for up to 22–23 days.
Final Remarks
Due to the lack of any biological activity, the syntheses of the different
ansa1−cytidines were not optimized. The described yields can thus certainly
be improved. Unfortunately, we do not know as yet, why the investigated
ansa1-cytidines are biologically inactive. My mandatory retirement from
the former Schering AG (now Bayer Schering Pharma AG) in summer

702
K. Krolokiewicz et al.
1995 resulted in the termination of all further chemical and biological
investigations.
EXPERIMENTAL
Melting points were determined using a Kofler block instrument and
are uncorrected. TLC was performed on Silicagel plates (Merck, layer
thickness 0.2 mm). SiO2 with particle size = 0.04–0.063 mm was used for
1
column chromatography. H-NMR-spectra were recorded on a Bruker AC
250 FT NMR-spectrometer at 250 MHz with TMS as an internal standard.
Although satisfactory combustion analytical data were obtained for all of the
compounds described, some of these combustion data are unfortunately not
anymore available.
3,5,6,7-Tetrahydro-2H-pyrrolo[2,3d]pyrimidin-2-one 5a
To
50 mmol) and triphenylphosphine (15.73
in dry N,N-dimethylformamide (DMF) (75 mL)
a
suspension of 5-(2-hydroxyethyl)cytosine[9] 15 (7.55
g
=
g
=
60 mmol)
solution of
a
1,2-dibromotetrachloroethane (17.91 g = 55mol) was added at ca 5◦C
with stirring within 1 hour and the reaction mixture stirred for 18 hours
at 21◦C. Ethyldisopropylamine (25.85 g = 200 mmol) was added and the
reaction mixture stirred for 2 hours at 82–84◦C oil bath temperature,
whereupon initially everything passed into solution followed after ca. 45
minutes by precipitation of crystals. After cooling to 65◦C the crystals were
filtered and washed with DMF (35 mL), whereupon crude 5a (2.51 g) was
obtained. The filtrate was evaporated in vacuo and the residue stirred with
ethyldiisopropylamine (20 mL) in CH2Cl2 (500 mL). The precipitate was
filtered and washed with ethyldiisopropylamine (10 ml) in CH2Cl2 (10
mL), whereupon a further crop of crude 5a (5.03 g) was obtained. The
combined batches of crude 5a were suspended in H2O (150 mL) and a
saturated solution of aqueous NaHCO3 added drop wise with stirring until
a pH = 8–9 was reached. After 1 hour stirring the aqueous solution was
evaporated in vacuo and the residue recrystallized from H2O (50 mL) with
addition of charcoal to give after filtration pure 5a, (4.8 g), m.p 310◦C
(dec.), which starts subliming at 260◦C. The mother liquor was evaporated
(2 g) and silylated with HMDS/TCS and the residue submitted to short
path vacuum distillation. The distillate (1.28 g) was recrystallized from H2O
(20 mL) with charcoal (0.3 g) to give after filtration an additional amount
of 5a (0.48 g). Combined yield of 5a = 5.28 g (77%). 1H-NMR (DMSO-D6)
δ: 2.68–2.73 (tr, CH2 C), 3.56–3.63 (tr, CH2 N), 7.18 (s, H C C)
Analysis calcd.for C6H7N3O (137.15): C52.54, H5.15, N30.64 Found:
C52.38, H4.97, N30.99.

Synthesis of Ansa1-Cytidines
703
7-Acetyl-3,5,6,7-tetrahydro-2H-pyrrolo[2,3d]pyrimidin-2-one 16
To a suspension of 3,5,6,7-tetrahydro-2H-pyrrolo[2,3d]pyrimidin-2-one
5a (3.7 g, 30 mmol) in abs. pyridine (50 mL) acetic anhydride (8 ml) was
added with stirring, whereupon the reaction mixture warmed up to 28◦C.
After 1 hour stirring the starting material had dissolved and stirring was
continued for further 18 hours. The solution was evaporated in vacuo and
evapo-ration was repeated three times after addition of 30 ml portions of
abs. xylene and the residue dried in vacuo. Recrystallization from methanol
(50 mL) and H2O (2 mL) gave a first crop (1.58 g) m.p. 274–279◦C of the N-
acetyl compound 16. Concentration of the mother liquor to 25 mL afforded
a second crop of 16 (0.68 g). The mother liquor was evaporated and the
residue stirred with pyridine (25 mL) and acetic anhydride (5 mL) for 20
hours. After repeated evaporation with xylene a further amount (2.1 g) of
nearly pure 16 was isolated m.p. = 274–279◦C. Combined yield of 16 = 4.36
g (81.1%).
1H-NMR (DMSO-D6) δ: 2–56 (s, CH3 CO), 2.72–2.78 (m, CH2 C C),
3.88–3.92 (m, CH2N), 7.56 (s, H C C), 11.05 (br, HN) Analysis calcd.for
C6H7N3O (137.15) Analysis calcd. for C8H9N3O2 (179.18): C53.62, H5.06,
N23.45; Found: C53.19, H5.21, N23.15.
3-(2ꢁ,3ꢁ,5ꢁ-Tri-O-benzoyl-ß-D-ribofuranosyl)-3,5,6,7-tetrahydro-
2H-pyrrolo[2.3d]-pyrimidin-2-one 19
3,5,6,7,-Tetrahydro-2H-pyrrolo[2,3d]pyrimidin-2-on 5a (4.11 g = 30
mmol) was heated for 1 hour with hexamethyldisilazane (HMDS) (30 ml)
in abs. pyridine (30 ml), whereupon some substance had not dissolved as
yet. Thus TCS (1 ml) was added and boiling continued for further 2.5
hours. The excess of HMDS and pyridine was evaporated in vacuo and the
residue dried at 0.1 mm vacuum, whereupon crystalline bis-trimethylsilyl
compound 17 was obtained. The silyl compound 17 and 1-O-acetyl-2,3,5-tri-
O-benzoyl-ß-D-ribofuranose 18 (15.14 g = 30 mmol) were dissolved in abs.
1,2-dichloroethane (150 mL), a solution of trimethylsilyl triflate (TMSOTf)
(6.6 mL = 36 mmol) in abs. 1,2-dichloroethane (30 mL) added within 0,5
hours with stirring at 22◦C and the reaction mixture kept for 16 hours at
22◦C. After dilution with CH2Cl2 (150 mL) the reaction mixture was shaken
with ice-cold sat. NaHCO3-solution (250 mL), the layers separated and the
aqueous phase re-extracted with two portions of CH2Cl2 (75 mL). The
combined organic phase was dried (Na2SO4) and evaporated. The residue
(18.64 g) was chromatographed in EtOAc on a column of silicagel (150 g).
Elution with EtOAc (1.5 L) gave only traces of side products. Subsequent
elution with EtOAc-ethanol (9:1) (500 mL) afforded yellowish 19 (0.31 g).
Continued elution with EtOAc-ethanol (9:1) (500 mL) gave rise to pure ho-

704
K. Krolokiewicz et al.
mogenous protected nucleoside 19 (13.42 g = 76.82%), which crystallized
from a small volume of methanol. m.p. = 224–226◦C.
1NMR (DMSO-D6): δ: 2.99 (tr,2H; CH2-C = C)), 3.74 (tr, 2H; CH2-N),
ꢁ
ꢁ
ꢁ
3.79–3.92 (m, 2H; H5 ), 4.13 (m, 4.13 (m, 1H, H4 ), 4.21 (m, 1H, H3 ),
ꢁ
4.28–4.32 (m, 1 h, H2 ), 7.48 (s, 1 H H-C = C).
3-ß-D-Ribofuranosyl-3,5,6,7-tetrahydro-2H-pyrrolo
[2,3-d]pyrimidin-2-one 20
2ꢁ,3ꢁ,5ꢁ-Tri-O-benzoate 19 (16.15 g = 27.8 mmol) was kept for 72 hours
in sat. methanolic ammonia (250 mL), whereupon t.l.c. (upper phase of
n-BuOH : AcOH : H2O = 4:1:5) indicated that no starting material 19
was anymore present. On evaporation in vacuo the nucleoside 20 started to
crystallize. The crystalline residue was dissolved in a mixture of water (300
ml) and methyl-t-butylether (200 mL) and shaken. After separation of the
phases, the aqueous phase was re-extracted with methyl-t-butylether (200
mL). After concentrating the aqueous phase to 150 ml, the hot yellowish
solution was decolorized with charcoal (2 g), the charcoal washed with hot
H2O (75 mL) and the combined aqueous filtrates evaporated to give crude
crystalline free nucleoside 20 (7.8 g). Recrystallization from a mixture of
ethanol (175 mL) and H2O (40 mL) afforded pure 20 (4.8 g), m.p. =
224–226◦C. On concentration of the mother liquor a second crop of pure
20 (1.84 g) was obtained. Combined yield of 20 = 6.64 g = 88.8%.
ꢁ
1H-NMR (D2O): δ = 3.7–3.9 (m), 4.07–4.12 (m, H4 ), 4.17–4.22 (m,
ꢁ
ꢁ
ꢁ
H3 ), 4.27–4.30 (m, H2 ), 5.92–5.95 (m, H1 ), 7.47 (s, H C C), Analysis
calcd. for C11H15N3O5 (269.25) C49.07, H5.61, N15.61, Found: C49.13,
H5.35, N15.54.
2,2ꢁ-Anhydro-3-(ß-D-arabinofuranosyl)-3,5,6,7-tetrahydro-
2H-pyrrolo[2,3d]-pyrimidin-2-one hydrochloride 22
To a stirred suspension of 3-ß-D-ribofuranosyl-3,4,6,7-tetrahydro-2H-
pyrrolo[2,3-d]pyri-midin-2-one 20 (1,35 g = 5 mmol) in abs. acetonitrile
(50 mL) α-acetoxyisobutyric acid chloride 21 (3,29 g = 20 mmol) was added
and the reaction stirred for 4 hours at 21◦C, whereupon a clear colourless
solution had formed, which did not contain any more starting material
20 acc to t.l.c. (upper phase of n-BuOH : AcOH : H2O = 4:1:5). After
evaporation in vacuo the colourless viscous residue was stirred three times
with diethylether (100 mL each) and the residue taken up in a 1 molar
solution of HCl in abs. methanol (75 mL). After stirring for 18 hours at
21◦C colourless crystals had precipitated, which were filtered and washed
with abs. methanol (40 mL) and dried to give pure crystalline 22 (1.14 g
= 79%), m.p. = 226–230-235◦C (dec.) Evaporation of the mother liquor
afforded only a small amount of residue (0.16 g).

Synthesis of Ansa1-Cytidines
705
1H-NMR (DMSO-D6): δ: 3.03–3.07 (ꢁtr, CH2-CH2ꢁN), 3.4–3.43 (m,
CH2OH),ꢁ3.82–3.86 (m, N-CH2), 4.22 (s, H4 ), 4.48 (s, H3 ), 5.04 (m, 5-OH),
ꢁ
5.4 (d, H2 ), 6.5 (d, H1 ), 7.96 (s, H C C).
3-(ß-D-Arabinofuranosyl)-3,5,6,7-tetrahydro-2H-pyrrolo
[2,3-d]pyrimidine-2-one 23
To a suspension of D-ribofuranoside 20 (2.69 g = 10 mmol) in abs.
acetonitrile (150 mL) α-acetoxyisobutyric chloride (6.58 g = 5.7 ml = 40
mmol) was added under nitrogen and stirred for 5 hours at 23◦C to give
after evaporation in vacuo and stirring of the residue for 15 minutes with
methyl-t-butyl ether (250 mL) a fine colourless precipitate. After filtration
the residue was washed with methyl-tert.butyl ether (300 mL) and dissolved
in 10% aqueous ammonia (25 mL) and stirred for 2 days at 22◦C. After
removal of the solvents in vacuo, the residue was twice evaporated after
addition of H2O (30 mL). The oily residue was suspended in methanol (50
mL), the colourless precipitate filtered, washed with methanol (10 mL) and
dried to give a first crop of 23 (0.268 g). The mother liquor was evaporated
and suspended in methanol (30 mL) and kept for 16 hours at 23◦C to give
on filtration and washing with of methanol (10 ml) a second crop of 23
(0.743 g). Because the mother liquor refused to crystallize, the substance
was twice co-distilled with toluene (50 mL) and stirred for 16 hours with
acetic anhydride (15 mL) and pyridine (30 mL), whereupon the mixture
warmed slightly and the residue passed into solution. The brown-yellow
reaction mixture was co-distilled twice with xylene (40 mL) in vacuo and
the residue dissolved in methylene chloride (100 mL). After extraction with
ice cold sat NaHCO3-solution (60 mL) and water (40 mL) the methylene
chloride solution was dried (Na2SO4) and the filtrate evaporated. The
residue (2.4 g) was dissolved in ethyl acetate (35 mL) and chromatographed
in ethyl acetate on a column of SiO2 (100 g). The first eluate (700 mL) was
discarded, whereas the subsequent fraction (800 mL) afforded a colourless
foam (1.9 g), which was kept for 16 hours in methanolic ammonia (50 mL).
After evaporation in vacuo the residue crystallized slowly from methanol (50
mL) to give in two crops further amounts (0.7 g) of crystalline 23. m.p. =
225◦/232–236◦C. Combined yield of 23 = 1.71 g = 63.5%.
H1-NMR (DMSO-D6): δ = 2.82 (tr. J = 7.8 Hz; CH2-CH2N), 3.53 (tr. J =
ꢁ
ꢁ
ꢁ
7.8 Hz; CH2-N), 3.59 (m. H5 ), 3.71 (dtr. J = 3, 4.9 Hz; H4 ), 3.87 (m, H3 ),
ꢁ
3.92 (m, H2 ), 6.03 (d, H1ꢁ), 7.37 (s, H C C), 7.78 (s, NH)
MS (EI): m/z = 269 (M+), 251, 238, 208, 177, 166, 138, 121, 110, 70,
Analysis calcd. for C11H15N3O5 (269.25) C49.06, H5.62, N15.61. Found:
48.76, H5.44, N15.12
MS (CI): m/z = 270 (M+1) 168, 138;
Crystal data for 23: C11H15N3O5,. Mr = 296.26, orthorhombic, space
group C222(1), crystal dimensions 0.5 × 0.15 × 0.05 mm3, unit cell

706
K. Krolokiewicz et al.
◦
˚
dimensions a = 6.9089(2), b = 18.5962(5), c = 18.0369(5)A, α = 90.0 ,
β = 90.0 , γ = 90.0 , V = 2317.37(11) A 3, Z = 8, ρcalcd = 1.544
◦
◦
˚
−3
−1
˚
Mgm , F (000) = 1136, µ(MoKα) = 1.049 mm , T = 100K, λ = 1.54178A,
◦
◦
˚
4.76 ≤ꢀ≤69.50 , max. Resolution = 0.82A, 8936 reflections collected of
which 2117 are independent [Rint = 0.0369, Friedel mates are not merged].
R indices (all data) R1 = ꢁ| Fo-F c| /ꢁFo = 0.0270 for I>2σ(I) and wR2 =
ꢁ[w(Fo -Fc2)2/ꢁwFo ]1/2 = 0.0681 for all data; min./max. electron density:
2
4
−3
˚
0.298/–0.204 eA . Intensity data for 23 was recorded for a shock-cooled
crystal mounted in an oil drop on a three circle diffractometer with a
Smart6000 CCD area detector using ω scans. Data was integrated using the
program SAINT. All data was corrected semi-empirical for systematic errors
such as absorption using the program SADABS. The structures were solved
by Direct Methods using the program SHELXS 96 and refined against F2
by least squares. All non-hydrogen atoms could be refined anisotropically.
All hydrogen atoms were placed in geometrical ideal positions and refined
using the riding model, in which the methyl groups could rotate about
their local threefold axes. The isotropic temperature factors of all hydrogen
atoms are 1.2 and 1.5 times the size of the temperature factors of the
corresponding heavy atoms. The absolute structure could be determined.
The Flack Parameter refined to -0.0088(0.0610).
The crystallographic data for the structure have been deposited at
the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK and copies can be
obtained on request, free of charge, by quoting the publication citation and
the deposition number CCDC.
3-(ß-D-Arabinofuranosyl)-3,5,6,7-tetrahydro-2H-pyrrolo
[2,3-d]pyrimidine-2-one hydro chloride 24
To a stirred solution of crude ansa-ara-C 23 (3.1 g = 11 mmol) in
methanol (120 mL) 2N NaOH (30 ml = 60 mmol) was added, whereupon
a distinct smell of NH3 could be recognized. After evaporation in vacuo,
the residue was taken up in methanol (100 mL) and stirred for 0.25 hours.
The insoluble part was filtered and washed with methanol (30 mL). To the
combined filtrate methanolic HCl was added carefully until the solution
had reached a pH = 3, whereupon NaCl was precipitated. After continued
stirring for 30 minutes the precipitated NaCl was filtered and washed with
methanol (30 mL). The filtrate was evaporated and the residue extracted
with abs. ethanol (75 mL), whereupon pure crystalline 24 (3.28 g) was
obtained, which was washed with methanol (30 mL). After evaporation of
the mother liquor, the residue was dissolved in boiling methanol (30 mL)
to give on cooling a further amount of 24 (0.23 g). Combined yield of 24 =
3.51 g (76.5%), m.p. = 204–207◦C (dec).

Synthesis of Ansa1-Cytidines
707
ꢁ
1H-NMR (D2O): δ: 2.95 (m, 2H, CH2-CH2N), 3.6 (m, 2 H, H5 ), 3.78,
ꢁ
ꢁ
ꢁ
(m, 1H, H4 ), 3.88 (m, 2H, CH2-N), 3.92 (m, 1H, H3 ), 4.04 (1 H, H2 ), 6.0
ꢁ
(m, 1H, H1 ), 7.72 (s, 1 H, H C C)
Analysis calcd. for C11H16N3O5Cl (305.73) C43.21, H5.28, N13.74,
Cl11.60. Found: C43.09, H5.35, N13.50, Cl11.50.
3-(ß-D-Arabinofuranosyl)-3,5,6,7-tetrahydro-2-H-pyrrolo
[2,3-d]pyrimidin-2-one-5ꢁ-O-phosphate 25a
To a stirred suspension of 3-(ß-D-arabinofuranosyl)-3,5,6,7-tetrahydro-
2-H-pyrrolo[2,3-d]-pyrimidin-2-one 23 (0.404 g = 1.5 mmol) in triethyl
phosphate (7.5 mL) phosphorous oxychloride (0.173 ml = 1.88 mmol)
was added slowly within one hour with a syringe at −25◦C. The reaction
mixture was stirred for another hour at −20◦ and then for two further
hours in an ice bath at + 2◦C. After addition with stirring to ice water (25
mL) the mixture was kept for two further hours at + 22◦C. The triethyl
phosphate was removed by extraction with six 25 ml portions of CH2Cl2.
The remaining aqueous phase was then gradually added to a solution of 1,2-
butyleneoxide (1 mL) in ethanol (180 mL). After 5 hours stirring at 22◦C,
the precipitated colourless substance was filtered and washed with ethanol
(25 mL), whereupon pure 5ꢁ-O-phosphate 25a (0.39 g) was obtained. After
evaporation of the mother liquor, the residue was taken up in H2O (5
mL) and the aqueous solution added to ethanol (75 ml), whereupon
another crop (0.093 g) of 25a was obtained. Combined yield of 25a = 0.483
g = 92.4%.
MS (FAB): m/z = 372 (M.H+).
Sodium 3-(ß-D-arabinofuranosyl)-3,5,6,7-tetrahydro-
2H-pyrrolo[2,3d]pyrimidim-2-one-5ꢁ-O-phosphate 25b
3-(ß-D-Arabinofuranosyl)-3,5,6,7-tetrahydro-2-H-pyrrolo[2,3-
d]pyrimidin-2-one-5ꢁ-O-phosphate 25a (0.2 g = 0.57 mmol) was suspended
in H2O (10 ml) and titrated with 1 N NaOH until the solution reached a
pH = 7. The clear solution was slowly added within 2 hours with stirring
to ethanol (70 mL), the crystals filtered and washed with ethanol (15 mL)
to give after drying in vacuo pure sodium 3-(ß-D-arabinofuranosyl)-3,5,6,7-
tetrahydro-2H-pyrrolo-[2,3d]pyrimidim-2-one-5ꢁ-O-phosphate 25b (0.196 g
= 92.9%).
MS (FAB): M/z = 394 (M+Na) 372 (M-H+) 273, 133
3-(2ꢁ-Deoxy-3ꢁ,5ꢁ-di-O-toluoyl-ß-D-ribofuranosyl)-
3,5,6,7-tetrahydro-2H-pyrrolo[2,3-d]-pyrimidin-2-one 28
7-Acetyl-3,5,6,7-tetrahydro-2H-pyrrolo[2,3-d]-pyrimidin-2-one 16 (1.79 g
= 10 mmol) was boiled for 2 hours with hexamethyldisilazane (HMDS) (2.1

708
K. Krolokiewicz et al.
mL = 10 mmol) and trimethyl-chlorosilane (TCS) (1.27 mL = 10 mmol) in
acetonitrile (45 mL), whereupon a clear solution of 26 formed and NH4Cl
had sublimed into the reflux condenser. After evaporation the residue
was boiled and evaporated with three 15 ml portions of abs. xylene. The
crystalline residue of 26 was suspended in 1,2-dichloroethane (120 mL) and
3,5-di-O-toluoyl-2-deoxy-α-D-ribofuranosyl chloride 27 (3.86 g = 10 mmol)
added. At + 5◦C a solution of trimethylsilyl triflate (TMSOTf) (1.99 mL =
11 mmol) was added slowly with stirring within 45 minutes and the reaction
mixture stirred for 4 hours at 21◦C and kept for 18 hours at + 4◦C. After
addition of an ice cold saturated aqueous solution of NaHCO3 (120 mL)
some red-brown substance was precipitated and an emulsion formed. After
filtration over a G 4 glass filter funnel and washing the filter with CH2Cl2,
the phases of the filtrate were separated and the aqueous phase extracted
twice with CH2Cl2 (60 mL). The combined organic phase gave after drying
(Na2SO4) and evaporation crude amorphous brownish product (4.75 g),
which was dissolved in EtOAc–CH2Cl2 (1:1) (40 mL) and chromatographed
over a column of silica gel (180 g). Elution with EtOAc–CH2Cl2 (1:1) (0.5
L) provided some unidentified material, which was discarded, whereas the
next fraction (0.5 L) afforded on evaporation some red-brown product (0.15
g). The next 0.5 L eluate furnished nearly colourless, partially crystalline
mixture (3.4 g) of the protected ß-anomer 28 and α- anomer 29. Further
elution with 1 L of EtOAc–CH2Cl2 (1:1) afforded nearly pure α-anomer
29 (0.4 g), which crystallized from a small amount of acetone. m.p. =
148–150◦C.
The mayor eluate fraction (3.4 g) crystallized from acetone-CH2Cl2
(ca.100 mL) to give pure protected ß-anomer 28 (1.5 g = 28.2%), m.p.
203–205◦C. The mother liquors contained acc. to t.l.c. (upper phase of
toluene-AcOH-H2O = 5:5:1) mainly the α-anomer 29 and was therefore
seeded with crystalline 29, whereupon a further amount of crystalline 29
was obtained. Combined yield of 28 and 29 = 4 g (75.3%).
1H-NMR (CDCl3): 28 δ: 2.23–2.26 (m, 1 H, CH2-N), 2.42 + 2.44 (s, 2x
Me-Aryl), 2.40–2.50 (m, 1 H, CH2-N), 2.69 (s, MeCO), 3.07 (d,d,d, J = 15
ꢁ
Hz 1 H, H2 ), 3.83–3.90 + 3.94–4.02 (m, 2x 1 H, CH2-N), 4.60 (dd, J = 3 Hz
ꢁ
ꢁ
and 11 Hz, 1 H, H5 ), 4.63 (dd; J = 2 + 3 Hz, 1 H, H4 ), 5.62 (d, J = 7 Hz, 1
ꢁ
ꢁ
H, H3 ); 6.39 (dd, J = 6 Hz and 8 Hz, 1 H, H1 ); 7.24 (d, J = 8 Hz, H-Ar); 7.28
(d, J = 8 Hz, H-Ar), 7.64 (s, 1 H, H-C = C), 7.85 (d, J = 8 Hz, H-Ar), 7.97
(d, J = 8 Hz, H-Ar) Analysis calcd for C29H29N3O4 (531.55) C65.52, H5.5,
N7.91 Found C 65.56, H5.29, N7.93.
3-(2ꢁ-Deoxy-ß-D-ribofuranosyl)-3,5,6,7-tetrahydro-2H-pyrrolo
[2,3-d]pyrimidin-2-one 30
A suspension of 3-(2ꢁ-deoxy-3ꢁ,5ꢁ-di-O-toluoyl-ß-D-ribofuranosyl)-3,5,6,7-
tetrahydro-2H-pyrrolo[2,3-d]-pyrimidin-2-one 28 (1.3 g = 2.45 mmol) in

Synthesis of Ansa1-Cytidines
709
methanolic ammonia (150 mL) was stirred for 48 hours at 22◦C, whereupon
a clear yellowish solution had formed. After evaporation in vacuo, the
residue was taken up in H2O (150 mL) and methyl-t-butylether (100 mL).
After separation, the aqueous phase was evaporated in vacuo and the
colourless crystalline residue (0.68 g) recrystallized from H2O (5 mL) to give
pure 30 (0.22 g), m.p. = 135–140◦–223–226◦C. The mother liquor afforded
on evaporation and recrystallization from ethanol-H2O = 9 : 1 (8 mL) a
second crop of 30 (0.17 g) m.p. = 134–150–224–228◦C. Combined yield of
30 = 0.39 g = 62.9%.
ꢁ
ꢁ
H1-NMR (D2O): δ: 2.24 (m, 2H, H2 ), 3.75 (m, J = 8 Hz, CH2-CH2N),
ꢁ
ꢁ
3.75 (m, CH2-N), 3.82 (m, 2H, H5 ), H4 ), 4.43 (m, J = 2 +3Hz, H3 ), 6.33
ꢁ
(tr. J = 6Hz, H1 ), 7.5 (s, H C C).
MS (CI): 254 (M + H+) 164, 138, Analysis calcd. for C11H15N3O4
(253.25) C52.17, H5.97, N16.59, Found: C48.79, H6.00, N15.48, calcd. for
C11H15N3O4 H2O (271.25) C48.7, H6.32, N15.49.
3-(3-O-Acetyl-5-O-benzoyl-2-deoxy-2-fluoro-ß-D-
arabinofuranosyl)-N7-acetyl-3,5,6,7-tetrahydro-2H-pyrrolo
[2,3-d]pyrimidin-2-one 32
N-Acetyl-ansa-cytosine 16 (0.896 g = 5 mmol) was silylated with HMDS-
TCS (cf. prepa-ration of 23) for 30 minutes in boiling acetonitrile (40 mL),
whereupon a clear solution of 26 had formed and NH4Cl had sublimed
into the reflux condenser. After evaporation in vacuo with careful exclusion
of humidity, followed twice by evaporation with abs. xylene (15 mL).
the residue was dissolved in abs. 1,2-dichloroethane (20 mL). A solution
of 3-O-acetyl-5-O-benzoyl-2-deoxy-2-fluoro-α-D-arabinofuranosyl bromide 31
(1.206 g = 5 mmol) was added and the reaction mixture refluxed for 14
hours under nitrogen. After dilution with CH2Cl2 (50 mL) an ice cold
saturated solution of NaHCO3 (75 mL) was added and the mixture shaken.
The phases were separated and the aqueous phase re-extracted with two 30
mL portions of CH2Cl2. The combined organic phase was dried (Na2SO4)
and evaporated. The crude product (2.53 g) was dissolved in the upper
phase (20 ml) of toluene : AcOH : H2O = 5:5:1 and chromatographed with
the same solvent mixture on a column of silicagel (120 g). After a fore run of
500 ml, the subsequent 150 mL eluted pure ß-anomer 32 (0.812 g = 35.4%),
whereas the subsequent 150 mL eluted a ß/α-mixture (0.21 g). The last 150
mL solvent mixture eluted pure α-anomer 33 (0.04 g = 1.7%).
1H-NMR (CDCl3): ß-Anomer 32 δ: 2.18,(s, 3H,COCH3), 2.7 (s,3H, N-
COCH3), 2.68 (m, 2H, CH2CH2N) 4.05 (tr.2H, J = 8 Hz, CH2N), 4.4 (tr,
ꢁ
ꢁ
ꢁ
2H, H4 ), 4.68 (dd,2H, J = 4 +12 Hz, H4 ), 4.76 (dd, 2H, J = 3 +12Hz, H5 )
ꢁ
ꢁ
5.30 (dd,1 H, J = 1 + 7 Hz, H2 ), 5.25–5.45 (m, H2 ), 6.28 + 6.34 (dd, 1 H, J
ꢁ
= 2 +17Hz, H1 ), 7.2–8.8 (m, H-ar), 7.58 (s, 1H, H-C = C),

710
K. Krolokiewicz et al.
MS (EI): m/z = 459 (M+), 439 (M-1 +F) 380, 338,318, 281, 219, 180,
137, 105
MS (CI) = 460, (M + H+)
3-(2-Deoxy-2-fluoro-ß-D-arabinofuranosyl)-3,5,6,7-tetrahydro-
2H-pyrrolo[2,3d]-pyrimidin-2-one 34
Pure N7-acetyl-3-(3-O-acetyl-5-O-benzoyl-2-deoxy-2-fluoro-ß-D-arabino-
furanosyl)- 3,5,6,7- tetrahydro-2H-pyrrolo[2,3-d]pyrimidin-2-one 32 (0.77 g
= 0.168 mmol) was stirred for 20 hours at 22◦C in methanolic ammonia and
the reaction mixture evaporated in vacuo. The residue was taken up in H2O
(150 mL) and methyl-t-butyl ether (75 ml), the aqueous phase re-extracted
twice with methyl-tert-butyl ether (50 mL) and once with CH2Cl2 (75 mL).
On evaporation of the aqueous phase in vacuo, the residue was dissolved
in H2O (10 mL), char-coal (0.2 g) added and filtered, whereupon the
char coal was washed with H2O (10 mL). After evaporation of the aqueous
filtrate the residue (0.54 g) was dissolved in boiling ethanol (30 mL) to
give on cooling pure free nucleoside 34 (0.290 g), m.p. = 219–221◦C.
Concentration of the mother liquor gave a second crop of 34 (0.038 g).
Combined yield of 34 = 0.328g = 71.9%.
1H-NMR (DMSO): δ 2.85 (tr. 2H, J = 8Hz, CH2CH2N), 3.5–3.6 (m, 3H,
ꢁ
ꢁ
CH2N), 3.78 (m,1H, H4 ), 4.12–4.21(m, 1H, H3 ), 4.83 (dd, J = 2 + 3Hz,
ꢁ
ꢁ
H2 ), 6.08–6.13(dd, J = 3 + 17 Hz, H1 ). 7.4 (s,1H,H-C = C)
MS (EI) m/z = 271 (M+), 251 (M-H2O), 204, 177, 137, 121, 110, 93, 82;
MS (CI) m/z = 272 (M+1) 252, 177, 138 Analysis cald. for C11H14N3FO4
(271.26) C48.71, H5.2, N14.49, F7.0, Found: C48.62, H5.21, N15.31, F6.73
3-(3,5-Di-O-benzoyl-2-deoxy-2,2-difluoro-ß-D-ribofuranosyl)-
N7-acetyl-3,5,6,7-tetrahydro-2H-pyrrolo[2,3d]pyrimidin-2-one 36
A suspension of 16 (0.896 g = 5 mmol) in abs. acetonitrile (50
mL) was heated with hexamethyldisilazane (HMDS) (0.63 mL) and
trimethylchlorosilane (TCS) = 38 mL) (cf. preparation of 27) for 90
minutes at reflux, whereupon 26 was formed and NH4Cl sublimed into
the reflux condenser. After evaporation, the residue was dried in vacuo for
4h at 40–50◦C and dissolved in dry 1,2-dichloroethane. The anomeric mix-
ture of 3,5-di-O-benzoyl-2-deoxy-2,2-difluoro-ribofuranosyl-1-O-mesylates 35
(0.896g = 5 mmol) was added as well as subsequently a solution of
trimethylsilyl triflate (TMSOTf) (0.93 mL = 5 mmol) with stirring at 22◦C.
After heating to reflux for 19 hours, the mixture was cooled, a further
amount of TMSOTf (0.37 mL = 2 mmol) added and the reaction mixture
heated again for 19 hours at reflux. Because the reaction was still not
complete, a final amount of TMSOTf (0.37 mL = 2 mmol) was added
and the reaction mixture refluxed again for further 5h, whereupon tlc.

Synthesis of Ansa1-Cytidines
711
(system: upper phase of toluene-AcOH-H2O = 5:5:1) indicated that no
unreacted base 16 was anymore present. After workup with CH2Cl2 and
ice cold sat. aqueous NaHCO3-solution (150 mL), the CH2Cl2 phase was
dried (Na2SO4), filtered and evaporated. The brownish oily crude protected
nucleoside (2.64 g) was chromatographed with the upper phase of toluene-
AcOH-H2O = 5:5:1 on a column of silica gel (120 g). After a forerun of
475 ml, the next 600 ml eluted a mixture (0.73 g), whereas the subsequent
600 mL afforded pure α-anomer 37 (0.48 g). The mixture (0.73 g) was
analogously re-chromatographed on a column of silica gel (120 g) to give
after a forerun of 0.5 L in the subsequent 0.5 L fraction pure ß-anomer 36
(0.540 g) as well as finally some pure α-anomer 37 (0.05 g). Combined yield
= 0.54 g = 20.9% of ß anomer 36 as well as 0.511 g = 19.7% of α-anomer
37:
1H-NMR (CDCl3): ß-Anomer 37 δ = 2.67 (tr. 2H, J = 8 Hz, CH2CH2N),
ꢁ
2.73 (s, 3H; CH3CO), 4.3 (tr. 2H, J = 8 Hz, CH2N), 4.6 (m, 1H, H4 ),
ꢁ
ꢁ
ꢁ
4.58–4.9 (m, 2H, H5 ), 5.63–5.68 (m, 1H, H3 ), 6.58–6.63 (m, 1H, H1 ), 7.41
(s, 1H, H C C), 7.45–8.13 (m, arom.H),
MS (CI): m/z = 540 (M + H); 498, 478; 436;
MS (EI): m/z = 600, 573, 539 (M+), 511, 497, 434, 399, 398, 390, 376,
361, 356
3-(2-Deoxy-2,2-difluoro-ß-D-ribofuranosyl)-3,5,6,7-tetrahydro-
2H-pyrrolo[2,3-d]-pyrimidin-2-one 38
A suspension of the ß-anomer 3(3,5-di-O-benzoyl-2-deoxy-2,2-difluoro-ß-
D-ribofurano-syl)-N7-acetyl-3,5,6,7-tetrahydro-2H-pyrrolo[2,3-d]pyrimidin-
2-one 36 (0.480 g = 0.89 mmol) in sat. methanolic ammonia (40 mL)
was stirred for 18 hours at 22◦C, whereupon a clear solution formed
after 0.5 hours. After evaporation and workup with H2O-CH2Cl2 followed
by extraction of the aqueous phase with CH2Cl2 and ethyl acetate, the
aqueous phase was evaporated and the yellowish crystalline residue (0.26
g) recrystallized from H2O (5 mL), whereupon pure nucleoside 38 was
obtained in two crops (0.161 g = 62.5%), mp. 167–170◦C
1H-NMR (DMSO-D6): δ = 2.85 (m, 2H, CH2CH2N), 3.58 (tr, 3H, J = 8
ꢁ
ꢁ
Hzꢁ, CH2CH2N), 3.63–3.65 (m, 1H, H4 ), 3.76 (m, 1H, H5 ), 4.13–4.18(m,1H,
ꢁ
H3 ), 6.1–6.15 (m, 1H, H1 ), 7.43 (s, 1H, H-C = C)
MS (CI): m/z 290 (M + H+) 138;
MS (EI): m/z = 290, 289 (M+) 272, 215, 208, 195, 172, 164, 138, 137,
121, 110, 109, 93, 82, 60, 44
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