Synthesis and biological evaluation of 2′,3′-didehydro- 2′,3-′dideoxy-9-deazaguanosine, a monophosphate prodrug and two analogues, 2′,3′-dideoxy-9-deazaguanosine and 2′,3′- didehydro-2′,3′-dideoxy-9-deazainosine

Article abstract of DOI:10.1081/NCN-200051898

2′,3′-Didehydro-2′,3′-dideoxy-9-deazaguanosine (1), its monophosphate prodrug (2), and two analogues, 2′,3′-dideoxy-9- deazaguanosine (3) and 2′,3′-didehydro-2′,3′-dideoxy-9- deazainosine (4), have been synthesized from benzoylated 9-deazaguanosine (5). B

Full text of DOI:10.1081/NCN-200051898

Nucleosides, Nucleotides, and Nucleic Acids, 24 (2):135–145, (2005)
Copyright D 2005 Taylor & Francis, Inc.
ISSN: 1525-7770 print/ 1532-2335 online
DOI: 10.1081/NCN-200051898
SYNTHESIS AND BIOLOGICAL EVALUATION OF 2’,3’-DIDEHYDRO-2’,
3’-DIDEOXY-9-DEAZAGUANOSINE, A MONOPHOSPHATE PRODRUG
AND TWO ANALOGUES, 2’,3’-DIDEOXY-9-DEAZAGUANOSINE AND
2’,3’-DIDEHYDRO-2’,3’-DIDEOXY-9-DEAZAINOSINE
Mao-Chin Liu, Mei-Zhen Luo, Diane E. Mozdziesz, Ginger E. Dutschman,
5
Elizabeth A. Gullen, Yung-Chi Cheng, and Alan C. Sartorelli
Department of
Pharmacology and Developmental Therapeutics Program, Cancer Center, Yale University School
of Medicine, New Haven, Connecticut, USA
5
2’,3’-Didehydro-2’,3’-dideoxy-9-deazaguanosine (1), its monophosphate prodrug (2), and two
analogues, 2’,3’-dideoxy-9-deazaguanosine (3) and 2’,3’-didehydro-2’,3’-dideoxy-9-deazainosine (4),
have been synthesized from benzoylated 9-deazaguanosine (5). Basic hydrolysis of 5, selective protection
of the 2-amino and 5’-hydroxy functions with isobutyryl and silyl groups, respectively, followed by reaction
with thiocarbonyldiimidazole gave the cyclic thiocarbonate, which, upon reaction with triethyl phosphite,
followed by deprotection, afforded 1. Treatment of 1 with phenyl methoxyalaninyl phosphochloridate and
N-methylimidazole gave 2. Catalytic hydrogenation of 1 gave 3. Hydrodediazoniation of 1 with tert-butyl
nitrite and tris(trimethylsilyl)silane gave 4. Compounds 1–4 were found to be inactive against the human
immunodeficiency virus and exhibited minimal to no cytotoxic activity against the L1210 leukemia,
CCRF-CEM lymphoblastic leukemia, and B16F10 melanoma in vitro.
Keywords C-Nucleosides, Synthesis of Unsaturated 9-Deazanucleosides, Monophosphate
Prodrug, Anti-HIV Activity, Cytotoxic Activity
INTRODUCTION
Numerous 2’,3’-dideoxy- and 2’,3’-didehydro-2’,3’-dideoxynucleosides have
emerged as potent in vitro inhibitors of HIV. From this group, two purine
nucleosides, ddI (didanosine, 2’,3’-dideoxyinosine) and Abacavir (1592U89) are
approved for use in the treatment of AIDS in the United States. The glycosidic
linkage between the purine base and the pentose moiety of these drugs is sus-
ceptible to the hydrolytic action of purine nucleoside phosphorylase, and ddI is also
Received 1 September 2004, accepted 17 December 2004.
This research was supported in part by a Drug Discovery and Development Award from GlaxoSmithKline.
Address correspondence to Alan C. Sartorelli, Department of Pharmacology and Developmental
Therapeutics Program, Cancer Center, Yale University School of Medicine, New Haven, CT, USA; E-mail:
alan.sartorelli@yale.edu
135
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M.-C. Liu et al.
FIGURE 1 Nucleoside and nucleotide analogues of quanine.
particularly unstable under acidic conditions.[1,2] The carbon–carbon linked 9-
deazapurine nucleoside analogues are resistant to purine nucleoside phosphorylase
and acidic cleavage,[3] and several agents of this class exhibit anticancer,[4,5]
antileishmanial,[6] and antitripanosomal activities.[7] We have synthesized 2’,3’-
didehydro-2’,3’-dideoxy-9-deazaguanosine (1) and its monophosphate prodrug (2),
which can be thought of as analogues of the carbocyclic nucleoside, Carbovir, and
its monophosphate analogue, respectively (Figure 1) and the analogues, 2’,3’-
dideoxy-9-deazaguanosine (3) and 2’,3’-didehydro-2’,3’-dideoxy-9-deazainosine (4).
Carbovir is a carbocyclic analogue of 2’,3’-didehydro-2’,3’-dideoxyguanosine in
which the oxygen of the carbohydrate moiety is substituted by a carbon atom.
Carbovir exhibited similar anti-HIV activity to Abacavir and both of these agents
were anabolized to carbovir monophosphate.[8–10] The newly synthesized agents
were designed to hopefully retain the anti-HIV activity of drugs such as Abacavir
and ddI and express complete resistance to purine nucleoside phosphorylase and
acidic cleavage.
CHEMISTRY
Several methods have been reported in the literature for the conversion of
ribonucleosides to the corresponding 2’,3’-unsaturated nucleosides.[11–15] Of these,
simultaneous deoxygenation of 5’-O–protected ribonucleosides via their 2’,3’-
bisxanthates or 2’,3’-cyclic thiocarbonates to form corresponding 2’,3’-unsaturated
derivatives were some of the generally used synthetic routes.[11–13] Recently, we

Synthesis of 2’,3’-Didehydro-2’,3’-Dideoxy-9-Deazaguanosine
137
SCHEME 1 Synthesis of 2’,3’-didehydro-2’,3’-dideoxy-9-deazaguanosine.
developed an efficient method for the synthesis of benzoylated 9-deazaguanosine
(5).[16] Compound 5 was used in the present work as a precursor for the synthesis
of compound 1 (Scheme 1). Deprotection of 5 with sodium methoxide in methanol
gave crude 9-deazaguanosine (6) in almost quantitative yield, which was then
treated with hexamethyldisilazane in anhydrous DMF, followed by pyridine and
isobutyric anhydride to afford N2-isobutyryl-9-deazaguanosine (7) in a total yield of
62%. The 5’-hydroxyl function of 7 was selectively protected by treatment with
imidazole and tert-butylchlorodiphenylsilane in anhydrous DMF to give a 69% yield
of the 5’-O-tert-butyldiphenylsilyl derivative 8. Condensation of compound 8 with
carbon disulfide in the presence of 50% aqueous sodium hydroxide solution,
followed by iodomethane produced the bisxanthate 9 in 37% yield along with two
1
side products 10 and 11. Based on the H NMR and mass spectra data, the
structures of compounds 10 and 11 suggest they are derivatives of compound 9.
Compound 9 showed two methylthio groups at d 2.55 and d 2.61, compound 10
showed three methylthio groups at d 2.51, d 2.57, and d 2.81, and compound 11
showed two methylthio groups at d 2.50 and d 2.55 and an N-methyl group at d
3.90. The lack of N1 substitution is likely due to the presence of the adjacent bulky
N2-isobutyryl group, which prevents the N1 substitution of the corresponding
guanosine derivative in a similar reaction.[11] The bisxanthate 9, upon treatment
with tri-n-butyltin hydride in the presence of azobisisobutyronitrile (AIBN) in

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M.-C. Liu et al.
SCHEME 2 Synthesis of the mononucleotide prodrug of 2’,3’-didehydro-2’,3’-dideoxy-9-deazaguanosine, 2’,3’-
dideoxy-9-deazaguanosine, and 2’3’-didehydro-2’,3’-dideoxy-9-deazainosine.
toluene, gave the 2’,3’-unsaturated nucleoside 13 in 75% yield. Because of the low
yield of the bisxanthate 9, we focused our attention on the synthesis of the
corresponding 2’,3’-cyclic thionocarbonate 12. Condensation of 8 with 1,1’-
thiocarbonatediimidazole in anhydrous methylene chloride at room temperature
gave compound 12 in 93% yield. Contrary to a report[11] that the similar protected
2’,3’-thionocarbonate derivative of guanosine only gave decomposition products in
refluxing triethyl phosphite, treatment of compound 12 with triethyl phosphite at
170°C (oil bath temperature) for 3 h afforded a surprisingly high yield (88%) of
compound 13 after silica gel chromatography. This result proved that the carbon–
carbon linked bond in compound 8 was relatively stable under aggressive reaction
conditions. Deprotection of compound 13 with tetra-n-butylammonium fluoride in
THF produced compound 14, which, upon reaction with ammonia saturated
ethanol in a pressure vessel, furnished the target compound 1.
The syntheses of the mononucleotide prodrug of 2’,3’-didehydro-2’,3’-dideoxy-
9-deazaguanosine (2), 2’,3’-dideoxy-9-deazaguanosine (3), and 2’,3’-didehydro-2’,3’-
dideoxy-9-deazainosine (4) are shown in Scheme 2. Treatment[17] of 1 with phenyl
methoxyalaninyl phosphochloridate and N-methylimidazole in anhydrous pyridine
afforded the target compound 2. Catalytic hydrogenation of compound 1 with 10%
palladium on carbon in ethanol at 35 psig gave 3 in an 83% yield. Hydro-
dediazoniation of 1 with tert-butyl nitrite and tris(trimethylsilyl)silane in anhydrous
THF gave a number of complicated products along with compound 4, which was
isolated in 10–15% yield by silica gel column chromatography. The results were
consistent with reports[18,19] that diazotization of electron-deficient heterocyclic

Synthesis of 2’,3’-Didehydro-2’,3’-Dideoxy-9-Deazaguanosine
139
amines was problematic and multiple decomposition pathways were possible for
transient purinediazonium species, which led to the various complicated products.
BIOLOGICAL EVALUATION
The synthesized compounds 1 4 were evaluated in vitro for their cytotoxicities
against the L1210 leukemia, the CCRF-CEM lymphoblastic leukemia, and the
B16F10 melanoma by previously reported methodologies.[20] 2’,3’-Didehydro-2’,3’-
dideoxy-9-deazaguanosine (1) produced an IC50 value of 100 mM against B16F10
cells, and the monophosphate prodrug (2) produced IC50 values of 50, 55, and 44
mM against L1210, CCRF-CEM, and B16F10 cells, respectively. The remaining
compounds had no activity up to 100 mM against these cell lines. Evaluation of the
compounds for antiviral activity[20] demonstrated that compounds 1 and 2 were
inactive against HIV-IIIB and also showed no cytotoxicity up to 100 mM against
HIV-IIIB.
EXPERIMENTAL SECTION
Melting points were determined with a Thomas-Hoover Unimelt apparatus and
are uncorrected. 1H NMR spectra were recorded on a Varian EM-390 (90 MHz) or
Gemini-300 (300 MHz) NMR spectrometer with Me4Si as the internal reference.
Mass spectra were recorded on a VG-ZAB-SE mass spectrometer in the fast
bombardment (FAB) mode (glycerol matrix). Column chromatography was
conducted with Merck silica gel 60, 230–400 mesh. The general ratio of silica gel to
crude product used to run the columns was 20–25:1. When a compound was
evaporated to dryness, a maximum bath temperature of 40°C was used. TLC was
performed on EM precoated silica gel sheets containing a fluorescent indicator.
Elemental analyses were carried out by the Baron Consulting Co., Orange,
Connecticut, USA.
2-Isobutyrylamino-7-b-D-ribofuranosyl-5H-pyrrolo[3,2-d]pyri-
midin-4-one (7, N2-Isobutyryl-9-deazaguanosine). To a suspension
of compound 5 (10 g, 16.8 mmol) in methanol (100 mL) was added drop-wise
enough sodium methoxide in methanol (1 g Na in 20 mL methanol) with stirring
until the pH reached about 12. The reaction mixture formed a clear solution within
a few minutes and was stirred at room temperature for 4 h, then cooled with an
ice-water bath and neutralized with acetic acid. A white solid precipitated imme-
diately with the addition of acetic acid and the resulting mixture was stirred at
0–5°C for 1 h, filtered, and washed with ethanol. The collected solid was re-
fluxed with ethanol (50 mL), cooled, filtered, and washed with ethanol to give crude
9-deazaguanosine (6) as a white solid (4.7 g, 99%), which was then stirred with
anhydrous DMF (21 mL), followed by hexamethyldisilazane (25 mL). The mixture

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M.-C. Liu et al.
was stirred at room temperature overnight, treated with anhydrous pyridine (25 mL)
and isobutyric anhydride (40 mL) and stirred for an additional 24 h, cooled to
0–5°C, treated with methanol (45 mL), and stirred for another 4 h. The reaction
mixture was evaporated with silica gel (20 g) to dryness and purified by silica
gel column chromatography, using a gradient of 5–33% EtOH in CH2Cl2 to give
3.7 g (62%) of compound 7 as a white solid: mp 218–220°C (lit.[21] 222–224°C);
1
TLC, Rf 0.34 (CH2Cl2/MeOH, 10:1, v/v); H NMR (DMSO-d6) d 1.12 (2s,
6H, 2Me), 2.77 (m, 1H, CH), 3.48 (d, 1H, 5’-HA), 3.55 (d, 1H, 5’-HB), 3.71 (m, 1H, 4’-
H), 3.93 (t, 1H, 3’-H), 4.07 (br s, 3H, 3OH, D2O exchangeable), 4.09 (t, 1H, 2-H),
4.81 (d, 1H, 1’-H, J = 6.5 Hz), 7.39 (s, 1H, 6-H), 11.30 and 11.93 (2br s, 3H, 3NH,
D2O exchangeable).
2-Isobutyrylamino-7-(5-tert-butyldiphenylsilyl-b-D-ribofurano-
syl)-5H-pyrrolo[3,2-d]pyrimidin-4-one (8). To a stirred suspension of
compound 7 (4.0 g, 11.4 mmol) in anhydrous DMF (160 mL) was added imidazole
(4.0 g, 57 mmol). After the reaction mixture formed a clear solution in about 20 min,
tert-butylchlorodiphenylsilane (3.6 mL, 13.8 mmol) was added and the mixture was
stirred with the exclusion of moisture overnight. The mixture was then evaporated
to dryness in vacuo and the residue was dissolved in methylene chloride (120 mL),
washed with water (40 mL Â 2) and brine (40 mL), dried (MgSO4), and filtered.
The filtrate and washings were evaporated to a small volume and purified by silica
gel column chromatography (CH2Cl2/MeOH, 30:1, v/v) to give 4.7 g (69%) of
product as an off-white foam: TLC, Rf 0.39 (CH2Cl2/MeOH, 30:1, v/v); MS m/z 591
1
(M + H)+; H NMR (DMSO-d6) d 0.99 (s, 9H, Me3CSi), 1.12 (2s, 6H, Me2C), 2.31
(m, 1H, CH), 3.77 and 3.80 (2 m, 2H, 5’-H), 3.86 (m, 1H, 4’-H), 4.08 (m, 1H, 3’-H),
4.14 (m, 1H, 2’-H), 4.78 and 4.82 (2 br s, 2H, 2OH, D2O exchangeable), 4.89 (d, 1H,
1’-H, J = 6.0 Hz), 7.32 (d, 1H, 6-H, J = 3.5 Hz), 7.37–7.56 (m, 10H, ArH), 11.30 and
11.97 (2 br s, 3H, 3NH, D2O exchangeable). Anal. Calcd. for C31H38N4O6-
Si Á 0.7CH3OH: C, 62.09; H, 6.70; N, 9.14. Found: C, 61.79; H, 6.83; N, 9.49.
2-Isobutyrylamino-7-[5-tert-butyldiphenylsilyl-2,3-bis-O-
(methylthio)thiocarbonyl-b-D-ribofuranosyl]-5H-pyrrolo[3,2-
d]pyrimidin-4-one (9). To a solution of compound 8 (1.9 g, 3.2 mmol) in a
mixture of CS2 (3 mL) and DMSO (4.5 mL) an aqueous 50% sodium hydroxide
solution (1.7 mL) at 15°C was added drop-wise with stirring. The red-colored
suspension was stirred for 5 min, followed by addition of iodomethane (2 mL),
which resulted in a yellow suspension that was stirred for 1 h at room temperature.
The mixture was then evaporated to dryness in vacuo and the residue was
dissolved in methylene chloride (100 mL), washed with water (30 mL Â 2) and
brine (30 mL), dried (MgSO4), and filtered. The filtrate and washings were
evaporated to a small volume and purified by silica gel column chromatography
(CH2Cl2/EtOH, 40:1, v/v) to give compound 9 (0.92 g, 37%) along with the side
products 10 (0.72 g, 26%) and 11 (0.4 g, 16%).

Synthesis of 2’,3’-Didehydro-2’,3’-Dideoxy-9-Deazaguanosine
141
Compound 9 was isolated as an oil: TLC, Rf 0.36 (CH2Cl2/EtOH, 40:1, v/v); MS
m/z 771 (M + H)+; 1H NMR (CDCl3) d 1.02 (s, 9H, Me3CSi), 1.20 (2s, 6H, Me2C),
2.48 (m, 1H, CH), 2.55 and 2.61 (2s, 6H, 2SMe), 3.92 (m, 2H, 5’-H), 4.37 (m, 1H, 4’-
H), 5.14 (d, 1H, 1’-H, J = 7.2 Hz), 6.48 (m, 1H, 3’-H), 6.71 (m, 1H, 2’-H), 7.10–7.58
(m, 11H, ArH and 6-H), 10.82 (br s, 2H, 2NH, D2O exchangeable). Anal. Calcd. for
C35H42N4O6S4Si: C, 54.51; H, 5.49; N, 7.27. Found: C, 54.43; H, 5.33; N, 7.01.
2-Isobutyrylamino-5-(methylthio)thiocarbonyl-7-[5-tert-butyl-
diphenylsilyl-2,3-bis-O-(methylthio)thiocarbonyl-b-D-ribofurano-
syl]-5H-pyrrolo[3,2-d]pyrimidin-4-one (10). Compound 10 was
isolated as an oil: TLC, Rf 0.76 (CH2Cl2/EtOH, 40:1, v/v); C37H44N4O6S6Si:
M = 861.22; MS m/z 862 (M + H)+; 1H NMR (CDCl3) d 1.05 (s, 9H, Me3CSi), 1.22
(2s, 6H, Me2C), 2.49 (m, 1H, CH), 2.51, 2.57, and 2.81 (3 s, 9H, 3SMe), 3.95 (m, 2H,
5’-H), 4.42 (m, 1H, 4’-H), 5.40 (d, 1H, 1’-H, J = 7.2 Hz), 6.50 (m, 1H, 3’-H), 6.72(m, 1H,
2’-H), 7.20–7.72 (m, 11H, ArH and 6-H), 10.80 (br s, 1H, NH, D2O exchangeable).
2-Isobutyrylamino-5-methyl-7-[5-tert-butyldiphenylsilyl-2,3-
bis-O-(methylthio)thiocarbonyl-b-D-ribofuranosyl]-5H-pyr-
rolo[3,2-d]pyrimidin-4-one (11). Compound 11 was isolated as an oil:
TLC, Rf 0.51 (CH2Cl2/EtOH, 40:1, v/v); C36H44N4O6S4Si: M = 785.09; MS m/z 786
(M + H)+; 1H NMR (CDCl3) d 1.04 (s, 9H, Me3CSi), 1.22 (2s, 6H, Me2C), 2.48 (m,
1H, CH), 2.50 and 2.55 (2 s, 6H, 2SMe), 3.90 (m, 5H, 5’-H and NMe), 4.32 (m, 1H,
4’-H), 5.12 (d, 1H, 1’-H, J = 7.2 Hz), 6.42 (m, 1H, 3’-H), 6.63 (m, 1H, 2’-H), 7.10–
7.61 (m, 11H, ArH and 6-H), 10.72 (br s, 1H, NH, D2O exchangeable).
2-Isobutyrylamino-7-(5-tert-butyldiphenylsilyl-2,3-O-thiocar-
bonyl-b-D-ribofuranosyl)-5H-pyrrolo[3,2-d]pyrimidin-4-one (12).
A mixture of compound 8 (8.55 g, 14.5 mmol) and 1,1’-thiocarbonyldiimidazole
(5.17 g, 29 mmol) in anhydrous methylene chloride (430 mL) was stirred overnight.
The reaction mixture was then washed with water (2 Â 100 mL), dried (MgSO4),
filtered, and concentrated in vacuo. The residue was purified by silica gel column
chromatography (CH2Cl2/EtOH, 30:1, v/v) to give 8.5 g (93%) as a foam. TLC, Rf
0.48 (CH2Cl2/EtOH, 20:1, v/v); MS m/z 633 (M + H)+; 1H NMR (CDCl3) d 1.04 (s,
9H, Me3CSi), 1:24 (2s, 6H, Me2C), 2.49 (m, 1H, CH), 3.79 and 3.85 (2 m, 2H, 5’-H),
4.31 (m, 1H, 4’-H), 5.23 (d, 1H, 1’-H, J = 6.0 Hz), 5.57 (m, 1H, 3’-H), 5.78 (m, 1H, 2’-
H), 7.13–7.62 (m, 11H, ArH and 6-H), 8.14 and 10.64 (2 br s, 3H, 3NH, D2O
exchangeable). Anal. Calcd. for C32H36N4O6SSi Á 0.1CH2Cl2: C, 60.10; H, 5.69; N,
8.74. Found: C, 59.94; H, 5.62; N, 8.80.
2-Isobutyrylamino-7-(5-tert-butyldiphenylsilyl-2,3-didehydro-
2,3-dideoxy-b-D-ribofuranosyl)-5H-pyrrolo[3,2-d]pyrimidin-4-one
(13). A solution of compound 12 (3.3 g, 5.2 mmol) in 50 mL of triethyl
phosphite was heated at 170°C (oil bath temperature) with stirring under nitrogen

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M.-C. Liu et al.
for 3 h until TLC showed the reaction was complete. After cooling, the reaction
mixture was evaporated in vacuo to dryness. The residue was purified by silica gel
column chromatography (CH2Cl2/EtOH, 30:1, v/v) to give 2.6 g (88%) as a foam.
TLC, Rf 0.37 (CH2Cl2/EtOH, 20:1, v/v); MS m/z 557 (M + H)+; 1H NMR (CDCl3) d
1.03 (s, 9H, Me3CSi), 1.18 (2s, 6H, Me2C), 2.36 (m, 1H, CH), 3.91 and 3.98 (2 m,
2H, 5’-H), 4.38 (m, 1H, 4’-H), 5.42 (d, 1H, 1’-H, J = 6.0 Hz), 6.55 (m, 1H, 2’-H), 6.78
(m, 1H, 3’-H), 7.18–7.65 (m, 11H, ArH and 6-H), 7.98, 10.21, and 11.91 (3 br s, 3H,
3NH, D2O exchangeable). Anal. Calcd. for C31H36N4O4Si Á 0.8CH2Cl2: C, 61.15;
H, 6.07; N, 8.97. Found: C, 61.44; H, 5.95; N, 8.60.
Method B, from Bisxanthate 9. To a solution of compound 9 (0.83 g,
1.1 mmol) in 15 mL of dry toluene was added azobisisobutyronitrile (AIBN, 80 mg)
and tri-n-butyltin hydride (1.1 mL, 4 mmol) with stirring. The reaction mixture was
stirred further at 65–70°C for 2 h and evaporated in vacuo to dryness. The residue
was purified by silica gel column chromatography, eluting first with (CH2Cl2/
EtOAc, 4:1, v/v), then with (CH2Cl2/EtOH, 20:1, v/v) to give 0.45 g (75%) of
compound 13.
2-Isobutyrylamino-7-(2,3-didehydro-2,3-dideoxy-b-D-ribofura-
nosyl)-5H-pyrrolo[3,2-d]pyrimidin-4-one (14). To a stirred solution
of compound 13 (2.8 g, 5 mmol) in THF (100 mL), 1.0 M tetra-n-butylammo-
nium fluoride in THF (20 mL, 20 mmol) was added at ambient temperature.
The reaction mixture was stirred for 1 h and evaporated in vacuo to dryness.
The residue was purified by silica gel column chromatography (CH2Cl2/EtOH,
30:1, v/v) to give 2.6 g (88%) of product as a white solid: mp 118°C (dec.); TLC,
1
Rf 0.27 (CH2Cl2/EtOH, 20:1, v/v); MS m/z 318 (M + H)+; H NMR (DMSO-d6) d
1.12 (2s, 6H, Me2C), 2.75 (m, 1H, CH), 3.44 (m, 2H, 5’-H), 4.70 (t, 1H, 5’-OH,
D2O exchangeable), 4.74 (d, 1H, 4’-H, J = 1.5 Hz), 5.93 (d, 1H, 1’-H, J = 6.0
Hz), 6.00 (d, 1H, 2’-H, J = 6.0 Hz), 6.05 (d, 1H, 3’-H, J = 6.0 Hz), 7.22 (d, 1H, 6-
H, J = 3.5 Hz), 11.33 and 11.96 (2 br s, 3H, 3NH, D2O exchangeable).
Anal. Calcd. for C15H18N4O4: C, 56.59; H, 5.70; N, 17.60. Found: C, 56.40; H,
5.92; N, 17.34.
2-Amino-7-(2,3-didehydro-2,3-dideoxy-b-D-ribofuranosyl)-5H-
pyrrolo[3,2-d]pyrimidin-4-one (1, 2’,3’-Didehydro-2’,3’-dideoxy-9-
deazaguanosine). A suspension of compound 14 (0.63 g, 0.96 mmol) in 50
mL of saturated ethanol-ammonia solution was stirred in a steel bomb at 82°C for
20 h. The cooled reaction mixture was evaporated to dryness with 4.5 g of silica
gel and the residue was purified by silica gel column chromatography, eluting
with a gradient of 10–30% EtOH in CH2Cl2 to obtain 0.75 g (64%) of product as a
white solid: mp 245–247°C; TLC, Rf 0.35 (CH2Cl2/EtOH, 3:1, v/v); MS m/z 249
1
(M + H)+; H NMR (DMSO-d6) d 3.51 (m, 2H, 5’-H), 4.75 (m, 1H, 4’-H), 5.41
(br s, 1H, 5’-OH, D2O exchangeable), 5.66 (br s, 2H, NH2, D2O exchangeable),

Synthesis of 2’,3’-Didehydro-2’,3’-Dideoxy-9-Deazaguanosine
143
5.81 (d, 1H, 2’-H, J = 5.0 Hz), 5.94 (m, 2H, 1’-H and 3’-H), 7.04 (d, 1H, 6-H,
J = 5.0 Hz), 10.42 and 11.39 (2 br s, 2H, 2NH, D2O exchangeable). Anal. Calcd.
for C11H12N4O3Á 0.5H2O: C, 51.35; H, 5.09; N, 21.78. Found: C, 51.41; H, 5.08;
N, 21.49.
2-Amino-7-[2,3-didehydro-2,3-dideoxy-5-(phenylmethoxyala-
ninyl)-b-D-ribofuranosyl]-5H-pyrrolo[3,2-d]pyrimidin-4-one (2).
To a stirred solution of compound 1 (100 mg, 0.40 mmol) in anhydrous pyridine
(15 mL) a solution of phenyl methoxyalaninyl phosphochloridate (0.56 g, 2 mmol)
in anhydrous THF (15 mL) was added drop-wise over 5 min at room temperature.
The reaction mixture was stirred for an additional 5 min, followed by the addition
of N-methylimidazole (0.4 mL, 4 mmol) with vigorous stirring. The mixture was
stirred for 22 h and evaporated in vacuo to dryness with 1 g of silica gel and the
residue was purified by silica gel column chromatography, eluting with a gradient
of 10–30% EtOH in CH2Cl2 to yield 48 mg (24%) of product as a white solid: mp
148–150°C; TLC, Rf 0.57(CH2Cl2/EtOH, 2:1, v/v); MS m/z 490 (M + H)+; 1H NMR
(DMSO-d6) d 1.15–1.25 (d, 3H, ala-Me), 3.56 (s, 3H, ala-OMe), 3.75–3.95 (m, 3H,
ala-CH and 5’-H), 4.93 (m, 1H, 4’-H), 5.84–5.96 (m, 5H, 2’-H, 3’-H, 2-NH2, and ala-
NH), 6.09 (d, 1H, 1’-H, J = 5.0 Hz), 7.02 (s, 1H, 6-H, J = 5.0 Hz), 7.15–7.37 (m, 5H,
ArH), 10.60 and 11.51 (2 br s, 2H, 2NH, D2O exchangeable). Anal. Calcd. for
C21H24N5O7P: C, 51.53; H, 4.94; N, 14.31. Found: C, 51.31; H, 5.20; N, 14.03.
2-Amino-7-(2,3-dideoxy-b-D-ribofuranosyl)-5H-pyrrolo[3,2-
d]pyrimidin-4-one (3, 2’,3’-Dideoxy-9-deazaguanosine). A mixture
of compound 1 (120 mg, 0.48 mmol) and 10% Pd/C (50 mg) in 100 mL of ethanol
was hydrogenated at 35 psig for 6 h. The catalyst was removed by filtration and
carefully washed with ethanol. The combined filtrate and washings were
evaporated in vacuo to give 100 mg (83%) as a white solid: mp 164–166°C;
TLC, Rf 0.58 (CH2Cl2/EtOH, 2:1, v/v); MS m/z 251 (M + H)+; 1H NMR (DMSO-d6)
d 1.82–2.03 (m, 4H, 2’-H and 3’-H), 3.40 (m, 1H, 5’-HA), 3.48 (m, 1H, 5’-HB), 3.92
(m, 1H, 4’-H), 4.86 (t, 1H, 1’-H, J = 12.0 Hz), 5.25 (br s, 1H, 5’-OH, D2O
exchangeable), 5.73 (br s, 2H, NH2, D2O exchangeable), 7.11 (d, 1H, 6-H, J = 5.0
Hz), 10.41 and 11.30 (2 br s, 2H, 2NH, D2O exchangeable). Anal. Calcd. for
C11H14N4O3: C, 52.79; H, 5.64; N, 22.39. Found: C, 53.07; H, 5.42; N, 22.32.
7-(2,3-Dideoxy-b-D-ribofuranosyl)-5H-pyrrolo[3,2-d]pyrimidin-
4-one (4, 2’,3’-Didehydro-2’,3’,-dideoxy-9-deazainosine). To a
stirred suspension of compound 1 (200 mg, 0.81 mmol) in anhydrous THF (50
mL) was added tris(trimethylsilyl)silane (1 mL, 3.2 mmol) and tert-butyl nitrite (2
mL, 16.8 mmol). The reaction mixture was stirred under nitrogen at room tem-
perature for 40 h, after which time the mixture became homogenous and TLC
showed that just a trace of starting material remained. The reaction mixture was
evaporated with 1 g of silica gel to dryness and the residue was purified by silica gel

144
M.-C. Liu et al.
column chromatography, eluting with a gradient of 1–10% EtOH in CH2Cl2 to
obtain 25 mg (13%) of product as a white solid: mp 182–184°C; TLC, Rf 0.26
(CH2Cl2/EtOH, 10:1, v/v); MS m/z 233 (M + H)+; 1H NMR (DMSO-d6) d 3.52 (m,
2H, 5’-H), 4.80 (m, 1H, 4’-H), 5.12 (t, 1H, 5’-OH, D2O exchangeable), 5.94–6.00 (m,
1H, 3H, 1’-H, 2’-H and 3’-H), 7.29 (d, 1H, 6-H, J = 5.0 Hz), 7.78 (d, 1H, 2-H, J = 5.0
Hz), 11.89 and 13.02 (2 br s, 2H, 2NH, D2O exchangeable). Anal. Calcd. for
C11H11N3O3: C, 56.65; H, 4.76; N, 18.02. Found: C, 56.47; H, 5.01; N, 17.82.
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