Nucleosides XI. Synthesis and antiviral evaluation of 5′-alkylthio- 5′-deoxy quinazolinone nucleoside derivatives as S-adenosyl-L-homocysteine analogs

Article abstract of DOI:10.1248/cpb.52.1422

4-Amino-1-(β-D-ribofuranosyl)quinazolin-2-one (3) was prepared by a direct glycosylation of 4-aminoquinazolin-2-one (7) using the Vorbruggen's silylation method and provided exclusively the β-anomer. This quinazoline nucleoside and its 2′,3′-O-isopropylid

Full text of DOI:10.1248/cpb.52.1422

1422
Chem. Pharm. Bull. 52(12) 1422—1426 (2004)
Vol. 52, No. 12
Nucleosides XI.1) Synthesis and Antiviral Evaluation of 5ꢀ-Alkylthio-5ꢀ-
deoxy Quinazolinone Nucleoside Derivatives as S-Adenosyl-L-
homocysteine Analogs
Tun-Cheng CHIEN,2) Chien-Shu CHEN, Fang-Hwa YU, and Ji-Wang CHERN*
School of Pharmacy, College of Medicine, National Taiwan University No. 1, Section 1; Ren-Ai Road, Taipei (100),
Taiwan. Received May 6, 2004; accepted July 28, 2004
4-Amino-1-(b-D-ribofuranosyl)quinazolin-2-one (3) was prepared by a direct glycosylation of 4-aminoquina-
zolin-2-one (7) using the Vorbruggen’s silylation method and provided exclusively the b-anomer. This quinazoline
nucleoside and its 2ꢀ,3ꢀ-O-isopropylidene derivative (9) did not undergo the coupling reaction with dialkyl disul-
fides in the presence of tri-n-butylphosphine unless their 4-amino groups were protected by N,N-dimethyl-
aminomethylidene. This approach provides a viable alternative synthetic route to 5ꢀ-alkylthio-5ꢀ-deoxy nucleo-
sides.
Key words quinazoline; tri-n-butylphosphine; AdoHcy; S-adenosyl-L-homocysteine
analog,20) and subsequently shown to display the antiviral ac-
Several nucleosides containing 5ꢀ-sulfur substituents have
tivity against herpes simplex virus.27) Other derivatives from
been discovered in nature and are involved in many impor-
this nucleoside have rarely been studied.20,21) In an effort to
tant biological processes. One of the most significant
explore the antivirial profiles and the chemical properties of
the 4-aminoquinazolin-2-one nucleoside (3), two target struc-
tures containing 5ꢀ-sulfur substituents (4, 5) were designed as
S-adenosyl-L-homocysteine (1, AdoHcy) analogs. Herein, we
report an improved synthesis of 3 and the synthesis of
5ꢀ-alkylthio-5ꢀ-deoxy quinazolinone nucleosides 4 and 5.
processes is the S-adenosyl-L-methionine (AdoMet)-depen-
dent transmethylations. Inhibition of these methyl transfer
processes has been correlated with antiviral activity and has
attracted considerable attention as a target for the discovery
of new antiviral agents.3,4) S-Adenosyl-L-homocysteine
(1, AdoHcy), the byproduct of these AdoMet-dependent
transmethylations, and some of its structural analogs have
been shown to be potent competitive product inhibitors of the
AdoMet-dependent methyltransferases.5—15) Our group has
also been interested in the synthesis and biological evaluation
of several 5ꢀ-sulfur containing nucleosides.16—18) In continua-
tion of our studies and our longstanding interest in the
biological activities of quinazoline derivatives,19) we initiated
an investigation on the synthesis and biological evaluation of
5ꢀ-sulfur containing quinazoline nucleoside derivatives.
Quinazoline nucleosides were first synthesized by Stout
and Robins in 1968 as pyrimidine nucleoside analogs20) and
consequent synthetic studies were contributed by Dunkel and
Pfleiderer in the 1990s.21—23) Quinazoline nucleosides were
once used as a conformationally restricted model to study the
syn–anti conformational preference of pyrimidine nucleo-
sides in solution.24,25) More recently, quinazoline nucleosides
have been incorporated into oligonucleotides as pyrimidine
nucleoside substitutes to study the binding affinity and base-
pairing selectivity.26) However, their biological activities are
still relatively less known in literature. 4-Amino-1-(b-D-ribo-
furanosyl)quinazolin-2-one (3) was chosen for our study.
This quinazoline nucleoside was previously synthesized from
quinazoline-2,4-dione by Stout and Robins as a cytidine (2)
Results and Discussion
A perusal of the literature revealed that most of 4-amino-
quinazolin-2-one nucleosides were synthesized by ribosyla-
tion of quinazoline-2,4-diones followed by functional group
interconversions.20,21) Our first effort was to develop a direct
synthetic route from 4-aminoquinazolin-2-one28,29) (7). The
heterocycle 7 was prepared via a 1,3-dicyclohexylcarbodi-
imide (DCC)—mediated cyclodesulfurative annulation reac-
tion developed in our laboratory.30,31) Anthranilamide (6) was
condensed with benzoyl isothiocyanate to form the thiourea
intermediate which was immediately treated with DCC fol-
lowed by ammonia to afford 4-aminoquinazolin-2-one (7) in
88% yield. Compound 7 was coupled with 1-O-acetyl-2,3,5-
tri-O-benzoyl-b-D-ribofuranose under modified Vorbruggen’s
condition.32,33) This reaction gave exclusively one anomer of
the sugar-protected ribonucleoside 8 which was subsequently
deprotected with ammonia to afford 4-amino-1-(b-D-ribofu-
ranosyl)quinazolin-2-one (3) in 74% yield (Chart 1).
The 2ꢀ,3ꢀ-diol of 3 was protected with acetone in the pres-
ence of acid to form the acetonide 9 in 74% yield. The struc-
tural elucidation was carried out by intensive NMR studies.
The chemical shift difference of the two isopropylidene
methyl groups (Dd) in 9 was 0.22 which indicates a
b-anomeric configuration based on Imbach’s empirical
rule.34) The 1-D NOE irradiation of 3 and 9 at 1ꢀ-H (d 6.12,
6.23) showed NOE enhancements at one of the aromatic pro-
tons (d 7.64, 7.57, assigned as 8-H) and vice versa. These
results suggested that the ribosylation of 7 was carried out at
the N1-position. The NOE study also revealed that 3 and 9
exist in the syn conformation. This observation is consistent
with M. P. Schweizer’s studies24,25) (Table 1).
∗ To whom correspondence should be addressed. e-mail: chern@jwc.mc.ntu.edu.tw
© 2004 Pharmaceutical Society of Japan

December 2004
1423
Reagents and conditions: (a) benzoyl isothiocyanate, DMF, r.t.; (b) DCC, r.t.; (c) NH4OH/MeOH/DMF, r.t., 88% from 6; (d) (i) BSTFA, CH3CN, 75 °C, 20 min; (ii) 1-O-acetyl-
2,3,5-tri-O-benzoyl-b-D-ribofuranose, TMSOTf, CH3CN, 75 °C, 1 h; (e) aq. NH4OH/MeOH/acetone, r.t., 26 h, 74% from 7.
Chart 1
Table 1. NOE Effects of Compounds 3 and 9
NOE effect
Compound
Proton
Chemical shift
Irradiated at 1ꢀ-H
2.70%
Irradiated at 8-H
3 R2ꢁR3ꢁH
8-H
1ꢀ-H
8-H
7.64 (m)
6.12 (d)
7.57 (m)
6.23 (s)
4.35%
1.20%
9 R2, R3ꢁCMe2
1.27%
1ꢀ-H
A convenient preparation of 5ꢀ-arylthio-5ꢀ-deoxynucleo-
sides was reported by T. Hata et al. involving the reaction of
nucleosides with dialkyl disulfides in the presence of tri-n-
butylphosphine in pyridine.5,9) In our attempt to synthesize
the 5ꢀ-arylthio-5ꢀ-deoxy 4-aminoquinazolin-2-one nucleo-
side (4), 3 or 9 was treated with bis(4-methoxyphenyl) disul-
fide under Hata’s condition, in the presence of tri-n-
butylphosphine in pyridine, but no desired product (4 or 12)
was observed in the reaction.
Nevertheless, 9 was first treated with N,N-dimethylform-
amide dimethyl acetal to protect the amino group at the
4-position, then reacted with bis(4-methoxyphenyl) disulfide
under Hata’s condition to form the desired product 11. Com-
pound 11, without purification, was immediately treated with
ammonium hydroxide to remove the protecting group to give
4-amino-1-[5-deoxy-5-((4-methoxyphenyl)thio)-2,3-O-iso-
propylidene-b-D-ribofuranosyl]quinazolin-2-one (12) in 62%
yield after 3 steps. The isopropylidene was removed by treat-
ment of 12 with 90% aqueous trifluoroacetic acid to afford
the desired product 4 in 71% yield (Chart 2).
This result indicated that the amino group at the 4-position
of quinazoline played an important role in the reaction. It is
noticeable that the conversion of cytidine (2) to 5ꢀ-arylthio-
5ꢀ-deoxycytidines under a similar condition has previously
been reported by T. Hata et al.5,9) However, the quinazoline
nucleosides 3 and 9 did not undergo the similar reaction as
cytidine under the same condition unless the amino group at
the 4-position of quinazoline was protected with dimeth-
ylaminomethylidene. Furthermore, the formation of O2,5ꢀ-
cyclic nucleosides by a Mitsunobu-type dehydration reaction
was not observed in the reaction.35)
Reagents and conditions: (a) HC(OEt)3, p-TsOH·H2O, acetone, r.t., 6 h, 74%; (b)
bis(4-methoxyphenyl) disulfide, 10 eq n-Bu3P, pyridine; (c) N,N-dimethylformamide di-
methyl acetal, DMF, r.t., 24 h; (d) bis(4-methoxyphenyl) disulfide, n-Bu3P, pyridine, r.t.,
24 h; (e) NH4OH/MeOH, 62% from 9; (f) TFA/H2O (9 : 1, v/v), r.t., 90 min, 71%.
Chart 2
strated that a suitably protected L-homocystine can be con-
densed with unprotected nucleosides under Hata’s condition
to give the protected AdoHcy analogs.11,12) The direct con-
densation of 3 with N,N-bis(trifluoroacetyl)-L-homocystine
dimethyl ester11,13) (13) in the presence of tri-n-butylphos-
phine proved unsuccessful as expected. However, with the
amino-protected quinazoline nucleoside (15) prepared from
The success in the synthesis of 4 prompted us to broaden
the scope of this strategy. P. Serafinowski et al. have demon-

1424
Vol. 52, No. 12
Reagents and conditions: (a) N,N-bis(trifluoroacetyl)-L-homocystine dimethyl ester (13), n-Bu3P, pyridine/DMF, r.t.; (b) N,N-dimethylformamide dimethyl acetal, DMF, r.t., 24 h;
(c) N,N-bis(trifluoroacetyl)-L-homocystine dimethyl ester (13), n-Bu3P, pyridine, r.t., 7 d, 5% from 3; (d) (i) Ba(OH)2, H2O/MeOH; (ii) Hꢃ, 50% from 16.
Chart 3
3, the coupling reaction proceeded but only gave 5% of the ried out at the 5ꢀ-position. The nucleoside derivatives 4 and
desired product 16 accompanied with unreacted starting 17 were screened for antiviral activities against herpes sim-
materials. The dialkyl disulfides are generally much less plex virus type-1 (HSV-1) and Epstein-Barr virus (EBV) and
reactive than diaryl disulfides in the phosphine-mediated showed no activity at non-cytotoxic concentrations. The un-
coupling reaction9,11,12,36) which resulted in the low reaction expected hydrolysis of the N,N-dimethylformamidinyl group
yield.
provides an alternative interconversion of functionalities. Its
Treatment of 16 with aqueous barium hydroxide followed synthetic application for other quinazoline derivatives is in
by neutralization with acid gave the fully deprotected product progress.
17 which was surprisingly not the desired product 5. EI-MS
(electron impact mass spectrometry) analysis (70 eV) of 17
showed strong fragment peaks at m/z 64 (18%), 92 (49%),
Experimental
General Chemical Procedures Melting points were obtained on an
Electrothermal apparatus and are uncorrected. NMR spectra were obtained
119 (85%), and 162 (100%). This result is consistent with
the fragment peaks of quinazoline-2,4-dione, which sug-
gested a quinazoline-2,4-dione nucleoside derivative was
obtained after the hydrolysis. ESI-HR-MS (electrospray ion-
ization) (formic acid) confirmed the proposed structure of
17. UV–Vis absorption spectroscopy also supported the
on Varian Gemini-300, JEOL JNM-EX400 or Bruker DRX500 spectrome-
ter. IR spectra were recorded on a Jasco A-100 infrared spectrophotometer.
Mass spectra were recorded on Finnigan TSQ-46C (EI), JEOL JMS-D300
(EI), VG 70-250S (FAB) or Micromass LCT (ESI) mass spectrometer. Ele-
mental analyses for C, H, and N were carried out either on a Heraeus ele-
mental analyzer or Perkin-Elmer 240 elemental analyzer and were within
ꢂ0.4% of the theoretical values. Thin-layer chromatography (TLC) was per-
assignment. The literature revealed that the lmax of 3 displays formed on Merck plates precoated with silica gel 60 containing fluorescent
indicator. Compounds on thin-layer chromatography were visualized by illu-
mination under UV light (254 nm), or dipped into 10% methanolic sulfuric
acid followed by charring on a hot plate. Solvent systems are expressed as a
percentage of the more polar component with respect to total volume
significant difference at pH 1 [326 nm (e 4700)] and pH 11
[317 nm (e 4500)] while the lmax of the quinazoline-2,4-
dione analog, 1-(b-D-ribofuranosyl)quinazoline-2,4-dione,
was not affected by pH [pH 1: 306 nm (e 3900); pH
(v/v%). Merck silica gel (230—400 mesh) was used for flash column chro-
7: 304 nm (e 3715); pH 11: 306 nm (e 4200)].20,21) Com-
matography as described by Still, W. C. et al.37) Evaporation was carried out
with a rotary evaporator under reduced pressure with the bath temperature
below 50 °C unless specified otherwise. Materials obtained from commercial
suppliers were used without further purification. The reported yields have
not been optimized.
pound 17 shows lmax at 306 nm (e 3433, pHꢁ1), 305 nm
(e 3830, MeOH/H2O), and 307 nm (e 2542, pHꢁ11). There-
fore, the structure of 17 was identified unambiguously as
S-[1-(quinazoline-2,4-dion-1-yl)-b-D-ribofuranosyl]-L-homo-
4-Aminoquinazolin-2-one (7) To a solution of anthranilamide (6,
5.00 g, 36.72 mmol) in anhydrous N,N-dimethylformamide (DMF) (50 ml)
was added benzoyl isothiocyanate (5.9 ml, 7.16 g, 43.89 mmol, 1.2 eq). After
the reaction mixture was stirred at room temperature under nitrogen for 2 h,
cysteine (Chart 3). This unexpected displacement of the N,N-
dimethylformamidinyl group has not been reported in the
literature.
dicyclohexylcarbodiimide (DCC) (16.69 g, 80.89 mmol, 2.2 eq) was added
and the mixture was stirred at room temperature for an additional 24 h. Ace-
Conclusion
tone (40 ml) was added to the mixture and the solution was vigorously
stirred for 20 min. The precipitated solid was collected by filtration and
washed with chloroform. The solid was then dissolved in a mixture
of methanol/28% concentrated ammonium hydroxide solution/DMF
(50 ml : 50 ml : 100 ml) and the reaction mixture was stirred at room temper-
ature for 24 h. The solvents were removed under reduced pressure to dry-
In summary, our investigation has provided an alternative
route for the synthesis of 5ꢀ-alkylthio-5ꢀ-deoxy nucleosides.
The use of N,N-dimethylaminomethylidene to protect the
amino group on the nucleoside bases can reduce the partici-
pation of base-functionalities in the reaction which was car- ness. Methanol (30 ml) was added to the resulting oil and the mixture was

December 2004
1425
vigorously stirred for 1 h. The precipitated solid was collected by filtration
and washed with chloroform to give 7 (8.59 g, 32.3 mmol, 88%). An analyti-
cal sample of 7 was recrystallized from EtOH/H2O. mp ꢄ360 °C (dec.)
(EtOH/H2O) [lit.29) ꢄ360 °C (DMF–EtOH)]; 1H-NMR (DMSO-d6,
113.5, 114.2, 116.9, 122.9, 128.8, 135.0, 143.6, 157.2, 159.3, 170.1
(–CHꢁN).
4-Amino-1-[5-deoxy-5-((4-methoxyphenyl)thio)-2,3-O-isopropylidene-
b-D-ribofuranosyl]quinazolin-2-one (12) To the crude product 10 and
300 MHz) d 7.05—7.13 (m, 2H, Ph), 7.52—7.57 (m, 1H, Ph), 7.78 (br s, bis(4-methoxyphenyl)disulfide (4.93 g, 17.73 mmol, 2.5 eq) in dry pyridine
(35 ml) was added tri-n-butylphosphine (24.4 ml, 3.57 g, 17.66 mmol, 2.5 eq)
via a syringe. The reaction was stirred for 24 h at room temperature under
nitrogen, then the solvent was evaporated under reduced pressure. Hexane
(50 ml) was added to the resulting oil and the mixture was stirred vigorously
at room temperature for 15 min. The hexane layer was decanted and the
resulting oil was concentrated to dryness. The resulting oil was treated with
28% concentrated ammonium hydroxide/methanol (140 ml, 1 : 1, (v/v)) and
the mixture was stirred at room temperature for 24 h. The solvents were
evaporated under reduced pressure and the resulting oil was purified by flash
column chromatography (CHCl3/MeOHꢁ97.5 : 2.5) to give 12 (2.00 g,
4.40 mmol, 62% from 9, Rfꢁ0.23 (CHCl3/MeOHꢁ95 : 5)). An analytical
sample of 12 was obtained by recrystallization from MeOH. mp 123 °C
1H, NH), 7.85 (br s, 1H, NH), 7.96—7.99 (d, 1H, Ph), 10.67 (br s, 1H, NH);
MS (EI, 70 eV) m/z 118 (76), 161 (100) (Mꢃ); MS (ESI, formic acid) m/z
162 (100) (Mꢃꢃ1); HR-MS (EI) Calcd for C8H7N3O: 161.0589, Found:
161.0590; Anal. Calcd for C8H7N3O·0.5H2O: C, 56.46; H, 4.74; N, 24.69.
Found: C, 56.59; H, 4.83; N, 24.92.
4-Amino-1-(b-D-ribofuranosyl)quinazolin-2-one (3) To a solution of 7
(5.00 g, 31.06 mmol) in acetonitrile (100 ml) was added bis(trimethylsilyl)tri-
fluoroacetamide (BSTFA) (33.0 ml, 31.98 g, 124.23 mmol, 4 eq) and the
reaction mixture was stirred at 75 °C for 25 min. This solution was treated
with 1-O-acetyl-2,3,5-tri-O-benzoyl-b-D-ribofuranose (19.00 g, 37.70 mmol,
1.21 eq) and trimethylsilyl trifluoromethanesulfonate (TMSOTf) (9.0 ml,
10.35 g, 46.57 mmol, 1.5 eq) and then stirred at 75 °C for an additional 1 h.
The reaction mixture was cooled to room temperature and the solvent was
removed under reduced pressure to dryness. The residue was dissolved in a
mixture of methanol/acetone/28% concentrated ammonium hydroxide solu-
tion (200 ml : 100 ml : 200 ml) and the reaction mixture was stirred at room
temperature for 30 h. The solvents were removed under reduced pressure.
The resulting oil-like residue was filtered and the collected solid was washed
with cold ethanol to give the first portion of the product. The filtrate was
concentrated to dryness. Acetone (40 ml) was added to the resulting oil and
the mixture was vigorously stirred for 30 min. The precipitated solid was
collected by filtration and washed with cold ethanol to give the second por-
tion of the product (3, 6.78 g overall, 23.11 mmol, 74%). An analytical sam-
ple of 3 was obtained by recrystallization from EtOH/H2O. mp 246—247 °C
(dec.) (EtOH/H2O) [lit.20) 259—260 °C (dec.)]; 1H-NMR (DMSO-d6,
300 MHz) d 3.52—3.78 (m, 3H, 4ꢀ and 5ꢀ-H), 4.13 (dd, 1H, Jꢁ12.4,
6.1 Hz), 4.53 (dd, 1H, Jꢁ12.2, 6.0 Hz), 4.93—4.96 (m, 2H, 2ꢅOH), 5.11 (d,
1H, Jꢁ5.9 Hz, OH), 6.12 (d, 1H, Jꢁ5.7 Hz, 1ꢀ-H), 7.18—7.23 (m, 1H, Ph),
7.61—7.66 (m, 2H, Ph), 7.96—8.06 (m, 3H, Ph and NH2); 13C-NMR
(DMSO-d6, 75 MHz) d 61.9 (5ꢀ-CH2), 69.6 (2ꢅCH), 84.7 (CH), 90.8 (1ꢀ-
CH), 110.8, 116.1 (CH), 122.0 (CH), 125.2 (CH), 134.0 (CH), 142.3, 155.7,
163.4; MS (FAB) m/z 137, 154, 162 (100), 185, 294 (42) (Mꢃꢃ1); Anal.
Calcd for C13H15N3O5·0.5H2O: C, 51.65; H, 5.34; N, 13.90. Found: C,
51.95; H, 5.15; N, 13.72.
4-Amino-1-(2,3-O-isopropylidene-b-D-ribofuranosyl)quinazolin-2-one
(9) Compound 3 (1.98 g, 6.76 mmol) was suspended in acetone (40 ml)
containing p-toluenesulfonic acid monohydrate (1.50 g, 7.89 mmol, 1.17 eq).
Triethyl orthoformate (4.0 ml, 3.56 g, 24.04 mol, 3.6 eq) was added at room
temperature with vigorous stirring. After all the solid dissolved, the reaction
mixture was stirred for an additional 4 h, and then the solution was adjusted
to pH 8 with diluted ammonia water. The solution was concentrated to 20 ml
under reduced pressure. The aqueous solution was extracted with ethyl
acetate (3ꢅ50 ml). The organic layer was combined and the solvent was
evaporated to give the crude product of 9 as a white solid (1.67 g,
5.02 mmol, 74%). The solid was recrystallized from ethanol to give
9 (0.6750 g, 2.03 mmol, 30%). mp 271—272 °C (EtOH); 1H-NMR (DMSO-
d6, 500 MHz) d 1.29 (s, 3H, CH3), 1.51 (s, 3H, CH3), 3.53—3.58 (m, 1H, 5ꢀ-
H), 3.63—3.67 (m, 1H, 5ꢀ-H), 4.02 (dd, 1H, Jꢁ9.7, 5.2 Hz), 4.91—4.94 (m,
2H, including one D2O exchangeable proton, 5ꢀ-OH), 5.26 (dd, 1H, Jꢁ6.6,
2.1 Hz), 6.23 (s, 1H, 1ꢀ-H), 7.23—7.26 (m, 1H, Ph), 7.56—7.57 (m, 1H,
Ph), 7.64—7.67 (m, 1H, Ph), 8.05—8.21 (m, 3H, 1ꢅPh and NH2); 13C-
NMR (DMSO-d6, 125 MHz) d 26.0 (CH3), 28.0 (CH3), 62.5 (5ꢀ-CH2), 82.2
(CH), 83.5 (CH), 88.2 (CH), 91.1 (1ꢀ-CH), 111.0, 113.8, 115.7 (CH), 122.8
(CH), 126.0 (CH), 134.9 (CH), 142.7, 155.6, 164.2; MS (FAB) m/z 162
(100), 334 (20) (Mꢃꢃ1); HR-MS (FAB) Calcd for C16H20N3O5: 334.1403,
found: 334.1402; Anal. Calcd for C16H19N3O5: C, 57.65; H, 5.75; N, 12.61.
Found: C, 57.61; H, 5.70; N, 12.67.
1
(MeOH); H-NMR (DMSO-d6, 300 MHz) d 1.28 (s, 3H, CH3), 1.45 (s, 3H,
CH3), 3.15 (dd, 1H, Jꢁ13.7, 6.6 Hz, 5ꢀ-H), 3.24 (dd, 1H, Jꢁ13.7, 7.4 Hz,
5ꢀ-H), 3.70 (s, 3 H, CH3), 4.04—4.09 (m, 1H), 4.94 (dd, 1H, Jꢁ6.2, 3.1 Hz),
5.34 (d, 1H, Jꢁ6.5 Hz), 6.07 (s, 1 H, 1ꢀ-H), 6.81 (d, 2H, Jꢁ8.6 Hz, Ph),
7.22—7.27 (m, 1H, Ph), 7.31 (d, 2H, Jꢁ8.6 Hz, Ph), 7.49—7.52 (m, 1H,
Ph), 7.64—7.69 (m, 1H, Ph), 8.06—8.14 (m, 3H, Ph and NH2); 13C-NMR
(DMSO-d6, 75 MHz) d 25.3 (CH3), 27.2 (CH3), 37.6 (5ꢀ-CH2), 55.5 (CH3),
84.1, 84.7, 87.4, 91.4 (1ꢀ-CH), 110.5, 112.7, 114.7, 115.0, 122.3, 125.4,
125.6, 132.6, 134.6, 142.5, 154.9, 158.7, 163.7; MS (EI/20 eV) m/z 100,
194, 294 (100), 455 (28) (Mꢃ); HR-MS (FAB) Calcd for C23H26N3O5S:
456.1593, Found: 456.1592; Anal. Calcd for C23H25N3O5S·0.5CH3OH: C,
59.86; H, 5.77; N, 8.91. Found: C, 60.09; H, 5.67; N, 8.91.
4-Amino-1-[5-deoxy-5-((4-methoxyphenyl)thio)-b-D-ribofuranosyl]
quinazolin-2-one (Trifluoroacetic Acid Salt) (4) Compound 12 (0.59 g,
1.30 mmol) was dissolved in a 90% aqueous trifluoroacetic acid solution
(13 ml) and the mixture was stirred at room temperature for 90 min. The sol-
vents were removed under reduced pressure and the resulting solid was re-
crysallized from ethanol to give 4 (0.49 g, 0.92 mmol, 71%). mp 175—
177 °C (dec.) (EtOH); 1H-NMR (DMSO-d6, 500 MHz) d 3.14 (dd, 1H,
Jꢁ13.8, 7.4 Hz, 5ꢀ-H), 3.32 (dd, 1H, Jꢁ13.8, 4.3 Hz, 5ꢀ-H), 3.73 (s, 3H,
CH3), 3.87 (dd, 1H, Jꢁ11.0, 6.8 Hz), 4.22 (t, 1H, Jꢁ6.3 Hz), 4.63 (t, 1H,
Jꢁ5.5 Hz), 6.03 (d, 1H, Jꢁ4.6 Hz, 1ꢀ-H), 6.88 (d, 2H, Jꢁ8.7 Hz, 4-MeOPh),
7.36 (d, 2H, Jꢁ8.7 Hz, 4-MeOPh), 7.41—7.44 (m, 1H, Ph), 7.64—7.66 (m,
1H, Ph), 7.84—7.87 (m, 1H, Ph), 8.30—8.32 (m, 1H, Ph), 9.40—9.85 (brs,
2H, NH2); 13C-NMR (DMSO-d6, 125 MHz) d 38.2 (5ꢀ-CH2), 56.0 (CH3),
70.8 (CH), 72.8 (CH), 82.8 (CH), 92.0 (1ꢀ-CH), 110.2, 115.6 (CH), 117.1
(CH), 117.3 (q, Jꢁ294 Hz, CF3 of TFA), 124.6 (CH), 126.8, 127.2 (CH),
133.0 (CH), 137.8 (CH), 141.8, 149.3, 159.2, 159.8 (q, Jꢁ34 Hz, CꢁO of
TFA), 160.3; MS (ESI, formic acid) m/z 162 (100), 255 (58), 416 (53)
(Mꢃꢃ1); HR-MS (ESI) Calcd for C20H22N3O5S: 416.1280, Found:
416.1284; Anal. Calcd for C20H21N3O5S·CF3COOH: C, 49.90; H, 4.19; N,
7.94. Found: C, 49.96; H, 4.23; N, 7.86.
N,N-Bis(trifluoroacetyl)-L-homocysteine
Dimethyl
Ester
(13).
[Method A]11) L-Homocystine (4.74 g, 17.67 mmol) was suspended in an-
hydrous methanol (30 ml) and cooled to 0 °C. Dry hydrogen chloride gas
was bubbled through the suspension till the solution became clear (approxi-
mately 30 min). Dimethyl sulfite (11.55 g, 104.9 mmol, 5.9 eq) was added to
the solution and the mixture was heated at 60 °C for 1 h. The solvent was re-
moved under reduced pressure. The resulting residue was dissolved in triflu-
oroacetic anhydride (17.17 g, 81.75 mmol, 4.6 eq) and the reaction mixture
was stirred at 60 °C for 1 h. The solvent was removed under reduced pres-
sure, and the residue was dissolved in EtOAc (100 ml), washed with satu-
rated NaHCO3 solution (50 ml), and saturated NaCl solution (50 ml), then
dried over anhydrous Na2SO4 and evaporated to dryness. The resulting
residue was purified by column chromatography (Hex/EtOAcꢁ75 : 25,
Rfꢁ0.11) to give 13 (4.11 g, 8.41 mmol, 48%).
4-(N,N-Dimethylformamidinyl)-1-(2,3-O-isopropylidene-b-D-ribofura-
nosyl)quinazolin-2-one (10) To a suspension of 9 (2.36 g, 7.08 mmol) in
DMF (47 ml) was added N,N-dimethylformamide dimethyl acetal (3.8 ml,
3.40 g, 28.51 mmol, 4 eq). The reaction mixture was stirred at room tempera-
ture under nitrogen for 24 h. The solvent was evaporated in vacuo to give the
crude product of 10. 1H-NMR (CDCl3, 300 MHz) d 1.35 (s, 3H, CH3), 1.59
(s, 3H, CH3), 3.23 (s, 3H, CH3), 3.27 (s, 3H, CH3), 3.83—4.03 (m, 3H, 5ꢀ-H
and OH), 4.35 (dd, 1H, Jꢁ6.3, 3.0 Hz), 5.29 (dd, 1H, Jꢁ6.0, 4.4 Hz), 5.48
(dd, 1H, Jꢁ6.5, 2.3 Hz), 6.21 (d, 1H, Jꢁ2.3 Hz, 1ꢀ-H), 7.19—7.24 (m, 1H,
Ph), 7.46—7.49 (m, 1H, Ph), 7.60—7.66 (m, 1H, Ph), 8.38—8.41 (m, 1H,
Ph), 8.93 (s, 1H); 13C-NMR (CDCl3, 75 MHz) d 25.8 (CH3), 27.9 (CH3),
36.1 (CH3), 42.2 (CH3), 63.7 (5ꢀ-CH2), 81.2, 84.5, 88.8, 92.4 (1ꢀ-CH),
[Method B] L-Homocystine (5.00 g, 18.63 mmol) was suspended in an-
hydrous methanol (100 ml) and cooled to ꢆ78 °C. To the suspension was
added thionyl chloride (10 ml, 16.38 g, 137.67 mmol, 7.39 eq) dropwise. The
reaction temperature was allowed to warm to room temperature and stirred
for an additional 16 h. The solvent was removed under reduced pressure, and
the residue was dried under reduced pressure. The residue was dissolved in
trifluoroacetic anhydride (25 ml, 37.18 g, 0.177 mol, 9.5 eq) and the reaction
mixture was stirred at 60 °C for 1.5 h. The solvent was removed under re-
duced pressure, and the residue was dissolved in ethyl actate (100 ml),
washed with saturated NaHCO3 solution (2ꢅ60 ml), and saturated NaCl so-
lution (60 ml), dried over anhydrous Na2SO4 and then evaporated to dryness.

1426
Vol. 52, No. 12
The resulting residue was purified by flash column chromatography
(Hex/EtOAcꢁ7 : 3, Rfꢁ0.24) to give 13 (8.59 g, 17.60 mmol, 95%). An ana-
lytical sample of 13 was obtained by recrystallization from methanol. mp
87—89 °C (MeOH) [lit.11) 89—90 °C (MeOH/H2O)]; 1H-NMR (CDCl3,
300 MHz) d 2.12 (m, 2H, b-H), 2.29 (m, 2H, b-H), 2.65 (dt, 4H, Jꢁ7.0,
4.3 Hz, g-H), 3.73 (s, 6H, OCH3), 4.68 (dt, 2H, Jꢁ8.0, 5.1 Hz, a-H), 7.70
(d, 2H, Jꢁ8.0 Hz, NH); 13C-NMR (CDCl3, 100 MHz) d 31.3, 33.8, 51.4,
52.8 (CH3), 115.2 (q, Jꢁ287 Hz, CF3), 156.7 (q, Jꢁ37 Hz, CF3–CꢁO),
170.4 (CꢁO); MS (EI/11 eV) m/z 212, 488 (100) (Mꢃ).
Methyl N-Trifluoroacetyl-S-[1-(4-(N,N-dimethylformamidinyl)quina-
zolin-2-on-1-yl)-b-D-ribofuranosyl]-L-homocysteine (16) To a suspen-
sion of 3 (0.59 g, 2.00 mmol) in DMF (12 ml) was added N,N-dimethylform-
amide dimethyl acetal (1.1 ml, 0.95 g, 8.00 mmol, 4 eq). The reaction mix-
ture was stirred at room temperature under nitrogen for 24 h. The solvent
was evaporated in vacuo to give the N-protected product 15. To 15 and the
protected amino acid 13 (2.75 g, 5.60 mmol, 2.8 eq) in dry pyridine (10 ml)
was added tri-n-butylphosphine (3.0 ml, 2.43 g, 12.00 mmol, 6 eq) via a sy-
ringe. The reaction was stirred for 7 d at room temperature under nitrogen.
Methanol (10 ml) was added and the solvents were evaporated under reduced
pressure. Hexane (30 ml) was added to the residue and the mixture was
stirred vigorously at room temperature for 10 min. The hexane layer was de-
canted and the resulting oil was purified by flash column chromatography
311 (1985).
4) Wolfe M. S., Borchardt R. T., J. Med. Chem., 34, 1521—1530 (1991).
5) Nakagawa I., Hata T., Tetrahedron Lett., 1975, 1409—1412 (1975).
6) Chang C. D., Coward J. K., J. Med. Chem., 19, 684—691 (1976).
7) Borchardt R. T., Wu Y. S., Wu B. S., J. Med. Chem., 21, 1307—1310
(1978).
8) Montgomery J. A., Thomas H. J., Thorpe M. C., Chiang P. K., J. Med.
Chem., 24, 1514—1516 (1981).
9) Nakagawa I., Aki K., Hata T., J. Chem. Soc. Perkin Trans. I, 1983,
1315—1318 (1983).
10) Shire D., Blanchard P., Raies A., Lawrence F., Robertgero M., Lederer
E., Nucleosides Nucleotides, 2, 21—31 (1983).
11) Serafinowski P., Synthesis, 1985, 926—928 (1985).
12) Serafinowski P., Dorland E., Harrap K. R., Balzarini J., De Clercq E.,
J. Med. Chem., 35, 4576—4583 (1992).
13) Johnson C. R., Esker J. L., Van Zandt M. C., J. Org. Chem., 59,
5854—5855 (1994).
14) Wnuk S. F., Stoeckler J. D., Robins M. J., Nucleosides Nucleotides, 13,
389—403 (1994).
15) Pignot M., Pljevaljcic G., Weinhold E., Eur. J. Org. Chem., 2000,
549—555 (2000).
16) Chern J.-W., Lee H.-Y., J. Chin. Chem. Soc. (Taipei), 34, 329—331
(1987).
(CHCl3/MeOHꢁ95 : 5) to give 16 (oil, 56 mg, 0.097 mmol, 5%, Rfꢁ0.24
1
(CHCl3/MeOHꢁ9 : 1)). H-NMR (CDCl3, 300 MHz) d 2.10—2.19 (m, 2H), 17) Chern J.-W., Lee H.-Y., Chen C. S., Shewach D. S., Daddona P. E.,
2.59—2.67 (m, 2H), 2.92 (dd, 1H, Jꢁ14.0, 6.5 Hz, 5ꢀ-H), 3.01 (dd, 1H,
Jꢁ14.0, 4.7 Hz, 5ꢀ-H), 3.23 (s, 3H, CH3), 3.26 (s, 3H, CH3), 3.68 (s, 3H, 18) Chern J.-W., Kuo C.-C., Chang M.-J., Liu L.-T., Nucleosides Nu-
CH3), 4.03—4.11 (m, 1H, a-H), 4.61 (dd, 1H, Jꢁ6.5, 2.8 Hz), 4.70 (t, 1H, cleotides, 12, 941—949 (1993).
Jꢁ7.0 Hz), 4.89 (dd, 1H, Jꢁ6.5, 2.7 Hz), 6.14 (d, 1H, Jꢁ2.8 Hz, 1ꢀ-H), 19) Chen G.-S., Kalchar S., Kuo C.-W., Chang C.-S., Usifoh C. O., Chern
7.18—7.23 (m, 1H, Ph), 7.48—7.51 (m, 1H, Ph), 7.58—7.64 (m, 1H, Ph), J.-W., J. Org. Chem., 68, 2502—2505 (2003).
Townsend L. B., J. Med. Chem., 36, 1024—1031 (1993).
7.72 (d, 1H, Jꢁ7.1 Hz, a-NH), 8.35—8.38 (m, 1H, Ph), 8.78 (s, 1H, 20) Stout M. G., Robins R. K., J. Org. Chem., 33, 1219—1225 (1968).
–CHꢁN); 13C-NMR (CDCl3, 75 MHz) d 29.4, 31.5, 34.9, 36.0, 42.2, 52.8, 21) Dunkel M., Pfleiderer W., Nucleosides Nucleotides, 10, 799—817
53.4, 72.7, 73.4, 83.8, 92.9, 114.5, 117.0, 122.9, 128.7, 134.8, 143.4, 157.1,
(1991).
159.1, 169.9, 171.5 (without CF3 and CF3–CꢁO); MS (FAB) m/z 136, 154 22) Dunkel M., Pfleiderer W., Nucleosides Nucleotides, 11, 787—819
(100), 219, 307, 418, 576 (10) (Mꢃꢃ1); HR-MS (FAB) Calcd for
C23H29N5O7F3S: 576.1740, Found: 576.1740.
S-[1-(Quinazoline-2,4-dion-1-yl)-b-D-ribofuranosyl]-L-homocysteine
(17) A solution of 16 (56 mg, 0.097 mmol) in methanol (10 ml) was diluted
with 0.5 M barium hydroxide solution (10 ml) and the reaction mixture was
stirred at room temperature for 12 h. The solution was acidified to pH 7 with
(1992).
23) Dunkel M., Pfleiderer W., Nucleosides Nucleotides, 12, 125—374
(1993).
24) Schweizer M. P., Witkowski J. T., Robins R. K., J. Am. Chem. Soc., 93,
277—279 (1971).
25) Schweizer M. P., Banta E. B., Witkowski J. T., Robins R. K., J. Am.
Chem. Soc., 95, 3770—3778 (1973).
0.5 M sulfuric acid, and the precipitate was collected by filtration to give
1
17 (20 mg, 0.049 mmol, 50%). mp 213—215 °C (dec.); H-NMR (DMSO- 26) Michel J., Gueguen G., Vercauteren J., Moreau S., Tetrahedron, 53,
d6, 300 MHz) d 1.78—1.85 (m, 1H, b-H), 1.95—2.06 (m, 1H, b-H), 2.64
(t, 2H, Jꢁ7.5 Hz, g-H), 2.81 (dd, 1H, Jꢁ13.7, 6.6 Hz, 5ꢀ-H), 2.95 (dd, 1H,
Jꢁ13.5, 4.5 Hz, 5ꢀ-H), 3.28 (dd, 1H, Jꢁ6.5, 5.4 Hz, a-H), 3.87 (dd, 1H,
Jꢁ10.7, 5.9 Hz), 4.13 (t, 1H, Jꢁ6.3 Hz), 4.54 (t, 1H, Jꢁ5.6 Hz), 5.45 (brs,
2H, 2ꢅOH), 6.07 (d, 1H, Jꢁ4.9 Hz, 1ꢀ-H), 7.29—7.34 (m, 1H, Ph), 7.54—
8457—8478 (1997).
27) Diwan A. R., Robins R. K., Prusoff W. H., Experientia, 25, 98—100
(1969).
28) Trattner R. B., Elion G. B., Hitchings G. H., Sharefkin D. M., J. Org.
Chem., 29, 2674—2677 (1964).
7.57 (m, 1H, Ph), 7.70—7.75 (m, 1H, Ph), 8.00—8.03 (m, 1H, Ph); 13C- 29) Yamamoto M., Inaba S., Yamamoto H., Chem. Pharm. Bull., 26,
NMR (DMSO-d6, 75 MHz) d 28.9, 31.7, 34.0, 53.4, 69.7, 72.1, 82.7, 90.8,
1633—1651 (1978).
116.3, 116.6, 123.7, 128.0, 135.4, 140.4, 150.3, 161.9, 170.0; UV lmax nm 30) Groziak M. P., Chern J.-W., Townsend L. B., J. Org. Chem., 51,
(e): 306 (3433, pHꢁ1), 305 (3830, MeOH/H2O), 307 (2542, pHꢁ11); MS
(ESI, formic acid) m/z 338 (45), 412 (100) (Mꢃꢃ1); HR-MS (ESI, formic
acid) Calcd for C17H22N3O7S (Mꢃ1): 412.1178, Found: 412.1172.
1065—1069 (1986).
31) Chern J.-W., Lin G.-S., Chen C.-S., Townsend L. B., J. Org. Chem., 56,
4213—4218 (1991).
32) Vorbruggen H., Krolikiewicz K., Bennua B., Chem. Ber., 114, 1234—
1255 (1981).
Acknowledgments We thank professor Carl R. Johnson of Wayne State
University (MI, U.S.A.) for his valuable suggestions for the preparation of 33) Vorbruggen H., Bennua B., Chem. Ber., 114, 1279—1286 (1981).
the protected L-homocystine (13). This investigation was supported by a 34) Maccoss M., Robins M. J., Rayner B., Imbach J. L., Carbohydr. Res.,
research grant (NSC84-2331-B-016-018) from the National Science Council
of Taiwan.
59, 575—579 (1977).
35) Chen G.-S., Chen C.-S., Chien T.-C., Yeh J.-Y., Kuo C.-C., Talekar R.
S., Chern J.-W., Nucleosides Nucleotides Nucleic Acids, 23, 347—359
(2004).
References and Notes
1) Chien T.-C., Chern J.-W., Carbohydr. Res., 339, 1215—1217 (2004).
2) Present address: Department of Chemistry, The University of Michi-
gan, Ann Arbor, MI 48109, U.S.A.
36) Serafinowski P., Dorland E., Balzarini J., De Clercq E., Nucleosides
Nucleotides, 14, 545—547 (1995).
37) Still W. C., Kahn M., Mitra A., J. Org. Chem., 43, 2923—2925 (1978).
3) De Clercq E., Cools M., Biochem. Biophys. Res. Commun., 129, 306—