Efficient syntheses of 2-chloro-2′-deoxyadenosine (cladribine) from 2′-deoxyguanosine

Article abstract of DOI:10.1021/jo020644k

We report efficient syntheses of the clinical agent cladribine (2-chloro-2′-deoxyadenosine, CldAdo), which is the drug of choice against hairy-cell leukemia and other neoplasms, from 2′-deoxyguanosine. Treatment of 3′,5′-di-O-acetyl- or benzoyl-2′-deoxyguanosine (1) with 2,4,6-triisopropyl- or 4-methylbenzenesulfonyl chloride gave high yields of the 6-O-arylsulfonyl derivatives 2 or 2′b. Deoxychlorination at C6 of 1 also proceeded to give the 2-amino-6-chloropurine derivative 5 in excellent yields. The nonaqueous diazotization/chloro dediazoniation (acetyl chloride/benzyltriethylammonium nitrite) of 2, 2′b, and 5 gave the 2-chloropurine derivatives 3, 3′b, and 6, respectively. The selective ammonolysis at C6 (arylsulfonate with 3 or chloride with 6) and accompanying deprotection of the sugar moiety gave CldAdo (64-75% overall yield from 1).

Full text of DOI:10.1021/jo020644k

Efficien t Syn th eses of 2-Ch lor o-2′-d eoxya d en osin e (Cla d r ibin e)
fr om 2′-Deoxygu a n osin e1
Zlatko J aneba, Paula Francom,† and Morris J . Robins*
Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602-5700
morris_robins@byu.edu
Received October 9, 2002
We report efficient syntheses of the clinical agent cladribine (2-chloro-2′-deoxyadenosine, CldAdo),
which is the drug of choice against hairy-cell leukemia and other neoplasms, from 2′-deoxyguanosine.
Treatment of 3′,5′-di-O-acetyl- or benzoyl-2′-deoxyguanosine (1) with 2,4,6-triisopropyl- or 4-me-
thylbenzenesulfonyl chloride gave high yields of the 6-O-arylsulfonyl derivatives 2 or 2′b.
Deoxychlorination at C6 of 1 also proceeded to give the 2-amino-6-chloropurine derivative 5 in
excellent yields. The nonaqueous diazotization/chloro dediazoniation (acetyl chloride/benzyltriethyl-
ammonium nitrite) of 2, 2′b, and 5 gave the 2-chloropurine derivatives 3, 3′b, and 6, respectively.
The selective ammonolysis at C6 (arylsulfonate with 3 or chloride with 6) and accompanying
deprotection of the sugar moiety gave CldAdo (64-75% overall yield from 1).
In tr od u ction
sequentially to CldADP and the active CldATP.2a,11a
Cladribine also is a good substrate for mitochondrial 2′-
deoxyguanosine (dGuo) kinase,11 and induction of pro-
grammed cell death by direct effects on mitochondria has
been implicated in its potent activity against indolent
lymphoid malignancies (via apoptosis) as well as in
proliferating cells.12,13
Venner reported the Fischer-Helferich syntheses of
naturally occurring 2′-deoxynucleosides in 196014 and
employed CldAdo as an intermediate for 2′-deoxygua-
nosine and -inosine. Ikehara and Tada also synthesized
dAdo with CldAdo as an intermediate [obtained by the
desulfurization of 8,2′-anhydro-9-(â-D-arabinofuranosyl)-
2-chloro-8-thioadenine].15
The syntheses of CldAdo as a target compound have
exploited the greater reactivity of leaving groups at C6
relative to those at C2 of the purine ring in SNAr
displacement reactions. Robins and Robins16 employed
the fusion coupling of 2,6-dichloropurine with 1,3,5-tri-
O-acetyl-2-deoxy-R-D-ribofuranose. The 9-(3,5-di-O-acetyl-
2-deoxy-R-D-erythro-pentofuranosyl)-2,6-dichloropurine
anomer was obtained by fractional crystallization. The
selective ammonolysis at C6 and accompanying depro-
tection gave 6-amino-2-chloro-9-(2-deoxy-R-D-erythro-
pentofuranosyl)purine. The pharmacologically active â
anomer (cladribine) was prepared by an analogous cou-
pling, chromatographic separation of anomers, and am-
monolysis.17
The lymphoselective toxicity of 2-chloro-2′-deoxyad-
enosine (CldAdo, cladribine) and its potential as a
chemotherapeutic agent against lymphoid neoplasms
were reported by Carson et al.2 This potent, deaminase-
resistant analogue of 2′-deoxyadenosine (dAdo) is cur-
rently the drug of choice for hairy-cell leukemia.3,4 It also
shows significant activity against chronic lymphocytic
leukemia,5,6 indolent non-Hodgkin’s lymphoma,7 and
Waldenstro¨m’s macroglobulinemia.8 Investigations with
cladribine treatment of multiple sclerosis,9 systemic lupus
erythematosis-associated glomerulonephritis,10 and other
rheumatoid and immune disorders are in progress.
Cladribine is a nucleoside prodrug, which is phosphory-
lated by deoxycytidine kinase to CldAMP and then
* Fax: (801) 422-0153.
† Present address: Biota, Inc., Carlsbad, CA.
(1) Nucleic Acid Related Compounds. 119. Patent application filed.
Paper 118: Francom, P.; Robins, M. J . J . Org. Chem. 2002, in press.
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10.1021/jo020644k CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/11/2003
J . Org. Chem. 2003, 68, 989-992
989

J aneba et al.
SCHEME 1 a
The stereoselective glycosylation of the sodium salts
of halopurines and analogues with 2-deoxy-3,5-di-O-p-
toluoyl-R-D-erythro-pentofuranosyl chloride gave â-nu-
cleoside anomers via predominantly Walden inver-
sion,18,19 and ammonolysis/deprotection gave CldAdo.20
Although the sodium salt glycosylation procedure usually
gave good anomeric stereoselectivity, minor quantities
of R anomers and >10% of the N7 regioisomers were
usually formed.21,22 This requires separations and results
in diminished yields of the desired N9 product. Carson
et al.2 had reported an enzymatic transfer of the 2-deoxy
sugar from thymidine to 2-chloroadenine (ClAde). Holy´
and co-workers noted that cells of a strain of Escherichia
coli performed glycosyl transfer from 2′-deoxyuridine to
2-chloro-6-[(dimethylaminomethylene)amino]purine to give
a derivative of CldAdo.23 Very recently Barai and co-
workers24 described an E. coli-mediated glycosyl transfer
synthesis of 2,6-diamino-9-(3-deoxy-â-D-erythro-pento-
furanosyl)purine25 and its enzymatic deamination to 3′-
deoxyguanosine.25 They reported glycosyl transfer from
2′-deoxyguanosine to ClAde and claimed an 81% yield of
CldAdo (on the basis of ClAde).26 However, a 3:1 ratio of
dGuo/ClAde was employed, so the yield of CldAdo was
<27% on the basis of dGuo.
Our chemical approach for the synthesis of regio- and
stereochemically pure CldAdo, which avoids the separa-
tion of mixtures with fusion and sodium salt glycosylation
procedures, employs the transformation of naturally
occurring nucleosides.27 The conversion of the 6-oxo
function of dGuo into the appropriate leaving groups,
diazotization/chloro dediazoniation of the 2-amino func-
tion, and selective C6 ammonolysis of 2-chloro-6-(substi-
tuted)purine derivatives provide a route from dGuo to
CldAdo with the retention of both â-anomeric stereo-
chemistry and N9-isomeric purity.
a
(a) TiPBS-Cl/Et3N/DMAP/CHCl3. (b) AcCl/BTEA-NO2/CH2Cl2,
-5 to 0 °C. (c) NH3/MeOH/CH2Cl2/∆. (d) POCl3/BTEA-Cl/N,N-
dimethylaniline/MeCN/∆.
benzyltriethylammonium nitrite (BTEA-NO2)-mediated
chloro dediazoniation of 6-O-2,4,6-triisopropylbenzene-
sulfonyl (TiPBS) or 6-chloro derivatives that are readily
obtained from dGuo.
Resu lts a n d Discu ssion
We have recently reported improved methods for the
replacement of an amino group on purine nucleoside
derivatives with chlorine, bromine, or iodine under
nonaqueous conditions.1,28 These mild diazotization/halo
dediazoniation methods were found to be applicable at
C6 of dAdo derivatives as well as at C2 of 2-amino-6-
chloropurine nucleosides. We now describe the efficient
syntheses of CldAdo, which employ acetyl chloride and
Our projected synthesis of CldAdo (4; Scheme 1) from
dGuo required the efficient transformation of the 6-oxo
function into good leaving groups without protection of
the 2-amino moiety, chloro dediazoniation at C2, and
selective ammonolysis at C6 with accompanying sugar
deprotection. Two approaches we evaluated for function-
alization at C6 were arylsulfonylation of O6 and chloro-
deoxygenation at C6.
Several acyl-protected 6-O-sulfonyl derivatives of dGuo
are readily available.29-31 The treatment of 3′,5′-di-O-
acetyl-2′-deoxyguanosine32 (1a ) or its 3′,5′-di-O-benzoyl
analogue 1b32 with TiPBS-Cl/Et3N/DMAP/CHCl3 by a
modification of the method of Hata et al.30 gave the 6-O-
TiPBS derivatives 2a 33 (91%) or 2b (86%), respectively.
The similar treatment of 1b with TsCl/Et3N/DMAP/
CHCl3 gave the 6-O-Ts derivative 2′b (89%). Efficient
displacement of sulfonate from C6 required a sterically
hindered arylsulfonyl derivative. Our attempts with a
more economical 6-O-Ts derivative gave poor yields at
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990 J . Org. Chem., Vol. 68, No. 3, 2003

2-Chloro-2′-deoxyadenosine (Cladribine)
spectra were determined with FAB (glycerol) unless otherwise
indicated. The chemicals and solvents were of reagent quality.
CH2Cl2 and MeCN were dried by reflux over and distillation
from CaH2. CHCl3 was dried over P2O5 and distilled. AcCl,
POCl3, and N,N-dimethylaniline were freshly distilled before
use. BTEA-NO2 was prepared from BTEA-Cl by ion exchange
[Dowex 1X2 (NO2-)]. Column chromatography (silica gel, 230-
400 mesh) was performed with CH2Cl2/MeOH. Compounds 1a
and 1b were prepared as described.32
Method 1 (nucleoside/TiPBS-Cl/DMAP/Et3N/CHCl3) is de-
scribed for 1a f 2a , method 2 (nucleoside/AcCl/BTEA-NO2/
CH2Cl2) for 2a f 3a, method 3 (nucleoside/N,N-dimethylaniline/
POCl3/BTEA-Cl/MeCN) for 1a f 5a , and method 4 (nucleoside/
NH3/MeOH/CH2Cl2/∆) for 3a f 4. Analogous reactions with
equivalent molar proportions of other nucleosides gave the
indicated products and quantities.
the final stage owing to attack of ammonia at both the
sulfonyl sulfur and C6 (3′b gave 4 in 43% yield). By
contrast, ammonolysis of the 6-O-TiPBS derivatives
proceeded efficiently at C6 with minimal attack at the
hindered sulfur atom. Both types of the arylsulfonate
derivatives, and especially the 6-O-Ts, underwent in-
creased nucleophilic attack at the sulfur with lower
temperatures (-20 to 0 °C) to give 6-oxopurine deriva-
tives. However, treatment of the 6-O-TiPBS compounds
with NH3/MeOH/CH2Cl2 in a pressure tube at 80 °C
strongly favored nucleophilic attack at C6 to give good
yields of CldAdo. This suggests a crossover of the activa-
tion-energy profiles for nucleophilic attack at the sulfonyl
sulfur versus C6 between 0 and 80 °C.
Chlorine has been the most frequently used leaving
group at C6 of purine nucleosides. Original studies on
deoxychlorination of guanosine34 (Guo) and dGuo35 de-
rivatives with POCl3 gave moderate (Guo) to poor (dGuo)
yields of 2-amino-6-chloropurine products, and improved
procedures have been reported.27a,36,37 We effected deoxy-
chlorination of the acid-labile 2′-deoxy derivatives 1 with
POCl3/N,N-dimethylaniline/BTEA-Cl/MeCN/∆27a,37 and
obtained the 6-chloro derivatives 5a (90%) and 5b (85%)
in high yields under carefully controlled conditions. Our
modified procedure for nonaqueous diazotization/chloro
dediazoniation1,28 (AcCl/BTEA-NO2/CH2Cl2, -5 to 0 °C)
worked well for the replacement of the 2-amino group of
2, 2′b, and 5 with chlorine to give 3a (89%), 3b (90%),
3′b (87%), 6a (95%), and 6b (91%).
The displacement of the hindered arylsulfonate (from
3) or chloride (from 6) at C6 with the accompanying
cleavage of the sugar esters was effected at 80 °C with
NH3/MeOH/CH2Cl2. CldAdo was obtained in high yields
from 3a (81%), 3b (83%), 6a (87%), and 6b (94%) but only
in moderate yield from the 6-O-Ts derivative 3′b (43%).
In summary, syntheses of the clinical drug cladribine
were accomplished in three steps from the readily avail-
able 1a or its dibenzoyl analogue 1b. The replacement
of the 2-amino group proceeded in high yields by diazo-
tization/chloro dediazoniation with AcCl/BTEA-NO2. The
selective ammonolysis of 3a and 3b (6-O-TiPBS) or 6 (6-
Cl), with accompanying deacylation, gave 4 (64-75%
overall yield). The ammonolysis of 3′b (6-O-Ts) was
problematic and gave 4 in poor overall yield (33%). The
routes that employed the deoxychlorination of 1 were
∼10% more efficient overall than those which involved
6-O-TiPBS intermediates.
9-(3,5-Di-O-acetyl-2-deoxy-â-D-er yth r o-pen tofu r an osyl)-
2-a m in o-6-O-(2,4,6-t r iisop r op ylb en zen esu lfon yl)p u r in e
(2a ). Meth od 1. Et3N (1.25 mL, 910 mg, 9.0 mmol) was added
to a stirred solution of 1a (1.67 g, 4.8 mmol), TiPBS-Cl (2.73
g, 9.0 mmol), and DMAP (72 mg, 0.6 mmol) in dried CHCl3
(70 mL) under N2. Stirring was continued for 24 h, and
volatiles were evaporated. The orange residue was chromato-
graphed (CH2Cl2/MeOH) to give 2a 33 (2.67 g, 91%) as a slightly
yellow foam: UV λmax 238, 291 nm, λmin 264 nm; 1H NMR (500
MHz) δ 1.26-1.32 (m, 18H), 2.08 (s, 3H), 2.14 (s, 3H), 2.54
(ddd, J ) 4.7, 9.0, 14.0 Hz, 1H), 2.91-2.99 (m, 2H), 4.22-4.37
(m, 3H), 4.43-4.47 (m, 2H), 4.97 (br s, 2H), 5.41-5.42 (“d”,
1H), 6.26-6.29 (m, 1H), 7.21 (s, 2H), 7.84 (s, 1H); LRMS m/z
618 (MH+ [C29H40N5O8S] ) 618); HRMS m/z 640.2413 (MNa+
[C29H39N5O8SNa] ) 640.2417).
2-Am in o-9-(3,5-di-O-ben zoyl-2-deoxy-â-D-er yth r o-pen to-
fu r a n osyl)-6-O-(2,4,6-t r iisop r op ylb en zen esu lfon yl)p u -
r in e (2b). Treatment of 1b (950 mg, 2.0 mmol) by method 1
gave 2b (1.27 g, 86%) as a white solid foam: UV λmax 289 nm,
1
λmin 264 nm; H NMR δ 1.29-1.32 (m, 18H), 2.76 (ddd, J )
2.1, 6.0, 14.3 Hz, 1H), 2.96 (“quint”, J ) 6.8 Hz, 1H), 3.15-
3.25 (m, 1H), 4.34 (“quint”, J ) 6.8 Hz, 2H), 4.65-4.74 (m,
2H), 4.85-4.90 (m, 1H), 5.00 (br s, 2H), 5.84-5.86 (“d”, 1H),
6.38-6.43 (m, 1H), 7.30 (s, 2H), 7.44-7.55 (m, 4H), 7.58-7.69
(m, 2H), 7.85 (s, 1H), 8.04 (d, J ) 7.1 Hz, 2H), 8.11 (d, J ) 7.1
Hz, 2H); LRMS m/z 742 (MH+ [C39H44N5O8S] ) 742), 764
(MNa+ [C39H43N5O8SNa] ) 764); HRMS m/z 764.2730 (MNa+
[C39H43N5O8SNa] ) 764.2730).
2-Am in o-9-(3,5-di-O-ben zoyl-2-deoxy-â-D-er yth r o-pen to-
fu r a n osyl)-6-O-(4-m eth ylben zen esu lfon yl)p u r in e (2′b).
Et3N (700 µL, 506 mg, 5.0 mmol) was added to a stirred
solution of 1b (1.43 g, 3.0 mmol), TsCl (858 mg, 4.5 mmol),
and DMAP (36 mg, 0.3 mmol) in dried CHCl3 (45 mL) under
N2. Stirring was continued for 15 h, and volatiles were
evaporated. The slightly yellow residue was chromatographed
(CH2Cl2/MeOH) to give 2′b (1.68 g, 89%) as a white solid
foam: UV λmax 300 nm; 1H NMR (DMSO-d6) δ 2.43 (s, 3H),
2.73 (ddd, J ) 2.1, 8.4, 14.4 Hz, 1H), 3.17-3.27 (“quint”, J )
7.2 Hz, 1H), 4.52-4.65 (m, 3H), 5.76-5.78 (“d”, 1H), 6.37-
6.41 (m, 1H), 6.95 (br s, 2H), 7.47-7.73 (m, 8H), 7.95 (d, J )
7.8 Hz, 2H), 8.03-8.11 (m, 4H), 8.30 (s, 1H); LRMS m/z 630
(MH+ [C31H28N5O8S] ) 630), 652 (MNa+ [C31H27N5O8SNa] )
652); HRMS m/z 652.1467 (MNa+ [C31H27N5O8SNa] ) 652.1478).
9-(3,5-Di-O-acetyl-2-deoxy-â-D-er yth r o-pen tofu r an osyl)-
2-ch lor o-6-O-(2,4,6-tr iisop r op ylben zen esu lfon yl)p u r in e
(3a ). Meth od 2. A solution of AcCl (200 µL, 220 mg, 2.8 mmol)
in dried CH2Cl2 (12 mL) under N2 was chilled in a NaCl/ice/
H2O bath (-5 to 0 °C) for 15 min. BTEA-NO2 (520 mg, 2.2
mmol) was dissolved in dried CH2Cl2 (8 mL), and this solution
was immediately added dropwise to the cold, stirred solution
of AcCl/CH2Cl2. A solution of 2a (288 mg, 0.5 mmol) in dried
CH2Cl2 (5 mL) was then added dropwise to the cold solution
and stirring was continued for 5 min (TLC, 95:5 CH2Cl2/MeOH,
showed complete conversion of 2a into a single product). The
reaction mixture was added dropwise at a rapid rate to a cold
(ice/H2O bath), vigorously stirred mixture of saturated NaHCO3/
Exp er im en ta l Section
The melting points for 4 were determined with a hot-stage
apparatus. UV spectra were recorded with solutions in MeOH.
1H NMR spectra were recorded at 300 MHz with solutions in
CDCl3 unless otherwise indicated. “Apparent” peak shapes are
in quotation marks when the first-order splitting should be
more complex or when the peaks were poorly resolved. Mass
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J . Org. Chem, Vol. 68, No. 3, 2003 991

J aneba et al.
H2O (100 mL)//CH2Cl2 (100 mL). The layers were separated,
and the organic phase was washed with cold (0 °C) H2O (2 ×
100 mL) and dried (MgSO4) for 1 h. Volatiles were evaporated,
and the residue was chromatographed (CH2Cl2/MeOH) to give
3a (267 mg, 89%) as a white solid foam: UV λmax 240, 266
2H), 7.48-7.71 (m, 6H), 7.96 (d, J ) 8.4 Hz, 2H), 8.06 (d, J )
8.7 Hz, 2H), 8.37 (s, 1H); LRMS m/z 494 (MH+ [C24H21ClN5O5]
) 494); HRMS m/z 516.1042 (MNa+ [C24H20ClN5O5Na] )
516.1051).
9-(3,5-Di-O-acetyl-2-deoxy-â-D-er yth r o-pen tofu r an osyl)-
2,6-d ich lor op u r in e (6a ). Treatment of 5a (265 mg, 0.7 mmol)
by method 2 gave 6a 38 (266 mg, 95%) as a white solid foam:
1
nm, λmin 255 nm; H NMR (500 MHz) δ 1.24-1.31 (m, 18H),
2.08 (s, 3H), 2.13 (s, 3H), 2.67 (ddd, J ) 2.5, 7.0, 15.5 Hz, 1H),
2.76-2.81 (m, 1H), 2.90-2.96 (“quint”, J ) 7.0 Hz, 1H), 4.28-
4.33 (“quint”, J ) 7.0 Hz, 2H), 4.35-4.39 (m, 3H), 5.38-5.39
(“d”, 1H), 6.42-6.45 (m, 1H), 7.22 (s, 2H), 8.23 (s, 1H); LRMS
m/z 637 (MH+ [C29H38ClN4O8S] ) 637); HRMS m/z 659.1902
(MNa+ [C29H37ClN4O8SNa] ) 659.1918).
1
UV λmax 274 nm, λmin 232 nm; H NMR (500 MHz) δ 2.12 (s,
3H), 2.15 (s, 3H), 2.73 (ddd, J ) 2.4, 5.9, 14.2 Hz, 1H), 2.83-
2.86 (m, 1H), 4.38-4.39 (m, 3H), 5.41-5.42 (“d”, 1H), 6.45-
6.50 (m, 1H), 8.33 (s, 1H); HRMS m/z 411.0230 (MNa+
[C14H14Cl2N4O5Na] ) 411.0239).
9-(3,5-Di-O-ben zoyl-2-d eoxy-â-D-er yth r o-p en tofu r a n o-
syl)-2-ch lor o-6-O-(2,4,6-tr iisop r op ylben zen esu lfon yl)p u -
r in e (3b). The treatment of 2b (1.20 g, 1.6 mmol) by method
2 gave 3b (1.10 g, 90%) as a yellow solid foam: UV λmax 230,
9-(3,5-Di-O-ben zoyl-2-d eoxy-â-D-er yth r o-p en tofu r a n o-
syl)-2,6-d ich lor op u r in e (6b). Treatment of 5b (407 mg, 0.8
mmol) by method 2 gave 6b (386 mg, 91%) as a slightly yellow
solid foam: UV λmax 274 nm, λmin 257 nm; 1H NMR (500 MHz,
DMSO-d6) δ 2.87 (ddd, J ) 3.5, 8.0, 17.5 Hz, 1H), 3.25-3.31
(m, 1H), 4.57-4.71 (m, 3H), 5.83-5.85 (“d”, 1H), 6.59-6.62
(m, 1H), 7.46-7.72 (m, 6H), 7.91 (d, J ) 7.5 Hz, 2H), 8.09 (d,
J ) 7.5 Hz, 2H), 8.96 (s, 1H); HRMS m/z 535.0562 (MNa+
[C24H18Cl2N4O5Na] ) 535.0552).
1
266 nm, λmin 255 nm; H NMR δ 1.22-1.34 (m, 18H), 2.92-
3.00 (m, 3H), 4.30-4.34 (m, 2H), 4.68-4.77 (m, 3H), 5.80-
5.82 (“d”, 1H), 6.54-6.57 (m, 1H), 7.42-7.64 (m, 8H), 8.00 (d,
J ) 8.4 Hz, 2H), 8.10 (d, J ) 8.4 Hz, 2H), 8.26 (s, 1H); HRMS
m/z 783.2224 (MNa+ [C39H41ClN4O8SNa] ) 783.2231).
9-(3,5-Di-O-ben zoyl-2-d eoxy-â-D-er yth r o-p en tofu r a n o-
syl)-2-ch lor o-6-O-(4-m eth ylben zen esu lfon yl)p u r in e (3′b).
Treatment of 2′b (1.45 g, 2.3 mmol) by method 2 gave 3′b (1.30
g, 87%) as a slightly yellow foam: UV λmax 267 nm, λmin 255
nm; 1H NMR (DMSO-d6) δ 2.45 (s, 3H), 2.86 (ddd, J ) 3.4,
6.2, 14.0 Hz, 1H), 3.21-3.30 (“quint”, J ) 7.0 Hz, 1H), 4.55-
4.67 (m, 3H), 5.82-5.84 (m, 1H), 6.56-6.61 (m, 1H), 7.42-
7.72 (m, 8H), 7.88 (d, J ) 7.8 Hz, 2H), 8.04-8.07 (m, 4H), 8.88
(s, 1H); HRMS m/z 671.0983 (MNa+ [C31H25ClN4O8SNa] )
671.0979).
2-Ch lor o-2′-d eoxya d en osin e (Cla d r ibin e, 4). Meth od 4.
NH3/MeOH (12 mL, saturated at 0 °C) was added to a solution
of 3a (159 mg, 0.25 mmol) in CH2Cl2 (8 mL) in a pressure tube.
The tube was sealed and immediately immersed in an oil bath
preheated to 80 °C. Heating (80 °C) was continued for 7 h,
and volatiles were evaporated. The residue was dissolved (H2O,
2 mL), the solution was applied to a column of Dowex 1X2
(OH-, 20 mL), and the flask was rinsed (H2O, 5 mL) and
applied to the column. The column was washed (H2O) until
the pH of the eluate was neutral and then MeOH/H2O (1:1)
was applied. UV-absorbing fractions were pooled, and volatiles
were evaporated. EtOH (3 × 10 mL) was added and evapo-
rated, and the residue was dried (in vacuo) to give 4 (58 mg,
81%). The white powder was recrystallized from MeOH to give
4 (2 crops, 84% recovery) with a mp > 300 °C (crystals slowly
became brown at ∼220 °C) or from H2O (2 crops, 72% recovery)
with a mp > 300 °C (lit. softening at 210-215 °C17 and then
9-(3,5-Di-O-acetyl-2-deoxy-â-D-er yth r o-pen tofu r an osyl)-
2-a m in o-6-ch lor op u r in e (5a ). Meth od 3. A mixture of 1a
(540 mg, 1.54 mmol), BTEA-Cl (710 mg, 3.1 mmol), N,N-
dimethylaniline (215 µL, 206 mg, 1.7 mmol), and POCl3 (720
µL, 1.2 g, 7.7 mmol) in MeCN (6 mL) was stirred in a preheated
oil bath (85 °C) for 10 min. Volatiles were flash evaporated
immediately (in vacuo), and the yellow foam was dissolved
(CHCl3, 15 mL) and stirred vigorously with crushed ice for 15
min. The layers were separated, and the aqueous phase was
extracted (CHCl3, 3 × 5 mL). Crushed ice was frequently added
to the combined organic phase, which was washed [ice/H2O (3
× 5 mL), 5% NaHCO3/H2O (to pH ∼7)] and dried (MgSO4).
Volatiles were evaporated, and the residue was chromato-
graphed (CH2Cl2/MeOH) to give 5a 36,37 (517 mg, 90%) as a
white solid foam: UV λmax 248, 310 nm, λmin 268 nm; 1H NMR
(500 MHz, DMSO-d6) δ 2.02 (s, 3H), 2.08 (s, 3H), 2.49-2.52
(m, 1H), 3.04-3.06 (m, 1H), 4.20-4.29 (m, 3H), 5.32-5.34 (“d”,
1H), 6.23-6.26 (m, 1H); 7.03 (br s, 2H), 8.35 (s, 1H); 1H NMR
δ 2.03 (s, 3H), 2.08 (s, 3H), 2.51 (ddd, J ) 2.7, 5.9, 14.2 Hz,
1H), 2.85-2.94 (“quint”, J ) 7.1 Hz, 1H), 4.28-4.42 (m, 3H),
5.35-5.37 (m, 1H), 6.21-6.26 (m, 1H), 7.89 (s, 1H); HRMS (EI)
m/z 369.0844 (M+ [C14H16ClN5O5] ) 369.0840).
1
dec; >300 °C;19,22 232 °C23); UV, H NMR, and MS data were
in agreement with published values.22,23 Anal. Calcd for C10H12
-
ClN5O3: C, 42.04; H, 4.23; N, 24.51. Found: C, 41.85; H, 4.40;
N, 24.46.
Treatment of 3b (83%), 3′b (43%), 6a (87%), or 6b (94%) by
method 4 gave 4 as white, TLC-homogeneous powders with
identical spectral data.
Ack n ow led gm en t. We thank the Brigham Young
University Technology Transfer Office and gift funds
for financial support.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
compounds 2a , 2b, 2′b, 3a , 3b, 3′b, 5b, and 6b. This material
is available free of charge via the Internet at http://pubs.acs.org.
2-Am in o-9-(3,5-di-O-ben zoyl-2-deoxy-â-D-er yth r o-pen to-
fu r a n osyl)-6-ch lor op u r in e (5b). Treatment of 1b (2.38 g, 5
mmol) by method 3 gave 5b (2.10 g, 85%) as a slightly yellow
solid foam: UV λmax 310 nm; 1H NMR (DMSO-d6) δ 2.69-2.78
(“ddd”, 1H), 3.20-3.24 (“quint”, J ) 7.2 Hz, 1H), 4.56-4.67
(m, 3H), 5.77-5.79 (“d”, 1H), 6.39-6.44 (m, 1H), 7.02 (br s,
J O020644K
(38) Montgomery, J . A.; Hewson, K. J . Med. Chem. 1969, 12, 498-
504.
992 J . Org. Chem., Vol. 68, No. 3, 2003