Methylene-gem-difluorocyclopropane analogues of nucleosides: Synthesis, cyclopropene-methylenecyclopropane rearrangement, and biological activity

Article abstract of DOI:10.1021/jm010191w

Alkylation-elimination of adenine and 2-amino-6-chloropurine with gem-difluorocyclopropane dibromide 10 gave E- and Z-methylene-gem-difluorocyclopropane 11a, 11b, 12a, and 12b and gem-difluorocyclopropenes 13a and 13b. Debenzylation of intermediates 11a,

Full text of DOI:10.1021/jm010191w

J . Med. Chem. 2001, 44, 4019-4022
4019
Meth ylen e-gem -Diflu or ocyclop r op a n e An a logu es of Nu cleosid es: Syn th esis,
Cyclop r op en e-Meth ylen ecyclop r op a n e Rea r r a n gem en t, a n d Biologica l Activity1
Ruifang Wang,† Mohamad B. Ksebati,‡ Thomas H. Corbett,† Earl R. Kern,§ J ohn C. Drach,| and J iri Zemlicka*,†
Developmental Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine,
110 East Warren Avenue, Detroit, Michigan 48201-1379, Central Instrumentation Facility, Department of Chemistry,
Wayne State University, Detroit, Michigan 48202, Department of Pediatrics, The University of Alabama at Birmingham,
Birmingham, Alabama 35294, and Department of Biological and Materials Science, School of Dentistry,
University of Michigan, Ann Arbor, Michigan 48019-1078
Received April 30, 2001
Alkylation-elimination of adenine and 2-amino-6-chloropurine with gem-difluorocyclopropane
dibromide 10 gave E- and Z-methylene-gem-difluorocyclopropanes 11a , 11b, 12a , and 12b
and gem-difluorocyclopropenes 13a and 13b. Debenzylation of intermediates 11a , 11b, 12a ,
and 12b afforded E- and Z-methylenecyclopropanes 4a , 4b, 5a , and 5b. Hydrolysis of 2-amino-
6-chloropurine derivatives 4b and 5b afforded guanine analogues 4c and 5c. Composition of
products (except 14b) obtained from alkylation-elimination reflects thermodynamically
controlled cyclopropene-methylenecyclopropene rearrangement. The E-isomer 4a was mod-
erately active against human cytomegalovirus and along with the Z-isomer 5a was active
against leukemia L1210 and solid tumors in vitro.
Ch a r t 1
In tr od u ction
Recently, we described a series of methylenecyclopro-
pane analogues of nucleosides 1 and 2 (Chart 1). The
Z-isomers 1 are broad-spectrum antiviral agents espe-
cially effective against human cytomegalovirus (HC-
MV).2,3 Replacing hydrogen with fluorine led in many
cases to biologically active compounds.4 Among nucleo-
sides fluorinated in the carbohydrate moiety,5 gem-
difluoro analogues play a significant role. The anticancer
drug gemcitabine6 (2′-deoxy-2′,2′-difluorocytidine) and
the acyclic nucleotide 9-(5,5-difluoro-5-phosphonopen-
tyl)guanine, an inhibitor of purine nucleoside phos-
phorylase,7 are notable examples. More recently, we
described8 also gem-difluorocyclopropane nucleoside
analogues 3. In view of a potent antiviral activity of
methylenecyclopropanes 1, structure-activity relation-
ships in this series of analogues are under active
investigation.9,10 As a part of this effort, gem-difluoro
analogues 4 and 5 have become of interest.
Sch em e 1
Resu lts a n d Discu ssion
The alkylation-elimination approach that was suc-
cessfully applied for synthesis of nonfluorinated ana-
logues2,3 1 and 2 seemed the most promising for
synthesis of 4 and 5. The starting methylene-gem-
difluorocyclopropane (6) was prepared from gem-difluo-
rocyclopropane8 7 by a modification of the described
procedure11 via selenide 8 and selenoxide 9 (Scheme 1).
6 was converted to the vicinal dibromocyclopropane 10
in 95% yield using pyridine‚HBr3 in CH2Cl2. Alkyla-
tion-elimination of sodium salt of adenine with 10 in
DMF was perfomed at room temperature. A mixture of
a
Key: (a) (o-NO2)C6H4SeCN, Bu3P, THF; (b) H2O2, THF; (c)
toluene, ∆; (d) pyridine‚HBr3, CH2Cl2; (e) NaH, DMF; (f) BCl3,
CH2Cl2, -78 °C.
three products was obtained, the E,Z-isomers 11a and
12a (21 and 7%, respectively) and, surprisingly, gem-
difluorocyclopropene 13a (31%). All three products were
readily separated by chromatography on a silica gel
column. Debenzylation of 11a and 12a using BCl3 in
CH2Cl2 at -78 °C was uneventful to give target ana-
logues 4a and 5a in 75 and 77% yield, respectively. An
* Corresponding author telephone: (313)833-0715, ext 2452; fax:
(313)832-7294; e-mail: zemlicka@kci.wayne.edu.
† Wayne State University School of Medicine.
‡ Wayne State University.
§ The University of Alabama at Birmingham.
| University of Michigan.
10.1021/jm010191w CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/10/2001

4020 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 23
Brief Articles
Ta ble 1. Antitumor Activity of Methylenecyclopropanes 1a , 4a , and 5a
mouse tumors
human colon tumors
compda
1a
leukemia L1210
C38
M17/Adr
H15
H116
normal cells (fibroblasts)
500-570
340-420
600-660
0-190
550-600
470
580
460
370
590
0-50
0-160
70-200
550
360
0-130
0-130
200-500
0-110
4a
5a
100-300
400-550
60-150
SR271425b
650-750
a
b
Disk-diffusion assay,14 500 µg/disk, 200 units ) 6 mm. 11 µg/disk.14
attempted deprotection of cyclopropene analogue 13a
led only to decomposition.
ratio 11b:12b:13b ) 3.6:1:5.4 resembled that found in
the above-mentioned preparative experiment with cy-
clopropene 13b. This ratio was not changed after a
prolonged reaction time or when excess of DBU was
used, but decomposition of the products gradually
occurred. Thus, the observed composition of products
is thermodynamically controlled.
The shelf life of methylene-gem-difluorocyclopro-
panes 4a -c and 5a -c is limited, and a prolonged
storage at low temperatures is mandatory. The least
stable are the guanine analogues 4c and 5c where
satisfactory elemental analyses could not be obtained
although both compounds were fully characterized by
spectroscopic methods.
Alkylation-elimination of 2-amino-6-chloropurine with
reagent 10 performed in a similar fashion (NaH in DMF
at room temperature) gave a mixture of four compounds
that were all separated by chromatography on silica gel.
The yields of the E- and Z-isomers 11b and 12b and
cyclopropene 13b were 12, 3.5, and 17%. The product
of a simple alkylation, bromo derivative 14b, was also
obtained in 10% yield. Debenzylation of 11b and 12b
gave compounds 4b and 5b in 81 and 77% yield,
respectively. Hydrolysis with 80% HCO2H afforded
guanine analogues 4c (66%) and 5c (71%).
The UV spectra of methylene-gem-difluorocyclopro-
panes reveal significant bathochromic shift throughout
the entire region of spectrum when compared with
nonfluorinated analogues.2
Biologica l Activity
Analogues 4a , 4c, 5a , and 5c were tested against
HCMV, HSV-1, HSV-2, EBV, HBV, VZV, and HIV-1 in
previously described assays.2 Only the E-isomer 4a had
activity against the Towne strain of HCMV propagated
in human foreskin fibroblast (HFF) cells (EC50 21 µM),
and it was non-cytotoxic (CC50 >100 µM). More moder-
ate effects were observed against herpes simplex virus
type 1 (HSV-1, EC50 70 µM) in BSC-1 cells as deter-
mined by ELISA assay and EBV in Daudi cells (EC50
77 µM). A decreased antiviral potency relative to that
of nonfluorinated analogue2 1a can be explained by a
limited capability of phosphorylation inside the infected
cells. Lesser chemical stability of 4a may also be a
factor. 4a and 5a also exhibited antitumor activity
(Table 1). The E-isomer 4a was more selective than
Z-isomer 5a . The activity of 4a corresponded to that of
the nonfluorinated analogue 1a , but unlike 5a , E-isomer
2a was inactive. In contrast to 1a and 2a , compounds
4a and 5a were not substrates for adenosine deaminase.
The E,Z-isomeric structures were assigned by NMR
spectra. The H8 values of the isomers with the hetero-
cyclic base juxtaposed to hydroxymethyl group (E-
isomers 4a -c and Z-isomers 1a -c) are significantly
deshielded relative to those of the Z-isomers 5a -c and
the E-isomers 2a -c. A selective deshielding of the H1′
alkene proton by fluorine in the cis position was
observed only in the E-isomers 4a -c. The absence of
alkene protons as well as the presence of three different
methylene groups excluded structures 15a and 15b as
possible alternatives for cyclopropenes 13a and 13b.
These assignments were confirmed by the NOE experi-
ments with isomers 4a and 5a . Thus, all protons of the
cyclopropane moiety of E-isomer 4a located in the
vicinity of H8 exhibit NOE enhancements whereas none
were found for a more distant H1′. An opposite situation
was encountered in the Z-isomer 5a . In this case, all
cyclopropane protons are closer to H1′ than to H8, and
consequently, NOE was observed at H1′ but not at H8.
Because the E- and Z-isomers 4a and 4c and 5a and
5c were the main targets of our study, we investigated
a possibility of isomerization of cyclopropene 13b into
the corresponding methylenecyclopropanes. Base-cata-
lyzed cyclopropene-methylene-cyclopropane rearrange-
ments have been described in both nonfluorinated12 and
gem-difluorocyclopropane series.13 Isomerization of cy-
clopropene 13b using DBU in DMF at 0 °C (2 min) gave
E-isomer 11b (37%), Z-isomer 12b (11.5%), and starting
material 13b (39%) that were separated by chromatog-
raphy on a silica gel column. The ratio of these compo-
nents resembled that obtained by alkylation-elimina-
tion of nucleic acid bases (Scheme 1). The result
indicated that isomerization of cyclopropene 13b to the
E- and Z-isomers 11b and 12b is possible but only to a
limited extent.
Exp er im en ta l Section
Gen er a l Meth od s. See ref 2. The UV spectra were recorded
in ethanol. The NMR spectra were determined at 300 or 400
MHz (1H), 75 or 100 MHz (13C), and 376 MHz (19F) in DMSO-
d6 unless specified otherwise. CFCl3 was used as a reference
for 19F spectra. For FAB-MS, the thioglycerol matrix was used.
2-Ben zyloxym eth yl-3,3-d iflu or o-1-m eth ylen ecyclop r o-
p a n e (6). The described procedure11 starting from gem-
difluorocyclopropane8 7 was modified as follows. Selenide 8
(4.4 g, 10.4 mmol) was treated with 30% H2O2 (10 mL) in THF
(50 mL) at 0 °C. The reaction mixture was allowed to stand at
room temperature for 16 h, and then it was diluted with EtOAc
(100 mL) and washed with saturated Na2S2O3 solution and
water. The organic phase was dried over Na2SO4, and the
solvent was evaporated to give a crude selenoxide 9 as a yellow
solid. A solution of 9 in toluene (50 mL) was heated at 80 °C
for 48 h, and the solvent was evaporated. The residue was
chromatographed on a silica gel column using hexane-EtOAc
(97:3) to give product 6 (1.56 g, 71%) as a colorless oil. The
1H, 13C, and 19F NMR spectral data corresponded to those
reported.11
Interconversion of all three components 11b, 12b, and
13b (catalysis with DBU in DMF at room temperature)
was investigated by HPLC. After 1 min, the average

Brief Articles
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 23 4021
(E,Z)-2-Ben zyloxym eth yl-1-br om o-1-br om om eth yl-3,3-
d iflu or ocyclop r op a n e (10). A solution of 6 (1.05 g, 5.0 mmol)
in CH2Cl2 (50 mL) was treated with pyridine hydrobromide
perbromide (2.56 g, 8 mmol) at 0 °C. The reaction mixture was
allowed to stand at room temperature for 16 h. It was diluted
with EtOAc (100 mL) and washed with saturated Na2S2O3-
NaHCO3 solution and water. The organic phase was dried over
Na2SO4, and the solvent was evaporated to give a pale yellow
liquid 10 (1.76 g, 95.1%), which was used directly in the next
step. 1H NMR (CDCl3) (δ): 1.96-2.03 and 2.42-2.49 (m, 1H),
3.61-3.85 (m, 4H), 4.50-4.58 (m, 2H), 7.30-7.39 (m, 5H).
(E )-9-{[2-(Be n zyloxym e t h yl)-3,3-d iflu or ocyclop r op -
ylid en e]m et h yl}a d en in e (11a ), (Z)-9-{[2-(Ben zyloxy-
m et h yl)-3,3-d iflu or ocyclop r op ylid en e]m et h yl}a d en in e
(12a ), a n d 9-{[2-(Ben zyloxym et h yl)-3,3-d iflu or ocyclo-
p r op en yl]m eth yl}a d en in e (13a ). A mixture of adenine
(1.485 g, 11 mmol) and NaH (60% oil suspension, 600 mg, 12.5
mmol) in DMF (100 mL) was stirred at room temperature for
4 h. The mixture was cooled to 0 °C, a solution of dibromide
10 (1.76 g, 4.76 mmol) in DMF (5 mL) was added dropwise,
and the stirring was continued at room temperature for 16 h.
The solvent was evaporated in vacuo, and the residue was
chromatographed on a silica gel column (CH2Cl2-MeOH, 49:
1) to give the products 11a (350 mg, 21.4%), 12a (120 mg,
7.4%), and 13a (510 mg, 31.2%) as white solids.
HRMS calcd. for C10H9F2N5O 253.0775, found: 253.0781. Anal.
(C10H9F2N5O) C, H, N.
(Z)-9-{[2-(H yd r oxym et h yl)-3,3-d iflu or ocyclop r op yli-
d en e]m eth yl}a d en in e (5a ). The reaction was performed as
described for 4a (60 mg, 0.17 mmol of 12a ) to give a white
solid 5a (33 mg, 76.7%), mp 256-260 °C; UV max 283 nm (ꢀ
5,700), 243 (ꢀ 22,200), 214 (ꢀ 14,100). 1H NMR: 2.82-2.90 (1H,
m), 3.44-3.53 (1H, m), 3.63-3.70 (1H, m), 5.24 (1H, brs), 7.48
(2H, s), 7.64 (1H, d, J ) 2.0 Hz), 8.16 (1H, s), 8.22 (1H, s). 13C
NMR: 31.2 (t, J ) 11.0 Hz), 58.2, 107.1 (t, J ) 286.4 Hz), 108.4
(t, J ) 6.0 Hz), 117.5, 119.4, 138.8, 149.1, 154.5, 156.8. 19F
NMR: 65.4 (d, J ) 175.2 Hz), 79.3 (dd, J ) 175.4, 6.3 Hz).
EI-MS 253 (M, 12.3), 252 (M - H, 6.7), 236 (M - OH, 100.0).
HRMS calcd. for C10H9F2N5O 253.0775, found: 253.0781. Anal.
(C10H9F2N5O) C, H, N.
(E)-2-Am in o-9-{[2-(ben zyloxym eth yl)-3,3 d iflu or ocyclo-
p r op ylid en e]m eth yl}-6-ch lor op u r in e (11b), (Z)-2-Am in o-
9-{[2-(ben zyloxym eth yl)-3,3-d iflu or ocyclop r op ylid en e]-
m eth yl}-6-ch lor op u r in e (12b), 2-Am in o-9-{[2-(ben zyloxy-
methyl)-3,3-difluorocyclopropenyl]methyl}-6-chloropur ine
(13b ), a n d (E,Z)-2-Am in o-9-{[1-b r om o-2-(b en zyloxy-
m eth yl)-3,3-d iflu or ocyclop r op yl]m eth yl}-6-ch lor op u r in e
(14b). The procedure described for adenine analogues was
followed with 2-amino-6-chloropurine (4.25 g, 25 mmol), NaH
(1.08 g, 22.5 mmol) in DMF (200 mL), and dibromide 10 (2.81
g, 8.00 mmol). The products were separated by column
chromatography on silica gel using hexane-EtOAc (3:1) to give
products 11b (350 mg, 11.6%), 12b (105 mg, 3.5%), 14b (350
mg, 9.6%), and 13b (510 mg, 16.9%).
11a : mp 254-255 °C; UV max 284 nm (ꢀ 6,000), 245 (ꢀ 24,-
1
100). H NMR (δ): 3.23-3.28 (1H, m), 3.60 (1H, dd, J ) 9.3
and 9.0 Hz), 3.85-3.91 (1H, m), 4.49 (1H, d, J ) 12.3 Hz),
4.54 (1H, d, J ) 12.3 Hz), 7.24-7.32 (5H, m), 7.50 (2H, s),
8.20 (1H, s), 8.25 (1H, d, J ) 3.0 Hz), 8.58 (s, 1H). 13C NMR:
31.0 (t, J ) 12.0 Hz), 66.5, 72.7, 107.5 (t, J ) 7.1 Hz), 108.0 (t,
J ) 285.3 Hz), 119.2, 119.4, 128.1, 128.2, 128.9, 138.5, 139.0,
149.3, 154.3, 156.8. 19F NMR: 65.5 (d, J ) 174.1 Hz), 77.8 (dd,
J ) 174.9, 6.0 Hz). EI-MS: 343 (M, 0.7), 342 (M - H, 1.1), 91
(100.0). HRMS calcd. for C17H14F2N5O (M - H) 342.1166,
found: 342.1164. Anal. (C17H15F2N5O) C, H, N.
11b: white solid, mp 138-139 °C; UV max 308 nm (ꢀ 7,-
800), 285 (ꢀ 8,100), 240 (ꢀ 26,000), 205 (ꢀ 21,500). 1H NMR
(CDCl3 δ): 2.85-2.96 (1H, m), 3.51-3.58 (1H, m), 3.88 (1H,
ddd, J ) 9.6, 6.0 and 1.8 Hz), 4.57 (2H, AB, J ) 12.9 and 12.9
Hz), 5.36 (2H, s, 7.27-7.36 (5H, m), 7.91 (1H, d, J ) 3.0 Hz),
8.78 (1H, s). 13C NMR: 30.4 (t, J ) 12.0 Hz), 66.0, 73.7, 105.8
(t, J ) 285.3 Hz), 108.5 (t, J ) 8.1 Hz), 117.1, 125.2, 128.2,
128.4, 128.8, 137.2, 139.8, 152.0, 153.0, 159.8. 19F NMR: 60.6
(dd, J ) 175.6 and 3.0 Hz), 72.2 (dd, J ) 175.4 and 9.4 Hz).
EI-MS: 379 (M, 1.2), 377 (M, 3.1), 91 (100.0). HRMS calcd.
12a : mp 232-234 °C; UV max 284 nm (ꢀ 6,700), 245 (ꢀ 24,-
1
200). H NMR (δ): 3.02-3.07 (1H, m), 3.52 (1H, dd, J ) 10.5,
9.6 Hz), 3.71-3.78 (1H, m), 4.54 (2H, s) 7.26-7.35 (5H, m),
7.48 (2H, s), 7.70 (1H, d, J ) 2.1 Hz), 8.19 (1H, s), 8.23 (1H,
s). 13C NMR: 28.4 (t, J ) 12.1 Hz), 66.2, 72.4, 106.7 (t, J )
247.0 Hz), 107.6 (t, J ) 7.8 Hz), 118.3, 119.4, 128.3, 129.0,
138.7, 139.0, 149.1, 154.5, 156.8. 19F NMR: 66.8 (d, J ) 172.6
Hz), 79.2 (d, J ) 173.7 Hz). EI-MS: 343 (M, 0.5), 342 (M - H,
1.0), 91 (100.0). HRMS calcd. for C17H14FN5O (M - HF)
323.1182, found: 323.1179. Anal. (C17H15F2N5O) C, H, N, F.
for C17H1435ClF2N5O 377.0855, found: 377.0856. Anal. (C17H14
ClF2N5O) C, H, N, Cl, F.
-
12b: white solid, mp 120-122 °C; UV max 307 nm (ꢀ 7,-
900), 284 (ꢀ 7,700), 241 (ꢀ 24,700), 206 (ꢀ 22,900). 1H NMR
(CDCl3 δ): 2.85-2.92 (1H, m), 3.68 (2H, d, J ) 7.2 Hz), 4.54
(1H, d, J ) 11.7 Hz), 4.60 (1H, d, J ) 12.3 Hz), 5.64 (2H, s),
7.27-7.35 (6H, m), 7.97 (1H, s). 13C NMR: 29.0 (t, J ) 12.0
Hz), 65.8, 73.2, 105.6 (t, J ) 288.4 Hz), 108.7 (t, J ) 7.1 Hz),
116.0, 125.2, 128.0, 128.2, 128.8, 137.7, 139.2, 152.1, 152.5,
160.1. 19F NMR: 60.1 (d, J ) 178.6 Hz), 72.2 (dd, J ) 176.9
and 7.5 Hz). EI-MS: 379 (M, 0.7), 377 (M, 1.6), 91 (100.0).
HRMS calcd. for C17H1435ClF2N5O 377.0855, found: 377.0851.
13b: white solid, mp 133-134 °C; UV max 310 nm (ꢀ 8,-
000), 247 (ꢀ 7,400), 220 (ꢀ 28,200). 1H NMR: 4.26 (2H, s), 4.33
(2H, s), 5.34 (2H, s), 7.00 (2H, s), 7.08-7.10 (2H, m), 7.24-
7.32 (3H, m), 8.17 (1H, s). 13C NMR: 37.8, 61.8, 72.5, 103.5 (t,
J ) 269.3 Hz), 123.9, 127.0 (t, J ) 12.0 Hz), 128.1, 128.4, 129.0,
129.4 (t, J ) 12.0 Hz), 137.7, 143.4, 150.2, 154.7, 160.6. 19F
NMR: 99.9. EI-MS: 379 (M, 1.5), 377 (M, 4.0), 91 (100.0).
HRMS calcd. for C17H1435ClF2N5O 377.0855, found: 377.0851.
14b: pale yellow solid, mp 51-54 °C; UV max 310 nm (ꢀ
7,900), 248 (ꢀ 7,300), 221 (ꢀ 27,200). 1H NMR (CDCl3 δ): 2.57-
2.65 (1H, m), 3.50-3.55 (1H, m), 3.68 (1H, dd, J ) 11.4 and
6.4 Hz), 4.37 (1H, d, J ) 12.0 Hz), 4.42 (1H, d, J ) 12.4 Hz),
4.45 (1H, d, J ) 15.2 Hz), 4.63 (1H, d, J ) 15.6 Hz), 5.40 (brs,
2H), 7.15-7.17 (2H, m), 7.24-7.32 (3H, m), 7.95 (1H, s). 13C
NMR: 32.9 (t, J ) 7.8 Hz), 39.3 (t, J ) 8.4 Hz), 48.6, 65.9,
73.1, 110.2 (dd, J ) 222.0 and 217.0 Hz), 125.0, 127.7, 128.2,
128.7, 137.4, 142.3, 151.7, 154.2, 159.5. 19F NMR: 61.1 (d, J
) 161.7 Hz), 64.9 (dd, J ) 160.0 and 15.0 Hz). EI-MS: 459
13a : mp 195-196 °C; UV max 261 nm (ꢀ 12,500), 209 (ꢀ
1
22,500). H NMR (δ): 4.30 (2H, s), 4.33 (2H, s), 5.45 (2H, s),
7.12-7.14 (2H, m), 7.24-7.32 (3H, m), 7.37 (2H, s), 8.17 (1H,
s), 8.21 (1H, s). 13C NMR: 37.6, 61.7, 72.5, 103.6 (t, J ) 269.3
Hz), 119.3, 127.3 (t, J ) 11.0 Hz), 128.3, 128.4, 129.0, 129.2
(t, J ) 11.0 Hz), 137.7, 141.2, 150.2, 153.5, 156.7. 19F NMR:
99.7. FAB-MS: 344 (M + H, 100.0). Anal. (C17H15F2N5O) C,
H, N, F.
(E)-9-{[2-(H yd r oxym et h yl)-3,3-d iflu or ocyclop r op yli-
d en e]m eth yl}a d en in e (4a ). Boron trichloride (1 M in CH2-
Cl2, 5.8 mL, 5.8 mmol) was added to a solution of 11a (200
mg, 0.58 mmol) in CH2Cl2 (50 mL) at -78 °C under N2 over
10 min with stirring. The stirring was continued for 5 h at
-78 °C. The reaction was quenched by a cautious addition of
MeOH (10 mL), NaHCO3 (5 g) was then added, and the
mixture was stirred at room temperature for 4 h. The insoluble
portion was filtered off, and it was washed with CH2Cl2-
MeOH (4:1, 100 mL). The combined organic phase was
evaporated, and the residue was chromatographed on a silica
gel column (CH2Cl2-MeOH, 20:1) to give a white solid 4a (110
mg, 74.8%), mp 268-270 °C; UV max 283 nm (ꢀ 6,800), 243 (ꢀ
27,300), 214 (ꢀ 18,000). 1H NMR (δ): 3.05-3.15 (1H, m), 3.62-
3.68 (1H, m), 3.71-3.78 (1H, m), 5.39 (1H, t, J ) 5.6 Hz), 7.48
(2H, s), 8.19 (1H, d, J ) 2.4 Hz), 8.21 (1H, s), 8.68 (1H, s). 13C
NMR: 33.4 (t, J ) 11.0 Hz), 58.2, 108.2 (t, J ) 285.4 Hz), 108.3
(t, J ) 7.0 Hz), 118.6, 119.2, 138.9, 149.3, 154.3, 156.8. 19F
NMR: 64.7 (d, J ) 170.7 Hz), 78.2 (dd, J ) 170.7 and 7.5 Hz).
EI-MS: 253 (M, 41.9), 252 (M - H, 10.9), 236 (M - OH, 100.0).
(M, 2.7), 457 (M, 2.1), 91 (100.0). HRMS calcd. for C17H15
-
79Br35ClF2N5O 457.0117, found: 457.0116.
(E)-2-Am in o-9-{[2-(h yd r oxym eth yl)-3,3-d iflu or ocyclo-
p r op ylid en e]m eth yl}-6-ch lor op u r in e (4b). This reaction
was performed as described for adenine analogue 4a with 11b

4022 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 23
Brief Articles
(360 mg, 0.95 mmol). The crude product was purified by silica
gel column chromatography (CH2Cl2-MeOH, 30:1) to give a
white solid 4b (220 mg, 80.7%), mp 239-241 °C; UV max 309
of Chemistry, Wayne State University (R. J . Hood,
Director) for mass spectra. The work described herein
was supported by U.S. Public Health Service Research
Grants RO1-CA32779 (J .Z.), RO1-CA46560 (T.H.C.)
from the National Cancer Institute, U19-AI31718
(J .C.D.), and Contract NO1-AI35177 (E.R.K.) from the
National Institute of Allergy and Infectious Diseases,
National Institutes of Health, Bethesda, MD.
1
nm (ꢀ 7,000), 284 (ꢀ 7,300), 240 (ꢀ 24,000), 204 (ꢀ 13,800). H
NMR (δ): 3.06-3.13 (1H, m), 3.58-3.64 (1H, m), 3.66-3.72
(1H, m), 5.30 (1H, t, J ) 5.6 Hz), 7.14 (2H, s), 8.00 (1H, d, J
) 2.4 Hz), 8.59 (1H, s). 13C NMR: 33.8 (t, J ) 11.9 Hz), 58.3,
108.3 (t, J ) 284.8 Hz), 109.2 (t, J ) 8.0 Hz), 118.2, 123.9,
140.8, 150.6, 153.6, 161.0. 19F NMR: 64.7 (d, J ) 170.7 Hz),
78.2 (dd, J ) 171.4 and 7.5 Hz). EI-MS: 289 (M, 16.9), 287
(M, 52.3), 270 (M - OH, 100.0). HRMS calcd. for C10H8-
35ClF2N5O 287.0385, found: 287.0383. Anal. (C10H8ClF2N5O)
C, H, N, Cl, F.
(Z)-2-Am in o-9-{[2-(h yd r oxym eth yl)-3,3-d iflu or ocyclo-
p r op ylid en e]m eth yl}-6-ch lor op u r in e (5b). The procedure
described above was performed with 12b (130 mg, 0.35 mmol).
The crude product was purified by chromatography (CH2Cl2-
MeOH, 20:1) to give a white solid 5b (77 mg, 76.7%), mp 227-
228 °C; UV max 307 nm (ꢀ 7,700), 284 (ꢀ 7,400), 240 (ꢀ 24,500),
202 (ꢀ 13,200). 1H NMR (δ): 2.85-2.93 (1H, m), 3.48-3.55 (1H,
m), 3.62-3.69 (1H, m), 5.23 (1H, brs), 7.07 (2H, s), 7.50 (1H,
s), 8.06 (1H, s). 13C NMR: 31.4 (t, J ) 11.9 Hz), 58.1, 106.9 (t,
J ) 287.0 Hz), 108.8 (t, J ) 7.3 Hz), 116.8, 123.9, 140.1, 150.7,
153.2, 161.1. 19F NMR: 65.1 (d, J ) 175.2 Hz), 79.0 (d, J )
175.2 Hz). EI-MS: 289 (M, 9.6), 287 (M, 28.5), 270 (M - OH,
100.0). HRMS calcd. for C10H835ClF2N5O 287.0385, found:
287.0380. Anal. (C10H8ClF2N5O) C, H, N, Cl, F.
(E)-9-{[2-(H yd r oxym et h yl)-3,3-d iflu or ocyclop r op yli-
d en e]m eth yl}gu a n in e (4c). A solution of 4b (210 mg, 0.73
mmol) in formic acid (80%, 30 mL) was heated at 90 °C for 6
h. After cooling, the solution was evaporated, and the residue
was dissolved in NH3/MeOH (20%, 10 mL). The mixture was
stirred at room temperature for 30 min. The volatile compo-
nents were evaporated, and the crude product was crystallized
from MeOH-H2O (1:2, active carbon) to afford a white solid
4c (180 mg, 92%), mp 304-307 °C (decomp.); UV max 292 nm
(ꢀ 5,500), 272 (ꢀ 7,500), 243 (ꢀ 28,100), 213 (ꢀ 16,000). 1H NMR
(δ): 3.01-3.09 (1H, m), 3.60-3.70 (2H, m), 5.31 (1H, t, J )
5.6 Hz), 6.64 (2H, s), 7.86 (1H, d, J ) 2.4 Hz), 8.27 (1H, s),
10.83 (1H, s). 13C NMR: 33.2 (t, J ) 11.9 Hz), 58.1, 108.1 (t,
J ) 6.6 Hz), 108.2 (t, J ) 285.7 Hz), 117.1, 118.2, 135.1, 151.1,
155.0, 157.2. 19F NMR: 64.9 (d, J ) 170.7 Hz), 78.2 (dd, J )
171.5 and 9.0 Hz). FAB-MS: (+ KCl) 308 (M + K, 6.9), 270
(M + H, 14.8), 253 (M + H - OH, 100.0).
Su p p or tin g In for m a tion Ava ila ble: Comparison of NMR
chemical shifts of fluorinated and nonfluorinated methylenecy-
clopropanes (Table 1), NOE data (Table 2), HPLC (cyclopro-
pene-methylenecyclopropane rearrangement, Table 3), and
UV spectra of 4a and 1a (Figure 1). This material is available
free of charge via the Internet at http://pubs.acs.org.
Refer en ces
(1) Proceedings of the XIV International Roundtable: Nucleosides,
Nucleotides and Their Biological Applications, September 10-
14, 2000, San Francisco, CA; Nucleosides, Nucleotides & Nucleic
Acids 2001, 20, 329-332.
(2) Qiu, Y.-L.; Ksebati, M. B.; Ptak, R. G.; Fan, B. Y.; Breitenbach,
J . M.; Lin, J .-S.; Cheng, Y.-C.; Kern, E. R.; Drach, J . C.; Zemlicka,
J . (Z)- and (E)-2-((Hydroxymethyl)cyclopropylidene)methyl-
adenine and -guanine. New Nucleoside Analogues with a Broad-
Spectrum Antiviral Activity. J . Med. Chem. 1998, 41, 1, 10-23.
(3) Qiu, Y.-L.; Geiser, F.; Kira, T.; Gullen, E.; Cheng, Y.-C.; Ptak,
R. G.; Breitenbach, J . M.; Drach, J . C.; Hartline, C. B.; Kern, E.
R.; Zemlicka, J . Synthesis and Enantioselectivity of the Antiviral
Effects of (R,Z)-, (S,Z)-Methylenecyclopropane Analogues of
Purine Nucleosides and Phosphoralaninate Prodrugs: Influence
of Heterocyclic Base, Type of Virus and Host Cells. Antiviral
Chem. Chemother. 2000, 11, 191-202.
(4) Welch, J . T.; Eswarakrishnan, S. Fluorine in Bioorganic Chem-
istry; Wiley: New York, 1991.
(5) Pankiewicz, K. W. Fluorinated Nucleosides. Carbohydr. Res.
2000, 327, 87-105.
(6) Hertel, L. W.; Boder, G. B.; Kroin, J . S.; Rinzel, S. M.; Poore, G.
A.; Todd, G. C.; Grindey, G. B. Evaluation of the Antitumor
Activity of Gemcitabine (2′,2′-Difluoro-2′-deoxycytidine). Cancer
Res. 1990, 50, 4417-4422.
(7) Halazy, S.; Ehrhard, A.; Danzin, C. 9-(Difluorophosphonoalkyl)-
guanines as a New Class of Multisubstrate Analogue Inhibitors
of Purine Nucleoside Phosphorylase. J . Am. Chem. Soc. 1991,
113, 315-317.
(8) Qiu, Y.-L.; Zemlicka, J . Synthesis of New Nucleoside Analogues
Comprising a Geminal Difluorocyclopropane Moiety as Potential
Antiviral/Antitumor Agents. Nucleosides Nucleotides 1999, 18,
2285-2300.
(9) Guan, H.-P.; Ksebati, M. B.; Cheng, Y.-C.; Drach, J . C.; Kern,
E. R.; Zemlicka, J . Spiropentane Mimics of Nucleosides: Ana-
logues of 2′-Deoxyadenosine and 2′-Deoxyguanosine. Synthesis
of All Stereoisomers, Isomeric Assignment, and Biological Activ-
ity. J . Org. Chem. 2000, 65, 1280-1290.
(10) Guan, H.-P.; Ksebati, M. B.; Kern, E. R.; Zemlicka, J . Approaches
to Unsaturated Analogues of Nucleosides Comprising Four- and
Six-Membered Rings. J . Org. Chem. 2000, 65, 5177-5184.
(11) Taguchi, T.; Kurishita, M.; Shibuya, A.; Aso, K. Preparation of
Methylene-gem-difluorocyclopropanes and Its Reactivity as
Michael Acceptor. Tetrahedron 1997, 53, 9497-9508.
(12) Halton, B.; Banwell, M. G. Cyclopropenes. In The Chemistry of
the Cyclopropyl Group; Rappoport, Z., Ed.; Wiley: New York,
1987; Part 2, pp 1223-1339, loc. cit. 1257-1258.
(13) Shibuya, A.; Okada, M.; Nakamura, Y.; Kibashi, M.; Horikawa,
H.; Taguchi, T. Preparation of Methylenedifluorocyclopropanes
via Cyclopropyl Anion Promoted â-Elimination. Tetrahedron
1999, 55, 10325-10340.
(Z)-9-{[2-(H yd r oxym et h yl)-3,3-d iflu or ocyclop r op yli-
d en e]m eth yl}gu a n in e (5c). The procedure described above
was performed with 5b (60 mg, 0.21 mmol) to give a white
solid 5c (40 mg, 71%), mp >350 °C (decomp.); UV max 292
1
nm (ꢀ 5,400), 272 (ꢀ 8,000), 244 (ꢀ 28,400), 211 (ꢀ 19,300). H
NMR (δ): 2.84-2.93 (1H, m), 3.47-3.53 (1H, m), 3.60-3.68
(1H, m), 5.20 (1H, t, J ) 5.6 Hz), 6.60 (2H, s), 7.38 (1H, s),
7.64 (1H, s), 10.83 (1H, s). 13C NMR: 31.5 (t, J ) 11.9 Hz),
58.1, 107.2 (t, J ) 287.0 Hz), 107.8 (t, J ) 6.4 Hz), 117.0, 117.3,
134.0, 150.8, 155.1, 157.2. 19F NMR: 64.1 (d, J ) 172.6 Hz),
78.1 (dd, J ) 174.1 and 7.9 Hz). FAB-MS: 270 (M + H, 67.7),
269 (M, 16.3), 232 (100.0).
Con ver sion of 13b to 11b a n d 12b . DBU (20 µL, 0.13
mmol) was added to a solution of 13b (410 mg, 1.09 mmol) in
DMF (5 mL) at 0 °C. After 2 min the solvent was evaporated,
and the residue was chromatographed on a silica gel column
to give products 11b (150 mg, 36.6%) and 12b (47 mg, 11.5%)
in addition to starting material 13b (160 mg, 39%).
Cyclop r op en e-Met h ylen ecyclop r op a n e R ea r r a n ge-
m en t of 11b, 12b, a n d 13b. A solution of 11b, 12b, or 13b
(0.24 µM) in DMF (50 µL) was treated with DBU (0.03 µM) in
DMF (5 µL) at room temperature. After 1 min, a sample was
analyzed by a reverse-phase HPLC (Waters µBondapak C18
,
(14) Corbett, T. H.; Panchapor, C.; Polin, L.; Lowichik, N.; Pugh, S.;
White, K.; Kushner, J .; Meyer, J .; Czarnecki, J .; Chinnukroh,
S.; Edelstein, M.; LoRusso, P.; Heilbrun, L.; Horwitz, J . P.;
Grieshaber, C.; Perni, R.; Wentland, M.; Coughlin, S.; Elenblass,
S.; Philion, R.; Rake, J . Preclinical Efficacy of Thioxanthone
SR271425 against Transplanted Solid Tumors of Mouse and
Human Origin. Invest. New Drugs 1999, 17, 17-27.
300 × 3.9 mm column, 45% MeCN in water, flow rate 0.9 mL/
min, detection at 310 nm). The average ratio 11b:12b:13b from
these experiments was 3.6:1:5.4. An excess of DBU or exten-
sion of the reaction time did not affect this ratio, but gradual
decomposition was observed.
Ack n ow led gm en t. We thank L. M. Hryhorczuk
from the Central Instrumentation Facility, Department
J M010191W