Synthesis of metabolites of the prodrug 2, 5-bis(4O-methoxyamidinophenyl)furan

Article abstract of DOI:10.3987/com-03-9716

The synthesis of three metabolites of the prodrug 2,5-bis (4-O-methoxyamidinophenyl)furan (1), 2-(4-hydroxyamidinophenyl)-5-(4-methoxyamidinophenyl)furan (MI), 2-(4-amidinophenyl)-5-(4-ethoxyamidinophenyl)-furan (M3) and 2-(4-amidinophenyl)-5-(4-hydroxyamidinophenyl)furan (M4), is reported. The key step in each of the syntheses involves the Heck reaction.

Full text of DOI:10.3987/com-03-9716

HETEROCYCLES, Vol. 60, No. 5, 2003
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HETEROCYCLES, Vol. 60, No. 5, 2003, pp. 1133 - 1145,
Received, 15th January, 2003, Accepted, 10th March, 2003, Published online, 10th March, 2003
SYNTHESIS OF METABOLITES OF THE PRODRUG 2, 5-BIS(4-
O-METHOXYAMIDINOPHENYL)FURAN
Mariappan Anbazhagan,1 Janelle Y. Saulter,2 James E. Hall,2 and David W.
Boykin1*
1Department of Chemistry, Georgia State University, Atlanta, GA 30303,
USA.2School of Pharmacy, The University of North Carolina, Chapel Hill, NC
27599, USA. E-mail: dboykin@gsu.edu
Abstract- The synthesis of three metabolites of the prodrug 2,5-bis-
(4-O-methoxyamidinophenyl)furan (1), 2-(4-hydroxyamidinophenyl)-5-(4-meth-
oxyamidinophenyl)furan (M1), 2-(4-amidinophenyl)-5-(4-ethoxyamidino-
phenyl)furan (M3) and 2-(4-amidinophenyl)-5-(4-hydroxyamidinophenyl)furan
(M4), is reported. The key step in each of the syntheses involves the Heck
reaction.
INTRODUCTION
2,5-Bis(4-O-methoxyamidinophenyl)furan (1), a prodrug of the antimicrobial agent, 2,5-bis(4-ami-
dinophenyl)furan (2), is effective when administered orally in an immunosupressed rat model for
Pneumocystis carinii pneumonia (PCP) and it also shows excellent activity in mouse models for human
African trypanosomiasis (See Figure 1).1,2 The bis-O-methylamidoxime prodrug is currently undergoing
phase II clinical trial against both of these diseases.2 MS spectral evidence suggests that 1is converted to
2 via a series of stepwise O-demethylations and dehydroxylations. Four major metabolites 2-(4-hydroxya-
midinophenyl)-5-(4-methoxyamidinophenyl)furan (M1), 2,5-bis(4-hydroxyamidinophenyl)furan (M2),
2-(4-amidinophenyl)-5-(4-methoxyamidinophenyl)furan (M3) and 2-(4-amidinophenyl)-5-(4-hydroxy-
amidinophenyl)furan (M4) in the bioconversion of 1 were detected using ion trap MS with electrospray
ionization (Figure 1).3 To unequivocally identify these metabolites, it is important to unambiguously
1
synthesize them. We have previously reported the synthesis of M2. In this article, we report the
synthesis of the postulated metabolites (M1, M3 and M4).

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HETEROCYCLES, Vol. 60, No. 5, 2003
Figure 1: METABOLIC PATHWAY OF 1 TO 2
O
CH ON
3
NOCH
NOH
1
3
NH
2
H N
2
O
CH ON
3
M1
NH
H N
2
2
O
O
HON
CH ON
3
NOH
NH
M2
M3
NH
NH
2
H N
2
H N
2
2
O
HON
NH
NH
M4
NH
NH
2
H N
2
O
HN
2
2
H N
2
RESULTS AND DISCUSSION
Our approach to the synthesis of M1 is outlined in Scheme 1. 2-(4-Cyanophenyl)furan (3) was prepared
according to a literature method.4 When 3 was treated with hydroxylamine hydrochloride and potassium
tert-butoxide in DMSO at an ambient temperature, 4 was obtained in 90 % yield. Compound (5) was
obtained in 80 % yield by treating the amidoxime (4) with dimethyl sulfate in the presence of sodium
hydroxide (2N)in dioxane at 0°C.5 Heck coupling of the methoxyamidoxime (5)with p-bromobenzonitrile
in presence of potassium acetate and Pd(0) catalyst gave 2-(4-cyanophenyl)-5-(4-methoxyamidino-
phenyl)furan (6) in 40 % yield. The relatively low yield of 6 obtained here is typical of Heck coupling
reactions with furans6 and other related Pd catalysed couplings with furan.7
2-(4-Hydroxyamidinophenyl)-5-(4-methoxyamidinophenyl)furan (M1) was obtained when 6 was reacted

HETEROCYCLES, Vol. 60, No. 5, 2003
1135
at room temperature for 12 h with hydroxylamine hydrochloride and potassium tert-butoxide in DMSO
solution to give an 85 % yield. The hydrochloride salt of M1 was made by passing hydrogen chloride gas
into an ethanol solution of the free base. Acetylation of M1 with acetic anhydride in acetic acid yielded
2-(4-acetoxyamidinophenyl)-5-(4-methoxyamidinophenyl)furan (7) in 90 % yield. Pd/C catalysed
hydrogenation8 of 7 in acetic acid-ethanol mixture gave the metabolite 2-(4-amidinophenyl)-
5-(4-methoxyamidinophenyl)furan (M3) in 65 % yield. Thus the synthesis of the metabolites (M1) and
(M3) was achieved in reasonably good yields using straightforward approaches.
Scheme 1
Pd(PPh3)4
+
Br
CN
dioxane, 100 oC, 12 h
SnBu3
O
O
CN
3
(CH3)2SO4, NaOH (2N)
dioxane, rt, 1 h
NH2OH.HCl, KOC4H9-t
O
O
NOH
NOCH3
DMSO, rt, overnight
NH2
NH2
4
5
NH2OH.HCl, KOC4H9-t
Br
CN
O
DMSO, rt, overnight
NOCH3
NC
Pd(PPh3)4, KOAc, DMF, 120 oC
6
NH2
(CH3CO)2O
O
O
AcOH, rt, 1 h
AcON
HON
NOCH3
NOCH3
7
NH2
NH2
NH2
NH2
H2, Pd/C, 50 psi, rt, 6 h
M1
C2H5OH, AcOH
O
HN
NOCH3
NH2
NH2
M3

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HETEROCYCLES, Vol. 60, No. 5, 2003
The synthesis of M4 turned out to be much more difficult. Scheme 2 outlines the first of three approaches
we explored for the synthesis of M4. The reaction of 3 under Pinner conditions yielded the amidine (8) in
50 % yield. Attempted Heck reaction of the amidine (8) with p-bromobenzonitrile failed; ammonia was
eliminated to reform 3.Toavoid this problem the butoxycarbonyl (Boc)protected amidine (9)was prepared
in high yield by treating the amidine with di-tert-butyl dicarbonate in DCM at 0 °C.9 The Heck reaction
of 9with p-bromobenzonitrile in DMF under Pd(0)catalysis gave 10but in rather low yield (23 %).When 10
was treated with hydroxylamine hydrochloride and potassium tert-butoxide as previously described, the
metabolite (M4) was obtained in quite low yield (3 %). Interestingly, the Boc protecting group was also
removed during this process.
Scheme 2
1. C2H5OH, HCl, rt, 10 days
2. C2H5OH, NH3, rt, 10 days
(Boc)2O, NaOH
CH2Cl2, 0 0C, 2 h
O
O
O
NBoc
NH
CN
NH2
NH2
9
8
3
Br
CN
NH2OH.HCl, KOC4H6-t
O
NBoc
DMSO, rt, overnight
Pd(PPh3)4, KOAc, DMF, 120 oC, 16 h
NC
10
NH2
O
HON
NH
NH2
NH2
M4
In an attempt to obtain M4 in higher yield, we decided to use a different strategy as outlined in Scheme 3.
Benzyloxyamidoxime (11) was prepared in 80 % yield using the same procedure employed for 5, but
benzyl bromide was used instead of dimethyl sulfate.5,10 The Heck reaction of 11with p-bromobenzonitrile
gave compound (12) in 30 % yield. In this approach, we decided to make the amidine unit prior to
converting the cyano group to the amidoxime. Palladium catalyzed hydrogenation of 12 gave the

HETEROCYCLES, Vol. 60, No. 5, 2003
1137
N-acetylamidine (13)in 25 %yield.Then 13 was reacted with hydroxylamine hydrochloride and potassium
tert-butoxide to yield an oily compound, which was purified to obtain
2-(4-N-acetylamidinophenyl)-5-(4-hydroxyamidinophenyl)furan (14) in 50 % yield. When 14 was
deacetylated by treatment with 1N NaOH at room temperature it gave M4 in the unsatisfactory yield of
5 %.
Scheme 3
Br
CN
C6H5CH2Br, NaOH
dioxane, rt, 2 h
O
O
Pd(PPh3)4, KOAc, DMF, 120 oC, 16 h
NOH
NOBn
NH2
11
NH2
4
H2, Pd/C, 50 psi, rt, 6 h
C2H5OH, AcOH
O
O
NCOCH3
NC
NOBn
NC
13
NH2
12
NH2
1N NaOH
O
NH2OH.HCl, KOC4H9-t
M4
HON
NCOCH3
DMSO, rt, overnight
14
NH2
NH2
The final approach which we used is outlined in Scheme 4 and employs a fully protected amidine group
as recently described by Liebeskind.11 Compound (15) was prepared according to the literature
procedure.11 Stille coupling of 15 with 2-(tributylstannyl)furan gave 16 in 80 % yield. Compound (16)
was subjected to Heck reaction conditions with p-bromobenzonitrile which gave compound (17) in 32 %
yield. Again the yield obtained from the Heck coupling process is consistent with that reported for similar
reactions with furans. Conversion of the cyano group to amidoxime as previously described gave 18 in
70 % yield. Deprotection of the blocked amidine group was achieved by treatment with trifluoroacetic
acid in dichloromethane. The hydrochloride salt of M4 was obtained in 33 % yield after isolation of the
free base using NaOH solution and subsequent treatment with ethanolic HCl .

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HETEROCYCLES, Vol. 60, No. 5, 2003
Scheme 4
B(OH)2
Br
SCH3
SCH3
1. NaH, DMF
2. SEMCl
BocHN
NBoc
BocHN
NBoc
CuTC, Pd(PPh3)4
SiMe3
O
Br
CN
NBoc
SnBu3
O
O
Br
NBoc
NBoc
SEM
Pd(PPh3)4, KOAc, DMF, 120 oC, 14 h
Pd(PPh3)4, dioxane, reflux, 12 h
BocN
SEM
16
15
O
NH2OH.HCl, KOC4H9-t
O
HON
NBoc
NBoc
SEM
DMSO, rt, overnight
NC
NH2
BocN
SEM
18
BocN
17
O
1. TFA:CH2Cl2 (1:1), rt, 12 h
HON
NH
2. NaOH (1N)
M4
NH2
NH2
3. C2H5OH, HCl
In conclusion, three major metabolites of the prodrug (1, M1, M3 and M4) were synthesized in reasonable
yields and provide samples which confirm their presence in the bioconversion process of 1 to 2 as
previously outlined.3
EXPERIMENTAL
Melting points were determined with a Mel-Temp 3.0 capillary melting point apparatus and are
1
13
uncorrected. H and C NMR spectra were recorded on a Varian Unity+300 or a Varian VRX 400
instrument, with peak assignment relative to residual DMSO (2.49 ppm) or CHCl3 (7.24 ppm). MS spectra
were recorded on a VG instruments 70-SE spectrometer at the Georgia Institute of Technology, Atlanta,
GA. Elemental analysis were performed by Atlantic Microlab, Norcross, GA. Unless otherwise stated all

HETEROCYCLES, Vol. 60, No. 5, 2003
1139
the reagent chemicals and solvents (including anhydrous solvents) were purchased from Aldrich Chemical
Co., Fisher Scienticfic, or Lancaster synthesis and used as received. 2-(4-Cyanophenyl)furan4 and
4-bromo-1-{1,3-bis(tert-butoxycarbonyl)-3-[2(trimethylsilyl)ethoxymethyl]}amidinobenzene10 were pre-
pared according to literature methods.
2-(4-N-Hydroxyamidinophenyl)furan (4):
Hydroxylamine hydrochloride (6.9 g, 100 mmol) was suspended in anhydrous DMSO (40 mL) and the
suspension was cooled in an ice bath. KOC4H9-t (11.2 g, 100 mmol) was added portion wise under nitrogen
atmosphere and the solution was stirred at rt for 1 h. Then 2-(4-cyanophenyl)furan (1.69 g, 10 mmol) was
added at once and the reaction mixture was stirred overnight at rt. It was poured into ice-water and the
product was filtered and the 2-(4-hydroxyamidinophenyl)furan was recrytallised from ethanol. Yield: 1.85
g (90%). Colorless crystals, mp 129-130 оC. 1H NMR δ 5.83 (br, 2H, NH2, exchangeable with D2O), 6.61
(q, 1H, J = 3.3 Hz), 7.00 (d, 1H, J = 3.3 Hz), 7.76 (m, 5H, Ar), 9.65 (s, 1H, OH, exchangeable with D2O);
13C NMR δ 106.3, 112.1, 123.04, 125.84, 130.6, 132.1, 143.1, 150.4, 152.6. Anal. Calcd for C11H10N2O2: C,
65.33; H, 4.98; N, 13.85. Found: C, 65.57; H, 4.80; N, 13.58.
2-(4-N-Methoxyamidinophenyl)furan (5):
2-(4-N-Hydroxyamidinophenyl)furan (1.61 g, 8 mmol) was dissolved in dioxane (10 mL) and cooled to 0
ºC. 2N NaOH (80 mL) solution was added slowly followed by dimethyl sulfate (1.3 g, 10 mmol) in dioxane
(5 mL) dropwise. After addition was complete the ice-bath was removed and the mixture was stirred at
room temperature for 1 h. After TLC showed the disappearance of the amidoxime, the mixture was
extracted with EtOAc (3 x 50 mL), combined organic layers were washed with water, brine and dried over
Na2SO4. The organic layer was filtered and the solvent was removed under reduced pressure. The crude
product was purified by passing thru a short silica gel column using 30% ethyl acetate in hexanes as an
о
eluent. The compound crystallized from the eluent as a pale yellow solid, mp 89.5-90 C. Yield: 1.38 g
(80%). 1H NMR δ 3.75 (s, 3H, OCH3), 6.16 (br, 2H, NH2, exchangeable with D2O), 6.59 (q, 1H, J = 3.3 Hz),
13
7.01 (d, 1H, J = 3.3 Hz), 7.75 (m, 5H, Ar); C NMR δ 60.6, 106.6, 112.2, 123.0, 126.2, 131.0, 132.0,
143.2, 150.8, 152.5. Anal. Calcd for C12H12N2O2: C, 66.65; H, 5.59; N, 12.95. Found: C, 66.35; H, 5.68; N,
12.67.
2-(4-Cyanophenyl)-5-(4-N-methoxyamidinophenyl)furan (6):
2-(4-N-Methoxyamidinophenyl)furan (1.08 g, 5 mmol) was treated with 4-bromobenzonitrile (910 mg, 5
mmol) in the presence of tetrakis(triphenylphosphine)palladium(0) (288 mg, 0.25 mmol) and potassium

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HETEROCYCLES, Vol. 60, No. 5, 2003
о
acetate (735 mg, 7.5 mmol) in DMF (10 mL). The mixture was heated at 120 C for 16 h. The reaction
mixture was cooled to rt and extracted with dichloromethane (3 x100 mL), the solution was filtered through
Celite. The filtrate was washed with water repeatedly and the DCM solution was dried (Na2SO4), filitered
and concentrated under reduced pressure. Flash chromatography of the crude product on silica gel with
DCM-hexanes (1:1) afforded 635 mg (40 %) of pure yellow solid, mp 163-164 оC. 1H NMR δ 3.95 (s, 3H,
OCH3), 4.83 (br, 2H, NH2, exchangeable with D2O), 6.83 (q, 1H, J = 3.3 Hz), 6.91 (d, 1H, J = 3.3 Hz), 7.74
(m, 8H, Ar); 13C NMR δ 61.5, 108.5, 110.2, 110.5, 118.9, 123.8, 124.0, 126.2, 131.2, 131.7, 132.6, 134.2,
151.2, 151.6, 154.2. EI-MS m/z: 317 (M+), 286, 271, 216, 140. Anal. Calcd for C19H15N3O2: C, 71.91; H,
4.76; N, 13.24. Found: C, 71.76; H, 4.82; N, 13.03.
2-(4-Hydroxyamidinophenyl)-5-(4-methoxyamidinophenyl)furan (M1):
The same procedure described for compound (4) was used with the following reagents. Hydroxylamine
hydrochloride (1.38 g, 20 mmol), potassium tert-butoxide (2.24g, 20 mmol), anhydrous DMSO (10 mL)
and compound (6)(634 mg, 2 mmol).Yield of M1:595 mg (85 %). The hydrochloric acid salt was made by
passing HClgas through an ethanol solution of M1.The precipitate was washed with ether and after drying
gave pure yellow solid, mp 162-163 оC. 1H NMR δ 3.75 (s, 3H, OCH3), 5.86 (br, 2H, NH2, exchangeable
with D2O), 6.11 (br, 2H, NH2, exchangeable with D2O), 7.14 (s, 2H, Furan), 7.77 (m, 8H, Ar), 9.72 (s, 1H,
13
OH, exchangeable with D2O); C NMR δ 60.6, 108.9, 109.1, 123.1, 125.8, 126.2, 130.2, 130.6, 131.3,
132.2, 150.3, 150.6, 152.3, 152.6.EI-MS m/z: 350 (M+),334, 317, 286, 244, 216, 189,136. Anal.Calcd for
C19H18N4O3: C, 65.13; H, 5.17; N, 15.99. Found: C, 64.98; H, 5.19; N, 15.82.
2-(4-Acetoxyamidinophenyl)-5-(4-methoxyamidinophenyl)furan (7):
2-(4-N-Hydroxyamidinophenyl)-5-(4-N-methoxyamidinophenyl)furan (350 mg, 1 mmol) was dissolved in
glacial acetic acid (5 mL) and acetic anhydride (0.5 mL) was added and the mixture was stirred overnight at
rt. TLC indicated complete acylation of the starting material. The residue was poured over ice-water
mixture, the precipitate was filtered and washed well with water and dried to get pure yellow powder, mp
191-192 оC. Yield: 355 mg (90%). 1H NMR δ 2.19 (s, 3H, COCH3), 3.85 (s, 3H, OCH3), 6.16 (br, 2H, NH2,
exchangeable with D2O), 6.85 (br, 2H, NH2, exchangeable with D2O), 7.19 (d, 1H, J = 3.3 Hz, furan), 7.23
13
(d, 1H, J = 3.3 Hz, furan), 7.87 (m, 8H, Ar); C NMR δ 19.8, 60.6, 109.1, 109.6, 123.26, 126.2, 127.2,
130.3, 130.5, 131.4, 131.6, 150.6, 152.2, 152.7, 155.9, 168.4. EI-MS m/z: 393 (MH+), 345, 335, 307, 288,
271, 225, 187. Anal. Calcd for C21H20N4O4: C, 64.27; H, 5.13; N, 14.27. Found: C, 64.30; H, 5.15; N,
14.37.

HETEROCYCLES, Vol. 60, No. 5, 2003
1141
2-(4-Amidinophenyl)-5-(4-methoxyamidinophenyl)furan (M3):
5 (392 mg,0.75 mmol) was dissolved in glacial acetic acid (20 mL)and ethanol (20 mL) was added.To the
mixture was added 200 mg of palladium on carbon (10 %) and the mixture was hydrogenated at 60 psi on
a Parr apparatus for 4 h.The mixture was filtered over Celite and the solution was concentrated to give the
amidine (M3)as its acetic acid salt.The hydrochloride salt of M3was obtained by isolation of the free base
using NaOH solution and subsequent treatment with ethanolic HCl.Yellow solid,65 %,mp 264-265 оC. 1H
NMR δ 3.85 (s,3H, OCH3),7.38 (d, 1H,J=3.6 Hz, furan), 7.43 (d, 1H, J = 3.6 Hz), 7.86-8.09 (m, 8H, Ar),
9.29 (br, 2H, NH2, exchangeable with D2O), 9.51 (br, 2H, NH2, exchangeable with D2O);13C NMR δ 62.1,
110.9, 112.0, 123.8, 124.3, 126.2, 127.8, 128.1, 129.1, 133.0, 134.5, 152.1, 153.0, 155.8, 165.3. FAB-MS
Calcd for C19H18N4O2: 334.371. Found: 334.378. Anal. Calcd for C19H18N4O2-2HCl-2H2O: C, 51.47; H,
5.45; N, 12.63. Found: C, 51.38; H, 5.29; N, 12.30.
2-(4-Amidinophenyl)furan (8):
2-(4-Cyanophenyl)furan (3) was subjected to the Pinner sequence according to a published procedure12 and
gave 2-(4-amidinophenyl)furan (8) in 50 % yield. The dark brown solid obtained directly from the
ammonia/ ethanol solution was washed with NaOH solution, water and ethanol and after drying gave pure
solid, mp 197-198 оC. 1H NMR δ 6.61 (q, 1H, J = 3.3 Hz, furan), 7.07 (d, 1H, J = 3.8 Hz, furan), 7.70-7.95
13
(m, 5H, Ar and furan); C NMR δ 107.3, 112.3, 123.0, 127.5, 132.2, 132.7, 143.6, 152.2, 162.6. Anal.
Calcd for C11H10N2O-0.5H2O: C, 67.67; H, 5.67; N, 14.34. Found: C, 67.47; H, 5.76; N, 14.39.
2-(4-N-Butoxycarbonylamidinophenyl)furan (9):
A solution of sodium hydroxide (1.0g, 25 mmol) in water (20 mL) was added dropwise at 0 оC to a stirred
suspension of 2-(4-amidinophenyl)furan (8) (1.86 g, 10 mmol) in THF (20 mL), and di-tert-butyl
dicarbonate (2.2 g, 10 mmol) was added immediately thereafter. After 1 h at 0 оC, ethyl acetate was added
and the organic phase was separated, washed with saturated NaCl solution,dried (Na2SO4),and evaporated
under reduced pressure.Crystallisation of the solid residue from hexane-dichloromathane gave pure 9(2.68
g, 93%). Pale yellow crystals, 143-144 оC. 1H NMR δ 1.44 (s, 9H, 3CH3), 6.51 (q, 1H,J = 3.8 Hz), 6.79 (d,
1H, J = 3.8 Hz), 7.52 (d, 1H, J = 3.8 Hz), 7.65 (d, 2H, J = 8.0 Hz, Ar), 7.85 ((d, 2H, J = 8.0 Hz, Ar); 13C
NMR δ 28.1, 79.7, 106.9, 111.9, 123.6, 127.6, 133.2, 134.0, 142.9, 152.8, 155.8, 161.7. EI-MS m/z: 286
(M+), 230, 212, 186, 170, 140, 115. Anal. Calcd for C16H18N2O3: C, 67.11; H, 6.33; N, 9.78. Found: C,
67.15; H, 6.39; N, 9.71.
2-(4-N-Butoxycarbonylamidinophenyl)-5-(4-cyanophenyl)furan (10):
The same procedure described for 6 was used with the following reagents: 2-(4-butoxycarbonyl-

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HETEROCYCLES, Vol. 60, No. 5, 2003
phenyl)furan (9) (1.43 g,5 mmol), p-bromobenzonitrile (910 mg, 5 mmol),KOAc (735 mg, 7.5 mmol) and
Pd(PPh3)4(288 mg, 0.25 mmol) in DMF (10 mL). Flash chromatography of the crude product on silica gel
with DCM-hexanes (1:1)afforded a yellow solid which precipitated from the eluent, mp 177-178 оC. Yield
of 10: 445 mg (23%). 1H NMR δ 1.50 (s, 9H, 3CH3), 6.81 (d, 1H, J = 3.6 Hz), 6.86 (d, 1H, J = 3.6 Hz),
13
7.60-7.97 (m, 8H, Ar); C NMR δ 28.1, 80.4, 109.6, 110.4, 110.5, 118.8, 123.6, 123.8, 128.0, 132.5,
132.9, 133.3, 133.9, 152.0, 153.5, 162.8,166.4.EI-MS m/z:388 (MH+),331, 314, 288, 270, 154,116. Anal.
Calcd for C23H21N3O3: C, 71.30; H, 5.46; N, 10.84. Found: C, 71.43; H, 5.59; N, 10.90.
2-(4-Amidinophenyl)-5-(4-hydroxyamidinophenyl)furan (M4):
The same procedure described for 4 was used with the following reagents: Hydroxylamine hydrochloride
(534 mg, 7.7 mmol), potassium tert-butoxide (862 mg, 7.7 mmol), anhydrous DMSO (4 mL) and
compound (10) (300 mg, 0.77 mmol). During the course of the reaction deprotection of the Boc group
also occurred.The yield of M4 was very low (7 mg,3%), yellow solid,mp 272-273 оC.1H NMR δ6.85 (br,
2H,2NH2, exchangeable with D2O),7.10 (d, 1H, J = 3.6 Hz),7.18 (d, 1H,J = 3.6 Hz),7.80-8.15 (m, 8H, Ar),
9.05 (br, 2H, NH2, exchangeable with D2O),9.88 (br, 1H, OH, exchangeable with D2O); 13C NMR δ 109.5,
111.0, 123.8, 124.3, 126.4, 127.1, 130.3, 130.5, 132.4, 133.2, 151.1, 152.0, 153.5, 158.5. EI-MS m/z: 321
(MH+), 303, 279, 256, 238. The hydrochloride salt of M4 was made for analysis by passing hydrogen
chloride gas into an ethanol solution of the free base. Anal.Calcd for C18H16N4O3-2HCl-2.4H2O:C, 49.62;
H, 5.27. Found: C, 49.87; H, 5.55.
2-(4-Benzyloxyamidinophenyl)furan (11):
The same procedure described for 5 was used with the following reagents: amidoxime (4) (4.04 g, 20
mmol),benzyl bromide (4.26 g, 25 mmol),2N NaOH (60 mL)and dioxane (50 mL).The crude product was
purified by passing thru a short silica gel column using 30% ethyl acetate in hexanes as an eluent. The
compound crystallized from the eluent as a pale yellow solid,mp 110-111 оC.The yield of 2-(4-benzyloxy-
amidinophenyl)furan (11) was 2.34 g (80%). 1H NMR δ 4.82 (br, 2H, NH2, exchangeable with D2O), 5.15
(s, 2H, PhCH2), 6.48 (q,1H, J = 3.9 Hz), 6.71 (d, 1H, J = 3.6 Hz),7.31-7.50 (m, 5H, Ar),7.76-7.71 (m, 4H,
Ar); 13C NMR δ 74.3, 106.5, 112.1, 123.0, 126.2, 127.2, 127.6, 128.1, 131.0, 131.2, 138.8, 143.2, 150.9,
152.5. EI-MS m/z: 292(M+),201,186, 70, 140, 115, 91,77.Anal.Calcd for C18H16N2O2: C, 73.95; H, 5.51;
N, 9.58. Found: C, 73.72; H, 5.61; N, 9.42.
2-(4-Benzyloxyamidinophenyl)-5-(4-cyanophenyl)furan (12):
The Heck reaction procedure described for 6 was used with the following reagents: 2-(4-benzyloxy-

HETEROCYCLES, Vol. 60, No. 5, 2003
1143
amidinophenyl)furan (9) (1.46 g, 5 mmol), p-bromobenzonitrile (910 mg, 5 mmol), KOAc (735 mg, 7.5
mmol) and Pd(PPh3)4 (288 mg, 0.25 mmol) in DMF (10 mL). Flash chromatography of the crude product
on silica gel with DCM-hexanes (1:1) afforded 490 mg (30 %) of pure yellow solid (12),mp 154-155 оC. 1H
NMR δ 4.83 (br, 2H, NH2, exchangeable with D2O),5.18 (s, 2H, PhCH2), 6.82 (d, 1H,J = 3.8 Hz), 6.90 (d,
1H, J = 3.8 Hz),7.32-7.49 (m, 5H, Ar),7.65-7.82 (m, 4H, Ar);13C NMR δ 74.4, 108.9, 109.1, 123.1, 125.8,
126.3, 127.3, 128.1, 130.2, 130.7, 131.3, 132.3, 138.8, 150.4, 151.0, 152.4, 152.6. EI-MS m/z: 393 (M+),
302, 287, 272, 214, 140, 91, 77. Anal.Calcd for C25H19N3O2: C, 76.31; H, 4.86; N, 10.68. Found:C, 76.39;
H, 4.84; N, 10.45.
2-(4-N-Acetylamidinophenyl)-5-(4-cyanophenyl)furan (13):
Compound (12)(393 mg, 0.61 mmol) was hydrogenated in acetic acid (25 mL) and ethanol (25 mL) using
Pd/C (200 mg) at 60 psi. The pure amidine (13) crystallized from ethanol as yellow powder (yield: 83 mg,
о
1
25%), mp 258-259 C. H NMR δ 1.78 (s, 3H, COCH3), 1.86 (s, 3H, CH3COO), 5.20 (br, 2H, NH2,
13
exchangeable with D2O), 7.11 (d, 1H, J = 3.3 Hz), 7.32 (d, 1H, J = 3.3 Hz), 7.80-8.01 (m, 8H, Ar); C
NMR δ 23.1, 106.3, 108.9, 112.1, 114.1, 121.5, 122.8, 123.0, 125.8, 125.9, 129.4, 132.5, 150.2, 150.3,
152.6, 154.8, 168.6. FAB-MS Calcd for C20H15N3O2: 329.116. Found: 329.112. Anal. Calcd for
C20H15N3O2-1.2H2O: C, 68.42; H, 4.99; N, 11.97. Found: C, 68.29; H, 5.31; N, 11.68.
2-(4-N-Acetylamidinophenyl)-5-(4-hydroxyamidinophenyl)furan (14):
The same procedure described for 4 was used with the following reagents: 2-(4-amidinophenyl)-
5-(4-cyanophenyl)furan (13) (75 mg, 0.22 mmol), hydroxylamine hydrochloride (157 mg, 2.2 mmol),
potassium tert-butoxide (254 mg, 2.2 mmol), anhydrous DMSO (2 mL). The yellow solid obtained was
о
1
washed with water and on drying gave 14, mp >300 C. Yield: 47 mg (50 %). H NMR δ 1.88 (s, 3H,
COCH3), 5.85 (br, 4H, 2NH2, exchangeable with D2O), 7.05 (d, 1H, J = 2.7 Hz), 7.11 (d, 1H, J = 2.7 Hz),
7.73-7.83 (m, 8H, Ar), 9.71 (s, 1H, OH, exchangeable with D2O); 13C NMR δ 22.9, 108.5, 109.4, 113.1,
123.7, 124.1, 126.5, 128.5, 129.1, 131.1, 132.2, 139.3, 151.4, 152.5, 153.4, 170.8. EI-MS m/z: 363 (MH+),
333, 317, 306, 271, 248, 168, 115, 77. Anal. Calcd for C20H18N4O3- 1.3H2O: C, 62.11; H, 5.39; N, 14.48.
Found: C, 62.29; H, 5.51; N, 14.19. This N-acetyl derivative on treatment with 1N NaOH at room
temperature for 5 h gave M4 in 5 % yield.
2-(4-{1,3-Bis(tert-butoxycarbonyl)-3-[2-(trimethylsilyl)ethoxymethyl]}amidinophenyl)furan (16):
Stille coupling reaction of 15 with 2-tributylstannylfuran in dioxane at reflux temperature for 15 hgave the
1
compound (16) in 80 % yield as an oil. H NMR δ 0.02 (s, 9H), 0.99 (t, 2H, J = 8.1 Hz,), 1.05(s, 9H),

1144
HETEROCYCLES, Vol. 60, No. 5, 2003
1.25(s, 9H), 3.75 (t, 2H, J = 8.1 Hz), 5.25 (s, 2H), 6.48 (q, 1H, J = 3.8 Hz,), 6.71 (d, 1H, J = 3.8 Hz),
7.48-7.67 (m, 5H); HRMS (FAB): Calcd for C27H40N2O6Si: 516.265; Found: 516.256. EI-MS m/z: 517
(MH+),461, 441, 405, 376, 332, 289, 276, 249. Anal. Calcd for C27H40N2O6Si:C, 62.76; H,7.80. Found: C,
62.40; H, 7.40.
2-(4-{1,3-Bis(tert-butoxycarbonyl)-3-[2-(trimethylsilyl)ethoxymethyl]}-5-(4-amidinophenyl)-5-(4-
cyanophenyl)furan (17):
The same procedure described for compound (6)was used with the following reagents:16 (2.58 g, 5 mmol),
p-bromobenzonitrile (910 mg,5 mmol), KOAc (735 mg,7.5 mmol) and Pd(PPh3)4 (288 mg, 0.25 mmol) in
DMF (10 mL). Yield: 986 mg (32 %).Semi-solid; 1H NMR δ -0.02 (s, 9H), 0.77 (t, 2H J = 8.0 Hz), 1.06(s,
9H), 1.37(s, 9H), 3.72 (t, 2H, J = 8.3 Hz), 5.30 (s, 2H), 6.79 (q, 1H, J = 3.0 Hz), 7.05 (d, 1H, J = 3.8 Hz),
7.48-7.67 (m, 8H); HRMS (FAB): Calcd for C34H43N3O6Si: 617.292; Found: 617.289. EI-MS m/z: 618
(MH+), 544, 517, 506, 461, 415, 388, 376, 286, 259. Anal. Calcd for C34H43N3O6Si: C, 66.09; H, 7.01; N,
6.80. Found: C, 66.24; H, 7.35; N, 6.57.
2-(4-{1,3-Bis(tert-butoxycarbonyl)-3-[2(trimethylsilyl)ethoxymethyl]}-5-(4-amidinophenyl)-5-(4-
hydroxyamidinophenyl)furan (18):
The same procedure described for compound (4) was used with the following reagents: 17 (617 mg, 1 mmol),
hydroxylamine hydrochloride (690 mg, 10 mmol), potassium tert-butoxide (1.2 g, 10 mmol), anhydrous
DMSO (10 mL). Compound (18) was obtained in a yield of 455 mg (70 %).Yellow solid, recrytallised from
ethanol, mp: 268-269 оC.1H NMR δ -0.01 (s, 9H), 0.97 (t, 2H, J = 8.0 Hz,), 1.12(s, 9H), 1.29(s, 9H), 4.35 (t,
2H, J = 8.0 Hz,), 5.88 (s, 2H), 6.82 (q, 1H, J = 3.2 Hz,), 7.11 (d, 1H, J = 3.4 Hz), 7.74-7.97 (m, 8H, Ar), 9.73
(s, 1H, OH, exchangeable with D2O); HRMS (FAB): Calcd for C34H46N4O7Si: 650.313; Found: 651.327
(MH+). EI-MS m/z: 651 (MH+), 565, 523, 467, 421, 377, 286, 251. Anal. Calcd for C34H46N4O7Si: C,
62.74; H, 7.12. Found: C, 62.89; H, 7.26.
2-(4-Amidinophenyl)-5-(4-hydroxyamidinophenyl)furan (M4):
Compound (18) (400 mg, 0.61 mmol) was treated with a solution of TFA (5 mL) and CH2Cl2 (5 mL) and
the mixture was allowed to stir at rt for 12 h. Ether was added to the reaction mixture and the solid was
filtered. Then it was basified with 1N NaOH and the solid was filtered. Finally the free base was dissolved
in ethanol and HCl gas was passed to obtain the HCl salt of M4. The yellow solid which precipitated was
washed with ether and dried to yield 65 mg (33 %).The spectral and analytical data obtained were identical
with the sample of M4 obtained according to Scheme 2.

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1145
ACKNOWLEDGEMENT
This work was supported by the Bill and Melinda Gates Foundation and NIH Grants AI-46365 and
R44AI40518.
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