Furoxan analogues of the histamine H3-receptor antagonist imoproxifan and related furazan derivatives

Article abstract of DOI:10.1016/j.bmc.2005.05.004

Synthesis and pharmacological characterisation of a series of compounds in which the oxime substructure present in imoproxifan was constrained in the pentatomic NO-donor furoxan ring, as well as their structurally related furazan analogues devoid of NO-do

Full text of DOI:10.1016/j.bmc.2005.05.004

Bioorganic & Medicinal Chemistry 13 (2005) 4750–4759
Furoxan analogues of the histamine H3-receptor antagonist
imoproxifan and related furazan derivatives
Paolo Tosco,a Massimo Bertinaria,a Antonella Di Stilo,a Clara Cena,a Giovanni Sorba,b
Roberta Frutteroa,* and Alberto Gascoa
aDipartimento di Scienza e Tecnologia del Farmaco, Via P. Giuria 9, I-10125 Torino, Italy
b
`
Dipartimento di Scienze Chimiche, Alimentari, Farmaceutiche e Farmacologiche, Universita degli Studi del Piemonte Orientale,
Viale Ferrucci 33, I-28100 Novara, Italy
Received 23 December 2004; revised 28 April 2005; accepted 3 May 2005
Available online 8 June 2005
Abstract—Synthesis and pharmacological characterisation of a series of compounds in which the oxime substructure present in imo-
proxifan was constrained in the pentatomic NO-donor furoxan ring, as well as their structurally related furazan analogues devoid
of NO-donating properties, are described. The whole series of products displayed reversible histamine H3-antagonistic activity on
guinea-pig ileum. 4-(4-(3-(1H-Imidazol-4-yl)propoxy)phenyl)furoxan-3-carbonitrile 16 was also able to induce partial relaxation
when added to the bath after electrical contraction of the guinea-pig ileum during the study of its H3-antagonistic properties.
This phenomenon seems to be dependent on NO-mediated sGC activation. The lipophilic–hydrophilic balance of all the
products was investigated.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
the preliminary pharmacological characterisation of a
series of products in which the oxime substructure
present in imoproxifan (1, 4-(3-(1H-imidazol-4-
yl)propoxy)phenylethanone oxime), which exists in
an (E)-configuration,5 was constrained in the appro-
priately substituted pentatomic NO-donor furoxan
ring (compounds 13–16). The corresponding furazan
derivatives, unable to release NO, are also described
(13a–16a).
In our continuing efforts toward the design of hybrid
structures in which an appropriate pharmacophoric
group is joined to a nitric oxide (NO) releasing moi-
ety,1 we have recently designed new selective histamine
H3-receptor antagonists endowed with NO-donor
properties. Part of these products was obtained by
coupling the H3-antagonist SKF 91486, a (3-(1H-imi-
dazol-4-yl)propyl)guanidine, with differently substi-
tuted NO-donor furoxan substructures.2 Other
selective NO-donor H3-antagonists, characterised by
a lipophilic–hydrophilic balance more appropriate to
enter the central nervous system, were obtained by
joining the 3-(1H-imidazol-4-yl)propoxy moiety of
the proxifan series3 with furoxan and nitrooxy NO-
donor moieties.4 The analogue compounds containing
in the side chain a S atom or a SO2 moiety in place of
the oxygen atom displayed H3-antagonist activity too,
but they were also partly active at the muscarinic
receptors.4 Here, we describe the synthesis and the
study of the lipophilic–hydrophilic balance as well as
2. Chemistry
The synthetic approach to the final products involves
the preparation of a series of phenol derivatives bearing
at the p-position the appropriate furoxan and furazan
moieties. These compounds were obtained according
Keywords: Histamine; H3-antagonists; Furoxans; Furazans.
*
Corresponding author. Tel.: +39 011 6707850; fax: +39 011
6707972; e-mail: roberta.fruttero@unito.it
0968-0896/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2005.05.004

P. Tosco et al. / Bioorg. Med. Chem. 13 (2005) 4750–4759
4751
Scheme 1. Reagents and conditions: (i) CH3SO2OH, DL-Met, 60 ꢁC; (ii) CCl4, NBS, cat. benzoyl peroxide, reflux; (iii) dioxane, H2O, CaCO3, reflux;
(iv) CH2Cl2, AlCl3, sealed flask, 60 ꢁC; (v) (CH3O)3P, reflux; (vi) Et2O, ethyl chloroformate, Et3N, ꢀ15 ꢁC; (vii) acetone, DHP, cat. CH3SO2OH,
0 ꢁC ! rt; (viii) acetone, H2O, NaOH, 0 ꢁC; (ix) dioxane, MnO2, reflux; (x) CH2Cl2, MnO2, rt; (xi) CH3CN, NH2OHÆHCl, dry pyridine, 60 ꢁC; (xii)
acetone, DHP, cat. CH3SO2OH, reflux; (xiii) acetone, H2O, NaOH, 0 ꢁC; (xiv) H2O, NaOH, 0 ꢁC; (xv) DMF, SOCl2, 0 ꢁC; (xvi) acetone, H2O,
K2CO3, rt.
to the pathway reported in Scheme 1. The 4-(4-methoxy-
phenyl)-3-methylfuroxan 2 and the furazan analogue 2a
were transformed into the corresponding phenol deriva-
tives 3 and 3a by means of DL-methionine in methane-
sulfonic acid solution. Compound 2 was also used as
the starting material to prepare the phenols 5 and 5a.

4752
P. Tosco et al. / Bioorg. Med. Chem. 13 (2005) 4750–4759
The furoxanic methyl of this product underwent free
radical bromination with N-bromosuccinimide in reflux-
ing CCl4 using benzoyl peroxide as initiator. The inter-
mediate bromomethyl derivative was immediately
hydrolysed to the corresponding hydroxymethyl deriva-
tive 4 in a dioxane/water solution in the presence of
CaCO3. The methyl aryl ether 4 was transformed into
the corresponding phenol 5 under the action of AlCl3
in CH2Cl2, heating at 60 ꢁC in a sealed vessel suitable
for high-pressure reactions. The latter was reduced to
the corresponding furazan 5a in refluxing trimethyl
phosphite. The phenol groups of 5 and 5a were pro-
tected as ethyl carbonate by means of ethyl chlorofor-
mate in the presence of triethylamine to give 6 and 6a
which, by acid-catalysed reaction with 3,4-dihydro-2H-
pyran (DHP) followed by alkaline deprotection of the
phenol groups, afforded the corresponding tetrahydro-
pyranyl ethers 7, 7a. The protected phenols 6 and 6a
were also transformed into the oximes 8, 8a through
MnO2 oxidation, followed by treatment with hydroxyl-
amine. The oximes 8, 8a were not isolated and charac-
terised but they were immediately deprotected in
NaOH solution and dehydrated to the cyano derivatives
9, 9a with SOCl2 in DMF. The furoxan and furazan-
carboxamides 10, 10a were obtained by hydrolysis of
the parent cyano derivatives in acetone/water solution
in the presence of K2CO3. The final products were pre-
pared by Mitsunobu coupling of 3-(1-trityl-1H-imi-
dazol-4-yl)-1-propanol 12 with the appropriate phenol
derivatives, according to Scheme 2. The reaction was
run in THF in the presence of Ph3P and diisopropylazo-
dicarboxylate (DIAD). The products thus obtained were
deprotected to the final compounds with trifluoroacetic
acid (TFA) in CH2Cl2. When the Mitsunobu coupling
was attempted with cyanofuroxan 9, extended decompo-
sition of the starting material occurred. Better results
were obtained using in this reaction the tetrahydropyra-
nyl derivative 11 of oxime 8, which was prepared as the
analogues 7, 7a. Selective hydrolysis of the tetrahydro-
pyranyl moiety by means of p-toluenesulfonic acid in
methanol, followed by SOCl2-mediated dehydration
and trityl group removal, afforded the final product 16.
3. Results and discussion
3.1. Detection of nitrite
The ability of furoxan derivatives to produce nitrite,
which is the most important oxidation product of NO
in aerobic water solution, was evaluated by the Griess
reaction.6 The assay was performed in a pH 7.4 buffered
solution at 37 ꢁC under the action of an excess of cyst-
eine (1:50), according to a previously reported proce-
dure;6 the results are reported in Table 1. The NO
release ranks in the order 16 > 15 > 14 ꢁ 13, in line with
the finding that the thiol-induced release from furoxans
is enhanced by the presence of electron-withdrawing
substituents at the ring.7
Table 1. H3-antagonism and NO-release properties of the compounds
under study
Compound H3-antagonism pA2 SEa NO2 (%)b(+ L-cys)
ꢀ
1c
13
8.42 0.05
7.34 0.09
7.99 0.04
6.41 0.07
6.59 0.08
6.10 0.05
—
0
—
13a
14
<1
—
14a
15
3.3 0.2
—
15a
16
6.62 0.11
d
—
(6.39 0.11)e
7.10 0.07
18.7 0.7
—
16a
—, not determined.
a pA2 values were estimated at the concentrations reported in Section 4.
b Yields are reported in % [mol/mol] SEM.
c pKi = 9.58 0.05 (Ref. 5).
d It was impossible to estimate pA2 value in the absence of ODQ
because at 1 lM concentration it determined 100% relaxation of
electrically stimulated guinea-pig ileum.
Scheme 2. Reagents and conditions: (i) dry THF, Ph3P, DIAD,
0 ꢁC ! rt; (ii) MeOH, p-TsOH, rt; (iii) DMF, SOCl2, ꢀ40 ꢁC ! 18 ꢁC;
(iv) 10% TFA in CH2Cl2, rt.
e In the presence of 1 lM ODQ.

P. Tosco et al. / Bioorg. Med. Chem. 13 (2005) 4750–4759
4753
ileum segments.13 pA2 values were calculated using the
Gaddum equation (pA2 = ꢀlog[B] + log[CR ꢀ 1]) and
they are reported in Table 1. Some experiments were as-
sessed in the presence of 1 lM ODQ (1H-[1,2,4]oxadiaz-
olo[4,3-a]quinoxalin-1-one), a well-known inhibitor of
the soluble guanylate cyclase (sGC). The analysis of
Table 1 shows that all the products display antagonist
activity at the H3-receptors, even if lower than that of
imoproxifan. Furoxan derivatives 13, 14 and 15, which
are feeble NO-donors, behave similarly to the furazan
analogues, being just a little less potent. The most active
products bear the methyl substituent and the least active
ones the carbamoyl substituent. The cyano substituted
furoxan derivative 16, which is a potent NO-donor, be-
haves in a particular manner. In fact, when the product
was added to the bath at 1 lM concentration, after the
electrical contraction of the tissue, a complete annul-
ment of the contraction was observed. When the experi-
ments were repeated in the presence of ODQ, the
contraction of the tissue to the electrical stimulus was
fully restored, suggesting that the tissue relaxation was
NO-dependent. The pA2 of this product, evaluated at
1 lM concentration, was 6.39, indicating a lower affinity
of the compound for the H3-receptor with respect to the
furazan analogue 16a.
Table 2. Dissociation constants and lipophilicity descriptors in octa-
nol/water of the compounds under study
Compound pKa SDa logPN SDb logPI SDc logD7.4d
13
7.18 0.01 2.40 0.02
7.18 0.01 2.92 0.02
7.16 0.01 2.03 0.02
7.14 0.01 2.15 0.01
7.16 0.02 1.57 0.03
7.15 0.01 1.79 0.03
7.16 0.01 3.19 0.02
7.14 0.01 3.24 0.02
ꢀ0.05 0.02 2.19
0.43 0.05 2.71
ꢀ0.32 0.01 1.83
ꢀ0.24 0.02 1.96
ꢀ0.47 0.02 1.37
ꢀ0.30 0.02 1.61
0.72 0.03 2.99
0.78 0.03 3.04
13a
14
14a
15
15a
16
16a
a Dissociation constants determined by aqueous titrations in the
presence of methanol as cosolvent (20–50 wt%) according to Yas-
uda–Shedlovsky procedure.
b logPoNct of the neutral form obtained with Sirius GLpKa.
c logPoIct of the ionised form obtained by the shake-flask technique at
pH 4.0.
d logD at pH 7.4 calculated from the following equation:
ꢀ
ꢁ
ꢀ
ꢁ
aꢀpH
10pK
1
D ¼ PN
ꢂ
þ PI ꢂ
1 þ 10pK
and validated by the shake-flask technique.
1 þ 10pK
aꢀpH
aꢀpH
3.2. Lipophilic–hydrophilic balance
Potentiometric titrations of the final products 13–16
and 13a–16a were performed with a Sirius GLpKa
automated potentiometric system. Owing to the low
aqueous solubility of the products, the titrations were
carried out using methanol in different ratios as a cosol-
vent.8 The aqueous pKa values were determined by
extrapolation to 0% methanol according to the Yas-
uda–Shedlovsky procedure. The pKa values obtained
are listed in Table 2. They lie, as expected, in the narrow
7.14–7.18 range, according to the presence in the struc-
tures of an imidazole ring. Partition coefficients (ex-
pressed as logP) between n-octanol and water were
measured by dual-phase titration using various amounts
of water-saturated n-octanol.9 Distribution coefficients
(expressed as logD) were calculated for each compound
at pH 7.4 from its pKa, logPN (partition coefficient of
the neutral form) and logPI (partition coefficient of
the ionised form); all values are listed in Table 2. Fre-
quently, logD values give better correlations with phar-
macokinetic parameters than logPN, probably because
the influence of ionisation is taken into account. The
most lipophilic compounds appear to be the cyano
derivatives, while the least are the carboxamide deriva-
tives. LogD values range from 1.37 to 3.04. Hansch
suggested an optimum logPoct value of about 2 0.5
for a compound to diffuse into the central nervous sys-
tem.10 However, a more careful treatment of this aspect
In conclusion, in this paper we describe new H3-antago-
nists in which the oxime moiety present in imoproxifan
is constrained in differently substituted furoxan and
furazan rings. All the products display lesser affinity
for the H3-receptor than the lead. The cyano substituted
furoxan 16 is able, at the concentration used in the as-
say, to relax electrically contracted guinea-pig ileum
with a NO-dependent mechanism and to display H3-
antagonist activity.
4. Experimental
4.1. Chemistry
All compounds were purified by recrystallisation before
characterisation. Melting points were determined with
a capillary apparatus (Buchi B-540) and are uncor-
¨
rected; the recrystallisation solvent is reported in paren-
theses. All the products were routinely checked by IR
1
(Shimadzu FT-IR 8101 M). H and 13C NMR spectra
were obtained on a Bruker Avance 300, at 300 and
75 MHz, respectively; d in ppm rel to SiMe4 as the
internal standard; coupling constants J in Hz. 13C
NMR spectra were fully decoupled. The following
abbreviations are used: s, singlet; d, doublet; t, triplet;
qt, quartet; qn, quintet; br, broad; Fx, furoxan; Fz,
furazan; THP, tetrahydropyran; *, uncertain assign-
ment. Mass spectra were recorded on a Finnigan-Mat
TSQ-700. Flash chromatography (FC) was performed
on BDH silica gel (particle size 40–63 lm). When not
otherwise specified, anhydrous magnesium sulfate
(MgSO4) was used as the drying agent of organic
phases. Analysis (C, H and N) of the new compounds
was performed by REDOX (Monza). Structures 1,5
2,14 2a15 and 1216 were synthesised according to re-
ported methods.
should include the evaluation of additional molecular
11
descriptors such as DlogP(logPoct ꢀ logPcyc
)
or sol-
vatochromic parameters.12
3.3. Pharmacology
The H3-antagonist activity of the products was assessed
by their ability to antagonise the concentration-depen-
dent inhibitory effect of (R)-a-methylhistamine (MHA)
on electrically evoked twitches of isolated guinea-pig

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P. Tosco et al. / Bioorg. Med. Chem. 13 (2005) 4750–4759
4.2. 4-(3-Methylfuroxan-4-yl)phenol (3)
Compound (5.00 g, 24.2 mmol), DL-methionine
upon cooling, 4 precipitated (22.6 g, 70%) as a white so-
lid. CIMS (isobutane): m/z 223 (MH+); mp 95.5–97 ꢁC
(n-hexane/CHCl3). 1H NMR (DMSO-d6): d, 7.86 (d,
2H, J = 8.8 Hz, Ph-2,6-H), 7.15 (d, 2H, J = 8.8 Hz,
Ph-3,5-H), 5.96 (t, 1H, J = 5.8 Hz, OH), 4.52 (d, 2H,
J = 5.8 Hz, CH2), 3.85 (s, 3H, CH3); 13C NMR
(DMSO-d6): d, 162.4 (Ph-4-C), 157.7 (Fx-4-C), 130.1
(Ph-2,6-C), 119.3 (Ph-1-C), 115.9 (Fx-3-C), 115.6 (Ph-
3,5-C), 56.3 (CH3), 53.0 (CH2). Anal. Calcd for
C10H10N2O4 (222.20): C, 54.05; H, 4.54; N, 12.61.
Found: C, 54.09; H, 4.50; N, 12.60.
2
(5.42 g, 36.3 mmol) and methanesulfonic acid (25 mL)
were stirred at 60 ꢁC under N2 for 4 h. After cooling,
the reaction mixture was poured into cold water
(500 ml) and extracted with Et2O (4 · 50 mL). The com-
bined organic phase was washed with brine (2 · 25 mL)
and then extracted with 1 N NaOH (3 · 50 mL). The
combined ethereal layers were washed with brine
(25 mL), dried and evaporated to recover the unreacted
starting material. The aqueous phase was acidified with
concd HCl and extracted with Et2O (4 · 50 mL); the
combined organic extracts were washed with a buffer
solution (0.750 M Na2CO3, 0.375 M NaHCO3;
6 · 25 mL), then with brine (25 mL), dried and evapo-
rated yielding 3 (2.93 g, 63%) as a white solid. CIMS
(isobutane): m/z 193 (MH+); mp 162–163 ꢁC (1,2-dichlo-
4.5. (4-(4-Hydroxyphenyl)furoxan-3-yl)methanol (5)
Compound 4 (16.0 g, 72.0 mmol) was suspended in
anhydrous CH2Cl2 (160 mL) in a glass vessel suitable
for high-pressure reactions; AlCl3 (48.0 g, 360 mmol)
was carefully added, then the vessel was tightly closed,
heated at 60 ꢁC and kept under vigorous stirring for
24 h. After cooling, the vessel was opened and the reac-
tion mixture was slowly poured into cold 1 N HCl
(500 mL) and extracted with Et2O (4 · 50 mL). The
combined organic phases were extracted with 1 N
NaOH (3 · 50 mL) and then discarded; the aqueous
phase was acidified with concd HCl and then extracted
again with Et2O (4 · 50 mL). The combined ethereal
layers were washed with a buffer solution (0.750 M
Na2CO3, 0.375 M NaHCO3; 6 · 25 mL), then with brine
(25 mL), dried and evaporated yielding 5 (12.4 g, 83%)
as a white solid. EIMS: m/z 208 (M+); mp 147–148 ꢁC
(1,2-dichloroethane). 1H NMR (DMSO-d6): d, 10.18
(s, 1H, Ph-OH), 7.75 (d, 2H, J = 8.6 Hz, Ph-2,6-H),
6.97 (d, 2H, J = 8.6 Hz, Ph-3,5-H), 5.93 (s, 1H,
CH2-OH), 4.51 (s, 2H, CH2-OH); 13C NMR (DMSO-
d6): d, 161.0 (Ph-4-C), 157.8 (Fx-4-C), 130.1 (Ph-2,6-
C), 117.6 (Ph-1-C), 116.9 (Ph-3,5-C), 115.8 (Fx-3-C),
53.0 (CH2). Anal. Calcd for C9H8N2O4 (208.17): C,
51.93; H, 3.87; N, 13.46. Found: C, 51.95; H, 3.89; N,
13.36.
1
roethane). H NMR (DMSO-d6): d, 10.17 (s, 1H, OH),
7.61 (d, 2H, J = 8.6 Hz, Ph-2,6-H), 6.97 (d, 2H,
J = 8.6 Hz, Ph-3,5-H), 2.29 (s, 3H, CH3); 13C NMR
(DMSO-d6): d, 160.8 (Ph-4-C), 157.9 (Fx-4-C), 129.9
(Ph-2,6-C), 117.8 (Ph-1-C), 116.9 (Ph-3,5-C), 113.6
(Fx-3-C), 9.9 (CH3). Anal. Calcd for C9H8N2O3
(192.17): C, 56.25; H, 4.20; N, 14.58. Found: C, 56.30;
H, 4.20; N, 14.50.
4.3. 4-(4-Methylfurazan-3-yl)phenol (3a)
Compound 2a (5.00 g, 26.3 mmol), DL-methionine
(5.89 g, 39.4 mmol) and methanesulfonic acid (25 mL)
were stirred at 60 ꢁC under N2 for 4 h. The reaction was
worked up as for 3 obtaining 3a (3.10 g, 67%) as a white
solid. CIMS (isobutane): m/z 177 (MH+); mp 93.5–
1
94 ꢁC (n-hexane/1,2-dichloroethane). H NMR (DMSO-
d6): d, 10.09 (s, 1H, OH), 7.65 (d, 2H, J = 8.6 Hz,
Ph-2,6-H), 6.96 (d, 2H, J = 8.6 Hz, Ph-3,5-H), 2.54 (s,
3H, CH3); 13C NMR (DMSO-d6): d, 160.4 (Ph-4-C),
154.5 (Fz-4-C), 151.1 (Fz-3-C), 130.5 (Ph-2,6-C), 116.9
(Ph-3,5-C), 116.8 (Ph-1-C), 10.2 (CH3). Anal. Calcd for
C9H8N2O2 (176.17): C, 61.36; H, 4.58; N, 15.90. Found:
C, 61.53; H, 4.52; N, 15.92.
4.6. (4-(4-Hydroxyphenyl)furazan-3-yl)methanol (5a)
Compound 5 (4.00 g, 19.2 mmol) was refluxed with
trimethylphosphite (40 mL) for 18 h. After cooling, the
reaction mixture was poured into cold 1 N HCl
(400 mL) and extracted with Et2O (4 · 50 mL). The
combined ethereal layers were extracted with 1 N NaOH
(3 · 50 mL) and then discarded. The aqueous phase was
acidified with concd HCl and extracted with Et2O
(4 · 50 mL); the combined organic extracts were washed
with a buffer solution (0.750 M Na2CO3, 0.375 M NaH-
CO3; 6 · 25 mL), then with brine (25 mL), dried and
evaporated to afford 5a (2.36 g, 64%) as a white solid.
CIMS: m/z 193 (MH+); mp 116.5–117.5 ꢁC (n-hexane/
4.4. (4-(4-Methoxyphenyl)furoxan-3-yl)methanol (4)
Compound 2 (30.0 g, 145 mmol) was suspended in CCl4
(300 mL), then NBS (33.0 g, 185 mmol) was added, fol-
lowed by benzoyl peroxide (1.00 g, 4.13 mmol). The
reaction mixture was refluxed under vigorous stirring
for 12 h, then benzoyl peroxide (1.00 g, 4.13 mmol)
was added and the reflux was continued for 12 more
hours. After cooling, the reaction mixture was stirred
for 12 h with powdered Na2S2O3 (30 g) then the solution
was filtered on a celite pad. The filtrate was evaporated
obtaining a yellow oil, which was dissolved in dioxane
(75 mL); H2O (75 mL) and CaCO3 (72.5 g, 725 mmol)
were added and then the reaction mixture was refluxed
under stirring for 12 h. After cooling, the solvent was
evaporated and the residue was treated with concd
HCl until CO2 ceased evolving, then the precipitate
was collected on a Buchner funnel and washed with
water. The crude product was dissolved in boiling
MeOH/water (1:2) decanting the insoluble dark oil;
1
1,2-dichloroethane). H NMR (DMSO-d6): d, 10.10 (s,
1H, Ph-OH), 7.79 (d, 2H, J = 8.6 Hz, Ph-2,6-H), 6.95
(d, 2H, J = 8.6 Hz, Ph-3,5-H), 5.90 (t, 1H, J = 5.1 Hz,
CH2–OH), 4.80 (d, 2H, J = 5.1 Hz, CH2–OH); 13C
NMR (DMSO-d6): d, 160.6 (Ph-4-C), 154.5* (Fz-4-C),
154.1* (Fz-3-C), 130.8 (Ph-2,6-C), 116.9 (Ph-3,5-C),
116.6 (Ph-1-C), 53.4 (CH2). Anal. Calcd for C9H8N2O3
(192.17): C, 56.25; H, 4.20; N, 14.58. Found: C, 56.26;
H, 4.15; N, 14.48.

P. Tosco et al. / Bioorg. Med. Chem. 13 (2005) 4750–4759
4755
4.7. Ethyl 4-(3-(hydroxymethyl)furoxan-4-yl)phenyl
carbonate (6)
(120 mL) and washed with Et2O (3 · 20 mL). The aque-
ous phase was cooled to 0 ꢁC and adjusted to pH 5 with
acetic acid, then extracted with CHCl3 (3 · 20 mL). The
combined organic layers were washed with 10% NaH-
CO3 (20 mL), brine (20 mL), dried and evaporated to
yield a crude oil. The latter was purified by FC (eluent:
CH2Cl2) obtaining 7 (1.83 g, 88%) as a white solid.
CIMS: m/z 293 (MH+); mp 109.5–110.5 ꢁC (n-hexane/
Compound 5 (11.4 g, 54.5 mmol) was dissolved in Et2O
(300 mL) and cooled to ꢀ15 ꢁC, then Et3N (8.44 mL,
60.0 mmol) was added. A solution of ethyl chlorofor-
mate (5.44 mL, 57.2 mmol) in Et2O (50 mL) was added
dropwise under stirring over 1 h. The reaction mixture
was washed with 1 N HCl (2 · 100 mL), H2O
(100 mL), 10% NaHCO3 (50 mL) and brine (25 mL),
dried and evaporated to yield crude 6 (11.8 g, 78%),
pure enough to be used as an intermediate. An analyt-
ical sample was obtained by FC (eluent: petroleum
ether in gradient from 20% to 30% of EtOAc), white
solid. CIMS: m/z 281 (MH+); mp 86–87 ꢁC (n-hexane/
iPr2O). 1H NMR (DMSO-d6): d, 7.97 (d, 2H,
J = 8.7 Hz, Ph-2,6-H), 7.50 (d, 2H, J = 8.7 Hz, Ph-
3,5-H), 5.98 (t, 1H, J = 5.7 Hz, OH), 4.55 (d, 2H,
J = 5.7 Hz, CH2–OH), 4.29 (qt, 2H, J = 7.1 Hz,
CH3–CH2–O), 1.32 (t, 3H, J = 7.1 Hz, CH3); 13C
NMR (DMSO-d6): d, 157.3 (Ph-4-C), 153.6* (C@O),
153.4* (Fx-4-C), 130.1 (Ph-2,6-C), 124.9 (Ph-1-C),
123.2 (Ph-3,5-C), 115.9 (Fx-3-C), 65.8 (CH3–CH2–O),
53.0 (CH2–OH), 14.8 (CH3). Anal. Calcd for
C12H12N2O6 (280.24): C, 51.43; H, 4.32; N, 10.00.
Found: C, 51.47; H, 4.31; N, 9.96.
1
CHCl3). H NMR (DMSO-d6): d, 10.21 (s, 1H, OH),
7.70 (d, 2H, J = 8.6 Hz, Ph-2,6-H), 6.98 (d, 2H,
J = 8.6 Hz, Ph-3,5-H), 4.74–4.59 (m, 3H, THP-CH–O,
Fx-CH2–O), 3.70–3.63 (m, 1H, THP-CH2–O), 3.43–
3.38 (m, 1H, THP-CH2–O), 1.64–1.46 (m, 6H, THP-
CH2); 13C NMR (DMSO-d6): d, 161.0 (Ph-4-C), 157.9
(Fx-4-C), 130.1 (Ph-2,6-C), 117.4 (Ph-1-C), 117.0
(Ph-3,5-C), 114.1 (Fx-3-C), 99.4 (THP-CH–O), 62.4
(THP-CH2–O), 58.2 (Fx-CH2–O), 30.7 (THP-CH2),
25.6 (THP-CH2), 19.6 (THP-CH2). Anal. Calcd for
C14H16N2O5 Æ 0.1H2O (294.09): C, 57.18; H, 5.55; N,
9.53. Found: C, 57.10; H, 5.48; N, 9.54.
4.10. 4-(4-((Tetrahydro-2H-pyran-2-yloxy)methyl)-
furazan-3-yl)phenol (7a)
Compound 6a (3.68 g, 13.9 mmol) was dissolved in ace-
tone (15 mL) and cooled to 0 ꢁC; 3,4-dihydro-2H-pyran
was added (6.34 mL, 69.5 mmol), followed by methane-
sulfonic acid (3 drops). After 1 h, the cooling bath was
removed and the reaction mixture was stirred for 1 h
at rt. It was cooled again to 0 ꢁC and acetone (15 mL)
was added, followed by 10% NaOH (10 mL). After
30 min, the reaction was worked up as for 7 obtaining
7a (3.30 g, 86%) as a white solid. CIMS: m/z 277
4.8. Ethyl 4-(4-(hydroxymethyl)furazan-3-yl)phenyl
carbonate (6a)
Compound 5a (7.42 g, 38.6 mmol) was dissolved in Et2O
(250 mL) and cooled to ꢀ15 ꢁC, then Et3N (5.92 mL,
42.5 mmol) was added. A solution of ethyl chlorofor-
mate (3.86 mL, 40.5 mmol) in Et2O (50 mL) was added
dropwise under stirring over 1 h. The reaction was
worked up as for 6 to yield crude 6a (9.22 g, 90%), pure
enough to be used as an intermediate. An analytical
sample was obtained by FC (eluent: petroleum ether in
gradient from 20% to 30% of EtOAc), white solid.
CIMS: m/z 265 (MH+); mp 73–74.5 ꢁC (n-hexane/
iPr2O). 1H NMR (DMSO-d6): d, 8.02 (d, 2H,
J = 8.4 Hz, Ph-2,6-H), 7.48 (d, 2H, J = 8.4 Hz, Ph-3,5-
H), 5.97 (t, 1H, J = 5.6 Hz, OH), 4.85 (d, 2H,
J = 5.6 Hz, CH2–OH), 4.29 (qt, 2H, J = 7.1 Hz,
CH3–CH2–O), 1.32 (t, 3H, J = 7.1 Hz, CH3); 13C
NMR (CDCl3): d, 154.4* (Ph-4-C), 154.2* (Fz-4-C),
153.5* (Fz-3-C), 153.3* (C@O), 130.8 (Ph-2,6-C),
124.0 (Ph-1-C), 123.1 (Ph-3,5-C), 65.8 (CH3–CH2–O),
53.3 (CH2–OH), 14.8 (CH3). Anal. Calcd for
C12H12N2O5 (264.24): C, 54.55; H, 4.58; N, 10.60.
Found: C, 54.66; H, 4.58; N, 10.53.
1
(MH+); mp 73.5–74.5 ꢁC (n-hexane/CHCl3). H NMR
(CDCl3): d, 7.77 (d, 2H, J = 8.2 Hz, Ph-2,6-H), 6.95
(d, 2H, J = 8.2 Hz, Ph-3,5-H), 6.20 (s, 1H, OH), 4.99–
4.82 (m, 3H, THP-CH–O, Fz-CH2–O), 3.91–3.85 (m,
1H, THP-CH2–O), 3.62–3.59 (m, 1H, THP-CH2–O),
1.79–1.58 (m, 6H, THP-CH2); 13C NMR (CDCl3): d,
158.0 (Ph-4-C), 154.0 (Fz-4-C), 150.2 (Fz-3-C), 130.3
(Ph-2,6-C), 117.7 (Ph-1-C), 116.2 (Ph-3,5-C), 98.5
(THP-CH–O), 62.6 (THP-CH2–O), 57.7 (Fz-CH2–O),
30.3 (THP-CH2), 25.2 (THP-CH2), 19.0 (THP-CH2).
Anal. Calcd for C14H16N2O4 (292.29): C, 60.86; H,
5.84; N, 10.14. Found: C, 60.85; H, 5.84; N, 10.13.
4.11. Procedure for the synthesis of derivatives 9, 11.
Synthesis of the common intermediate ethyl
4-(3-((E)-(hydroxyimino)methyl)furoxan-4-yl)phenyl
carbonate (8)
A solution of 6 (15.5 g, 55.4 mmol) in CH2Cl2 (100 mL)
was stirred for 12 h with activated MnO2 (48.2 g,
554 mmol). After filtration on a celite pad, the solvent
was evaporated and the residue was dissolved in
CH3CN (100 mL). NH2OHÆHCl (4.23 g, 60.9 mmol)
was added, followed by dry pyridine (4.92 mL,
60.9 mmol), then the reaction mixture was stirred at
60 ꢁC for 1 h. After cooling, the solvent was evaporated,
the residue was taken up in 1 N HCl (100 mL) and ex-
tracted with Et2O (4 · 50 mL). The combined organic
layers were washed with brine (20 mL), dried and
evaporated to yield 8 as a crude product. 1H NMR
4.9. 4-(3-((Tetrahydro-2H-pyran-2-yloxy)methyl)-
furoxan-4-yl)phenol (7)
Compound 6 (2.00 g, 7.14 mmol) was dissolved in ace-
tone (8 mL) and cooled to 0 ꢁC; 3,4-dihydro-2H-pyran
(3.26 mL, 35.7 mmol) was added, followed by methane-
sulfonic acid (3 drops). After 1 h, the cooling bath was
removed and the reaction mixture was stirred for 1 h
at rt. It was cooled again to 0 ꢁC and acetone (8 mL)
was added, followed by 10% NaOH (6 mL). After
30 min, the reaction mixture was diluted with H2O

4756
P. Tosco et al. / Bioorg. Med. Chem. 13 (2005) 4750–4759
(DMSO-d6): d, 12.49 (s, 1H, OH), 7.93 (s, CH@N), 7.84
(d, 2H, J = 8.6 Hz, Ph-2,6-H), 7.46 (d, 2H, J = 8.6 Hz,
Ph-3,5-H), 4.29 (qt, 2H, J = 7.1 Hz, CH2), 1.32 (t, 3H,
J = 7.1 Hz, CH3); 13C NMR (DMSO-d6): d, 160.0 (Ph-
4-C), 155.2 (Fx-4-C), 152.6 (C@O), 135.0 (C@N),
130.3 (Ph-2,6-C), 123.7 (Ph-1-C), 121.8 (Ph-3,5-C),
111.5 (Fx-3-C), 64.9 (CH2), 13.9 (CH3). Owing to its
instability, 8 was not further characterised, but readily
reacted in the following step.
(THP-CH2–O), 28.88 (THP-CH2), 25.41 (THP-CH2),
19.56 (THP-CH2). Anal. Calcd for C14H15N3O5
(305.29): C, 55.08; H, 4.95; N, 13.76. Found: C, 55.18;
H, 5.03; N, 13.68.
4.14. 4-(4-Hydroxyphenyl)furazan-3-carbonitrile (9a)
A solution of 6a (15.1 g, 57.2 mmol) in dioxane
(100 mL) was stirred under reflux for 6 h with activated
MnO2 (49.7 g, 572 mmol). After cooling, the reaction
mixture was filtered on a celite pad, the solvent was
evaporated and the residue was dissolved in CH3CN
(100 mL). NH2OHÆHCl (4.37 g, 62.9 mmol) was added,
followed by dry pyridine (5.09 mL, 62.9 mmol), then
the reaction mixture was stirred at 60 ꢁC for 1 h. After
cooling, the solvent was evaporated, the residue was
taken up in 1 N HCl (100 mL) and extracted with
Et2O (4 · 50 mL). The combined ethereal layers were
cooled to 0 ꢁC, extracted with ice-cold 10% NaOH
(3 · 50 mL) and then discarded. The combined aqueous
phase was washed with Et2O (50 mL), then adjusted to
pH 5 with acetic acid and extracted with Et2O
(4 · 50 mL). The combined ethereal extracts were
washed with 10% NaHCO3 (3 · 25 mL), brine (25 mL),
dried and evaporated to yield a crude solid. The latter
was dissolved in DMF (40 mL) and cooled to 0 ꢁC, then
SOCl2 (8.35 mL, 114 mmol) was added. After 30 min,
the reaction mixture was poured into ice/water
(400 mL) and extracted with Et2O (4 · 50 mL). The
combined ethereal layers were washed with 10% NaH-
CO3 (6 · 25 mL), brine (25 mL), dried and evaporated
to yield a crude oil, which was purified by flash chromat-
ography (eluent: petroleum ether with 20% EtOAc)
obtaining 9a (5.03 g, 47%) as a white solid. CIMS: m/z
188 (MH+); mp 116–117 ꢁC (n-hexane/CHCl3). 1H
NMR (DMSO-d6): d, 10.44 (s, 1H, OH), 7.84 (d, 2H,
J = 8.7 Hz, Ph-2,6-H), 7.04 (d, 2H, J = 8.7 Hz, Ph-3,5-
H); 13C NMR (DMSO-d6): d, 161.0 (Ph-4-C), 154.4
(Fz-4-C), 131.8 (Fz-3-C), 129.6 (Ph-2,6-C), 116.4 (Ph-
3,5-C), 112.9 (Ph-1-C), 109.1 (CN). Anal. Calcd for
C9H5N3O2Æ0.1H2O (188.96): C, 57.21; H, 2.77; N,
22.24. Found: C, 57.48; H, 2.73; N, 21.85.
4.12. 4-(4-Hydroxyphenyl)furoxan-3-carbonitrile (9)
Compound 8 was dissolved in 10% ice-cold NaOH.
After 10 min, the reaction mixture was washed with
Et2O (50 mL), then adjusted to pH 5 with acetic acid
and extracted with Et2O (4 · 50 mL). The combined
ethereal extracts were washed with 10% NaHCO3
(3 · 25 mL), brine (25 mL), dried and evaporated to
yield a crude solid. The latter was dissolved in DMF
(40 mL) and cooled to 0 ꢁC, then SOCl2 (8.10 mL,
111 mmol) was added. After 30 min, the reaction mix-
ture was poured into ice/water (400 mL) and extracted
with Et2O (4 · 50 mL). The combined ethereal layers
were washed with 10% NaHCO3 (6 · 25 mL), brine
(25 mL), dried and evaporated to yield a crude oil,
which was purified by FC (eluent: petroleum ether/
EtOAc 9:1) obtaining 9 (4.61 g, 41% from 6) as a
yellow solid. CIMS: m/z 204 (MH+); mp 134–135 ꢁC
(n-hexane/iPr2O). 1H NMR (DMSO-d6): d, 10.49 (s,
1H, OH), 7.74 (d, 2H, J = 9.6 Hz, Ph-2,6-H), 7.04 (d,
2H, J = 9.6 Hz, Ph-3,5-H); 13C NMR (DMSO-d6): d,
162.1 (Ph-4-C), 155.7 (Fx-4-C), 129.6 (Ph-2,6-C),
117.4 (Ph-3,5-C), 115.2 (Ph-1-C), 108.5 (CN), 98.8
(Fx-3-C). Anal. Calcd for C9H5N3O3Æ0.1H2O (204.96):
C, 52.74; H, 2.56; N, 20.50. Found: C, 53.00; H,
2.51; N, 20.25.
4.13. 4-(4-Hydroxyphenyl)furoxan-3-carbaldehyde
O-(tetrahydro-2H-pyran-2-yl)oxime (11)
Compound 8 was dissolved in acetone (100 mL), 3,4-
dihydro-2H-pyran (10.1 mL, 111 mmol) was added,
followed by methanesulfonic acid (5 drops), then the
reaction mixture was refluxed for 2 h. After cooling at
0 ꢁC, acetone (100 mL) was added, followed by 10%
NaOH (50 mL). After 1 h, the reaction mixture was
poured into ice/water (500 mL) and washed with Et2O
(4 · 50 mL), then adjusted to pH 5 with acetic acid
and extracted with Et2O (4 · 50 mL). The combined
ethereal extracts were washed with 10% NaHCO3
(2 · 50 mL), brine (25 mL), dried and evaporated to
yield a crude oil, which was purified by FC (eluent:
petroleum ether in gradient from 10% to 20% of
EtOAc) obtaining 11 (8.32 g, 49% from 6) as a white so-
lid. CIMS: m/z 306 (MH+); mp 141–142 ꢁC (n-hexane/
iPr2O). 1H NMR (DMSO-d6): d, 10.20 (s, 1H, OH),
8.11 (s, CH@N), 7.66 (d, 2H, J = 8.4 Hz, Ph-2,6-H),
6.93 (d, 2H, J = 8.4 Hz, Ph-3,5-H), 5.29 (s, 1 H, THP-
CH–O), 3.76 (m, 1H, THP-CH2–O), 3.54 (m, 1H,
THP-CH2–O), 1.74–1.53 (m, 6H, THP-CH2); 13C
NMR (DMSO-d6): d, 161.0 (Ph-4-C), 156.6 (Fx-4-C),
138.1 (C@N), 131.2 (Ph-2,6-C), 116.8 (Ph-1-C), 116.4
(Ph-3,5-C), 111.4 (Fx-3-C), 101.90 (THP-CH–O), 62.6
4.15. 4-(4-Hydroxyphenyl)furoxan-3-carboxamide (10)
To a solution of 9 (3.12 g, 15.4 mmol) in acetone
(20 mL), 0.5 M K2CO3 (120 mL) was added. After 5
days under stirring, the reaction mixture was diluted
with H2O (100 mL), adjusted to pH 5 with acetic acid
and then extracted with EtOAc (4 · 25 mL). The com-
bined organic layers were washed with NaHCO3
(10 · 10 mL), brine (10 mL), dried and evaporated to
yield a crude product, which was purified by FC (eluent:
petroleum ether/EtOAc 1:1) obtaining 10 (1.60 g, 47%)
as a pale yellow solid. CIMS: m/z 222 (MH+); mp
184 ꢁC (dec) (iPr2O). 1H NMR (DMSO-d6): d, 10.19
(s, 1H, OH), 8.46 (s, NH2), 8.38 (s, NH2), 7.62 (d, 2H,
J = 8.2 Hz, Ph-2,6-H), 6.93 (d, 2H, J = 8.2 Hz, Ph-3,5-
H); 13C NMR (DMSO-d6): d, 161.1 (Ph-4-C), 157.2*
(Fx-4-C), 156.0* (C=O), 130.2 (Ph-2,6-C), 116.9
(Ph-1-C), 116.6 (Ph-3,5-C), 112.1 (Fx-3-C). Anal. Calcd
for C9H7N3O4 (221.17): C, 48.88; H, 3.19; N, 19.00.
Found: C, 48.72; H, 3.37; N, 18.79.

P. Tosco et al. / Bioorg. Med. Chem. 13 (2005) 4750–4759
4757
4.16. 4-(4-Hydroxyphenyl)furazan-3-carboxamide (10a)
J = 8.8 Hz, Ph-2,6-H), 7.50 (s, Im-5-H), 7.14 (d, 2H,
J = 8.8 Hz, Ph-3,5-H), 4.11 (t, 2H, J = 6.1 Hz, CH2–
O), 2.86 (t, 2H, J = 7.5 Hz, Im-CH2), 2.56 (s, 3H,
CH3), 2.15 (qn, 2H, J = 7.0 Hz, Im-CH2–CH2–CH2–
O); 13C NMR (DMSO-d6): d, 160.3 (Ph-4-C), 153.7
(Fz-4-C), 150.5 (Fz-3-C), 133.6 (Im-2-C), 132.8 (Im-4-
C), 129.8 (Ph-2,6-C), 117.7 (Ph-1-C), 115.6 (Im-5-C),
115.3 (Ph-3,5-C), 66.8 (CH2–O), 27.6 (Im-CH2), 20.8
(Im-CH2–CH2–CH2–O), 9.4 (CH3). Anal. Calcd for
C15H17ClN4O2Æ0.2H2O (324.38): C, 55.54; H, 5.41; N,
17.27. Found: C, 55.65; H, 5.37; N, 17.19.
To a solution of 9a (3.56 g, 19.0 mmol) in acetone
(20 mL), 0.5 M K2CO3 (120 mL) was added. After 5
days under stirring, the reaction mixture was worked
up as for 10 obtaining 10a (3.43 g, 88%) as a white solid.
CIMS: m/z 206 (MH+); mp 191–192 ꢁC (dec) (n-hexane/
iPr2O). 1H NMR (DMSO-d6): d, 10.16 (s, 1H, OH), 8.65
(s, NH2), 8.32 (s, NH2), 7.72 (d, 2H, J = 8.4 Hz, Ph-2,6-
H), 6.94 (d, 2H, J = 8.4 Hz, Ph-3,5-H); 13C NMR
(DMSO-d6): d, 160.0 (Ph-4-C), 159.6 (C@O), 152.4
(Fz-4-C), 148.9 (Fz-3-C), 130.0 (Ph-2,6-C), 115.9 (Ph-
3,5-C), 114.7 (Ph-1-C). Anal. Calcd for C9H7N3O3
(205.17): C, 52.69; H, 3.44; N, 20.48. Found: C, 52.84;
H, 3.66; N, 20.08.
4.20. (4-(4-(3-(1H-Imidazol-4-yl)propoxy)phenyl)furo-
xan-3-yl)methanol hydrochloride (14)
The crude precipitate was dissolved in warm MeOH
(20 mL) and then Boc2O (0.50 g, 2.29 mmol) was added.
After 1 h, the solvent was evaporated and the residue was
purified by FC (eluent: CH2Cl2 in gradient from 1 to 5%
of MeOH) obtaining a white solid. A stream of HCl(g)
was bubbled in a methanolic solution of the latter for
10 min; after 1 h, the solvent was evaporated and the res-
idue was recrystallised from cold MeOH/Et2O obtaining
14 (0.36 g, 38%) as a white solid. Mp 166–167 ꢁC (dec)
4.17. General procedure for the synthesis of derivatives
13–15 and 13a–16a
To a solution of 12 (1.00 g, 2.71 mmol) in dry THF
(30 mL) kept under N2, the appropriate oxadiazole
(Scheme 2, 3.25 mmol) and Ph3P (1.42 g, 5.42 mmol)
were added. The reaction mixture was cooled to 0 ꢁC
and DIAD (1.07 mL, 5.42 mmol) was added dropwise
over 10 min; after 12 h under stirring at rt, the reaction
mixture was evaporated to yield an orange oil. The latter
was dissolved in 10% TFA in CH2Cl2 (40 mL) and stirred
for 12 h; the reaction mixture was evaporated and the
residue was dissolved in 1 N HCl (50 mL), filtering the
insoluble matter on a celite pad. The filtrate was washed
with Et2O (3 · 20 mL), then the pH was adjusted to 8
with NaHCO3, precipitating a white solid, which was
collected on a Buchner funnel and washed with H2O.
1
(MeOH/Et2O). H NMR (D2O + CD3OD): d, 8.46 (s,
1H, Im-2-H), 7.53 (d, 2H, J = 8.7 Hz, Ph-2,6-H), 7.09
(s, Im-5-H), 6.90 (d, 2H, J = 8.7 Hz, Ph-3,5-H), 4.49 (s,
2H, CH2–OH), 3.97 (t, 2H, J = 5.8 Hz, –CH2–CH2–O),
2.77 (t, 2H, J = 7.4 Hz, Im-CH2), 2.01 (qn, 2H,
J = 6.6 Hz,
Im-CH2–CH2–CH2–O);
13C
NMR
(D2O + CD3OD): d, 161.5 (Ph-4-C), 157.3 (Fx-4-C),
134.0 (Im-4-C), 133.5 (Im-2-C), 129.5 (Ph-2,6-C), 119.2
(Ph-1-C), 115.9 (Im-5-C), 115.3 (Ph-3,5-C), 115.3 (Fx-
3-C), 67.1 (–CH2–CH2–O), 52.5 (CH2–OH), 28.1 (Im-
CH2), 21.3 (Im-CH2–CH2–CH2–O). Anal. Calcd for
C15H16N4O4Æ1.5HClÆ0.3H2O (376.41): C, 47.86; H,
4.85; N, 14.88. Found: C, 47.51; H, 4.68; N, 15.22.
4.18. 4-(4-(3-(1H-Imidazol-4-yl)propoxy)phenyl)-3-meth-
ylfuroxan hydrochloride (13)
The crude precipitate was purified by FC (eluent:
CH2Cl2 in gradient from 2.5% to 3.5% of MeOH)
obtaining a white solid. A stream of HCl(g) was bubbled
in a methanolic solution of the latter for 10 min; after
1 h, the solvent was evaporated and the residue was
recrystallised from cold MeOH/Et2O obtaining 13
4.21. (4-(4-(3-(1H-Imidazol-4-yl)propoxy)phenyl)fura-
zan-3-yl)methanol hydrochloride (14a)
Operating as for 14, 14a was obtained (0.29 g, 32%) as a
white solid. Mp 159–160.5 ꢁC (abs EtOH/acetone). H
1
(0.55 g, 60%) as
a
white solid. Mp 185–186 ꢁC
NMR (DMSO-d6): d, 8.99 (s, 1H, Im-2-H), 7.89 (d,
2H, J = 8.8 Hz, Ph-2,6-H), 7.46 (s, Im-5-H), 7.12 (d,
2H, J = 8.8 Hz, Ph-3,5-H), 5.97 (br s, 1H, OH), 4.80 (s,
2H, CH2–OH), 4.11 (t, 2H, J = 6.1 Hz, –CH2–CH2–O),
2.84 (t, 2H, J = 7.5 Hz, Im-CH2), 2.13 (qn, 2H,
J = 6.8 Hz, Im-CH2–CH2–CH2–O); 13C NMR (DMSO-
d6): d, 160.4 (Ph-4-C), 153.6* (Fz-4-C), 153.4* (Fz-3-
C), 133.6 (Im-2-C), 132.7 (Im-4-C), 130.0 (Ph-2,6-C),
117.5 (Ph-1-C), 115.6 (Im-5-C), 115.2 (Ph-3,5-C), 66.8
(–CH2–CH2–O), 52.5 (CH2–OH), 27.5 (Im-CH2),
20.8 (Im-CH2–CH2–CH2–O). Anal. Calcd for
C15H16N4O3ÆHClÆ0.4H2O (343.98): C, 52.38; H, 5.22;
N, 16.29. Found: C, 52.65; H, 5.24; N, 16.00.
1
(MeOH/Et2O). H NMR (DMSO-d6): d, 9.08 (s, 1H,
Im-2-H), 7.72 (d, 2H, J = 8.8 Hz, Ph-2,6-H), 7.49 (s,
Im-5-H), 7.15 (d, 2H, J = 8.8 Hz, Ph-3,5-H), 4.12 (t,
2H, J = 6.1 Hz, CH2–O), 2.86 (t, 2H, J = 7.5 Hz, Im-
CH2), 2.30 (s, 3H, CH3), 2.16 (qn, 2H, J = 7.2 Hz, Im-
CH2–CH2–CH2–O); 13C NMR (DMSO-d6): d, 160.7
(Ph-4-C), 157.1 (Fx-4-C), 133.6 (Im-2-C), 132.7 (Im-4-
C), 129.3 (Ph-2,6-C), 118.7 (Ph-1-C), 115.6 (Im-5-C),
115.3 (Ph-3,5-C), 113.0 (Fx-3-C), 66.9 (CH2–O), 27.5
(Im-CH2), 20.8 (Im-CH2–CH2–CH2–O), 9.1 (CH3).
Anal. Calcd for C15H17ClN4O3 (336.78): C, 53.50; H,
5.09; N, 16.64. Found: C, 53.60; H, 5.23; N, 16.54.
4.19. 3-(4-(3-(1H-Imidazol-4-yl)propoxy)phenyl)-4-meth-
ylfurazan hydrochloride (13a)
4.22. 4-(4-(3-(1H-Imidazol-4-yl)propoxy)phenyl)furoxan-
3-carboxamide hydrochloride (15)
Operating as for 13, 13a was obtained (0.51 g, 59%) as a
white solid. Mp 162–163 ꢁC (MeOH/Et2O). H NMR
(DMSO-d6): d, 9.07 (s, 1H, Im-2-H), 7.76 (d, 2H,
The crude precipitate was dissolved in warm MeOH
(20 mL) and then Boc2O (0.30 g, 1.37 mmol) was added.
After 1 h, the solvent was evaporated and the residue
1

4758
P. Tosco et al. / Bioorg. Med. Chem. 13 (2005) 4750–4759
was purified by FC (eluent: petroleum ether/EtOAc 1:1)
obtaining a white solid. To a solution of the latter in ace-
tone (20 mL), Et2O saturated with HCl(g) (10 mL) was
added. After refluxing for 1 h, the solvent was evapo-
rated and the residue was recrystallised from abs
EtOH/acetone obtaining 15 (0.28 g, 28%) as a white
solid. Mp 179–180 ꢁC (abs EtOH/acetone). 1H NMR
(CD3OD): d, 8.83 (s, 1H, Im-2-H), 7.75 (d, 2H,
J = 8.8 Hz, Ph-2,6-H), 7.37 (s, Im-5-H), 7.04 (d, 2H,
J = 8.8 Hz, Ph-3,5-H), 4.15 (t, 2H, J = 5.9 Hz,
CH2–O), 2.98 (t, 2H, J = 7.5 Hz, Im-CH2), 2.22 (qn,
2H, J = 7.0 Hz, Im-CH2–CH2–CH2–O); 13C NMR
(CD3OD): d, 161.5 (Ph-4-C), 157.6 (Fx-4-C), 156.8
(C@O), 134.0 (Im-4-C), 133.7 (Im-2-C), 130.6 (Ph-2,6-
C), 118.8 (Ph-1-C), 115.9 (Im-5-C), 114.5 (Ph-3,5-C),
111.3 (Fx-3-C), 66.9 (CH2–O), 28.1 (Im-CH2), 21.2
(Im-CH2–CH2–CH2–O). Anal. Calcd for C15H15N5O4Æ
HCl (365.78): C, 49.26; H, 4.41; N, 19.15. Found: C,
49.19; H, 4.49; N, 18.78.
4.25. 4-(4-(3-(1H-Imidazol-4-yl)propoxy)phenyl)furoxan-
3-carbonitrile hydrochloride (16)
To a solution of 12 (1.48 g, 4.02 mmol) in dry THF
(40 mL) kept under N2, 11 (1.47 g, 4.82 mmol) and
Ph3P (2.11 g, 8.04 mmol) were added. The reaction mix-
ture was cooled to 0 ꢁC and DIAD (1.58 mL, 8.04 mmol)
was added dropwise over 10 min; after 12 h under stir-
ring at rt, the reaction mixture was evaporated to yield
an orange oil, which was dissolved in 1 N p-toluenesulf-
onic acid in MeOH (50 mL). After 4 h, the reaction mix-
ture was cooled to 0 ꢁC and Et3N (7 mL) was added, then
it was poured into water (500 mL) and extracted with
Et2O (4 · 50 mL). The combined organic layers were
washed with 5% citric acid (50 mL), brine (25 mL), dried
and evaporated to yield a yellow oil. To a solution of the
latter in DMF (20 mL) kept under N2 at ꢀ40 ꢁC SOCl2
(4 mL, 54.8 mmol) was added dropwise over 30 min
and then the cooling bath was removed. When the reac-
tion mixture reached 18 ꢁC, it was poured into water
(500 mL) and extracted with Et2O (4 · 50 mL). The com-
bined organic layers were washed with 10% NaHCO3
(3 · 50 mL), brine (25 mL), dried and evaporated to
yield a crude oil, which was purified by FC (eluent: petro-
leum ether/EtOAc 6:4). The product was dissolved in
10% TFA in CH2Cl2 (40 mL) and stirred for 12 h; the
reaction mixture was evaporated and the residue was dis-
solved in 1 N HCl (50 mL), filtering the insoluble matter
on a celite pad. The filtrate was washed with Et2O
(3 · 20 mL), then the pH was adjusted to 8 with
NaHCO3, precipitating a white solid, which was col-
lected on a Buchner funnel and washed with H2O. The
crude precipitate was dissolved in warm CH3CN
(20 mL) and then Boc2O (0.50 g, 2.29 mmol) was added.
After 1 h, the solvent was evaporated and the residue was
purified by FC (eluent: petroleum ether/EtOAc 7:3)
obtaining a white solid. To a solution of the latter in ace-
tone (20 mL), Et2O saturated with HCl(g) (10 mL) was
added. After refluxing for 1 h, the solvent was evapo-
rated and the residue was recrystallised from CH3CN/
acetone obtaining 16 (0.31 g, 22%) as a white solid. Mp
4.23. 4-(4-(3-(1H-Imidazol-4-yl)propoxy)phenyl)furazan-
3-carboxamide hydrochloride (15a)
Operating as for 15, 15a was obtained (0.32 g, 34%) as a
white solid. Mp 178.5–179.5 ꢁC (abs EtOH/acetone). 1H
NMR (D2O): d, 8.46 (s, 1H, Im-2-H), 7.63 (d, 2H,
J = 8.8 Hz, Ph-2,6-H), 7.12 (s, Im-5-H), 6.95 (d, 2H,
J = 8.8 Hz, Ph-3,5-H), 4.06 (t, 2H, J = 6.0 Hz,
CH2–O), 2.83 (t, 2H, J = 7.3 Hz, Im-CH2), 2.08 (qn,
2H, J = 6.6 Hz, Im-CH2–CH2–CH2–O); 13C NMR
(D2O): d, 161.4 (C@O), 160.6 (Ph-4-C), 153.5 (Fz-4-
C), 148.1 (Fz-3-C), 133.3 (Im-4-C), 133.1 (Im-2-C),
130.8 (Ph-2,6-C), 116.5 (Ph-1-C), 115.6 (Im-5-C), 115.1
(Ph-3,5-C), 67.3 (CH2–O), 27.4 (Im-CH2), 20.9
(Im-CH2–CH2–CH2–O). Anal. Calcd for C15H15N5O3Æ
HCl (349.78): C, 51.51; H, 4.61; N, 20.02. Found: C,
51.34; H, 4.61; N, 19.72.
4.24. 4-(4-(3-(1H-Imidazol-4-yl)propoxy)phenyl)furazan-
3-carbonitrile hydrochloride (16a)
1
The crude precipitate was dissolved in acetone (20 mL)
and then Boc2O (0.50 g, 2.29 mmol) was added. After
1 h, the solvent was evaporated and the residue was
purified by FC (eluent: petroleum ether/EtOAc 7:3)
obtaining a white solid. To a solution of the latter in
acetone (20 mL), Et2O saturated with HCl(g) (10 mL)
was added. After refluxing for 1 h, the solvent was
evaporated and the residue was recrystallised from ace-
tone/iPr2O obtaining 16a (0.24 g, 26%) as a white solid.
Mp 190–191 ꢁC (dec) (acetone/iPr2O). 1H NMR
(DMSO-d6): d, 9.06 (s, 1H, Im-2-H), 7.92 (d, 2H,
J = 8.7 Hz, Ph-2,6-H), 7.48 (s, Im-5-H), 7.23 (d, 2H,
J = 8.7 Hz, Ph-3,5-H), 4.14 (t, 2H, J = 6.1 Hz,
CH2–O), 2.85 (t, 2H, J = 7.5 Hz, Im-CH2), 2.16 (qn,
2H, J = 6.8 Hz, Im-CH2–CH2–CH2–O); 13C NMR
(DMSO-d6): d, 162.3 (Ph-4-C), 155.2 (Fz-4-C), 134.3
(Im-2-C), 133.4* (Fz-3-C), 133.0* (Im-4-C), 130.6
(Ph-2,6-C), 116.5 (Ph-3,5-C), 116.4 (Im-5-C), 115.6
(Ph-1-C), 110.0 (CN), 67.8 (CH2–O), 28.2 (Im-CH2),
21.5 (Im-CH2–CH2–CH2–O). Anal. Calcd for
C15H13N5O2ÆHCl (331.76): C, 54.31; H, 4.25; N,
21.11. Found: C, 54.14; H, 4.30; N, 20.78.
174 ꢁC (dec) (CH3CN/acetone). H NMR (DMSO-d6):
d, 9.08 (s, 1H, Im-2-H), 7.82 (d, 2H, J = 7.7 Hz, Ph-2,6-
H), 7.48 (s, Im-5-H), 7.23 (d, 2H, J = 7.7 Hz, Ph-3,5-H),
4.14 (s, 2H, CH2–O), 2.86 (s, 2H, Im-CH2), 2.17 (s, 2H,
Im-CH2–CH2–CH2–O); 13C NMR (DMSO-d6): d,
161.6 (Ph-4-C), 154.6 (Fx-4-C), 133.3 (Im-2-C), 132.5
(Im-4-C), 128.6 (Ph-2,6-C), 115.9 (Ph-1-C), 115.6 (Ph-
3,5-C), 115.4 (Im-5-C), 107.5 (CN), 98.1 (Fx-3-C), 66.9
(CH2–O), 27.3 (Im-CH2), 20.6 (Im-CH2–CH2–CH2–O).
Anal. Calcd for C15H13N5O3ÆHCl (347.76): C, 51.81;
H, 4.06; N, 20.14. Found: C, 51.76; H, 4.05; N, 19.96.
4.26. Lipophilicity studies
Potentiometric titrations were performed with the
GLpKa apparatus (Sirius Analytical Instruments Ltd,
Forrest Row, East Sussex, UK).9 Ionisation constants
were determined by four separate titrations for each
compound (ca. 0.5 mM).17 The low aqueous solubility
of the compounds required titrations in the presence
of variable amounts of methanol as cosolvent (20–50
wt%); pKa values were determined by extrapolation to

P. Tosco et al. / Bioorg. Med. Chem. 13 (2005) 4750–4759
4759
zero content of cosolvent according to the Yasuda–
Acknowledgment
Shedlovsky procedure.18 To obtain lipophilicity data,
at least four separate titrations for each compound
(ca. 0.5 mM), containing various volumes of octan-1-ol
(from 1 mL of organic solvent/15 mL of H2O to 10 mL
of organic solvent/5 mL of H2O), were performed in
the pH range 2–11.5. LogP data were obtained by the
Multiset approach.17,19 All titrations were carried out
under Ar at 25.0 0.1 ꢁC.19
This work was supported by a MIUR (COFIN 2004)
grant.
References and notes
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Ileum segments were isolated from male albino guinea-
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with CO2 and killed by decapitation. All animals were
treated humanely in accordance with recognised guide-
lines on experimentation. As few animals as possible
were used. The purposes and the protocols of our stud-
ies have been approved by the Ministero della Salute,
Rome, Italy. The tissues were mounted in organ baths
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and continuously gassed with 95% O2–5% CO2 (pH
7.4). After equilibration for 2 h, with washings every
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same preparation. From each animal four segments of
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for 13 and 13a (0.1 and 0.3 lM) and at one concentra-
tion for the other compounds (1 lM). Responses were
recorded by an isometric transducer connected to the
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