Synthesis and antiviral evaluation of benzimidazoles, quinoxalines and indoles from dehydroabietic acid

Article abstract of DOI:10.1016/j.bmc.2003.10.013

Several heterocycles, such as benzimidazoles, quinoxalines and indoles incorporated into a hydrophenanthrene and naphthalene skeleton, were synthesised from two useful ortho-bromonitro precursors derived from dehydroabietic acid: methyl 12-bromo-13-nitro-deisopropyldehydroabietate and methyl 12-bromo-13,14-dinitro-deisopropyldehydroabietate. The new heterocycles were evaluated for their activity in vitro against several RNA and DNA viruses.

Full text of DOI:10.1016/j.bmc.2003.10.013

Bioorganic & Medicinal Chemistry 12 (2004) 103–112
Synthesis and antiviral evaluation of benzimidazoles, quinoxalines
and indoles from dehydroabietic acid
a,c,y
a,
b
c
Tatiana Fonseca,
Ba
´
rbara Gigante, * M. Matilde Marques, Thomas L. Gilchrist
and Erik De Clercqd
aINETI–Departamento deTecnologia de Ind u´ strias Quı´micas, Estrada do Pa c¸ o do Lumiar, 1649-038 Lisbon, Portugal
bCentro de Quı´mica Estrutural, Complexo I, Instituto Superior Te´cnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
cDepartment of Chemistry, The University of Liverpool, Liverpool L697ZD, UK
dRega Institute for Medical Research, Katholieke Universiteit Leuven, B-3000, Belgium
Received 18 July 2003; accepted 10 October 2003
Abstract—Several heterocycles, such as benzimidazoles, quinoxalines and indoles incorporated into a hydrophenanthrene and
naphthalene skeleton, were synthesised from two useful ortho-bromonitro precursors derived from dehydroabietic acid: methyl 12-
bromo-13-nitro-deisopropyldehydroabietate and methyl 12-bromo-13,14-dinitro-deisopropyldehydroabietate. The new heterocycles
were evaluated for their activity in vitro against several RNA and DNA viruses.
#
2003 Elsevier Ltd. All rights reserved.
1
. Introduction
depending on the nitric acid concentration (Scheme 1).
Subsequent catalytic hydrogenation of 3a allowed us to
prepare two new ortho-diamines (4a and 4b) that gave
several benzimidazoles (5a–7a, 5b–7b and 8) and qui-
noxalines (9, 10 and 11) (Scheme 2) by cyclocondensation.
Furthermore, two new indoles (14 and 15) were synthe-
sised from 3b via two different pathways (Scheme 3). All
the novel heterocycles described in this work were
evaluated for their potential antiviral activity.
Recent work1 has demonstrated that resin acid deri-
vatives can be a useful tool in the synthesis of drugs
active against viruses. The potential of resin acid
derivatives, and the known antiviral activity of sev-
4
eral benzimidazoles, quinoxalines, and indoles as
nucleoside analogues or non-nucleoside inhibitors of HIV-
À3
1
À3
5
6
1
reverse transcriptase (NNRTIs), led us to search for new
heterocyclic agents through functionalisation of the aro-
matic moiety of dehydroabietic acid (1a, Scheme 1).
2. Results and discussion
7
In previous work, we have described the synthesis of
imidazoles fused to the aromatic ring C, using a deiso-
propylated nitroarene derived from 1a as a precursor. In
the present study, a different route for the construction
of imidazoles, diazines and indoles, fused to ring C, is
reported. The functionalisation was accomplished
through nitro-deisopropylation of the brominated
intermediate 2, from which a new ortho-dinitro (3a) or a
mononitro (3b) compound was obtained in one step,
2.1. Synthetic approach
The starting material, dehydroabietic acid (1a) and the
intermediates, methyl dehydroabietate (1b) and methyl
12-bromo-dehydroabietate (2), were obtained by proce-
dures described before.
derivatives of 1b, maintaining the hydrophenanthrene
8À10
Nitrodeisopropylation of
1
1À13
structure, has also been reported.
Particularly, in
1
3
previous nitration studies of 2, methyl 12-bromo-13-
nitrodeisopropyl dehydroabietate (3b) was obtained; in
addition, an uncharacterised dinitro compound was also
mentioned, but not isolated, when mixtures of nitric and
sulphuric acids with different concentrations were used.
The possibility of the two nitro groups being located
ortho to each other prompted us to further investigate
Keywords: Diterpenes; Resin acids; Benzimidazoles; Quinoxalines;
Indoles.
*
Corresponding author. Tel.: +351-217-165141; fax: +351-217-
68100; e-mail: barbara.gigante@ineti.pt
1
y
Present address: Institute of Cancer Research, CRUK Laboratories,
Sutton SM2 5NG, UK.
0
968-0896/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2003.10.013

104
T. Fonseca et al. / Bioorg. Med. Chem. 12 (2004) 103–112
ꢀ
ꢀ
Scheme 1. (i) Br
2
, Montmorillonite K10, 0 C; (ii) HNO /H
3
2
SO
4
, À18 C.
4
Scheme 2. (i) H
iv) diketone, CH
2
(100 psi), Pd/C, MeOH, Et
CO H, ꢀ.
3
N (only for 4a); (ii) R CO H, ꢀ; (iii) CH
2
3
O
2
C–NH–C(SCH
3
)¼N–CO
2
CH
3
, CH
3
CO H, ꢀ;
2
(
3
2
4.
N, ꢀ (ii) Fe/FeSO .7H
2
O, HCl (0.1 M), C
6
ꢀ
Scheme 3. (i) HCꢁCSi(CH
3
)
3
, Pd(PPh
ꢀ
3
)
2
Cl
2
, Cul, Et
3
H
6
, MeOH, ꢀ (iii) Cul, DMF, 100 C;
(
iv) CH
2
¼CHMgBr, THF, À78 C.
this reaction, since this type of compound can easily be
reduced to produce ortho-diamines. It is well known
yielded 3b while the desired, but unexpected, methyl 12-
bromo-13,14-dinitrodehydroabietate (3a) was obtained
when fuming nitric acid (100%, d=1.52) was used
instead (Scheme 1). These observations stimulated the
1
4À16
from the literature
that ortho-phenylenediamines
are useful reagents for the synthesis of 2-substituted
benzimidazoles and quinoxalines by simple cyclo-
condensations with carboxylic acids and vic-diketones,
respectively.
1
13
study described in this paper. The IR, MS, H and
NMRspectral data (chemical shifts and multiplicities,
C
1
3
2D HETCORin combination with DEPT for
C
1
13
NMR, and COLOC for long-range H– C NMR
correlation experiments) allowed us to assign all the
protons and carbons. Moreover, the ortho disposition of
In our studies, nitration of 2 with nitric acid (88%,
d=1.47) and concentrated sulphuric acid (95–97%)

T. Fonseca et al. / Bioorg. Med. Chem. 12 (2004) 103–112
105
the nitro groups in 3a, was confirmed from the observed
three- and two-bond correlations between H-11 (s, 7.73
ppm) and C-8 (129.3 ppm), C-10 (38.0 ppm), C-13
2.1.2. Indoles. The synthesis of methyl 12-bromo-13-
nitro-deisopropyldehydroabietate (3b) allowed the pre-
paration of two indoles.
(
hydrolysis of the ester group of 2 was prevented by
keeping the temperature below 0 C during its addition
to the acid mixture.
141.6 ppm) and C-12 (111.9 ppm). In these reactions,
Thus, coupling of 3b with trimethylsilylacetylene cata-
lysed by a complex of palladium in the presence of
ꢀ
2
7
cuprous iodide to yield 12 (Scheme 3), followed by
reduction of the nitro group of 12 to an amine, with Fe/
2
8
Catalytic hydrogenation of 3a produced the ortho-dia-
mine intermediates 4a or 4b (Scheme 2), depending on
the reaction conditions used. The reactions were best
conducted under pressure (100 psi), with palladium as
the catalyst, either in the presence or absence of tri-
HCl (0.1 M), gave the ortho-alkynylaniline 13 in good
yield (83%). Cyclisation of 13 with cuprous iodide in
ꢀ
29
dimethylformamide at 100 C gave the indole 14 in
moderate yield (60%).
1
3
ethylamine. The presence of triethylamine was clearly
essential to produce the dehalogenated diamine (4a).
The synthetic versatility of the ortho-bromonitro com-
pound 3b was further probed by the efficient one-step
synthesis of the brominated indole 15, which was
obtained in good yield (70%) by reaction with vinyl
The ortho coupling (J ca. 8 Hz) observed for the two
aromatic protons in 4a afforded additional confirmation
that the nitro groups in the precursor 3a were vicinal.
3
0
magnesium bromide under Bartoli’s conditions.
IR, MS, H and 13C NMRspectral data were fully
consistent with those expected for the assigned struc-
tures (12–15). The chemoselectivity of the palladium
coupling reaction was inferred from the MS spectrum of
1
Similar examples of dehalogenation under catalytic
hydrogenation conditions can be found in the
1
7,18
literature.
12, which lacked isotopomeric peaks ascribable to the
presence of bromine. The presence of the characteristic
2
.1.1. Benzimidazoles and quinoxalines. Ready forma-
À1
tion of benzimidazoles (5a–7a, 5b–7b and 8) and qui-
noxalines (9–11) through reaction of the ortho-diamines
4
vic-diketones, respectively, further confirmed the ortho
relationship of the amino groups in both diamines, and
consequently of the nitro groups in the parent compound
(3a). Benzimidazoles 5a–7a and 5b–7b were obtained in
moderate to good yields (53–72%) by condensation of the
band of the triple bond (CꢁC) at ca. 2150 cm was
also noteworthy in the IRspectra of both 12 and 13.
The formation of indole 14 was easily confirmed by its
a or 4b with carboxylic acids, an iminocarbamate or
1
H NMRspectrum, due to the presence of resonances
corresponding to four aromatic protons (d 6.44–7.52
ppm), in addition to a broad one-proton singlet at d
7.91 ppm corresponding to the indole NH. The MS
spectrum of the second indole (15) displayed iso-
topomeric fragments consistent with the presence of
bromine in the aromatic ring C. Furthermore, forma-
tion of the heterocyclic ring of 15 was confirmed by
intermediate diamines 4a and 4b with formic, acetic or
1
6,19
trifluoracetic acids under Phillips’ conditions. Benzi-
midazole 8, an analogue of the broad spectrum fungicide
1
20
1
Carbendazim , was synthesised in a similar manner, by
reaction of 4a with an iminocarbamate, [methyl (methoxy-
carbonylamino)(methylthiomethylene)-carbamate].2
Three different quinoxalines (9–11) were prepared by
mild acid catalysed condensation of the free diamine 4a
with 2,3-butanedione, benzil and 1,2-cyclohexanedione,
analysis of its H NMRspectrum, which displayed
resonances at d 6.54 ppm (dd), d 7.21 (t) and d 8.25
(brs), associated with the three protons of the five-
membered ring (H2, H3, and H1, respectively), in addi-
tion to a singlet at d 7.27 ppm corresponding to the only
proton of the aromatic ring (C).
0À22
2
3À25
under reflux.
These new quinoxalines were
obtained in moderate to good yields (61, 70 and 42%,
respectively).
2.2. Biological activity tests
The biological activity of the newly synthesised com-
pounds was assessed against herpes simplex virus (HSV-
1 and HSV-2), vaccinia virus and vesicular stomatitis
The structural assignments of the new benzimidazoles
(5a–7a, 5b–7b and 8) and quinoxalines (9–11) were
1
13
based on IR, MS, H and C NMRspectral data,
which were fully consistent with the proposed struc-
virus in human skin-muscle fibroblasts (E SM); against
6
Coxsackie B4 and respiratory syncytial virus (RSV) in
HeLa cell cultures; against parainfluenza-3, reo-1, Sind-
bis, and Punta Toro in Vero cell cultures; and against
human immunodeficiency virus (HIV-1 and HIV-2) in
MT-4 cells. No specific activity against any of these
viruses could be discerned with any of the compounds
tested (5–8, 10, 11, 14 and 15), up to the highest con-
centration (400 pg/mL) used in the experiments. How-
ever, some of the compounds (7a, 5b, 11 and 15) were
found to inhibit both varicella-zoster virus (VZV) and
cytomegalovirus (CMV) replication at a concentration
ca. 5- to 10-fold lower than the cytotoxic concentration
(MCC or CC ), when tested in human embryonic lung
1
tures. The H NMRspectra of the non-brominated
benzimidazoles (5a–7a and 8) and quinoxalines (9–11)
had similar features, showing two aromatic doublets
(
ca. 7.61–7.73 and 7.76–7.96 ppm) downfield from the
corresponding resonances of the diamine precursor
4a), due to the deshielding effect caused by formation
(
of the heterocyclic aromatic moiety. The coupling con-
stant values (ca. 8–9 Hz) further substantiated the
ortho disposition of the two protons in the aromatic
2
6
1
ring C. The H NMRspectra of the brominated
benzimidazoles (5b–7b) showed the presence of a sing-
let at ca. 7.3–7.5 ppm as the signal for the only proton
in the aromatic ring C.
5
0
(HEL) cells (see Table 1). These compounds can there-

106
T. Fonseca et al. / Bioorg. Med. Chem. 12 (2004) 103–112
Table 1. Activity of compounds 5–11, 14 and 15 against human cytomegalovirus (CMV) and varicella-zoster virus (VZV) in HEL cells
a
Compd
Antiviral potency IC50 (mg/mL)
Cytotoxicity
CMV
VZV
Cell morphology
b
Cell growth
CC50 (mg/mL)
c
MCC (mg/mL)
5
6
7
5
6
7
8
9
1
1
1
1
a
a
a
b
b
b
>0.2
>5
1.0–1.2
1.1–3.2
2–4
1.0
>2
ND
>5–15
0.9–1.1
5
1.5–1.6
—
0.9–1.5
0.2–0.5
2.1–4.6
0.8–1.4
0.6–2.8
0.8–1.4
>2
>2
ND
>20
0.3–0.9
1.5–2.6
0.7–2
0.3–3.0
—
ꢂ0.5
20
5
20
20
5
5
ND
ꢂ20
ꢂ5
20
ꢂ5
>50
>50
5.1
15.1
10.8
3.9
2.9
0.7
4.5
ND
>50
13
0
1
4
5
16
12.5
>200
200
Acyclovir
Ganciclovir
a
Inhibitory concentration required to reduce virus plaque formation by 50%. CMV input was 100 plaque forming units (PFU), VZV input was 20
PFU. Data represent range of values for two CMV strains (AD-169, Davis) and four VZV strains (YS, OKA, 07/1 and YS/R).
Minimum cytotoxic concentration causing a microscopically detectable alteration of cell morphology.
Cytotoxic concentration required to reduce cell growth by 50%.
b
c
9
fore be accredited with some specificity in their anti-
VZV and anti-CMV action. The potencies of 5a, 7a, 5b,
b, 11, 14 and 15 as anti-VZV agents were comparable
Methyl dehydroabietate 1b was prepared by methyla-
tion of 1a with diazomethane. Methyl 12-bromodehy-
droabietate 2 was prepared by bromination of methyl
6
3
1
to that of acyclovir; the potencies of 5a, 7a, 5b, 11 and
dehydroabietate 1b using the system Br /Montmor-
2
1
0
1
ganciclovir.
5 as anti-CMV agents were comparable to that of
3
illonite K10 as described previously. Light petroleum
ꢀ
2
ether refers to the bp 40–60 C fraction and ether refers
to diethyl ether. Silica gel used for column chromato-
graphy was 230–400 mesh.
3
. Conclusions
Melting points were determined in a Reichert Thermo-
var apparatus and were not corrected. Spectra were
obtained as follows: FTIRspectra were recorded on a
We have explored the ability of dehydroabietic acid
derivatives to act as synthetic precursors of heteroaro-
matic compounds with potential biological activities.
We describe here the synthesis of several new hetero-
cycles, such as benzimidazoles (5–8), quinoxalines (9,
1
Perkin-Elmer 1725 spectrometer; H NMRspectra were
1
3
recorded at 300 MHz, and C NMRat 75.5 MHz, on a
Varian Gemini 300 instrument; mass spectra were
recorded on a VG micromass 7070E instrument under
electron impact at 70 eV. Microanalyses were performed
on a Carlo Erba model 1106 CHN analyser.
1
0, 11), and indoles (14, 15), obtained from methyl
dehydroabietate (1b). These fused heterocyclic-diterpe-
nic compounds were prepared through several synthetic
routes, involving in some instances an interesting ortho-
dinitration step, followed by a catalytic hydrogenation
process. Preliminary biological evaluation showed that
some of the new heterocycles possess activity against
human cytomegalovirus (CMV) and varicella-zoster
virus (VZV), suggesting that these benzimidazole, qui-
noxaline and indole types fused to diterpenic structures
may become useful as antiviral agents. The possible
improvement of the antiviral properties of these basic
structures, through modulation of the ring substituents
and/or further functionalisation, warrants further
investigation.
4.1.1. Methyl 12-bromo-13,14-dinitro-deisopropyldehy-
droabietate (3a). Methyl 12-bromo-dehydroabietate 2
(3.38 g, 8.62 mmol) was added with vigorous stirring,
during 40 min, to a previously prepared mixture of
fuming nitric acid (100%) (18.4 mL) and concentrated
sulphuric acid (95–97%) (1.4 mL) maintained in an ice-
ꢀ
NaCl bath (À18 C). The resulting mixture was quen-
ched in ice-water, the solution was made basic by addi-
tion of saturated aqueous sodium carbonate and was
then extracted with ether. The organic phase was dried
over anhydrous sodium sulphate, filtered and con-
centrated under reduced pressure. The gum obtained
(3.64 g) was purified by silica column chromatography
with ether-light petroleum ether (1:1) as the eluent.
Upon recrystallisation, white crystals of the dinitro
compound 3a (2.10 g, 4.77 mmol, 58%) were obtained,
4
. Experimental
4
.1. Materials
ꢀ
mp 171–172.8 C (from ether); IR(Nujol)
n
1544, 1354, 1252, 1188, 1136, 1119 1046 cm ; H NMR
1720,
max
À1
1
All reagents were of analytical grade, dried and purified
when necessary. Dehydroabietic acid 1a was obtained
from commercially disproportionated rosin and purified
(CDCl ) d 1.25 (3H, s, 10-CH ), 1.29 (3H, s, 4-CH ),
3
3
3
1.51–1.59 (2H, m, 1-Ha and 6-Hb), 1.71–1.87 (5H, m, 2-
H , 3-H and 6-Ha), 2.19 (1H, dd, J=12.6 and 2.4 Hz,
8
by repeated crystallisation of the ethanolamine salt.
2
2

T. Fonseca et al. / Bioorg. Med. Chem. 12 (2004) 103–112
107
5
m, 7-H ), 3.70 (3H, s, CO CH ), 7.72 (1H, s, 11-H)
-Ha), 2.30 (1H, brd, J=12.9 Hz, 1-Hb), 2.82–2.90 (2H,
exchangeable with D O), 3.65 (3H, s, CO CH ), 6.60
2 2 3
(1H, d, J=8.1 Hz, 12-H), 6.65 (1H, d, J=8.4 Hz, 11-H)
13
2
2
3
1
3
ppm; C NMR(CDCl ) d 16.5 (4-CH ), 18.2 (C-2),
ppm; C NMR(CDCl ) d 16.4 (4-CH ), 18.6 (C-2),
3
3
3
3
2
0.0 (C-6), 24.7 (10-CH ), 25.0 (C-7), 36.3 (C-3), 38.0
21.2 (C-6), 25.1 (10-CH ), 25.3 (C-7), 36.6 (C-10), 36.7
(C-3), 38.4 (C-1), 44.3 (C-5), 47.6 (C-4), 51.8 (CO CH ),
3
3
(
(
C-10), 38.5 (C-1), 43.4 (C-5), 47.2 (C-4), 52.0
CO CH ), 111.9 (C-12), 129.3 (C-8), 132.3 (C-11),
2
3
114.8 (C-12), 115.5 (C-11), 120.7 (C-8), 130.8 (C-13 or
C-14), 133.0 (C-14 or C-13), 142.9 (C-9), 179.4
2
3
1
41.6 (C-13), 144.5 (C-14), 156.4 (C-9), 177.8 (CO CH )
2 3
+
+
ppm; MS m/z 442 (3%), 440 M (3%), 425 (42%), 423
43%), 367 (39%), 365 (70%), 301 (97%), 299 (100%).
Anal. calcd for C H BrN O : C 48.99, H 4.80, N 6.35;
(CO CH ) ppm; MS m/z: 302 M (40%), 287 (25%),
2
3
(
227 (100%). Anal. calcd for C H N O C 71.49, H
18 26 2 2
8.66, N 9.26; found: C 71.26, H 8.63, N 9.21%.
1
8
21
2
6
found: C 49.08, H 4.81, N 6.34%.
4.1.4. Methyl 12-bromo-13,14-diaminodeisopropyldehy-
4
.1.2. Methyl 12-bromo-13-nitro-deisopropyldehydro-
droabietate (4b). A mixture of methyl 12-bromo-13,14-
dinitrodeisopropyldehydroabietate 3a (402 mg, 0.91
mmol), 5% Pd/C (41 mg) and ethanol (15 mL) was
abietate (3b). The procedure was identical to that
described above, starting from methyl 12-bromo-dehy-
droabietate 2 (3.64 g, 9.29 mmol), but using a mixture of
nitric acid (88%, d=1.47) (21 mL) and concentrated
sulphuric acid (95-97%) (0.99 mL). The gum obtained
hydrogenated (H , 100 psi) in a pressure reactor at
2
room temperature. After the reaction was completed (4
h 45 min), the reaction mixture was filtered over Celite,
washed with dichloromethane, and the solution was
evaporated to dryness. The resulting oil was purified by
silica column chromatography with dichloromethane–
methanol (9.6:0.4). The bromodiamine 4b was obtained
as a yellow foam (180 mg, 0.47 mmol, 50%); IR(film)
nmax 3423, 1722, 1621, 1470, 1428, 1247, 1176, 1128,
(
3.40 g) was purified by silica column chromatography
with ether-light petroleum ether (1:1) as the eluent.
Upon recrystallisation, yellow crystals of the mono-
nitro compound 3b (2.00 g, 5.1 mmol, 53%) were
ꢀ
13
obtained, mp 133–134 C (from ether/methanol) (lit:
1
ꢀ
246, 1175, 1132, 1110, 1085, 967, 911, 750 cm ; H
32 C); IR(KBr) n
1
1728, 1561, 1524, 1430, 1334,
max
À1
1
À1
1
1043, 730, 665 cm ; H NMR(CDCl ) d 1.19 (3H, s,
3
NMR(CDCl ) d 1.22 (3H, s, 10-CH ), 1.28 (3H, s, 4-
10-CH ), 1.26 (3H, s, 4-CH ), 1.39–1.55 (2H, m, 1-Ha
3
3
3
3
CH ), 1.41–1.58 (2H, m, 1-Ha and 6-Hb), 1.66–1.80
and 6-Hb), 1.61–1.80 (5H, m, 2-H and 3-H , 6-Ha),
3
2
2
(
4H, m, 2-H and 3-H ), 1.80–1.90 (1H, m, 6-Ha), 2.17
2.16 (1H, dd, J=12.6 and 2.4 Hz, 5-Ha), 2.20 (1H, d,
2
2
(
1H, dd, J=12.3 and 1.8 Hz, 5-Ha), 2.28 (1H, brd,
J=13.2 Hz, 1-Hb), 2.48–2.56 (2H, m, 7-H ), 3.28 (4H,
2
J=12.9 Hz, 1-Hb), 2.82–2.97 (2H, m, 7-H ), 3.69 (3H, s,
brs, 2ÂNH , exchangeable with D O), 3.66 (3H, s,
2
2
2
1
3
CO CH ), 7.56 (1H, s, 11-H or 14-H), 7.58 (1H, s, 14-H
1
CO CH ), 6.90 (1H, s, 11-H) ppm; C NMR(CDCl ) d
2
3
2
3
3
3
or 11-H) ppm; C NMR(CDCl ) d 16.5 (4-CH ), 18.2
16.5 (4-CH ), 18.5 (C-2), 21.1 (C-6), 25.2 (10-CH ), 25.2
(C-7), 36.6 (C-3), 36.8 (C-10), 38.4 (C-1), 44.2 (C-5),
47.5 (C-4), 51.9 (CO CH ), 110.1 (C-12), 118.1 (C-11),
3
3
3
3
(
C-2), 20.9 (C-6), 24.8 (10-CH ), 29.2 (C-7), 36.4 (C-3),
3
3
(
7.6 (C-1), 37.7 (C-10), 43.9 (C-5), 47.4 (C-4), 52.1
CO CH ), 111.2 (C-12), 126.3 (C-14), 131.2 (C-11),
2
3
119.7 (C-8), 129.2 (C-13), 133.7 (C-14), 143.5 (C-9),
+
179.1 (CO CH ) ppm; MS m/z: 382 (61%), 380 M
2
3
1
36.2 (C-8), 146.8 (C-13), 155.9 (C-9), 178.5 (CO CH )
2
3
2
3
+
ppm; MS m/z 397 (9%), 395 M (9%), 380 (49%), 378
44%), 322 (83%), 320 (100%). Anal. calcd for
C H BrNO : C 54.56, H 5.60, N 3.53; found: C 54.49;
(54%), 367 (29%), 365 (27%), 307 (100%), 305 (97%).
Anal. calcd for C H BrN O : C 56.70, H 6.61, N 7.35;
found: C 56.65, H 6.57, N 7.09%; HRMS: calcd for
(
1
8
25
2
2
1
8
22
4
7
9
H 5.57, N 3.48%.
C H BrN O : 380.10995; found: 380.10974.
18 25 2 2
4
(
.1.3. Methyl 13,14-diaminodeisopropyldehydroabietate
4a). mixture of methyl 12-bromo-13,14-dini-
trodeisopropyldehydroabietate 3a (709 mg, 1.61 mmol),
% Pd/C (160 mg), ethanol (19 mL) and triethylamine
2 mL) was hydrogenated (H , 100 psi) in a pressure
4.1.5. Methyl 13,14-imidazolyl-deisopropyldehydroabie-
tate (5a). A mixture of methyl 13,14-diaminodeisopro-
pyldehydroabietate 4a (70 mg, 0.23 mmol) and formic
acid (98–100%; 2.5 mL) was heated under reflux for 4 h.
The solution was then neutralized with aqueous sodium
hydroxide (20%) and extracted with ether. The organic
phase was washed with water, dried over anhydrous
magnesium sulphate and evaporated to dryness. The
residue (66 mg) was purified by preparative thin layer
chromatography on silica gel, with dichloromethane-
methanol (9.7:0.3) as eluent. The imidazole 5a was
obtained as a white foam (41 mg, 0.13 mmol, 55%), IR
A
5
(
2
reactor at rt. After the reaction was completed (19 h),
the reaction mixture was filtered over Celite, washed
with dichloromethane and the solution evaporated to
dryness. The extract was dissolved in ether, washed with
water, dried over anhydrous magnesium sulphate and
then filtered. Evaporation of the solvent gave a white
foam (414 mg) that was purified by silica column chro-
matography with dichloromethane-methanol (9.5:0.5)
as eluent. Upon recrystallisation, white crystals of the
diamine 4a (362 mg, 1.19 mmol, 74%) were obtained,
À1
1
(film) nmax 3415, 1724, 1589, 1254, 1115, 731 cm ; H
NMR(CDCl ) d 1.26 (3H, s, 10-CH ), 1.31 (3H, s, 4-
3
3
CH ), 1.42–1.58 (2H, m, 1-Ha and 6-Hb), 1.66–1.95
3
ꢀ
mp 143–144 C (from ethanol); IR(film) nmax 3351,
(5H, m, 2-H , 3-H and 6-Ha), 2.34 (1H, d, J=12.9 Hz,
2
2
1
722, 1620, 1491, 1447, 1300, 1245, 1174 and 1123
À1
5-Ha), 2.41 (1H, brs, 1-Hb), 3.04–3.22 (2H, m, 7-H2),
3.68 (3H, s, CO CH ), 7.24 (1H, d, J=8.7 Hz, 11-H or
12-H), 7.46 (1H, d, J=8.4 Hz, 12-H or 11-H), 8.06 (1H,
1
cm ; H NMR(CDCl ) d 1.20 (3H, s, 10-CH ), 1.27
3
3
2
3
(
3H, s, 4-CH ), 1.41–1.55 (2H, m, 1-Ha and 6-Hb),
3
0
13
1
.61–1.92 (5H, m, 2-H and 3-H , 6-Ha), 2.20 (1H, dd,
brs, 2 -H) ppm; C NMR(CDCl ) d 16.5 (4-CH ), 18.6
2
2
3
3
J=12.8 and 2.4 Hz, 5-Ha), 2.26 (1H, d, J=10.2 Hz, 1-
Hb), 2.54–2.64 (2H, m, 7-H ), 3.06 (4H, brs, 2ÂNH ,
(C-2), 21.1 (C-6), 25.2 (10-CH ), 25.6 (C-7), 36.7 (C-3),
37.4 (C-10), 38.4 (C-1), 45.2 (C-5), 47.8 (C-4), 52.0
3
2
2

108
T. Fonseca et al. / Bioorg. Med. Chem. 12 (2004) 103–112
(
1
1
CO CH ), 113.4 (C-12), 120.0 (C-11), 122.1 (C-8),
2
35.1 (C-13 or C-14), 135.6 (C-14 or C-13), 140.0 (C-2 ),
min, methyl chloroformate (0.66 mL, 8.62 mmol) in dry
and freshly distilled dichloromethane (5 mL) was added
to the reaction mixture in an ice bath. After 2 h, a buffer
solution of 0.1 M KH PO /Na HPO (pH=7) was
3
0
+
44.4 (C-9), 179.2 (CO CH ) ppm; MS m/z: 312 M
2
3
(16%), 297 (20%), 237 (100%); HRMS: calcd for
C H N O : 312.18378, found: 312.18396.
2
4
2
4
added to the reaction mixture in an ice bath, followed
by extraction with diethyl ether. The organic phase was
washed with brine, dried over anhydrous sodium sul-
phate, filtered and evaporated to dryness, affording
CH O CNH–C(SCH )¼N–CO CH as white crystals
1
9
24
2
2
0
.1.6. Methyl 2 -methyl-13,14-imidazolyl-deisopropylde-
4
hydroabietate (6a). Diamine 4a (67 mg, 0.22 mmol),
glacial acetic acid (4 mL), and 4 M hydrochloric acid (1
mL) were heated under reflux for 1 h 30 min. The resi-
due (64 mg) was purified by preparative thin layer
chromatography on silica gel, with dichloromethane–
methanol (9.5:0.5) as eluent. The imidazole 6a was
obtained as a white foam (50 mg, 0.15 mmol, 67%), IR
3
2
3
2
3
ꢀ
22
(322 mg, 1.56 mmol, 44%), mp 98–100 C (lit:
ꢀ
1403, 1281, 1215, 1062, 808, 752 cm
100 C); IR(film) nmax 3583, 1753, 1657, 1594, 1438,
À1
1
;
H NMR
(CDCl ) d 2.43 (3H, s), 3.82 (6H, s), and 11.86 (1H, s);
3
+
m/z 206 M (41%), 174 (74%), 83 (47%), 71 (54%), 59
(100%), 47 (34%). Anal. calcd for C H N O :S C
À1
1
(
film) nmax 2937, 1725, 1539, 1252, 1114, 730 cm ; H
6
10
2
4
NMR(CDCl ) d 1.24 (3H, s, 10-CH ), 1.30 (3H, s, 4-
34.95, H 4.89, N 13.58; found: C 35.16, H 4.88, N
13.64%.
3
3
CH ), 1.48–1.56 (2H, m, 1-Ha and 6-Hb), 1.66–1.92
3
(
5H, m, 2-H , 3-H and 6-Ha), 2,32 (1H, dd, J=12,6
2
2
0
and 1,9 Hz, 5-Ha), 2,39 (1H, brs, 1-Hb), 2,56 (3H, s, 2 -
CH ), 3.00–3.13 (2H, m, 7-H ), 3.67 (3H, s, CO CH ),
(b) Cyclisation. Diamine 4a (68 mg, 0.23 mmol), gla-
cial acetic acid (4 mL), and CH O CNHC
3
2
2
3
7
.15 (1H, d, J=8.6 Hz, 11-H or 12-H), 7.32 (1H, d,
1
3
2
3
J=8,7 Hz, 12-H or 11-H) ppm; C NMR(CDCl ) d
(SCH )¼NCO CH (49 mg, 0.24 mmol) were heated
3
3
2
3
0
1
4.2 (2 -CH ), 16.5 (4-CH ), 18.6 (C-2), 21.1 (C-6), 25.3
under reflux for 3 h 30 min. The residue (105 mg) was
purified by preparative thin layer chromatography on
silica gel with dichloromethane–methanol (9.7:0.3) as
eluent. The imidazole 8 was obtained as a white solid
3
3
(
C-7), 25.5 (10-CH ), 36.7 (C-3), 37.3 (C-10), 38.4 (C-1),
3
4
1
5.2 (C-5), 47.7 (C-4), 52.0 (CO CH ), 112.3 (C-12),
2 3
19.3 (C-11), 121.2 (C-8), 135.1 (C-13 or C-14), 135.8
0
CO CH ) ppm; MS m/z: 326 M (18%), 311 (23%),
ꢀ
(
C-14 or C-13), 143.9 (C-9), 150.4 (C-2 ), 179.3
+
(31 mg, 0.08 mmol, 35%), mp 276–278 C; IR(film)
À1
1
(
nmax 3409, 2949, 1723, 1646, 1605, 1264, 1162 cm ; H
NMR(CDCl ) d 1.28 (3H, s, 10-CH ), 1.32 (3H, s, 4-
2
3
251 (100%); HRMS: calcd for C H N O : 326.19943,
20 26 2 2
found: 326.19931.
3
3
CH ), 1.55–1.59 (2H, m, 1-Ha and 6-Hb), 1.66–1.97
3
(
5H, m, 2-H , 3-H and 6-Ha), 2.34 (1H, dd, J=12.6
2
2
0
4
.1.7. Methyl 2 -trifluoromethyl-13,14-imidazolyl-deiso-
and 1.8 Hz, 5-Ha), 2.41 (1H, brs, 1-Hb), 2.97–3.02 (2H,
m, 7-H ), 3.69 (3H, s, CO CH ), 3.92 (3H, s,
NHCO CH ), 7.16 (1H, d, J=8.7 Hz, 11-H or 12-H),
7.33 (1H, d, J=9 Hz, 12-H or 11-H) ppm; C NMR
(CDCl ) d 16.5 (4-CH ), 18.7 (C-2), 21.0 (C-6), 25.2 (10-
propyldehydroabietate (7a). Diamine 4a (79 mg, 0.26
mmol), trifluoroacetic acid (0.4 mL), and 4 M hydro-
chloric acid (0.6 mL) were heated under reflux for 3 h.
The residue (83 mg) was purified by preparative thin
layer chromatography on silica gel with dichloro-
methane–methanol (9.5:0.5) as eluent. The imidazole 7a
2
2
3
2
3
1
3
3
3
CH ), 25.4 (C-7), 36.7 (C-3), 37.3 (C-10), 38.5 (C-1),
3
45.1 (C-5), 47.8 (C-4), 52.0 (CO CH ), 52.7 (CO CH ),
3
2
3
2
was obtained as a white solid (70 mg, 0.18 mmol, 70%),
ꢀ
112.7 (C-8), 118.8 (C-11 and C-12), 131.0 (C-13 or C-
14), 133.9 (C-14 or C-13), 143.5 (C-9), 149.2 (C-2 ),
0
157.3 (NHCO CH ), 179.2 (CO CH ) ppm; MS m/z
mp 236–238 C; IR(film) n
2941, 1727, 1540, 1254,
max
À1
1
1
1
1
147 cm ; H NMR(CDCl ) d 1.28 (3H, s, 10-CH ),
3
3
2
3
2
3
+
.33 (3H, s, 4-CH ), 1.48–1.56 (2H, m, 1-Ha and 6-Hb),
385 M (9%), 370 (7%), 353 (23%), 310 (24%), 278
(100%), 44 (42%). Anal. calcd for C H N O : C
3
.73–1.98 (5H, m, 2-H , 3-H and 6-Ha), 2.35 (1H, d,
2
2
21 27
3
4
J=12.6 Hz, 5-Ha), 2.41 (1H, brs, 1-Hb), 3.01 (2H, m, 7-
H ), 3.71 (3H, s, CO CH ), 7.31 (1H, d, J=7.8 Hz, 11-
H or 12-H), 7.63 (1H, d, J=8.4 Hz, 12-H or 11-H) ppm;
65.44, H 7.06, N 10.90; found: C 65.43, H 7.06, N
10.87%.
2
2
3
1
3
C NMR(CDCl ) d 16.4 (4-CH ), 18.5 (C-2), 21.0 (C-
4.1.9. Methyl 12-bromo-13,14-imidazolyl-deisopropylde-
hydroabietate (5b). Diamine 4b (47 mg, 0.12 mmol) and
formic acid (3 mL) were heated under reflux for 2 h. The
residue (40 mg) was purified by preparative thin layer
chromatography on silica gel with dichloromethane–
methanol (9.5:0.5) as eluent. The imidazole 5b was
obtained as an amorphous white solid (27 mg, 0.07
3
3
6
3
), 25.1 (C-7), 25.5 (10-CH ), 36.8 (C-3), 37.5 (C-10),
8.2 (C-1), 45.1 (C-5), 47.8 (C-4), 52.2 (CO CH ), 117.2
3
2
3
(
C-11), 124.4 (C-8), 132.6 (C-13 and C-14), 139.9 (C-2 ,
CF , J=271 Hz), 118.5 (C-11 or C-12), 120.9 (C-12 or
3
0
J=40.1 Hz), 146.6 (C-9), 179.8 (CO CH ) ppm; MS m/z
2
3
+
380 M (10%), 365 (12%), 305 (100%). Anal. calcd for
C H F N O : C 63.15, H 6.09, N 7.36; found: C
mmol, 59%); IR(Nujol) n
1125, 1104, 1033, 737 cm ; H NMR(CDCl ) d 1.26
3082, 2949, 1721, 1259,
2
0
23
3
2
2
max
À1
1
6
3.07, H 6.14, N 7.33%.
3
(
3H, s, 10-CH ), 1.30 (3H, s, 4-CH ), 1.43–1.57 (2H, m,
3 3
0
4
.1.8. Methyl 2 -methoxycarbonylamino-13,14-imidazo-
1-Ha and 6-Hb), 1.67–1.94 (5H, m, 2-H , 3-H and 6-
2
2
lyl-deisopropyldehydroabietate (8) (a) Preparation of
Bis(tri-
methylsilyl)acetamide (2.1 mL, 8.62 mmol) was added
to a solution of S-methylisothiourea (500 mg, 3.60
mmol) in dry and recently distilled dichloromethane (5
Ha), 2.30 (1H, dd, J=13 and 2.1 Hz, 5-Ha), 2.37 (1H,
[
CH O CNHC(SCH )¼NCO CH ]. N,O
-
brs, 1-Hb), 2.91–3.18 (2H, m, 7-H ), 3.68 (3H, s,
3
2
3
2
3
2
0
CO CH ), 7.38 (1H, s, 11-H), 8.06 (1H, s, 2 -H) ppm;
1
2
3
3
C NMR(CDCl ) d 16.5 (4-CH ), 18.6 (C-2), 20.9 (C-
3
3
6), 25.2 (10-CH ), 25.4 (C-7), 36.7 (C-3), 37.5 (C-10),
38.4 (C-1), 45.1 (C-5), 47.7 (C-4), 52.1 (CO CH ), 106.1
3
mL), with vigorous stirring, under N at rt. After 1 h 10
2
2
3

T. Fonseca et al. / Bioorg. Med. Chem. 12 (2004) 103–112
109
(
1
(
C-12), 121.7 (C-8), 122.6 (C-11), 135.0 (C-13 or C-14),
36.8 (C-14 or C-13), 140.4 (C-2 ), 145.8 (C-9), 179.2
+
2 3
mmol), butane-2,3-dione (0.3 mL, 0.34 mmol) and gla-
cial acetic acid (2 mL) was heated under reflux and N2
for 40 min. The solvent was evaporated under reduced
pressure after cooling down the reaction mixture to rt.
The residue (133 mg) was purified by preparative thin
layer chromatography on silica gel with dichloro-
methane–methanol (9.9:0.1). The quinoxaline 9 (113
mg, 0.32 mmol, 61%) was obtained as a white foam; IR
0
CO CH ) ppm; MS m/z 392 (15%), 390 M (17%),
3
Anal. calcd for C H BrN O : C 58.32, H 5.92, N 7.16;
77 (11%), 375 (12%), 317 (100%), and 315 (93%).
1
9
23
2
2
found: C 57.69, H 6.09, N 6.82%; HRMS: calcd for
7
9
C H
1
BrN O 390.09430, found 390.09431.
2 2
9
23
0
4
.1.10. Methyl 2 -methyl-12-bromo-13,14-imidazolyl-dei-
(film) n
2946, 1727, 1451, 1338, 1247, 1173, 1116, 733
max
À1
1
sopropyldehydroabietate (6b). Diamine 4b (73 mg, 0.19
mmol), glacial acetic acid (4 mL) and 4 M hydrochloric
acid (1 mL) were heated under reflux for 1 h 20 min.
The residue (85 mg) was purified by preparative thin
layer chromatography on silica gel with dichloro-
methane–methanol (9.6:0.4). Upon recrystallisation,
cm ; H NMR(CDCl ) d 1.29 (3H, s, 10-CH ), 1.32
3
3
(3H, s, 4-CH ), 1.50–1.68 (2H, m, 1-Ha and 6-Hb),
3
1.72–1.97 (5H, m, 2-H , 3-H and 6-Ha), 2.33 (1H, dd,
2
2
J=12.6 and 2.1 Hz, 5-Ha), 2.41 (1H, brs, 1-Hb), 2.70
0
0
(6H, s, 2 -CH and 3 -CH ), 3.15–3.28 (1H, m, 7-Ha or
3
3
7-Hb), 3.55–3.66 (1H, m, 7-Hb or 7-Ha), 3.68 (3H, s,
CO CH ), 7.61 (1H, d, J=8.9 Hz, 12-H), 7.76 (1H, d,
white crystals of the imidazole 6b (56 mg, 0.14 mmol,
ꢀ
2
3
13
7
(
(
2%) were obtained, mp 168–170 C (from ether); IR
1
J=8.9 Hz, 11-H) ppm; C NMR(CDCl ) d 16.5 (4-
3
À1
0 0
CH ), 18.6 (C-2), 21.3 (C-6), 22.9 (2 - or 3 -CH ), 23.2
3 3
film) nmax 1725, 1251, 1128, 1036, 731 cm ; H NMR
0 0
(2 - or 3 -CH ), 24.6 (10-CH ), 25.7 (C-7), 36.5 (C-3),
3 3
CDCl ) d 1.25 (3H, s, 10-CH ), 1.29 (3H, s, 4-CH ),
3
3
3
1
.48–1.57 (2H, m, 1-Ha and 6-Hb), 1.63–1.95 (5H, m, 2-
37.7 (C-10), 38.0 (C-1), 45.2 (C-5), 47.7 (C-4), 51.9
(CO CH ), 125.8 (C-11), 126.0 (C-12), 132.4 (C-8),
H , 3-H and 6-Ha), 2.30 (1H, d, J=11.4 Hz, 5-Ha),
2
2
2
3
0
2H, m, 7-H ), 3.67 (3H, s, CO CH ), 7.30 (1H, s, 11-H)
0
2
(
.35 (1H, brs, 1-Hb), 2.52 (3H, s, 2 -CH ), 2.88–3.12
139.2 (C-13), 140.0 (C-14), 149.0 (C-9), 151.9 (C-2 or C-
3
0 0 0
3 ), 152.0 (C-3 or C-2 ), 179.0 (CO CH ) ppm; MS m/z
2 3
2
2
3
1
3
0
8.5 (C-2), 21.0 (C-6), 25.3 (C-7), 25.4 (10-CH ), 36.6
+
ppm; C NMR(CDCl ) d 14.8 (2 -CH ), 16.4 (4-CH ),
1
352 M (93%), 337 (17%), 293 (18%), 277 (100%), 223
(24%). Anal. calcd for C H N O : C 74.97, H 8.01, N
7.95; found: C 74.64, H 8.19, N 7.86%.
3
3
3
3
22 28
2
2
(
C-3), 37.4 (C-10), 38.4 (C-1), 45.0 (C-5), 47.7 (C-4),
5
1
1
4
2.0 (CO CH ), 105.4 (C-12), 120.4 (C-8), 121.6 (C-11),
2 3
0
0
35.9 (C-13 or C-14), 137.1 (C-14 or C-13), 145.1 (C-9),
51.1 (C-2 ), 179.2 (CO CH ) ppm; MS m/z 406 (15%),
+
4.1.13. Methyl 2 ,3 -diphenyl-13,14-pyrazinyl-deisopro-
pyldehydroabietate (10). A mixture of 4a (90 mg, 0.30
mmol), benzil (65 mg, 0.30 mmol) and glacial acetic acid
0
04 [M] (16%), 391 (13%), 389 (14%), 331 (100%), 329
2
3
(
N 6.91; found: C 59.66, H 6.22%, N 6.86%; HRMS:
91%). Anal. calcd for C H BrN O : C 59.26, H 6.22,
(3 mL) was heated under reflux and N for 2 h. After
2
2
0
25
2
2
cooling down to room temperature, the reaction mix-
ture was quenched in ice-water (50 mL), and a white
precipitate was formed. The solid was filtered and
washed with water. Upon recrystallisation, the qui-
noxaline 10 (113 mg, 0.24 mmol, 79%) was obtained as
7
9
calcd for C H
0
BrN O : 404.10992, found: 404.10904.
2 2
2
25
0
.1.11. Methyl 2 -trifluoromethyl-12-bromo-13,14-imida-
4
zolyl-deisopropyldehydroabietate (7b). Diamine 4b (64
mg, 0.17 mmol), trifluoroacetic acid (0.4 mL) and 4 M
hydrochloric acid (0.6 mL) were heated under reflux for
ꢀ
white crystals, mp 138–140 C (from ether–methanol);
IR(Nujol) nmax 1723, 1462, 1378, 1350, 1246, 1173,
À1
1
2
h. The residue (61 mg) was purified by preparative
1116, 766, 697 cm ; H NMR(CDCl ) d 1.33 (3H, s,
3
thin layer chromatography on silica gel with dichloro-
methane–methanol (9.7:0.3). Upon recrystallisation,
white crystals of the imidazole 7b (42 mg, 0.09 mmol,
10-CH ), 1.34 (3H, s, 4-CH ), 1.55–1.70 (2H, m, 1-Ha
3
3
and 6-Hb), 1.79–2.00 (5H, m, 2-H , 3-H and 6-Ha),
2
2
2.38 (1H, dd, J=12.3 and 1.8 Hz, 5-Ha), 2.45 (1H, d,
J=11.4 Hz, 1-Hb), 3.27–3.40 (1H, m, 7-Ha or 7-Hb),
3.66–3.75 (1H, m, 7-Hb or 7-Ha), 3.68 (3H, s,
CO CH ), 7.30–7.36 (6H, m, 6ÂH-Ar), 7.49-7.55 (4H,
ꢀ
5
3%) were obtained, mp 151–153 C (dichloromethane–
hexane); IR(Nujol) n
2949, 1726, 1582, 1254, 1145,
max
À1
1
1
035, 731 cm ; H NMR(CDCl ) d 1.27 (3H, s, 10-
3
2
3
CH ), 1.31 (3H, s, 4- CH ), 1.42-1.57 (2H, m, 1-Ha and
m, 4ÂH–Ar), 7.73 (1H, d, J=9.3 Hz, 11-H), 7.96 (1H,
3
3
1
3
6
-Hb), 1.73–1.98 (5H, m, 2-H , 3-H and 6-Ha), 2.30
d, J=9.3 Hz, 12-H) ppm; C NMR(CDCl ) d 16.5 (4-
2
2
3
(
1H, d, J=12.3 Hz, 5-Ha), 2.37 (1H, brs, 1-Hb), 3.02–
CH ), 18.6 (C-2), 21.3 (C-6), 24.5 (10-CH ), 25.7 (C-7),
36.5 (C-3), 37.8 (C-10), 37.9 (C-1), 45.2 (C-5), 47.8 (C-
4), 52.0 (CO CH ), 126.6 (C-12), 127.5 (C-11), 128.1
3
3
3
1
2
.08 (2H, m, 7-H ), 3.70 (3H, s, CO CH ), 7.48 (1H, s,
1
2
2
3
3
1-H) ppm; C NMR(CDCl ) d 16.3 (4-CH ), 18.4 (C-
3
3
2
3
), 20.8 (C-6), 25.1 (10-CH ), 25.3 (C-7), 36.7 (C-3), 37.6
(2ÂCH–Ar), 128.3 (2ÂCH–Ar), 128.6 (2ÂCH–Ar),
129.8 (2ÂCH–Ar), 130.2 (2ÂCH–Ar), 133.3 (C-8), 139.3
(C-13), 139.6 (2ÂC–Ar), 140.0 (C-14), 150.2 (C-9), 151.7
3
(
(
(
1
(
C-10), 38.2 (C-1), 45.0 (C-5), 47.7 (C-4), 52.1
CO CH ),102.7 (C-12), 116.9 (CF , J=270.5 Hz) 124.4
C-8 and C-11), 134.7 (C-13 or C-14), 136.7 (C-14 or C-
2
3
3
0 0 0 0
(C-2 or C-3 ), 152.3 (C-3 or C-2 ), 179.0 (CO CH );
2 3
0
CO CH ) ppm; MS m/z 460 (15%), 458 M (16%),
+
3), 140.8 (C-2 , J=40.7 Hz), 147.4 (C-9), 179.6
+
MS m/z 476 M (100%), 461 (16%), 417 (15%), 401
(54%), 347 (21%). Anal. calcd for C H N O : C
80.64; H 6.77, N 5.88; found: C 80.34, H 6.74, N 5.84%.
2
3
32 32
2
2
4
Anal. calcd for C H BrF N O : C 52.30, H 4.83, N
6.10; found: C 52.80, H 5.15, N 5.63%; HRMS: calcd
for C H BrF N O : 458.08167, found: 458.08076.
45 (8%), 443 (9%), 385 (96%), 383 (100%), 305 (57%).
2
0
22
3
2
2
0
0
4.1.14. Methyl 2 ,3 -cyclohexyl-13,14-pyrazinyl-deisopro-
pyldehydroabietate (11). A mixture of the diamine 4a
2
0
22
3
2
2
(
100 mg, 0.33 mmol), cyclohexane-1,2-dione (37 mg,
0
0
pyldehydroabietate (9). A mixture of 4a (102 mg, 0.34
4
.1.12. Methyl 2 ,3 -dimethyl-13,14-pyrazinyldeisopro-
0.33 mmol), sodium acetate (52 mg, 0.63 mmol) and
glacial acetic acid (2 mL) was heated under reflux and

110
T. Fonseca et al. / Bioorg. Med. Chem. 12 (2004) 103–112
+
N for 1 h 30 min. The reaction mixture was quenched
2
(CO CH ) ppm; MS m/z 413 [M] (4%), 398 (8%), 338
2 3
with water (40 mL). The pH was then made alkaline by
addition of 1 N sodium hydroxide, and the product was
extracted with ether. The organic phase was washed
with water, dried with anhydrous magnesium sulphate,
filtered and evaporated to dryness under reduced pres-
sure. The residue (99 mg) was purified by preparative
thin layer chromatography on silica gel with dichloro-
methane–methanol (9.9:0.1) as eluent. The quinoxaline
(11%), 310 (23%), 73 (100%). Anal. calcd for
C H NO Si: C 66.79, H 7.55, N 3.39; found: C 67.09,
H 7.64, N 3.61%.
2
3
31
4
4.1.16. Methyl 12-trimethylsylilethinyl-13-amino-deiso-
propyldehydroabietate (13). According to the procedure
2
8
described in the literature, iron (515 mg, 0.01 mmol)
and iron (II) sulphate heptahydrate (175 mg, 0.62
mmol) were added to a mixture of methyl 12-tri-
methylsylilethinyl-13-nitro-deisopropyldehydroabietate
12 (98 mg, 0.24 mmol), benzene (2 mL), methanol (0.5
mL) and 0.1 M hydrochloric acid (5.5 mL) with vigor-
ous stirring. The mixture was refluxed during 8 h. Upon
conclusion, the reaction mixture was cooled to room
temperature, extracted with ether and washed with
water. The organic phase was dried with anhydrous
magnesium sulphate, filtered and evaporated to dryness.
The extract (85 mg) was purified by silica column chro-
matography, using hexane–ether (1:1) as eluent. Com-
pound 13 was obtained as a colorless oil (75 mg, 0.20
mmol, 83%), IR(film) nmax 3483, 3384, 2927, 2141,
1
1 (52 mg, 0.14 mmol, 42%) was obtained as a white
foam, IR(film) nmax 2941, 1727, 1488, 1446, 1429, 1340,
À1
1
1
246, 1184, 1172, 1115, and 731 cm
;
H NMR
(
CDCl ) d 1.29 (3H, s, 10-CH ), 1.32 (3H, s, 4-CH ),
3
3
3
1
.50–1.68 (2H, m, 1-Ha and 6-Hb), 1.74–1.94 (5H, m, 2-
H , 3-H and 6-Ha), 1.97–2.03 (4H, m, 2ÂCH -cyclo-
2
2
2
hexyl), 2.33 (1H, dd, J=12.3 and 2.1 Hz, 5-Ha), 2.41
(
1H, d, J=11.7 Hz, 1-Hb), 3.12 (4H, s, 2ÂCH -cyclo-
2
hexyl), 3.17–3.27 (1H, m, 7-Ha or 7-Hb), 3.53–3.62 (1H,
m, 7-Hb or 7-Ha), 3.68 (3H, s, CO CH ), 7.61 (1H, d, J
9
2
3
1
3
Hz, 12-H), 7.76 (1H, d, J=9 Hz, 11-H) ppm;
C
NMR(CDCl ) d 16.5 (4-CH ), 18.6 (C-2), 21.3 (C-6),
3
3
2
3
3
3.0 (2ÂCH -cyclohexyl), 24.5 (10-CH ), 25.8 (C-7),
2
3
À1
1
2.9 (CH -cyclohexyl), 33.4 (CH -cyclohexyl), 36.5 (C-
2 2
1731, 1621, 1462, 1249, 1133, 863, 840, 665 cm ; H
), 37.7 (C-10), 37.9 (C-1), 45.2 (C-5), 47.7 (C-4), 51.9
NMR(CDCl ) d 0.25 (9H, s, Si(CH ) ), 1.15 (3H, s, 10-
3
3 3
(
CO CH ), 125.8 (C-11), 126.3 (C-12), 132.4 (C-8),
2
CH ), 1.25 (3H, s, 4-CH ), 1.33–1.49 (2H, m, 1-Ha and
3
3
3
0
), 152.7 (C-3 or C-2 ), 179.0 (CO CH ) ppm; MS m/z
+
1
3
3
39.3 (C-13), 140.2 (C-14), 149.0 (C-9), 152.6 (C-2 or C-
6-Hb), 1.61–1.82 (5H, m, 2-H , 3-H and 6-Ha), 2.14
2
2
0
0
78 M (90%), 363 (17%), 319 (20%), 303 (100%), 249
0
(1H, dd, J=12.6 and 2.1 Hz, 5-Ha), 2.24 (1H, d,
2
3
J=13.2 Hz, 1-Hb), 2.75–2.80 (2H, m, 7-H ), 3.66 (3H, s,
2
(
7
35%). Anal. calcd for C H N O : C 76.16, H 7.99, N
2
.40; found: C 75.99, H 7.99, N 7.38%.
CO CH ), 4.02 (2H, brs, NH , exchangeable with D O),
6.36 (1H, s, 11-H or 14-H), 7.16 (1H, s, 14-H or 11-H)
2
4
30
2
2
3
2
2
1
3
ppm; C NMR(CDCl ) d 0.15 (Si(CH ) ), 16.4 (4-
3
3 3
4
.1.15. Methyl 12-trimethylsylilethinyl-13-nitro-deisopro-
pyldehydroabietate (12). According to the procedure
CH ), 18.5 (C-2), 21.5 (C-6), 25.0 (10-CH ), 30.0 (C-7),
36.5 (C-3), 36.6 (C-10), 38.1 (C-1), 45.0 (C-5), 47.5 (C-
3
3
2
7
described in the literature, palladium dichloro bis-
triphenylphosphine (32 mg, 0.05 mmol) and copper (I)
iodide (34 mg, 0.34 mmol) were added to a mixture of
trimethylsylilacetylene (0.3 mL, 2.1 mmol) and methyl
4), 51.8 (CO CH ), 98.4 (CꢁC), 102.5 (CꢁC), 106.1 (C-
2
3
12), 114.1 (C-14), 128.2 (C-11), 137.6 (C-8), 140.0 (C-
+
13), 145.6 (C-9), 179.1 (CO CH ) ppm; MS m/z 383 M
2
3
(40%), 368 (38%), 324 (5%), 308 (100%), 73 (42%);
HRMS: calcd for C H NO Si: 383.22809; found:
383.22836.
1
2-bromo-13-nitro-deisopropyldehydroabietate 3b (513
2
3
33
2
mg, 1.3 mmol) in triethylamine (17 mL). The reaction
proceeded for 18 h at room temperature, under nitrogen
and with vigorous stirring. Upon conclusion, the solvent
was evaporated to dryness. The residue was dissolved in
ether and washed with water. The organic phase was
dried with anhydrous magnesium sulphate, filtered and
evaporated to dryness. The extract (542 mg) was pur-
ified by silica column chromatography, using hexane–
ether (6:4) as eluent. Upon recrystallisation, white crys-
tals of methyl 12-trimethylsylilethinyl-13-nitro-deiso-
propyldehydroabietate 12 (502 mg, 1.21 mmol, 93%)
4.1.17. Methyl 12,13d-pyrrolyldeisopropyldehydroabi-
etate (14). According to the procedure described in the
2
9
literature, a mixture of methyl 12-trimethylsylilethi-
nyl-13-amino-deisopropyl-dehydroabietate 13 (49 mg,
0.13 mmol) and copper(I) iodide (28 mg, 0.15 mmol) in
ꢀ
dimethylformamide (3 mL) was heated to 100 C, under
N , during 1 h 10 min. The reaction mixture was filtered
2
through a layer of Celite and washed with ether, after
being cooled to room temperature. The organic solution
was washed with a concentrated solution of brine, dried
with anhydrous magnesium sulphate, filtered and eva-
porated under reduced pressure. The extract (43 mg)
was purified by silica column chromatography using
hexane–ether (4:6) as eluent. The indole 14 (23 mg,
0.074 mmol, 60%) was obtained as a colourless oil, IR
(film) nmax 3394, 2927, 1727, 1463, 1246, 1107, 1132,
ꢀ
were obtained, mp 166–168 C (from light petroleum
ether); IR(Nujol) nmax 2928, 2154, 1731, 1555, 1519,
À1
1
1
340, 1245, 1185, 1111, 865, 840, 759 cm ; H NMR
(
CDCl ) d 0.28 (9H, s, Si(CH ) ), 1.21 (3H, s, 10-CH ),
3
3 3
3
1
1
.28 (3H, s, 4-CH ), 1.46-1.55 (2H, m, 1-Ha and 6-Hb),
3
.63–1.88 (5H, m, 2-H , 3-H and 6-Ha), 2.17 (1H, dd,
2
2
J=12.3 and 2.1 Hz, 5-Ha), 2.34 (1H, d, J=12.6 Hz, 1-
Hb), 2.93–2.98 (2H, m, 7-H ), 3.69 (3H, s, CO CH ),
7
À1
1
833, 723, 665 cm ; H NMR(CDCl ) d 1.26 (3H, s, 10-
2
2
3
3
1
3
.50 (1H, s, 11-H), 7.72 (1H, s, 14-H) ppm; C NMR
CH ), 1.31 (3H, s, 4-CH ), 1.38–1.58 (2H, m, 1-Ha and
3
3
(
(
3
(
(
CDCl ) d 0.0 (Si(CH ) ), 16.8 (4-CH ), 18.6 (C-2), 21.3
6-Hb), 1.58–1.97 (5H, m, 2-H , 3-H and 6-Ha), 2.30
(1H, dd, J=12.3 and 2.7 Hz, 5-Ha), 2.44 (1H, d,
3
3 3
3
2
2
C-6), 25.0 (10-CH ), 30.0 (C-7), 36.8 (C-3), 37.9 (C-10),
8.0 (C-1), 44.4 (C-5), 47.8 (C-4), 52.4 (CO CH ), 100.6
3
J=11.8 Hz, 1-Hb), 3.02–3.07 (2H, m, 7-H ), 3.66 (3H, s,
2
3
2
0
7.09 (1H, t, J=2.8 Hz, 2 -H), 7.52 (1H, s, 14-H), 7.91
CꢁC), 101.8 (CꢁC), 115.9 (C-12), 125.5 (C-14), 131.8
CO CH ), 6.44–6.46 (1H, m, 3 -H), 7.04 (1H, s, 11-H),
0
2
3
C-11), 137.7 (C-8), 147.8 (C-13), 155.4 (C-9), 178.9

T. Fonseca et al. / Bioorg. Med. Chem. 12 (2004) 103–112
111
(
(
1H, brs, NH, exchangeable with D O) ppm; 13C NMR
References and notes
2
CDCl ) d 16.6 (4-CH ), 18.8 (C-2), 22.0 (C-6), 25.6 (10-
3
3
CH ), 30.3 (C-7), 36.8 (C-3), 37.4 (C-10), 38.8 (C-1),
1. Tagat, J. R.; Nazareno, D. V.; Puar, M. H.; McCombie,
S. W.; Ganguly, A. K. Bioorg. Med. Chem. Lett. 1994, 4,
3
0
4
1
1
5.2 (C-5), 47.8 (C-4), 51.9 (CO CH ), 102.4 (3 -CH),
2
3
0
1
101.
10.3 (C-14), 115.6 (C-11), 124.0 (2 -CH), 126.6 (C-12),
29.8 (C-8), 134.7 (C-13), 142.6 (C-9), 179.4 (CO CH )
2
3
. Mauldin, S.C.; Monroe, J. E., US Patent 6,180,815 B1,
2001, and references therein.
. Gigante, B.; Santos, C.; Silva, A. M.; Curto, M. J. M.;
Nascimento, M. S. J.; Pinto, E.; Pedro, M.; Cerqueira, F.;
Pinto, M. M.; Duarte, M. P.; Laires, A.; Rueff, J.; Gon-
2
3
+
ppm; MS m/z 311 [M] (28%), 296 (13.7%), 252 (3%),
36 (100%); HRMS: calcd for C H NO 311.18854;
20 25 2
2
found 311.18850.
c
¸
alves, J.; Pegado, M. I. and Valdeira, M. L. Bioorg. Med.
4.1.18. Methyl 12-bromo-13,14b-pyrrolyl-deisopropylde-
hydroabietate (15). Vinyl magnesium bromide (1.8 mL)
was added dropwise to a solution of methyl 12-
bromo-13-nitro-deisopropyldehydroabietate 3b (209
Chem. 2003, 11, 1631.
4. Roth, T.; Morningstar, M. L.; Boyer, P. L.; Hughes, S. H.;
Buckheit, R. W.; Michejda, C. J. J. Med. Chem. 1997, 49,
4199. Migawa, M. T.; Girardet, J. L.; Walker, J. A.;
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A. R.; Devivar, R. V.; Kucera, L. S.; Drach, J. C.;
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L.; Roberti, M.; Cermelli, C. Bioorg. Med. Chem. Lett.
3
0
mg, 0.53 mmol) in dry and freshly distilled tetra-
ꢀ
hydrofuran (2.5 mL) at À78 C and under N , with vig-
2
ꢀ
orous stirring. The reaction proceeded at À78 C for 3
h. After quenching by addition of a concentrated
ammonium chloride solution, the mixture was extracted
with ether. A concentrated ammonium chloride solution
was added to the reaction mixture, followed by extrac-
tion with ether. The organic phase was then dried with
anhydrous magnesium sulphate, filtered and evaporated
under reduced pressure. The residue (232 mg) was puri-
fied by silica column chromatography using hexane–
ether (1:1) as eluent. The bromo-indole 15 was obtained
1
999, 9, 2525. Zou, R. M.; Kawashima, E.; Freeman,
G. A.; Kolszalka, G. W.; Drach, J. C.; Townsend, L. B.
Nucleos. Nucleot. Nucl. 2000, 19, 125.
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`
Chem. 2000, 43, 3824.
. Cutignano, A.; Bifulco, G.; Bruno, I.; Casapullo, A.;
6
as a yellow precipitate (143 mg, 0.37 mmol, 70%), mp
ꢀ
328, 1260, 1174, 1131, 1114, 1095, 725, 665 cm ; H
Gomez-Paloma, L.; Riccio, R. Tetrahedron 2000, 56,
3
1
1
1
71–173 C; IR(film) n
3354, 2932, 1708, 1485, 1435,
max
743. Hayashi, H.; Ohmoto, S.; Somei, M. Heterocycles
997, 45, 1647.
À1
1
NMR(CDCl ) d 1.26 (3H, s, 10-CH ), 1.30 (3H, s, 4-
3
3
7. Fonseca, T.; Gigante, B.; Gilchrist, T. L. Tetrahedron
2001, 57, 1793.
CH ), 1.48–1.56 (2H, m, 1-Ha and 6-Hb), 1.61–1.99
3
(
5H, m, 2-H , 3-H and 6-Ha), 2.32 (1H, dd, J=12.6
8. Halbrook, N. J.; Lawrence, R. V. J. Org. Chem. 1966, 31,
4246.
2
2
and 2.1 Hz, 5-Ha), 2.33 (1H, d, J=12.6 Hz, 1-Hb), 2.91-
.06 (2H, m, 7-H ), 3.68 (3H, s, CO CH ), 6.54 (1H, dd,
3
9. Zinkel, D. F.; Han, J. S. Naval Stores Rev. 1986, 96, 11.
0. Esteves, M. A.; Narender, N.; Gigante, B.; Curto, M. J. M.;
Alvarez, M. F. Synth. Commun. 1999, 29, 275.
2
2
3
0
0
1
J=2.2 and 3.2 Hz, 3 -H), 7.21 (1H, t, J=2.8 Hz, 2 -H),
.27 (1H, s, 11-H), 8.25 (1H, brs, NH, exchangeable
7
1
3
11. Cambie, R. C.; Franich, R. A. J. Chem. Soc., Chem.
Commun 1970, 845.
with D O) ppm; C NMR(CDCl ) d 16.4 (4-CH ),
1
(
2
3
3
8.6 (C-2), 21.2 (C-6), 25.3 (10-CH ), 27.1 (C-7), 36.6
3
1
2. Tahara, A.; Akita, H.; Ohtsuka, Y. Chem. Pharm. Bull.
974, 22, 1555, and references therein.
C-3), 37.3 (C-10), 38.6 (C-1), 45.3 (C-5), 47.8 (C-4),
1.9 (CO CH ), 102.1 (3 -CH), 120.9 (C-12), 121.4
1
0
C-11), 124.2 (2 -CH), 126.2 (C-8), 128.3 (C-14), 132.2
5
(
(
2
3
13. Yamamoto, J.; Uchikawa, A.; Kawato, A.; Shibata, A.;
Muzitani, T. and Nakashima, R. J. Chem. Soc. Jpn,
Chem. Ind. Chem. (Nippon Kagaku Kaishi) 1992, 874.
14. Gilchrist, T. L. Heterocyclic Chemistry, 3rd ed; Addison
Wesley Longman: Harlow, 1997; p 284.
0
C-13), 142.4 (C-9), 179.2 (CO CH ) ppm; MS m/z
2
3
+
3
91 (26%), 389 [M] (28%), 376 (15%), 374 (15%),
16 (91%), 314 (100%). Anal. calcd for
3
C H BrNO : C 61.54, H 6.20, N 3.59; found: C
6
1
5. Eicher, T.; Hauptmann, S. The Chemistry of Heterocycles;
Thieme Organic Chemistry Monograph Series; Thieme:
Stuttgart, New York, 1995, p 174, 433.
2
0
24
2
1.69, H 6.24, N 3.32%.
1
1
6. Grimmet, M. R. Imidazole and Benzimidazole Synthesis;
Academic: London, 1997.
7. March, J. Advanced Organic Chemistry, Reactions,
Mechanisms and Structure, 4th ed.; John Wiley & Sons:
New York, 1992; p 510.
4
.2. In vitro antiviral assays
Evaluations of antiviral activity of the reported com-
pounds against different viruses, in particular cytome-
galovirus (CMV) and varicella-zoster virus (VZV) in
human embryonic lung (HEL) cells, were performed as
18. Hudlicky, M. Reductions in Organic Chemistry; John
Wiley & Sons: New York, 1984; p 26, 67.
19. Phillips, M. A. J. Chem. Soc 1931, 1143.
3
3
previously described.
2
0. Matolcsy, G.; Nadasy, M.; Andriska, V. Pesticide Chem-
´
istry; Elsevier: Amsterdam, 1988; p 388.
2
2
1. Raucher, S.; Jones, D. S. Synth. Commun. 1985, 15, 1025.
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1
974, 81, 25412.
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980.
4. Bost, R. W.; Towel, E. E. J. Am. Chem. Soc. 1948, 70, 903.
Acknowledgements
2
2
2
We thank Fundac
FCT) for a PhD Grant (BD 11539/97) (to T.F.) and A.
I. Rodrigues for 2-D NMR spectra.
˜
¸ ao para a Cieˆ ncia e a Tecnologia
(
25. Morley, J. S. J. Chem. Soc 1952, 4008.
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2
2
3
0. Bartoli, G.; Palmieri, G.; Bosco, M.; Dalpozzo, R. Tetra-
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