Unprecedented synthesis of a novel amino quinone ring system via oxidative decarboxylation of quinone-based α,α-amino esters

Article abstract of DOI:10.1039/b918898c

An unusual and efficient method for the synthesis of new quinone-based amine and its derivatives from the corresponding α,α-amino ester is described. The procedure involves the quinone-based system's oxidative decarboxylation via hydride transfer throughout basic hydrolysis. This synthetic method provides, with good yields, rapid access to new potentially cytotoxic quinones.

Full text of DOI:10.1039/b918898c

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Unprecedented synthesis of a novel amino quinone ring system via oxidative
decarboxylation of quinone-based a,a-amino esters†
Pietro Campiglia,a Claudio Aquino,b Alessia Bertamino,b Nicoletta De Simone,b Marina Sala,b
Sabrina Castellano,a Marisabella Santoriello,a Paolo Grieco,b Ettore Novellinob and
Isabel M. Gomez-Monterrey*b
Received 11th September 2009, Accepted 4th November 2009
First published as an Advance Article on the web 8th December 2009
DOI: 10.1039/b918898c
An unusual and efficient method for the synthesis of new quinone-based amine and its derivatives from
the corresponding a,a-amino ester is described. The procedure involves the quinone-based system’s
oxidative decarboxylation via hydride transfer throughout basic hydrolysis. This synthetic method
provides, with good yields, rapid access to new potentially cytotoxic quinones.
Introduction
Extensive research has been devoted to the development of new
potential anticancer agents related to anthracyclines (daunoru-
bicin and doxorubicin) and anthracenediones (mitoxantrone) with
improved pharmacokinetic properties, potency or spectrum and
lower side effects.1,2 In this regard and in connection with an
ongoing research program aimed at discovering new quinone-
based derivatives as potential cytotoxic agents, we have developed
four different series of compounds containing a planar ring
system, the 3-amino-3-(ethoxycarbonyl)-2,3-dihydrothieno[2,3-
b]naphtho-4,9-dione system (1, DTNQ).3 In fact, the function-
alisation at N-3 position of this a,a-disubtituted amino ester with
different acyl-derivatives (amino acids, phosgene, chloroacetyl
chloride) gave the appropriate intermediate for the formation
of pseudodipeptide (series I)4 or spirohydantoins (series II)5 or
Fig. 1 Structures of the DTNQ derivatives.
spirodiketopiperazine (series III and IV)6 derivatives.
Some of these derivatives belonging to series II (R2
aminoalkyl), III (R1 = thioalkyl or cycloalkyl), and IV (R2 =
aminoalkyl) showed remarkable cytotoxic activity against several
human solid tumor and doxorubicin- and cis-platinum-resistant
human cell lines.5,6
aromatic quinone-based amine system, the 3-aminonaphtho[2,3-
=
b]thiophene-4,9-dione 3 (TNQ), that presents a more planar
structure respect to DTNQ system and maintains the functional
amine group.
According to these findings and with the aim to closely
examine the structure–activity relationships (SARs) of this com-
pound class we have recently reported convenient methods for
the synthesis of the aza analogues 3-amino-3-(ethoxycarbonyl)-
2,3-dihydrothieno[2,3-g and 3,2-g] quinoline-4,9-dione (2a, 2b,
DTQQs, Fig. 1) which showed interesting cytotoxic activity.7
In view of the importance of quinone based system in the
development of anticancer agents, we considered investigating
new reactions that allow a more effective exploration of chemical
space defined by this biologically active class of compounds. In
this paper we present an efficient synthesis of a new and fully
Results and discussion
The access to this quinone-based system was first planned
via direct dealkoxycarbonylation reaction by thermolysis using
NaCN, NaCl or LiCl and water in dipolar aprotic solvents such
as DMSO and DMF (Scheme 1, via A).8 Instead, when these
conditions were applied to the DTNQ (1), the formation of the
corresponding derivative 3 was not observed. (See Table 1, entries
1, 2, and 3).
A second approach, involving hydrolysis and successive decar-
boxylation of the corresponding a,a-disubstituted amino acid,
was taken in consideration (via B).9
Interestingly, during the first hydrolysis step of 1 in ethanol using
2 M NaOHaq as the base, we observed the formation of a complex
mixture from which a blue colored product was isolated in 10%
yield (Table 1, entry 4). The mass of the new compound in ES-MS
(m/z 229.02) corresponded to the same molecular formula as that
of decarboxylated derivative 3. With respect to starting DTNQ
aDepartment of Pharmaceutical Science, University of Salerno, I-84084,
Fisciano, Salerno, Italy
bDepartment of Pharmaceutical and Toxicological Chemistry, University of
Naples “Federico II”, I-80131, Naples, Italy. E-mail: imgomez@unina.it;
Fax: +39 081678630; Tel: +39 081678637
† Electronic supplementary information (ESI) available: 1H and 13C NMR
spectra of compound 3, 5, 7a and 7b, in addition spectrum of 12, as sample
of acyl derivatives. See DOI: 10.1039/b918898c
1
the H NMR spectrum in CD3OD of compound 3 showed the
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Table 1 Oxidative decarboxylation of 1, 4, and 4¢¢derivatives
Entry
Starting DTNQ
Solvent
Salt
Base
T/◦C
Time/h
Amine Yield (%)
1
2
3
4
5
6
7
8
1
1
1
1
4
4
4
4
4
4
4
4
4
4¢¢
1
4
DMSO–H2O
DMF–H2O
DMF
EtOH
EtOH
EtOH
EtOH
MeOH
dry MeOH
MeOH
MeOH–H2O
MeOH–H2O
dry pyridine
MeOH
MeOH–H2O
MeOH–H2O
NaCl
NaCl
LiCl
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
160
130
130
25
25
25
25
25
25
25
25
reflux
25
25
25
48
48
24
3
1
1
1
0.5
1
1
0.5
1
3 (-)
3 (-)
3 (-)
2 M NaOH
2 M NaOH
2 M KOH
2 M LiOH
2 M LiOH
DBU
DBU
DBU
DBU
DBU
3 (10)
5 (63)
5 (58)
5 (69)
5 (75)
5 (-)
9
10
11
12
13
14
15
16a
5 (10)
5 (82)
5 (-)
1
12
2
5 (-)
—
DBU
DBU
5 (49)
3 (15)
5 (80)
25
0.5
a The reaction was carried out under inert nitrogen atmosphere using a deoxygenated MeOH–H2O solution.
b]thiophene-4,9-dione (5). The amount of the base used was an
excess of 10 eq. in the case of alkali hydroxides or 3 eq. in the
case of the DBU. All the other reaction conditions are indicated in
Table 1. It is worth noting that the reaction conducted in complete
absence of water (entries 9 and 13) did not afford product 5, while a
partial formation of our compound (10%, entry 10) was observed
after one hour using a DBU/MeOH solution, probably due to
hydroxide generated from water traces in the reaction medium.
These results confirmed the reaction course via the not isolable
hydrolyzed intermediate 4¢. The best conditions were either 2 M
LiOH solution in methanol (entry 8) or the combination of DBU
and methanol–water (90/10%) at room temperature (entry 11). An
increase of temperature reaction, until reflux temperature, leads to
a complete degradation within 10 min (entry 12).
To gain further information on the reaction mechanism, after
complete hydrolysis using 2 M LiOHaq as base, we treated
immediately the reaction mixture with an aqueous 10% solution
of citric acid up to pH 5.11 Even if more slowly (entry 14), the
decarboxylated product was obtained, probably through the non
ionic form 4¢¢, obtained after protonation of 4¢.
Finally, the decarboxylation of DTNQ 1 with DBU and
methanol–water (90/10%) at room temperature provided only
a slight increase of yield in the formation of 3 (entry 15 versus
entry 4), confirming its previously hypothesized instability and
negative influence of the 3-amino group on reaction outcome in
basic media.
According to these findings, the formation of derivatives 3 and 5
involves a spontaneous oxidative decarboxylation of the quinone
system. To the best of our knowledge, no previous examples of
this type of reaction performed according the above described
conditions were reported.12
Moreover, the data are consistent with a double pH dependent
mechanism. In basic conditions (Scheme 2), we hypothesized two
alternative routes involving A) a concerted elimination of CO2
and hydride from the ionized form, and B) an initial step of CO2
elimination that conduce to an electronic movement through the
quinone system with subsequent loss of hydride.
Scheme 1 Decarboxylation of the DTNQ system.
disappearance of both the ethyl ester and the AB proton system
and the appearance of the corresponding aromatic H-2 proton
as single signal at 6.78 ppm. Accordingly, the 13C NMR spectra
showed the C-2 and C-3 signals at d = 118.3 and 127.2 ppm,
respectively.10
In order to avoid the possible negative influence of amino group
in the reaction course, we have performed the reaction starting
from N-Boc DTNQ derivative (4) obtaining the decarboxylated
compound 5 after 1 h in higher yield (50%, entry 5). According to
this preliminary result we propose that this unusual decarboxyla-
tion reaction goes via the hydrolyzed intermediate 4¢.
With the aim to optimize the yield and to shed light on
the reaction mechanism, we performed a study of the influence
of temperature, bases and solvents on this hydrolysis reaction
(Scheme 1, Table 1). All the reactions were conducted from the
N-Boc DTNQ derivative (4) dissolving it in methanol, ethanol,
methanol–water, or pyridine/water and adding dropwise the base
(2 M LiOHaq, 2 M NaOHaq, 2 M KOHaq, or DBU), until depletion
of 4. After the hydrolysis was complete, the dissociated form
(4¢) appeared to be unstable and evolved, spontaneously, toward
the formation of 3-(tertbutyloxy carbonyl)aminonaphtho[2,3-
As shown in Scheme 3, the non-ionized form could evolve to
decarboxylated product through a cyclic transition structure13
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Scheme 4 Formation of TQQ derivatives 7a and 7b.
derivatives (Scheme 5). Thus, treatment of Boc-DTQQ derivatives
6a and 6b with DBU in MeOH–H2O (9/1) solution for 30 min
provided the 3-(tertbutyloxycarbonyl)aminothieno[2,3-g and 3,2-
g]quinoline-4,9-dione derivatives 7a and 7b (TQQs) in 81 and
83% yield, respectively. According to these results, the electron
withdrawing effect of the quinoline nitrogen atom doesn’t seem to
play a significant role on the reaction outcome.
Scheme 2 Proposed mechanisms of DTNQ decarboxylation in basic
condition.
Scheme 3 Proposed mechanisms of decarboxylation in acidic conditions.
by essentially proton transfer from the carboxylic group to
the g-carbonyl oxygen of quinone system followed by hydride
elimination.
Scheme 5 Synthesis of N-acyl decarboxylates.
Decarboxylation reaction implicates the substrate oxidation
via hydride transfer to an electrophile14 partner; we considered
that the same DTNQ derivative could be first reduced and
stepwise reoxidized by atmospheric oxygen. As a matter of
fact Eriksson et al. have recently provided spectroscopic and
theoretical evidences that some quinone systems could be reduced
by NADH via hydride transfer.15
To further evaluate the worth of this reaction in the prepara-
tion of various quinone-containing compounds, we applied the
procedure to pseudopeptide derivatives of DTNQ (1) or DTQQ
(2a, 2b). Decarboxylation of compounds 8, 9, 10a, 10b, 11a,
and 11b, obtained by condensation of DTNQ (1) or DTQQ
(2a, 2b) with Boc-Ala-OH or Boc-Phe-OH according standard
procedures,6a afforded good yields (45–53% overall yield) of
the desired 3-(acyl)aminonaphtho[2,3-b]thiophene-4,9-dione (12,
13) or the aza analogues 3-(acyl)aminothieno[2,3-g]quinoline-4,9-
dione (14a, 15a) and the 3-(acyl)aminothieno[3,2-g]quinoline-4,9-
dione (14b, 15b).
To evaluate this option, we conducted the reaction in complete
absence of oxygen. The comparable reaction outcome (entry 16
versus 11), however, indicated that the DTNQ intermediate is
not involved in this redox reaction. In addition, the high yield
(>50%) of the final compound seems to indicate that the DTNQ
naphtoquinone core didn’t act as hydride scavenger agent.
For these reasons we hypothesized that the reaction pathway
probably includes a rapid quenching of the hydride by MeOH–
H2O medium. The reaction mechanism, suggested for the amine
3 (TNQ) and 5 formation, justifies both the speediness of
reaction and the absence of secondary compounds in solution.
After removal of the N-Boc protecting group using 20% TFA
in dichloromethane and triethylsilane as scavenger, the amine
3 TNQ was obtained in 92% yield as trifluoroacetate salt. At
this point we evaluated the potentiality of our new scaffold as a
cytotoxic agent against two cellular lines.16 This compound showed
interesting cytotoxic activity toward the MCF-7 human breast
carcinoma (IC50 = 3.2 mM) and SW 620 human colon carcinoma
cell lines (IC50 = 4.0 mM) indicating that the TNQ system could
be considered a potential starting point in discovering new and
potent cytotoxic agents.
Conclusion
In conclusion, the chemistry described here defines an efficient
protocol for the synthesis of new quinone-based amine and amide
derivatives. This unusual a,a-amino ester oxidative decarboxyla-
tion represents a new possibility of molecular diversification of our
quinone systems, providing rapid access to TNQ or TQQ moieties,
new building blocks for the development of potential antitumoral
agents. Studies that include the synthesis and cytotoxic activity of
new derivatives are actually in progress.
Experimental
General
Reagents, starting material and solvents were purchased from
commercial suppliers and used as received. Analytical TLC was
performed on plates coated with a 0.25 mm layer of silica gel
60 F254 Merck and preparative TLC on 20 ¥ 20 cm glass plates
coated with a 2 mm layer of silica gel PF254 Merck. Silica gel
60 (300–400 mesh, Merck) was used for flash chromatography.
Melting points were measured with a Ko¨fler apparatus and
With the aim to assess both the scope of this reaction and
its utility as synthetic approach to pharmacologically important
thiophenequinone heterocyclics,17 we performed the synthesis
either of new aminoquinones from the conveniently protected
DTQQ derivatives 2a and 2b (Scheme 4), or of aminoacyl
quinone adducts from some DTNQ and DTQQ pseudodipeptide
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are uncorrected. Mass spectra were obtained using an ES-MS
spectrometer. 1H and 13C NMR spectra were recorded with
a Bruker 400 spectrometer operating at 400 and 100 MHz,
respectively. Chemical shifts are reported in d values (ppm) relative
to internal Me4Si and J values are reported.
Na2SO4. The title compounds were purified by flash chromatog-
raphy (FC) using different eluent systems.
3-(tert-Butyloxycarbonyl)aminonaphtho[2,3-b]thiophene-4,9-
dione (5). FC: n-hexane: EtOAc (4 : 1 v/v). Orange solid (54 mg,
82%) mp. 201–202 ◦C. (Found: C, 61.71; H, 4.34; N, 4.68; S,
10.01%; ES-MS, 329.31. C17H15NO4S requires C, 61.99; H, 4.59;
N, 4.25; S, 9.74%; M 329.37). dH (400 MHz; CDCl3; Me4Si) 1.54
(9H, s, CH3 Boc). 7.78–7.76 (2H, m, H-6 and H-7); 8.09 (1H, s,
H-2); 8.24–8.20 (2H, m, H-5 and H-8); 9.43 (1H, s, NH); dC
(100 MHz, CDCl3; Me4Si) 28.5 (CH3 Boc), 79.2 (C Boc); 116.6
(C-2); 127.8 (C-6 and C-7); 129.6 (C-3); 133.7 (C-8a); 134.1 (C-4a);
134.7 (C-5 and C-8); 138.7 (C-3a); 142.8 (C-9a); 152.7; 177.8; and
The
3-amino-3-ethoxycarbonyl-2,3-dihydrothieno[2,3-b]
naphtho-4,9-dione system (DTNQ) (1), the 3-(N-tert-butyloxy-
aminoacyl)aminonaphtho[2,3-b]thiophene-4,9-dione (8–9), the
3-(N-tert-butyloxyaminoacyl) aminothiophene[2,3-g]quinoline-
4,9-dione (10a–11a) and 3-(N-tert-butyloxy aminoacyl)amino-
thiophene[3,2-g]quinoline-4,9-dione (10b–11b) derivatives were
synthesized according to the procedure previously described.3,7
=
181.2 (C O). FAB-MS m/z calc. for C17H15NO4S; found 329.36.
General procedure for the synthesis of N-protected quinone systems
3-(tert-Butyloxycarbonyl)aminothieno[2,3-g]quinoline-4,9-dione
(7a). FC: EtOAc: n-hexane (1 : 1 v/v). Orange solid (54 mg,
81%), m.p. 165–167 ◦C (Found: C, 58.27; H, 4.01; N, 8.17; S,
10.09%; ES-MS 330.26. C16H14N2O4S requires C, 58.17; H, 4.27;
N, 8.48; S, 9.71%; M, 330.07). dH (400 MHz; CDCl3; Me4Si) 1.48
(9 H, s, CH3 Boc), 7.72–7.73 (1 H, m, H-7), 8.21 (1H, s, H-2),
8.57–8.59 (1 H, d, J 7.6 Hz, H-8), 9.07–9.08 (1 H, d, J 4.4, H-6),
9.42 (1H, s, NH). dC (100 MHz, CDCl3) 28.5 (CH3 Boc), 80.2 (C
Boc); 110.1 (C-2), 127.0 (C-7); 129.6 (C-8a), 131.2 (C-3), 134.3
(C-8), 142.9 (C-3a) 147.2 (C-4a), 150.1 (C-9a), 154.7 (C-6), 161.1,
Synthesis of Boc-DTNQ (4), Boc-DTQQ (6a, 6b).
Di-tert-butyl dicarbonate (1.2 eq.) was added to a solution of
DTNQ (1) or DTQQ (2a or 2b) (0.2 mmol) and triethylamine
(1.2 eq.) in dichloromethane (15 mmol). After 24–48 h at
room temperature the solvent was washed with water and dried
with Na2SO4. The protected derivatives were purified by flash
chromatography (FC) using different eluent systems
3-(tert-Butyloxycarbonyl)-amino-3-ethoxycarbonyl-2,3-di hy-
drothieno[2,3-b]naphtho-4,9-dione (4). FC: n-hexane–EtOAc
(4 : 1 v/v). Orange oil (63 mg, 79%) (Found 403.04 ES-
MS. C20H21NO6S requires 403.10). dH (400 MHz; CDCl3; Me4Si)
1.26–1.30 (m, 3 H, CH3 ester), 1.37 (s, 9H, CH3 Boc), 3.0–3.82
(m, 2H, H-2), 4.28–4.30 (m, 2H, OCH2), 6.31 (s, 1H, NHBoc),
7.72–7.80 (2H, m, H-6, H-7), 8.05 (1 H, d, J 7.8, H-5), 8.10 (1H,
d, J = 7.7 Hz, H-8).
=
176.9 and 179.0 (C O).
3-(tert-Butyloxycarbonyl)aminothieno[3,2-g]quinoline-4,9-dione
(7b). FC: EtOAc: n-hexane (1 : 1 v/v). Orange solid (55 mg,
83%), m.p. 172–173 ◦C (Found: C, 58.38; H, 4.31; N, 8.01; S,
10.0%; ES-MS, 330.18. C16H14N2O4S requires C, 58.17; H, 4.27;
N, 8.48; S, 9.71%, M, 330.07). dH (400 MHz; CDCl3; Me4Si) 1.48
(s, 9 H, CH3 Boc), 7.71–7.74 (m, 1 H, H-6), 8.19 (s, 1H, H-2),
8.55–8.57 (d, J = 7.6 Hz, 1 H, H-5), 9.07–9.08 (d, J = 4.4 Hz, 1
H, H-7) 9.32 (s, 1H, NH). dC (100 MHz, CDCl3) 28.0 (CH3 Boc),
80.1 (C Boc); 111.0 (C-2), 126.9 (C-7); 129.5 (C-4a), 131.2 (C-3),
134.3 (C-5), 142.9 (C-3a) 147.2 (C-8a), 150.1 (C-9a), 154.7 (C-6),
3-(tert-Butyloxycarbonyl)-amino-3-ethoxycarbonyl-2,3-dihy-
drothienothieno[2,3-g]quinoline-4,9-dione (6a). FC: EtOAc: n-
hexane (5 : 1 v/v). Orange oil (56 mg, 70%) (Found 404.22 ES-
MS. C19H20N2O6S requires 404.11). dH (400 MHz; CDCl3; Me4Si)
1.23–1.26 (3 H, m, CH3 ester) 1.38 (9H, s, CH3 Boc); 3.82–3.85
(2H, m, CH2), 4.27–4.30 (2 H, m, OCH2) 6.31 (1 H, s, NHBoc),
7.62–7.65 (1H, m, H-7), 8.40–8.43 (1 H, d, J 9.6, H-8); 8.99–9.01
(1H, d, J 5.6, H-6).
=
161.0, 177.6 and 179.7 (C O).
3-(N -tert-Butyloxyalanyl)aminonaphtho[2,3-b]thiophene-4,9-
dione (12). FC: n-hexane: EtOAc (3 : 2 v/v). Orange solid (64 mg,
80%), m.p. 189–190 ◦C (Found:C, 60.39;H, 4.81; N, 6.92; S, 8,42%;
ES-MS, 400.25. C20H20N2O5S requires C, 59.99; H, 5.03; N, 7.00;
S, 8.01%; M, 400.11). dH (400 MHz; CDCl3; Me4Si) 1.51 (9 H, s,
CH3 Boc), 1.53 (3 H, d, b-CH3), 4.41–4.43 (1 H, m, a-CH), 5.07
(1 H, s, NH), 7.77–7.78 (2 H, m, H-6 and H-7), 8.21–8.25 (2 H, m,
H-5 and H-8), 8.47 (1H, s, H-2), 10.82 (1H, s, NH). dC (100 MHz,
CDCl3; Me4Si) 18.8 (b-CH3), 28.5 (CH3 Boc), 49.5 (a-CH), 79.8
(C Boc); 116.8 (C-2); 127.8 (C-6 and C-7); 129.6 (C-3); 133.7 (C-
8a); 134.1 (C-4a); 134.7 (C-5 and C-8); 138.7 (C-3a); 142.8 (C-9a);
3-(tert-Butyloxycarbonyl)-amino-3-ethoxycarbonyl-2,3-dihydro-
thieno[3,2-g]quinoline-4,9-dione (6b). FC: EtOAc: n-hexane
(5 : 1 v/v). Orange oil (54 mg, 67%) (Found 404.19 ES-
MS. C19H20N2O6S requires 404.11). dH (400 MHz; CDCl3; Me4Si)
1.22–1.27 (m, 3 H, CH3 ester) 1.34 (s, 9H, CH3 Boc); 3.83–3.84 (m,
2H, CH2), 4.27–4.30 (m, 2 H, OCH2) 6.26 (s, 1 H, NHBoc), 7.64–
7.67 (m, 1H, H-6), 8.35–8.37 (d, J = 8.0 Hz, 1 H, H-5); 8.98–9.99
(d, J = 2.8 Hz, 1H, H-7).
=
General procedure for the decarboxylation of quinone-based
a,a-amino esters and quinone-based pseudopeptides
153.7, 173.1, 177.8, and 181.2 (C O).
3-(N-tert-Butyloxyphenylalanyl)aminonaphtho[2,3-b] thiophene-
4,9-dione (13). FC: n-hexane–EtOAc (4 : 1). Orange solid (73 mg,
76%), m.p. 201–203 ◦C (Found:C, 65.13;H, 4.88; N, 5.51; S, 7.02%;
ES-MS, 476.34. C26H24N2O5S requires C, 65.53; H, 5.08; N, 5.88;
S, 6.73%; M, 476.14). dH (400 MHz; CDCl3; Me4Si) 1.49 (s, 9 H,
CH3 Boc), 2.95–3.05 (2 H, m, b-CH2), 4.42–4.45 (1 H, m, a-CH),
5.07 (1 H, s, NH), 7.12–7.22 (5 H, m, aryl), 7.77–7.78 (2 H, m,
H-6 and H-7), 8.21–8.25 (2 H, m, H-5 and H-8), 8.47 (1H, s, H-2),
10.82 (1H, s, NH). dC (100 MHz, CDCl3; Me4Si) 28.5 (CH3 Boc),
Synthesis of Boc-TNQ (5), Boc-TQQ (7a,7b), N-acyl-TNQ (12,
13), and N-acyl-TQQ (14a,14b, 15a, and 15b) derivatives.
DBU (0.6 mmol) was added dropwise to a solution of the
corresponding Boc-protected DTNQ (4), or DTQQ (6a or 6b),
or Boc-pseudopeptide (8, 9, 10a, 10b, 11a, or 11b) (0.2 mmol) in
methanol–water (9 : 1, 10 mL). After 30 min at room temperature
the solvents were evaporated and the reaction residues were
dissolved in chloroform and washed with water and dried with
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37.5 (b-CH2), 50.5 (a-CH), 81.2 (C Boc); 116.8 (C-2); 127.8 (C-6
and C-7); 125.9, 127.6, 128.3, 128.9 and 137.9 (aryl), 130.6 (C-
3); 133.7 (C-8a); 134.1 (C-4a); 134.7 (C-5 and C-8); 138.7 (C-3a);
Cytotoxic activity
The human breast adenocarcinoma MCF-7 and SW 620 colon
carcinoma human were obtained from American Type Culture
Collection. The cells were grown as monolayers in RPMI-1640
(Life Technologies, Inc.) containing 10% fetal bovine serum (Life
Technologies, Inc., NY) and were allowed to attach and recover
for another 24 h. Varying concentrations of drugs alone were
then added to each well, and the plates were incubated in an
atmosphere of 5% CO2 and 95% air at 37 ◦C for an additional
24 h; then the plates were washed to remove the drug and incubated
for 48 h. At the end of the treatment, cell viability was assessed
by the sulforhodamine B (SRB) assay.16 Data were expressed as
%(T/C) (OD of treated cells/OD of control cells) ¥ 100, and the
concentration of the test compound causing a 50% inhibition of
cell growth (IC50) was calculated from the dose/effect curve for
each tested compound. Every assay was performed in triplicate,
and the drug IC50 of each cell line was the average of at least three
independent experiments.
=
142.8 (C-9a); 151.9, 174.3, 176.9, and 180.1 (C O).
3-(N-tert-Butyloxylalanyl)aminothiophene[2,3-g]quinoline-4,9-
dione (14a). FC: EtOAc: n-hexane (4 : 1 v/v). Orange solid
(67 mg, 83%), m.p. 170 ◦C (dec) (Found: C, 57.05; H, 4.41; N,
10.00; S, 8.36%; ES-MS, 401.23. C19H19N3O5S requires C, 56.85;
H, 4.77; N, 10.47; S, 7.99%; M, 401.11). dH (400 MHz; CDCl3;
Me4Si) 1.58 (s, 9 H, CH3 Boc), 1.53 (3 H, d, b-CH3), 4.39–4.41 (1
H, m, a-CH), 5.07 (1 H, s, NH), 7.71–7.74 (1 H, m, H-7), 8.57–
8.59 (2 H, m, H-2 and H-8), 9.07–9.08 (1 H, m, H-6) 10.73 (1H, s,
NH). dC (100 MHz, CDCl3; Me4Si) 18.8 (b-CH3), 28.5 (CH3 Boc),
48.3 (a-CH), 81.0 (C Boc); 110.6 (C-2), 126.9 (C-7); 129.8 (C-8a),
131.0 (C-3), 133.7 (C-8), 142.6 (C-3a) 147.0 (C-4a), 149.8 (C-9a),
=
153.5 (C-6), 161.0, 173.6, 177.6, and 179.7 (C O).
3-(N-tert-Butyloxylalanyl)aminothiophene[3,2-g]quinoline-4,9-
dione (14b). FC: EtOAc: n-hexane (4 : 1 v/v). Orange solid
(65 mg, 81%), m.p. 169–170 ◦C (Found: C, 57.01; H, 4.39; N,
10.03; S, 8.39%; ES-MS, 401.30. C19H19N3O5S requires C, 56.85;
H, 4.77; N, 10.47; S, 7.99%; M, 401.11. dH (400 MHz; CDCl3;
Me4Si) 1.57–1.55 (m, 12 H, CH3 Boc and b-CH3), 4.25–4.29 (m, 1
H, a-CH), 5.05 (s, 1 H, NH), 7.72–7.75 (m, 1 H, H-7), 8.45 (s, 1H,
H-2), 8.54–8.56 (m, 1 H, H-6), 9.08–9.09 (m, 1 H, H-6) 10.71 (s,
1H, NH). dC (100 MHz, CDCl3; Me4Si) 19.8 (b-CH3), 28.7 (CH3
Boc), 50.1 (a-CH), 81.2 (C Boc); 110.8 (C-2), 126.3 (C-7); 130.0
(C-4a), 131.1 (C-3), 133.9 (C-5), 143.5 (C-3a) 146.9 (C-8a), 149.9
Acknowledgements
The ES-MS and NMR spectral data were provided by Centro
di Ricerca Interdipartimentale di Analisi Strumentale, Universita`
degli Studi di Napoli ‘Federico II’. The assistance of the staff is
gratefully appreciated.
Notes and references
1 V. T. De Vita, S. Hellman and S. A. Rosenberg, Cancer: Principles
and Practice of Oncology, ed. Lippincott, Williams and Wilkins,
Philadelphia, PA, 6nd edn, 2001.
=
(C-9a), 154.0 (C-6), 160.7, 172.8, 177.6, and 179.7 (C O).
3-(N -tert -Butyloxylphenylalanyl)aminothiophene[2, 3- g]qui-
noline-4,9-dione (15a). FC: EtOAc: n-hexane (3 : 1 v/v). Orange
solid (68 mg, 71%), m.p. 190–192 ◦C (Found: C, 62.31; H, 4.45; N,
8.39; S, 7.04%; ES-MS, 477.23. C25H23N3O5S requires C, 62.88; H,
4.85; N, 8.80; S, 6.70%; M, 477.14. dH (400 MHz; CDCl3; Me4Si)
d, 1.58 (s, 9 H, CH3 Boc), 2.95–3.00 (m, 1 H, b-CH2), 3.04–3.10
(m, 1 H, b-CH2), 4.58–4.61 (m, 1 H, a-CH), 6.01 (s, 1 H, NH),
7.22–7.31 (m, 5 H, aryl), 7.69–7.72 (m, 1 H, H-7), 8.56–8.59 (m,
2 H, H-2 and H-8), 9.05–9.07 (m, 1 H, H-6), 10.62 (s, 1H, NH).
dC (100 MHz, CDCl3; Me4Si) 27.1 (CH3 Boc), 33.6 (b-CH2), 51.1
(a-CH), 80.3 (C Boc); 111.6 (C-2), 126.1, 127.8, 128.9, and 138.2
(aryl), 126.1(C-7); 129.2 (C-8a), 130.9 (C-3), 133.9 (C-8), 141.9
(C-3a) 146.8 (C-4a), 150.1 (C-9a), 153.6 (C-6), 159.9, 173.0, 176.9,
2 J. T. Thigpen, Commun. Oncol., 2005, 2(S1), 3.
3 I. Gomez-Monterrey, P. Campiglia, O. Mazzoni, E. Novellino and M. V.
Diurno, Tetrahedron Lett., 2001, 42, 5755.
4 I. Gomez-Monterrey, P. Campiglia, P. Grieco, M. V. Diurno, A.
Bolognese, P. La Colla and E. Novellino, Bioorg. Med. Chem., 2003,
11, 3769.
5 I. Gomez-Monterrey, G. Santelli, P. Campiglia, D. Califano, F.
Falasconi, C. Pisano, L. Vesci, T. Lama, P. Grieco and E. Novellino,
J. Med. Chem., 2005, 48, 1152.
6 (a) I. Gomez-Monterrey, P. Campiglia, A. Carotenuto, D. Califano,
C. Pisano, L. Vesci, T. Lama, A. Bertamino, M. Sala, A. Mazzella di
Bosco, P. Grieco and E. Novellino, J. Med. Chem., 2007, 50, 1787;
(b) I. Gomez-Monterrey, P. Campiglia, A. Carotenuto, P. Stiuso, A.
Bertamino, M. Sala, C. Aquino, P. Grieco, S. Morello, A. Pinto, P.
Ianelli and E. Novellino, J. Med. Chem., 2008, 51, 2924.
7 (a) I. Gomez-Monterrey, P. Campiglia, T. Lama, P. La Colla, M. V.
Diurno, P. Grieco and E. Novellino, ARKIVOC, 2004, 51, 85; (b) S.
Castellano, A. Bertamino, I. Gomez-Monterrey, M. Santoriello, P.
Grieco, P. Campiglia, G. Sbardella and E. Novellino, Tetrahedron Lett.,
2008, 49, 583.
8 A. P. Krapcho, ARKIVOC, 2007, 54, and references herein.
9 Some used methods for the decarboxylation of amino acids (a) K. Dose,
Nature, 1957, 179, 734; (b) M. Hashimoto, Y. Eda, Y. Osanai, T. Iwai
and S. Aoki, Chem. Lett., 1986, 893; (c) S. Wallbaum, T. Mehler and J.
Martens, Synth. Commun., 1994, 24, 1381; (d) R. Grigg, D. Henderson
and A. J. Hudson, Tetrahedron Lett., 1989, 30, 2841; (e) R. Grigg, J.
Idle, P. McMeekin, S. Surendrakumar and D. Vipond, J. Chem. Soc.,
Perkin Trans. 1, 1988, 2703; (f) H. Nakai, Y. Sato, T. Mizoguchi, Y.
Kanaoka, P. McMeekin, S. Surendrakumar and D. Vipond, Synthesis,
1982, 141; (g) T. Kametani, S. Takano, S. Hibino and M. Takeshita,
Synthesis, 1972, 475; (h) K. Rossen, P. M. Simpson and K. Wells, Synth.
Commun., 1993, 23, 1071; (i) R. D. Bach and C. Canepa, J. Am. Chem.
Soc., 1997, 119, 11725.
=
and 179.6 (C O).
3-(N -tert -Butyloxylphenylalanyl)aminothiophene[3, 2- g]qui-
noline-4,9-dione (15b). FC: EtOAc: n-hexane (3 : 1 v/v). Orange
solid (70 mg, 73%), m.p. 188–190 ◦C (Found: C, 62.36; H, 4.38; N,
8.47; S, 7.01%; ES-MS, 477.18. C25H23N3O5S requires C, 62.88; H,
4.85; N, 8.80; S, 6.70%, M, 477.14). dH (400 MHz; CDCl3; Me4Si)
1.50 (s, 9 H, CH3 Boc), 2.92–3.01 (m, 1 H, b-CH2), 3.04–3.07
(m, 1 H, b-CH2), 4.51–4.58 (m, 1 H, a-CH), 5.94 (s, 1 H, NH),
7.26–7.37 (m, 5 H, aryl), 7.68–7.72 (m, 1 H, H-7), 8.53–8.55 (m,
2 H, H-2 and H-8), 9.02–9.03 (m, 1 H, H-6), 10.60 (s, 1H, NH).
dC (100 MHz, CDCl3; Me4Si) 25.9 (CH3 Boc), 32.3 (b-CH2), 50.9
(a-CH), 81.0 (C Boc); 111.1 (C-2), 126.1, 127.6, 127.9, 128.6, and
138.9 (aryl), 126.2 (C-7); 128.9 (C-4a), 131.1 (C-3), 134.0 (C-5),
141.3 (C-3a) 148.0 (C-8a), 149.2 (C-9a), 153.7 (C-6), 161.0, 171.8,
10 The compound 3 was obtained as a blue oil. (Found C, 62.45; H, 2.98;
N, 5.98; S, 14.09% ES-MS, 228.81. C12H7NO2S requires C, 62.87; H,
3.08; N, 6.11; O, 13.96; S, 13.99%; M, 229,02). dH (400 MHz; CDCl3;
=
177.5, and 179.9 (C O).
626 | Org. Biomol. Chem., 2010, 8, 622–627
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Me4Si) 5.1 (2H, s br, NH2), 7. 19 (1H, s, H-2); 7.88-7.92 (2H, m,
H-6 and H-7); 7.98-8.01 (2H, m, H-5 and H-8). dC (100 MHz, CDCl3;
Me4Si) 108.4 (C-2); 120.2 (C-3); 128.2 (C-5 and C-8); 129.7 (C-8a);
130.1 (C-4a); 134.7 (C-6 and C-7); 147.2 (C-3a); 149.7 (C-9a); 178.2,
Chem., 2001, 66, 7796; (e) M. A. Iglesias-Arteaga, C. G. Avila-Ortiz
and E. Guaristi, Tetrahedron Lett., 2002, 43, 5297; (f) G. Laval and
B. T. Golding, Synlett, 2003, 542.
13 R. T. Arnold, O. C. Elmer and R. M. Dodson, J. Am. Chem. Soc., 1950,
72, 4359.
14 (a) P. O’Brien, Chem.-Biol. Interact., 1991, 80, 1; (b) C. Valente, R.
Moreira, R. C. Guedes, J. Iley, M. Jaffar and K. T. Douglas, Bioorg.
Med. Chem., 2007, 15, 5340.
15 N. Scherbak, A. Strid and L. A. Eriksson, Chem. Phys. Lett., 2005,
414, 243.
16 P. Skehan, R. Storeng, D. Scudiero, A. Monks, J. McMahon, D. Vistica,
J. T. Warren, H. Bokesch, S. Kenney and M. R. Boyd, J. Natl. Cancer
Inst., 1990, 82, 1107–1112.
=
179.8 (C O).
11 After acidification, the reaction mixture was stirred for 12 h at
room temperature. The solvents were evaporated and the reaction
residue was dissolved in chloroform, washed with water, dried with
Na2SO4, evaporated, and purified by flash chromatography using
n-hexane: EtOAc (4 : 1 v/v). The compound 5 was obtained with
49% yield.
12 For oxidative decarboxylation of a-amino acids see: (a) D. Crich and L.
Quintero, Chem. Rev., 1989, 89, 1413; (b) A. Boto, R. Hernandez and E.
Suarez, Tetrahedron Lett., 2000, 41, 2495; (c) A. Boto, R. Hernandez
and E. Suarez, J. Org. Chem., 2000, 65, 4930, and references cited
therein; (d) A. Boto, R. Hernandez, Y. Leon and E. Suarez, J. Org.
17 J. A. Valderrama, C. Astudillo, R. A. Tapia, E. Prina, E. Estrabaud,
R. Mahieux and A. Fournet, Chem. Pharm. Bull., 2002, 50, 1215 and
references herein.
This journal is
The Royal Society of Chemistry 2010
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©