1,2-Dithiolan-3-ones and derivatives structurally related to leinamycin. Synthesis and biological evaluation

Article abstract of DOI:10.1016/S0014-827X(03)00134-4

Leinamycin, an antitumor antibiotic isolated from Streptomyces sp., shows a 1,2-dithiolan-3-one 1-oxide heterocycle that appears to be involved in the biological activity. Several derivatives related to 1,2-dithiolan-3-one 1-oxide have been prepared and their activity as antineoplastic agents have been investigated. The synthesized compounds did not display a significative antitumor or cytotoxic activity in vitro.

Full text of DOI:10.1016/S0014-827X(03)00134-4

Il Farmaco 58 (2003) 995ꢀ998
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www.elsevier.com/locate/farmac
1,2-Dithiolan-3-ones and derivatives structurally related to
leinamycin. Synthesis and biological evaluation
Raul Salvetti, Giovanni Martinetti 1, Daniela Ubiali, Massimo Pregnolato *,
Giuseppe Pagani
Dipartimento di Chimica Farmaceutica, Universita` degli Studi di Pavia, via Taramelli 12, I- 27100 Pavia, Italy
Received 22 November 2002; accepted 31 January 2003
Abstract
Leinamycin, an antitumor antibiotic isolated from Streptomyces sp., shows a 1,2-dithiolan-3-one 1-oxide heterocycle that appears
to be involved in the biological activity. Several derivatives related to 1,2-dithiolan-3-one 1-oxide have been prepared and their
activity as antineoplastic agents have been investigated. The synthesized compounds did not display a significative antitumor or
cytotoxic activity in vitro.
´
# 2003 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
Keywords: Leinamycin; 1,2-Dithiolan-3-ones-1-oxide; Antineoplastic activity
1. Introduction
the reaction between thiols and simplified leinamycin
models (Fig. 1, compounds 1 and 2) performed by
Gates’ group [3] revealed both a thiol-triggered DNA
damage mechanism and a thiol-independent mode of
DNA alkylation by this antibiotic. The similarities
between thiol-independent and thiol-triggered DNA
damage by leinamycin suggested that a common alky-
lating agent might be involved in both processes [4].
Particularly, the 1,2-dithiolan-3-one 1-oxide is unstable
in aqueous solution and the attack of water was proved
to initiate a cascade of chemical reactions leading to
DNA alkylation. Indeed, the hydrolysis of the unstable
1,2-dithiolan-3-one 1-oxide heterocycle seems to un-
mask leinamycin’s latent alkylating abilities.
Many antibiotics are routinely used as antineoplastic
agents. Leinamycin (Fig. 1), an antitumor antibiotic
isolated from Streptomyces sp. [1], displays potent
antitumor and cytotoxic activities and an interesting
activity against Gram-positive bacteria [2].
The antibiotic contains a number of interesting
features, including a 5-(thiazol-4-yl)penta-2,4-dieneone
system embedded in its 18-membered macrolactam and
a 1,2-ditholan-3-one 1-oxide heterocycle that is unique
to this natural product. It has been reported that, due to
its intrinsec high reactivity, the 1,2-dithiolan-3-one 1-
oxide heterocycle is likely to play a crucial role in the
events that culminate in DNA damage [3]. Leinamycin is
bioactivated by reaction with cellular thiols. Studies of
According to this, we have synthesized some 1,2-
dithiolan-3-one and 3-thione derivatives a d and their
/
ꢀ
phore in order to investigate their potential activity as
corresponding bioisosters eꢀ/h (Fig. 2) as simplified
structures of the leinamycin hypothesized pharmaco-
* Corresponding author.
E-mail address: maxp@pbl.unipv.it (M. Pregnolato).
antitumor agents. Compounds a
according to the NCI program of screening in vitro
/h have been tested
ꢀ
1
Present address: Farmaceutici Formenti,Validation & Analytical
Development, Via Di Vittorio, 2, I-21040 Origgio (VA), Italy.
against 60 different human tumor cell lines [5].
´
0014-827X/03/$ - see front matter # 2003 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
doi:10.1016/S0014-827X(03)00134-4

996
R. Salvetti et al. / Il Farmaco 58 (2003) 995ꢀ998
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2.2. Synthesis of 3H-1,2-pyridindithiol-3-thione (e) and -
3-one (f) and 3H-1,2-pyridindithiol-3-thione 1-oxide (g)
These compounds have been prepared by the same
procedure described above (Scheme 1) using 2-mercap-
tonicotinic acid (3, XꢁN) as starting material.
/
2.3. Synthesis of 3H-1,2-thiophendithiol-3-thione (h)
Fig. 1. Leinamycin and structures discussed in the text.
This compound was prepared as previously described
[6] starting from 2-chloroacrylonitrile (4) (Scheme 2) and
ethyl thioglycolate (5) which, by cyclization in presence
of sodium ethoxide, gave 3-amino-2-ethoxycarbo-
nylthiophene (6). By treatment with NaNO2/HCl and
ethylxanthogenate, 3-mercapto-2-ethoxycarbonylthio-
phene (7) was easily obtained. Cyclization of compound
7 with phosphorus pentasulfide in anhydrous pyridine
afforded 3H-1,2-thiophendithiol-3-thione (h).
Several attempts to obtain the bioisoster of 3H-1,2-
benzodithiol-3-one 1-oxide bearing a pyridine ring
instead of a phenyl were unsuccessful (data not shown).
All compounds were characterized by 1H NMR, IR and
mass spectrometry. Analytical data for known com-
pounds were in agreement with those previously re-
ported.
Fig. 2. Structures of compounds described in the text (aꢀh).
/
2. Chemistry
2.1. Synthesis of 3H-1,2-benzodithiol-3-thione (a) and -
3-one (b) and their corresponding 1-oxide derivatives (c
and d)
2.4. Antitumor activity
The intramolecular cyclization of 2,2?-dithiosalicylic
The anticancer assays were performed at the National
Cancer Institute (NCI, Bethesda, USA) according to the
program of screening in vitro against 60 different human
tumor cell lines [5,7,8]. Generally, all compounds
displayed poor or absent antineoplastic activity (data
not reported). A weak cell grow inhibition was observed
for 3H-1,2-benzodithiol-3-thione-1-oxide (c) (NSC
706184) against leukemia cell lines CCRF-CEM and
HL-60 (TB) (Fig. 3).
acid (3, XꢁCH) (Scheme 1) with phosphorus penta-
/
sulfide in anhydrous pyridine afforded 3H-1,2-benzo-
dithiol-3-thione (a) which, by oxidation with H2O2
(30%) in acetic acid, gave 3H-1,2-benzodithiol-3-thione
1-oxide (c). The oxidative desulfuration of 3H-1,2-
benzodithiol-3-thione (a) with mercuric acetate, af-
forded the 3H-1,2-benzodithiol-3-one (b) which was
then oxidized to (d) by the same procedure described
above.
Scheme 1. Reagents: 1) P4S10, anhydr. pyridine; 2) and 4) H2O2 30%, AcOH; 3) Hg(OAc)2, AcOH/CHCl3

R. Salvetti et al. / Il Farmaco 58 (2003) 995ꢀ
/998
997
Scheme 2. Reagents: 1) EtONa; 2) NaNO2/HCl, HSCSOEt/Na2CO3; 3) P4S10, anhydr. pyridine
dithiol-3-thione 1-oxide (c) as a red solid (0.280 g; yield:
86%), m.p.ꢁ
125 8C. 1H NMR: d 7.71 (d, 1H, HA), 7.55
(dd, 1H, HD), 7.32 (m, 2H, HB, HC). MS: m/z (200): 69,
76, 96, 108, 120, 140, 200, 202 (Mꢃ2). Elemental
analysis (C7H4S3O): Cꢁ42.03%; Hꢁ2.01%; Found:
Cꢁ42.29%; Hꢁ2.36%.
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/
/
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/
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3.3. H-1,2-Pyridindithiol-3-thione 1-oxide (g)
A solution of H2O2 (30%) (0.245 ml, 8.1 mmol) was
added to a stirred suspension of e (0.250 g, 1.35 mmol)
in glacial acetic acid (50 ml) at room temperature. After
14 h the suspension was filtered and the filtrate was
added to crushed ice until the complete deposition of a
brownish precipitate. The residue was filtered under
reduced pressure, washed with water and dissolved in
dichloromethane. After extraction with dichloro-
Fig. 3. Doseꢀ
HL-60 (TB).
/
response curve for leukemia cell lines CCRF-CEM and
3. Experimental
3.1. Chemistry
methane (3ꢂ100 ml), the collected organic phases
were dried over anhydrous magnesium sulfate and
evaporated sub vacuum. The residue was purified by
/
Melting points were determined on a Kofler hot-stage
1
apparatus and are uncorrected. H NMR spectra were
recorded on a Bruker ACE-300 spectrometer in deuter-
1
ochloroform. H chemical shifts (d) were reported with
chromatography (hexaneꢀ
/
ethyl acetate 1:2) to give 3H-
red
163 8C; H NMR: d
8.60 (dd, 1H, HA), 8.00 (dd, 1H, HC), 7.20 (dd, 1H, HB);
MS: m/z (201): 109, 153, 169, 185, 201, 203 (Mꢃ2).
Elemental analysis (C7H4S3ON): Cꢁ41.82%; Hꢁ
1.99%; Found: Cꢁ41.9%; Hꢁ2.00%.
1,2-pyridindithiol-3-thione 1-oxide g as a brownꢀ
/
tetramethylsilane (dꢁ
The following abbreviations are used: sꢁ
doublet; ddꢁdouble doublet; tꢁtriplet; mꢁ
/
0.00 ppm) as internal standard.
singlet; dꢁ
multiplet.
1
solid (0.054 g; yield: 20%), m.p.ꢁ
/
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/
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Thin-layer chromatography (TLC) was performed on
0.25 mm Merck silica gel (60 F254) and visualized by UV
/
/
/
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light (lꢁ
performed using silica gel 60 (60ꢀ
Elemental analyses were performed on a Carlo Erba
1106 elemental analyser and were within 90.35% of the
/
264 or 365 nm); flash chromatography was
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200 mm, Merck).
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4. Results and discussion
theoretical values. Mass spectra (EI, 70 eV) were
performed on a gc-ms Finnigan ITD instrument.
Compounds a [9], b [10], d [11], e [12], f [12], h [6] have
been prepared as previously described.
In this paper we reported the synthesis and the
biological evaluation as antitumor agents of some
compounds structurally related to leynamicin, an im-
portant antibiotic potentially useful in cancer therapy.
Particularly, as the peculiar 1,2-dithiolan-3-one 1-oxide
heterocycle contained in the complex structure of
leynamycin was recently pointed out to be directly
involved in its antitumor and citotoxic activity [3,4],
we thought to prepare some simplified derivatives
bearing this moyety. Our attention was focused onto
3.2. H-1,2-Benzodithiol-3-thione 1-oxide (c)
A solution of H2O2 (30%) (0.296 ml, 9.78 mmol) was
added to a stirred suspension of b (0.300 g, 1.63 mmol)
in glacial acetic acid (50 ml) at room temperature. After
14 h, the reaction mixture was heated at 40 8C for 2 h.
The suspension was filtered and the filtrate was added to
crushed ice. The red crystalline precipitate obtained was
washed with water and dissolved in dichloromethane.
3H-1,2-benzodithiol-3-thione and -3-one 1-oxides (cꢀd)
/
and their corresponding bioisosters 3H-1,2-pyridin-
dithiol-3-thione 1-oxide (g) and 3H-1,2-thiophen-
dithiol-3-thione (h). Another evidence seemed to
support our hypothesis; in fact, the purposed com-
pounds and their precursors, share the same mechanism
of action of leinamycin, being both bioactivated by
reaction with cellular thiols.
After extraction with dichloromethane (3ꢂ100 ml), the
/
organic phases were dried over anhydrous magnesium
sulfate, filtered and then evaporated under reduced
pressure. The residue was purified by chromatography
(hexaneꢀethyl acetate 1:1.5) to give 3H-1,2-benzo-
/

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R. Salvetti et al. / Il Farmaco 58 (2003) 995ꢀ998
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[6] M. Pregnolato, P. Borgna, M. Terreni, Synthesis of 3H-
thieno[3,2-c]-1,2-dithiole-3-thione and its reaction with n-butyla-
Unfortunately, the new substances were biologically
inactive, being the high reactivity of the 1,2-dithiolan-3-
one 1-oxide heterocycle in itself probably not sufficient
to explain the antitumor activity of leinamycin. Never-
theless, a facile oxidation procedure has been developed
affording, at least for the benzene series, S-oxide
derivatives in high yields.
mine, J. Heter. Chem. 32 (1995) 847ꢀ850.
/
[7] M.R. Grever, S.A. Schepartz, B.A. Chabner, The National
Cancer Institute: Cancer Drug Discovery and Development
Program, Semin. Oncol. 19 (1992) 622ꢀ638.
/
[8] M.R. Boyd, K.D. Paull, Some practical considerations and
applications of the National Cancer Institute in vitro anticancer
drug discovery screen, Drug Dev. Res. 34 (1995) 91ꢀ
/
109.
[9] L. Legrand, Y. Mollier, N. Lozac’h, Sulfuration des compose´s
organiques (IV) dithiole-1-2 thiones-3 comportant des substi-
tuants hydrocarbone´s ou des noyaux condense´s, Bull. Soc. Chim.
References
[1] M. Hara, I. Takahashi, M. Yoshida, K. Asano, I. Kawamoto, M.
Morimoto, H. Nakano, DC 107, a novel antitumor antibiotic
Fr. 20 (1953) 327ꢀ31.
[10] S. Palazzo, L.I. Giannola, M. Neri, Synthesis of 5H-[1,2]-
/
produced by a Streptomyces sp, J. Antibiot. 42 (1989) 333ꢀ335.
/
benzisothiazolo[2,3-a]quinazolin-5-one, J. Heter. Chem. 12
[2] M. Hara, Y. Saitoh, H. Nakano, DNA strand scission by the
novel antitumor antibiotic leinamycin, Biochemistry 29 (1990)
(1975) 1077ꢀ8.
/
[11] R.P. Iyer, L.R. Phillips, W. Egan, J.B. Regan, S.L. Beaucage, The
automated synthesis of sulfur-containing oligodeoxyribonucleo-
tides using 3H-1,2-benzodithiol-3-one 1,1-dioxide as a sulfur-
5676ꢀ
[3] K.S. Gates, Mechanisms of DNA damage by leinamycin, Chem.
Res. Toxicol. 13 (2000) 953ꢀ956.
/
5681.
/
transfer reagent, J. Org. Chem. 55 (1990) 4693ꢀ
4699.
/
[4] L. Breydo, H. Zang, K. Mitra, K.S. Gates, Thiol-independent
DNA alkylation by leinamycin, J. Am. Chem. Soc. 123 (2001)
[12] M. Pregnolato, M. Terreni, D. Ubiali, G. Pagani, P. Borgna, F.
Pastoni, F. Zampollo, 3H-[1,2]Dithiolo[3,4-b]pyridine-3-thione
and its derivatives. synthesis and antimicrobial activity, Farmaco
2060ꢀ
[5] MR. Boyd, in: V.T. De Vita, Jr, S. Hellman, S.A. Rosenberg
(Eds.), Cancer: Principles Practice of Oncology, vol. 3,
Lippincott, Philadelphia, PA, 1989, pp. 1ꢀ12.
/
2061.
&
55 (2000) 669ꢀ679.
/
/