2-Azetidinones: Synthesis of new bis(indolyl)butyl-β-lactams

Article abstract of DOI:10.1039/c0nj00463d

New β-lactam compounds containing a bis(indolyl)-framework were synthesized. The key step in the synthetic strategy was a nucleophilic addition of unprotected indole to a suitable butyl aldehyde anchored on the C-4 side chain of azetidinone intermediates.

Full text of DOI:10.1039/c0nj00463d

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/njc | New Journal of Chemistry
2-Azetidinones: synthesis of new bis(indolyl)butyl-b-lactams
Paola Galletti,a Arianna Quintavalla,a Caterina Ventrici,a Giuseppe Giannini,b
Walter Cabrib and Daria Giacomini*a
Received (in Gainesville, FL, USA) 15th June 2010, Accepted 5th August 2010
DOI: 10.1039/c0nj00463d
New b-lactam compounds containing a bis(indolyl)-framework were synthesized. The key step in
the synthetic strategy was a nucleophilic addition of unprotected indole to a suitable butyl
aldehyde anchored on the C-4 side chain of azetidinone intermediates. The use of an ionic liquid
as reaction medium allowed the use of a catalytic amount of Dy(OTf)3 for the nucleophilic
addition and facilitated the isolation of the product.
Introduction
b-Lactams have historically been viewed as a class of
antimicrobials, but in the last few decades their role as enzyme
inhibitors has been expanded.1 b-Lactams are well-known as
potent inhibitors of some enzymes that contain serine as the
catalytic residue, including the bacterial penicillin binding
proteins (PBPs) and Class A and Class C b-lactamases.2
b-Lactams have also been appropriately modified to
develop active site-directed and mechanism-based inhibitors
of Human Leukocyte Elastase (HLE),3 and in this field some
new monocyclic b-lactams have shown important activities as
HLE inhibitors,4 new antibiotics towards resistant bacteria,5
and as inhibitors of platelet aggregation.6
Recently, relevant studies appeared on b-lactam compounds
Fig. 1 New 3,30-bis(indolyl)azetidinones designed on the pharmaco-
as anti-tumor drugs. Some aryl-b-lactam derivatives have been
evaluated for cytotoxicity against a number of human tumour
and normal cell lines.7 In particular N-thiolated-b-lactams
were found to induce DNA damage, cell growth arrest, and
apoptosis in cultured human cancer cells, and anti proliferative
effects on human breast cancer cells of some new azetidinones
were evaluated.8 Some bicyclic b-lactams were recently
reported as inhibitors of Histone Deacetylases (HDACs), a
family of proteins involved in the pattern of acetylation
of chromatin proteins and thus in the regulation of gene
expression.9
phore model of HDAC inhibitors and synthetic strategy.
inhibition (Fig. 1), with the azetidinone as the zinc-binding
group and a bis(indolyl)methane as capping group for specific
receptor interaction, according to the finding of Giannini et al.
on the HDAC activity of bis(indolyl)-hydroxamic acids,11and
of Guo et al. on the role of bis(indolyl)methane on selective
proteasomal degradation of Class I Histone Deacetylases.12
The synthetic route for the new b-lactam compounds was
accurately designed because of the sensitivity of the azetidinone
ring towards ring-opening reaction by nucleophiles, and to
preserve, at the same time, all the NH groups free (Fig. 1).
We recently reported the synthesis of some azetidinone
derivatives which showed good affinity and specificity towards
HDAC8 and HDAC6.10 The design of those new azetidinones
was based on the pharmacophore model of HDAC inhibitors
which consists in a modular structure with a cap-group that
interacts with receptor residues at the active site entrance,
a linker group that binds in a hydrophobic channel and
positions the metal-binding group for the interactions with
the zinc atom in the active site. The azetidinone was identified
as the zinc-binding group with an alkyl- or alkenyl chain as the
linker, and a capping group typical of some known HDACs
inhibitors.
Results and discussion
Indole fragment is featured in a wide variety of pharma-
cologically and biologically active compounds, and bis(indolyl)-
alkanes are found in bioactive metabolites of terrestrial and
marine origin.13 Therefore, there is a great deal of interest in
the synthesis of this class of compounds.14 Among several
methods reported, the synthesis in the presence of Lewis acids,
Brønsted acids or montmorillonite clay K-10 to promote the
reaction of indoles with aromatic or aliphatic aldehydes and
ketones has been widely studied.13 More recently, bis(indolyl)-
methanes (3,30-BIMs) were found to be formed in acetonitrile
in the presence of catalysts such as InCl3, In(OTf)3, and I2.15
However, many of these Lewis acids are deactivated or some-
times decomposed by nitrogen containing reactants. So, the
In this paper, we report the synthesis of new azetidinones
specifically designed on the modular structure for HDAC
a Department of Chemistry ‘‘G. Ciamician’’, University of Bologna
Via Selmi 2, 40126 Bologna, Italy. E-mail: daria.giacomini@unibo.it
b R&D Sigma-Tau S.p.A., Via Pontina, km 30,400, I-00040 Pomezia,
Italy
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010 New J. Chem., 2010, 34, 2861–2866 2861

View Article Online
derivatives 2a or 2b. The preliminary sulfonylation was dictated
by the poor yields of the direct conversion of 4-acetoxy-
azetidinones to 4-pentenyl derivatives 2a,b. Retention of
stereochemistry in substitution reactions on the C-4 position
of 4-acetoxy- or 4-sulfonyloxy-azetidinones is typical, and the
3,4-trans configuration for compound 2a was confirmed by 1H
NMR analysis which showed a low value of J coupling of
H3–H4 on the azetidinone ring (2.2 Hz, see Experimental
section). The ozonolysis of the CQC bond required a
preliminary protection of the amide group and treatment with
tert-butyldimethylsilyl chloride and TEA gave in good yields
N-tert-butyldimethylsilyl-derivatives 3a and 3b. Then ozono-
lysis in dichloromethane at low temperature followed by
dimethylsulfide addition (DMS) gave aldehydes 4a and 4b.
Syntheses of bis(indolyl)methanes were already reported
starting from aromatic or aliphatic aldehydes under various
conditions.13 Green and eco-friendly conditions have also
been explored and ionic liquids, as green solvents with low
vapor pressure, have been already used in the synthesis of
3,30-BIMs.16 After a careful evaluation of the reaction conditions
reported in the literature and with the requirement to have
mild reaction conditions and reagents which preserve the quite
susceptible azetidinone intermediates, we turned our attention
to dysprosium triflate (Dy(OTf)3) as Lewis acid immobilized in
the ionic liquid 1-n-butyl-3-methyl-imidazolium tetrafluoroborate,
[bmim]BF4.17 The condensation of two equivalents of indole
with aldehydes 4a or 4b with 2% of Dy(OTf)3 was successful
(Scheme 2). The use of ionic liquid [bmim]BF4 as reaction
medium at room temperature served a double purpose, it was
strategic to use Dy(OTf)3 in a catalytic amount and to an easy
recovery of the BIM-azetidinones 5 and 8, since they were
Scheme 1 Reagents and conditions: (a) PhSO2Na, H2O, reflux;
(b) 4-pentenylMgBr, THF, ꢀ78 1C to rt; (c) tBuMe2SiCl, DMF, TEA,
0 1C to rt; (d) O3, DCM, ꢀ78 1C, then DMS ꢀ78 1C to rt.
synthesis of b-lactams containing
a bis(indolyl) moiety
presented some intrinsic difficulties. With the aim to limit to
a minimum extent the use of protecting groups, we envisaged
the possibility to insert the bis(indolyl) moiety at the end of the
synthetic pathway on an azetidinone–aldehyde obtained with
few steps from commercially available 4-acetoxy-azetidinone
intermediates (Scheme 1).
The synthetic route to aldehyde intermediates was illustrated
in Scheme 1. Starting from the commercially available
enantiopure (3S,4R)-4-acetoxy-3-[(1R)-1-(tert-butyldimethyl-
silyloxy)-ethyl]-azetidin-2-one or the racemic 4-acetoxy-
azetidinone, they were converted to sulfones 1a or 1b. Treatment
with 4-pentenylmagnesium bromide afforded the C4-alkylated
Scheme 2 Reagents and conditions: (a) indole, Dy(OTf)3 2%, [bmim]BF4; (b) TBAF, THF, 0 1C; (c) BF3ꢁOEt2, CH3CN, 0 1C.
c
2862 New J. Chem., 2010, 34, 2861–2866 This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010

View Article Online
weakly soluble in the ionic phase and were easily separated by
simple extraction with diethyl ether. The bis(indolyl)azetidinone
5 was then selectively deprotected at the b-lactam nitrogen
atom with tetrabutylammonium fluoride (TBAF) or fully
deprotected with BF3ꢁOEt2 to give enantiopure compounds 6
and 7 in 59% and 57% yield, respectively, after flash chromato-
graphy. Deprotection of the C-3 unsubstituted derivative 8 with
TBAF gave 9 in 76% yield.
As above mentioned, 3,30-BIMs showed important biological
activities, in particular they induce responses in multiple
cancer cell lines and tumors including growth inhibition,
apoptosis and antiangiogenic activities.12,18 We thus submitted
the new bis(indolyl)azetidinones 5, 6, 7, and 9 to a preliminary
evaluation. At present the derivatives did not show a cytotoxic
activity at a significant level on two tumor cell lines (HCT-116
or NB4) and showed a low potency in HDAC inhibitory
activity on in vitro tests. Further investigations on the
biological activities, especially as antibiotics of these new
molecules are in due course.
HP1100 column ZOBRAX-Eclipse XDB-C8 coupled with
MSD1100 single-quadrupole mass spectrometer, full-scan
mode from m/z 50 to m/z 2600, scan time 0.1 s in positive
ion mode, ESI spray voltage 4500 V, nitrogen gas 35 psi,
drying gas flow 11.5 mL minꢀ1, fragmentor voltage 20 V.
Elemental analysis: Perkin-Elmer 2400 Series II CHN analyser.
The [a]D25 values are given in 10ꢀ1 deg cm2 gꢀ1, determined with
a Perkin-Elmer 343 polarimeter. b-Lactams 1a, 2b, 3b, and 4b
are known, but obtained with different procedures.19
4-Benzenesulfonyl-azetidin-2-one (1b) was prepared from
commercially available 4-acetoxy-azetidin-2-one in 85% yield,
following the procedure reported in ref. 20.
(3S,4R)-4-Benzenesulfonyl-3-((1R)-1-(tert-butyldimethyl-
silanyloxy)-ethyl)-azetidin-2-one 1a. Sodium phenyl sulfinate
(189 mg, 1.15 mmol) was added to (3S,4R)-4-acetoxy-3-[(1R)-
1-(tert-butyldimethylsilyloxy)-ethyl]-azetidin-2-one (300 mg,
1.1 mmol) in water (3 mL). The reaction was refluxed for
20 min and then was extracted with dichloromethane. The
organic layer was dried over Na2SO4 and evaporated in vacuo,
to afford product 1a (400 mg, quantitative yield) as a white
solid (found C, 55.2; H, 7.5; N, 3.8%. C17H27NO4SSi requires
C, 55.25; H, 7.4; N, 3.8%); [a]2D5 ꢀ16 (c 1.1, CHCl3), nmax
(CH2Cl2)/cmꢀ1 3166, 2954, 2921, 2848, 1781, 1446, 1262, 1148,
and 727; dH (200 MHz, CDCl3) 0.01 (3 H, s, Me), 0.04 (3 H, s,
Me), 0.82 (9 H, s, tBu), 1.10 (3 H, d, J 6.6, Me), 3.42 (1 H, d,
J 2.2, 3-H), 4.25 (1 H, dq, J 2.2 and 6.2, CH(OTBS)), 4.80
(1 H, d, J 2.2, 4-H), 6.61 (1 H, br s, NH), 7.57–7.76 (3 H, m,
Ph), 7.92–7.96 (2 H, m, Ph); dC (50 MHz, CDCl3) ꢀ5.3, ꢀ4.5,
17.8, 22.2, 25.6, 63.0, 63.4, 66.7, 129.3, 129.6, 134.7, 135.3,
and 166.2.
Conclusions
In conclusion, new b-lactam compounds containing
a
bis(indolyl)methane framework were synthesized. A butyl-
aldehyde as the C-4 side chain was identified as suitable
intermediate and obtained in a concise synthesis from the
commercially available (3S,4R)-4-acetoxy-3-[(1R)-1-(tert-
butyldimethylsilyloxy)-ethyl]-azetidin-2-one or the racemic
4-acetoxy-azetidinone. The use of an ionic liquid as reaction
medium allowed the use of a catalytic amount of Dy(OTf)3 for
the nucleophilic addition of indole to the azetidinone-aldehydes
4a,b and greatly facilitated the recovery of the bis(indolyl)butyl-
azetidinones. Simple management of protecting groups allows
the access to new b-lactam-bis(indolyl)methane hybrids. The
novelty of these molecules obtained through the combination
of two pharmacophores in one frame, azetidinone and 3,30-
BIMs, deserves further investigations and tests on biological
activities of these new molecules are in progress.
(3S,4R)-3-((1R)-1-(tert-Butyldimethylsilanyloxy)-ethyl)-4-pent-
4-enyl-azetidin-2-one 2a. 4-Pentenylmagnesium bromide,
freshly prepared from Mg (300 mg, 12.3 mmol) and 4-pentenyl-
bromide (2.3 g, 15.4 mmol) in THF (12 mL), was added drop
by drop to a solution of 1a (1.9 g, 5.14 mmol) in THF (40 mL)
at ꢀ78 1C. The mixture was stirred at 0 1C for 5 h, NH4Cl sat.
sol. was added, the aqueous layer was extracted with Et2O, the
organic layer was dried over Na2SO4 and concentrated. The
residue was purified by flash-chromatography (cyclohexane/
ethyl acetate, 80 : 20) to afford product 2a (671 mg, 44%) as a
colorless oil (found C, 64.7; H, 10.6; N, 4.7%. C16H31NO2Si
requires C, 64.6; H, 10.5; N, 4.7%); nmax (CH2Cl2)/cmꢀ1 3161,
2922, 1756, 1704, and 1586; dH (200 MHz, CDCl3) 0.07 (6 H, s,
2 ꢂ Me), 0.88 (9 H, s, tBu), 1.24 (3 H, d, J 6.2, Me), 1.36–1.71
(4 H, m, 2 ꢂ CH2), 2.05–2.16 (2 H, m, CH2), 2.72 (1 H, ddd,
J 1.2, 2.2 and 5.2, 3-H), 3.63 (1 H, dt, J 2.2 and 6.6, 4-H), 4.16
(1 H, dq, J 5.2 and 6.2, CH(OTBS)), 4.96–5.07 (2 H, m,
CHQCH2), 5.68–5.90 (1 H, m, CHQCH2), 6.00 (1 H, br s,
1-NH); dC (50 MHz, CDCl3) ꢀ5.0, ꢀ4.3, 17.9, 22.7, 25.7, 25.8,
33.5, 34.5, 51.2, 64.3, 65.6, 115.0, 138.0, and 169.0; HPLC-MS
(ESI) Rt = 12.70 min, m/z 298.1 [M + H]+, 320.1
[M + Na]+, 595.5 [2M + H]+, 617.3 [2M + Na]+.
Experimental
General remarks
All reactions were performed under an inert atmosphere (N2).
Commercial reagents were used as received without additional
purification. Anhydrous solvents (CH3CN, CH2Cl2, THF,
1
DMF) were obtained commercially. H and 13C NMR values
were recorded on a Varian INOVA 400, INOVA 300, or a
GEMINI 200 instrument with a 5 mm probe. All chemical
shifts have been quoted relative to deuterated solvent signals,
d in ppm and J in Hz. FT-IR: Nicolet 205, measured as films
between NaCl plates and wavenumbers reported in cmꢀ1
.
TLC: Merck 60 F254. Column chromatography: Merck silica
gel 200–300 mesh. GC-MS: Agilent Technologies, column
HP5 5% Ph-Me Silicon. HPLC: Agilent Technologies
HP1100, column ZOBRAX-Eclipse XDB-C8 Agilent
Technologies, mobile phase: H2O/CH3CN, gradient from
30% to 80% of CH3CN in 8 min, 80% of CH3CN until
25 min, 0.4 mL minꢀ1. HPLC-MS: Agilent Technologies
4-Pent-4-enyl-azetidin-2-one 2b. 4-Pentenyl magnesium
bromide, freshly prepared from Mg (0.042 g, 1.74 mmol)
and 4-pentenylbromide (0.277 g, 1.86 mmol) in THF (5 mL),
was added drop by drop to a solution of 1b (0.131 g,
0.62 mmol) in THF (3 mL) at ꢀ78 1C. The mixture was stirred
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010 New J. Chem., 2010, 34, 2861–2866 2863

View Article Online
at 0 1C for 5 h, NH4Cl sat. sol. was added, the aqueous layer
was extracted with Et2O, the organic layer was dried over
Na2SO4 and concentrated. The residue was purified by flash-
chromatography (cyclohexane/ethyl acetate, 80 : 20) to afford
product 2b (57 mg, 66%) as a colorless oil. Characterization
resulted in agreement with the reported data.19
and 7.0, CHCH2), 2.75 (1 H, dd, J 2.6 and 6.2, 3-H), 3.50 (1 H,
dt, J 2.6 and 5.6 4-H), 4.10 (1 H, dq, J 5.6 and 6.2,
CH(OTBS)), 9.78 (1 H, t, J 1.0, CHO). dC (50 MHz, CDCl3)
ꢀ5.9, ꢀ5.1, ꢀ4.6, ꢀ4.4, 17.9, 18.1, 18.6, 23.0, 25.8, 26.2, 35.3,
43.6, 52.7, 64.7, 66.4, 173.1, and 198.0; GC-MS Rt = 22.3 min,
m/z: 284 (2), 242 (90), 224 (50), 75 (100).
(3S,4R)-1-(tert-Butyldimethylsilanyl)-3-((1R)-1-(tert-butyl-
dimethylsilanyloxy)-ethyl)-4-pent-4-enyl-azetidin-2-one 3a. Et3N
(0.657 mL, 4.72 mmol) and tBuMe2SiCl (283 mg, 1.9 mmol)
were added to a solution of 2a (470 mg, 1.57 mmol) in DMF
(10 mL) at 0 1C and the mixture was stirred overnight at room
temperature. To the reaction mixture was added sat. aq.
NaHCO3, the aqueous layer was extracted with Et2O, the
organic layer was washed with H2O and brine, dried over
Na2SO4 and concentrated. The residue was purified by flash-
chromatography (cyclohexane/ethyl acetate, 90 : 10) to afford 3a
(600 mg, 93%) the product as a colorless oil (found C, 64.4; H,
11.0; N, 3.4%. C22H45NO2Si2 requires C, 64.2; H, 11.0; N,
3.4%); [a]2D5 ꢀ41 (c 1.3, CHCl3); nmax (CH2Cl2)/cmꢀ1 2928,
2860, 1740, 1642, 1471, and 1258; dH (200 MHz, CDCl3) 0.06
(3 H, s, Me), 0.08 (3 H, s, Me), 0.21 (3 H, s, Me), 0.23 (3 H, s,
Me), 0.89 (9 H, s, tBu), 0.96 (9 H, s, tBu), 1.22 (3 H, d, J 6.2, Me),
1.36–1.51 (3 H, m, CH2CHH), 1.76–1.90 (1 H, m, CH2CHH),
2.04–2.14 (2 H, m, CH2), 2.71 (1 H, dd, J 2.6 and 5.8, 3-H),
3.46–3.53 (1 H, m, 4-H), 4.10 (1 H, quintet, J 6.2, CH(OTBS)),
4.90–5.07 (2 H, m, CHQCH2), 5.68–5.90 (1 H, m, CHQCH2);
dH (75 MHz, CDCl3) ꢀ5.8, ꢀ5.1, ꢀ4.6, ꢀ4.4, 17.9, 18.2, 23.0,
25.3, 25.9, 26.3, 33.7, 35.4, 52.8, 64.6, 66.2, 114.9, 138.1, 173.5;
HPLC-MS (ESI) Rt = 9.9 min, m/z: 412 [M + H]+.
4-(1-(tert-Butyldimethylsilanyl)-4-oxo-azetidin-2-yl)-butanal
4b. A solution of 3b (138 mg, 0.54 mmol) in CH2Cl2 (20 mL)
was cooled to ꢀ78 1C and treated with a stream of O3 at
ꢀ78 1C until the reagent completely disappeared. The reaction
mixture was treated with a stream of O2 at ꢀ78 1C to remove
the excess of O3. To the solution was added Me2S (2.5 mL) at
ꢀ78 1C, the mixture was allowed to stir at room temperature
overnight and then concentrated. The residue was purified by
flash-chromatography (cyclohexane/ethyl acetate, 80 : 20)
to afford product 4b (70 mg, 51%) as a pale yellow oil.
Characterization resulted in agreement with the reported
data.19
4-(3S,4R)-(4,4-Bis-(1H-indol-3-yl)-butyl)-1-(tert-butyldimethyl-
silanyl)-3-((1R)-1-(tert-butyldimethylsilanyloxy)-ethyl)-azetidin-
2-one 5. Indole (63 mg, 0.54 mmol) and aldehyde 4a (113 mg,
0.27 mmol) were added to a solution of Dy(OTf)3 (3.3 mg,
2% mol) in [bmim]BF4 (0.5 mL). The mixture was stirred
overnight at room temperature, extracted with Et2O and
concentrated. The residue was purified by flash-chromato-
graphy (cyclohexane/ethyl acetate, 70 : 30) to afford product
5 (100 mg, 59%) as a pale brown oil (found C, 70.6; H, 8.9; N,
6.75%; C37H55N3O2Si2 requires C, 70.5; H, 8.8; N, 6.7%);
[a]2D5 ꢀ29 (c 0.9, CHCl3); nmax (CH2Cl2)/cmꢀ1 3414, 3330,
2919, 2854, 1734, 1462, and 1269; dH (200 MHz, CDCl3)
ꢀ0.01 (3 H, s, Me), 0.03 (3 H, s, Me), 0.14 (3 H, s, Me),
0.18 (3 H, s, Me), 0.84 (9 H, s, tBu), 0.92 (9 H, s, tBu), 1.03 (3
H, d, J 6.2, Me), 1.35–1.90 (4 H, m, 2 ꢂ CH2), 2.20–2.36 (2 H,
m, CHCH2), 2.60 (1 H, dd, J 2.6 and 4.8, 3-H), 3.42–3.52 (1 H,
m, 4-H), 4.04 (1 H, dt, J 5.4 and 6.2, CH(OTBS)), 4.48 (1 H, t,
J 7.4, CH(ind)2), 6.99–7.07 (2H, m, arom), 7.03 (2 H, s, CH
arom ind), 7.03 (2 H, t, J 7.4, arom), 7.34 (2 H, d, J 7.2, arom),
7.58 (2 H, d, J 7.5, arom), 7.94 (2 H, br s, 2 ꢂ NH); dC
(75 MHz, CDCl3) ꢀ5.6, ꢀ4.8, ꢀ4.3, ꢀ4.2, 18.2, 18.4, 23.1,
25.0, 26.2, 26.6, 34.3, 36.1, 36.3, 52.7, 64.6, 66.0, 111.4, 119.3,
119.8, 119.9, 120.2, 121.6, 121.7, 122.0, 127.2, 127.3, 136.9,
and 174.0; HPLC-MS (ESI) Rt = 27.7 min, m/z 630
[M + H]+, 652 [M + Na]+.
1-(tert-Butyldimethylsilanyl)-4-pent-4-enyl-azetidin-2-one 3b.
Et3N (0.31 mL, 2.25 mmol) and tBuMe2SiCl (148 mg, 1 mmol)
were added to a solution of 2b (104 mg, 0.75 mmol) in DMF
(6 mL) at 0 1C and the mixture was stirred overnight at room
temperature. To the reaction mixture was added sat. aq.
NaHCO3, the aqueous layer was extracted with Et2O, the
organic layer was washed with H2O and brine, dried over
Na2SO4 and concentrated. The residue was purified by
flash-chromatography (cyclohexane/ethyl acetate, 90 : 10) to
afford product 3b (138 mg, 73%) as a colorless oil. Character-
ization resulted in agreement with the reported data.19
4-((2R,3S)-1-(tert-Butyldimethylsilanyl)-3-((1R)-1-(tert-butyl-
dimethylsilanyloxy)-ethyl)-4-oxoazetidin-2-yl)-butanal 4a.
A
solution of 3a (301 mg, 2 mmol) in CH2Cl2 (40 mL) was
cooled to ꢀ78 1C and treated with a stream of O3 at ꢀ78 1C
until the reagent completely disappeared. The reaction mixture
was treated with a stream of O2 at ꢀ78 1C to remove an excess
amount of O3. To the solution was added Me2S (3 mL) at
ꢀ78 1C, the mixture was allowed to stir at room temperature
overnight and then concentrated. The residue was purified by
flash-chromatography (cyclohexane/ethyl acetate, 80 : 20) to
afford product 4a (117 mg, 39%) as a pale yellow oil (found C,
60.8; H, 10.5; N, 3.3%; C21H43NO3Si2 requires C, 61.0; H,
10.5; N, 3.4%); [a]2D5 ꢀ42 (c 1, CHCl3); nmax (CH2Cl2)/cmꢀ1
2954, 2926, 2855, 1742, 1475, and 1258; dH (200 MHz, CDCl3)
0.05 (3 H, s, Me), 0.08 (3 H, s, Me), 0.20 (3 H, s, Me), 0.22
(3 H, s, Me), 0.88 (9 H, s, tBu), 0.94 (9 H, s, tBu), 1.23 (3 H, d,
J 6.2, Me), 1.38–1.90 (4 H, m, 2 ꢂ CH2), 2.50 (2 H, dt, J 1.0
4-(3S,4R)-(4,4-Bis-(1H-indol-3-yl)-butyl)-3-((1R)-1-(tert-
butyldimethylsilanyloxy)-ethyl)-azetidin-2-one 6. TBAF (1 M
in THF, 0.185 mL, 0.185 mmol) was added to a solution of 5
(35 mg, 0.056 mmol) in THF (2 mL) at 0 1C. The mixture was
stirred overnight at 0 1C. After adding phosphate buffer
(0.1 M, pH 6.5) to the mixture at 0 1C, the aqueous mixture
was extracted with EtOAc. The organic layer was dried over
Na2SO4 and evaporated in vacuo. The residue was purified by
flash-chromatography (cyclohexane/ethyl acetate, 60 : 40) to
afford product 6 (17 mg, 59%) as a pale yellow oil (found C,
72.2; H, 8.1; N, 8.1%; C31H41N3O2Si requires C, 72.2; H, 8.0;
N, 8.15%); [a]D25 ꢀ2 (c 1.0, CHCl3); nmax (CH2Cl2)/cmꢀ1 3421,
3300, 3055, 2929, 2852, 1740, 1617, 1455, 1255; dH (200 MHz,
CDCl3) 0.05 (3 H, s), 0.07 (3 H, s, Me), 0.87 (9 H, s, tBu), 1.14
c
2864 New J. Chem., 2010, 34, 2861–2866 This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010

View Article Online
(3 H, d, J 6.6, Me), 1.40–1.76 (4 H, m, 2 ꢂ CH2), 2.24–2.36
(2 H, m, CHCH2), 2.67 (1 H, dd, J 1.6 and 4.8, 3-H), 3.60 (1 H,
dt, J 4.8 and 6.6, 4-H), 4.13 (1 H, quintet, J 6.6, CH(OTBS)),
4.51 (1 H, t, J 7.4, CH(ind)2), 5.68 (1 H, br s, 1-NH), 7.00–7.21
(6 H, m, arom), 7.37 (2 H, d, J 8.0, arom), 7.61 (2 H, d, J 8.2,
arom), 7.98 (2 H, br s, 2 ꢂ NH); dC (50 MHz, CDCl3) ꢀ4.9,
ꢀ4.2, 18.0, 22.7, 25.4, 25.9, 34.1, 35.3, 35.6, 51.1, 64.4, 65.5,
111.3, 119.2, 119.6, 120.0, 120.1, 121.4, 121.5, 122.0, 127.1,
127.2, 136.7, and 169.0; HPLC-MS (ESI) Rt = 12.83 min, m/z:
538 [M + Na]+.
was extracted with EtOAc. The organic layer was dried over
Na2SO4 and evaporated in vacuo. The residue was purified by
flash-chromatography (cyclohexane/ethyl acetate, 60 : 40) to
afford product 9 (30 mg, 76%) as a pale yellow oil (found C,
77.4; H, 6.5; N, 11.7%. C23H23N3O requires C, 77.3; H, 6.5; N,
11.8%); nmax (CH2Cl2)/cmꢀ1 3406, 2927, 2855, 1736, 1592,
and 1459; dH (200 MHz, CDCl3) 1.34–1.73 (4 H, m, 2 ꢂ CH2),
2.18–2.23 (2 H, m, CH2CH), 2.49 (1 H, d, J 14.8, 3-HH), 2.98
(1 H, ddd, J 1.8 and 4.6 and 14.8, 3-HH), 3.48–3.57 (1 H, m,
4-H), 4.48 (1 H, t, J 7.8, CH(ind)2), 5.75 (1 H, br s, 1-NH),
6.98–7.62 (10 H, m, arom), 7.99 (2 H, br s, 2 ꢂ NH); dC
(75 MHz, CDCl3) 24.9, 33.9, 35.2, 35.3, 43.4, 48.1, 111.2,
119.0, 119.4, 119.8, 121.4, 121.8, 126.9, 136.6, and 168.2;
HPLC-MS (ESI) Rt = 8.0 min, m/z 380 [M + Na]+, 737
[2M + Na]+.
4-(3S,4R)-(4,4-Bis-(1H-indol-3-yl)-butyl)-3-((1R)-1-hydroxy-
ethyl)-azetidin-2-one 7. BF3ꢁOEt2 (8.9 mL, 0.07 mmol) was
added to a solution of 5 (22 mg, 0.035 mmol) in CH3CN
(1 mL) at 0 1C. The mixture was allowed to stir at 0 1C for
3 days. The reaction was quenched by addition of ice-cold
phosphate buffer (0.1 M, pH 6) and ethyl acetate. The organic
layer was dried over Na2SO4 and concentrated. The residue
was purified by flash-chromatography (cyclohexane/ethyl
acetate, 20 : 80) to afford product 7 (8 mg, 57%) as a white
solid (found C, 74.9; H, 6.85; N, 10.4%. C25H27N3O2 requires
C, 74.8; H, 6.8; N, 10.5%); [a]2D5 +12 (c 0.5, CHCl3). nmax
(CH2Cl2)/cmꢀ1 3346, 2921, 1736, 1703, and 1458. dH
(200 MHz, CDCl3) 1.25 (3 H, d, J 6.2, Me), 1.26–1.78 (4 H,
m, 2 ꢂ CH2), 2.20–2.34 (2 H, m, CHCH2), 2.74–2.78 (1 H, m,
3-H), 3.56–3.64 (1 H, m, 4-H), 4.10–4.20 (1 H, m, CH(OH)),
4.41 (1 H, t, J = 7.6, CH(ind)2), 5.81 (1 H, br s, 1-NH), 6.50
(1 H, s, OH), 7.01–7.61 (10 H, m, arom), 7.86 (1 H, br s, NH),
8.14 (1 H, br s, NH). dC (100 MHz, CDCl3) 25.6, 29.4, 34.1,
34.9, 36.4, 51.5, 63.8, 65.2, 111.3, 119.4, 119.8, 121.1, 121.9,
122.5, 126.5, 128.6, 135.8, 136.6, and 168.4. HPLC-MS (ESI):
Rt = 8.0 min, m/z: 402 [M + H]+, 424 [M + Na]+, 440
[M + K]+, 825 [2M + Na]+.
Acknowledgements
We would like to thank MIUR, University of Bologna,
Fondazione del Monte di Bologna e Ravenna, and Sigma-
Tau Industrie Farmaceutiche Riunite S.p.A. for biological
testing.
References
1 M. I. Konaklieva, Curr. Med. Chem., 2002, 1, 215–238.
2 J. C. Powers, J. L. Asgian, O. D. Ekici and K. E. James, Chem.
Rev., 2002, 102, 4639–4750.
3 B. Xing, J. Rao and R. Liu, Mini-Rev. Med. Chem., 2008, 8,
455–471; S. Gerard, M. Galleni, G. Dive and J. Marchand-
Brynaert, Bioorg. Med. Chem., 2004, 12, 129–138.
4 D. Giacomini, A. Quintavalla, F. Calabrese, C. Giacometti,
E. Brunetta, F. Piazza, C. Agostini and S. Garbisa,
J. Pharmacol. Exp. Ther., 2006, 316, 539–546; G. Cainelli,
P. Galletti, S. Garbisa, D. Giacomini, L. Sartor and
A. Quintavalla, Bioorg. Med. Chem., 2005, 13, 6120–6132;
G. Cainelli, D. Giacomini, P. Galletti and A. Quintavalla, Eur.
J. Org. Chem., 2003, 1765–1774.
5 F. Broccolo, G. Cainelli, G. Caltabiano, C. E. A. Cocuzza,
C. G. Fortuna, P. Galletti, D. Giacomini, G. Musumarra,
R. Musumeci and A. Quintavalla, J. Med. Chem., 2006, 49,
2804–2811.
6 M. Pavanetto, A. Zarpellon, D. Giacomini, P. Galletti,
A. Quintavalla, G. Cainelli, A. Folda, G. Scutari and R. Deana,
Platelets, 2007, 18, 357–364.
4-(4,4-Bis-(1H-indol-3-yl)-pentyl)-1-(tert-butyldimethylsilanyl)-
azetidin-2-one 8. Indole (63 mg, 0.54 mmol) and aldehyde 4b
(70 mg, 0.27 mmol) were added to a solution of Dy(OTf)3
(3.3 mg, 2% mol) in [bmim]BF4 (0.5 mL). The mixture
was stirred overnight at room temperature, extracted with
Et2O and concentrated. The residue was purified by flash-
chromatography (cyclohexane/ethyl acetate, 70 : 30) to afford
product 8 (53 mg, 42%) as a pale brown oil (found C, 73.7; H,
7.9; N, 8.8%. C29H37N3OSi requires C, 73.8; H, 7.9; N, 8.9%);
nmax (CH2Cl2)/cmꢀ1 3406, 3323, 2926, 2848, 1720, and 1464;
7 B. K. Banik, F. F. Becker and I. Banik, Bioorg. Med. Chem., 2004,
12, 2523–2528.
8 D. Chen, S. C. Falsetti, M. Frezza, V. Milacic, A. Kazi, Q. C. Cui,
T. E. Long, E. Turos and Q. P. Dou, Cancer Lett., 2008, 268,
63–69.
d
H (300 MHz, CDCl3) 0.20 (6 H, s, 2 ꢂ Me), 0.95 (9 H, s, tBu),
1.30–1.50 (3 H, m, CH2CHH), 1.80–1.95 (1 H, m, CH2CHH),
2.19–2.32 (2 H, m, CH2CH), 2.49 (1 H, dd, J 2.7 and 15.0,
3-HH), 3.00 (1 H, dd, J 5.4 and 15.0, 3-HH), 3.40–3.50 (1 H,
m, 4-H), 4.48 (1 H, t, J 7.5, CH2CH), 7.00–7.62 (10 H, m,
arom), 8.02 (2 H, br s, 2 ꢂ NH); dC (75 MHz, CDCl3) ꢀ5.8,
ꢀ5.3, 18.3, 24.3, 26.2, 34.1, 35.5, 36.3, 43.7, 49.4, 111.1, 119.1,
119.5, 120.0, 121.3, 121.4, 121.9, 127.0, 136.6, and 170.1;
HPLC-MS (ESI) Rt = 12.3 min, m/z 489 [M + H2O]+, 494
[M + Na]+, 961 [2MH + H2O]+.
9 S. Oha and J.-C. Jung, Z. Naturforsch., B: J. Chem. Sci., 2007, 62b,
1459–1464.
10 P. Galletti, A. Quintavalla, C. Ventrici, G. Giannini, W.
Cabri, S. Penco, G. Gallo, S. Vincenti and D. Giacomini,
ChemMedChem, 2009, 4, 1991–2001.
11 G. Giannini, M. Marzi, M. Di Marzo, G. Battistuzzi, R. Pezzi,
T. Brunetti, W. Cabri, L. Vesci and C. Pisano, Bioorg. Med. Chem.
Lett., 2009, 19, 2840–2843.
12 Y. Li, X. Li and B. Guo, Cancer Res., 2010, 70, 646–654.
13 M. Shiri, M. A. Zolfigol, H. G. Kruger and Z. Tanbakouchian,
Chem. Rev., 2010, 110, 2250–2293 and references cited therein;
V. Sharma, P. Kumar and D. Pathakand, J. Heterocycl. Chem.,
2010, 47, 491–502.
4-(4,4-Bis-(1H-indol-3-yl)-pentyl)-azetidin-2-one 9. TBAF
(1 M in THF, 0.250 mL, 0.25 mmol) was added to a solution
of 8 (53 mg, 0.11 mmol) in THF (1.5 mL) at 0 1C. The mixture
was stirred overnight at 0 1C. After adding phosphate buffer
(0.1 M, pH 6.5) to the mixture at 0 1C, the aqueous mixture
14 M. Bandini and A. Eichholzer, Angew. Chem., Int. Ed., 2009, 48,
9608–9644.
15 R. Nagarajan and P. T. Perumal, Tetrahedron, 2002, 58,
1229–1232; B. P. Bandgar and K. A. Shaikh, Tetrahedron Lett.,
2003, 44, 1959–1961.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010 New J. Chem., 2010, 34, 2861–2866 2865

View Article Online
16 J. S. Yadav, B. V. S. Reddy and S. Sunitha, Adv. Synth. Catal.,
2003, 345, 349–352.
17 J.S. Yadav, B. V. S. Reddy and J. S. S. Reddy, J. Chem. Soc.,
Perkin Trans. 1, 2002, 2390–2394; K. Binnemans, Chem. Rev.,
2007, 107, 2592–2614.
19 A. G. M. Barrett, G. G. Graboski and M. A. Russell,
J. Org. Chem., 1985, 50, 2603–2605; A. G. M. Barrett,
G. G. Graboski, M. Sabat and S. J. Taylor, J. Org. Chem.,
1987, 52, 4693–4702; M. Shiozaki, N. Ishida, T. Hiraoka and
H. Yanagisawa, Tetrahedron Lett., 1981, 22, 5205–5208.
20 S. Meiries and R. Marquez, J. Org. Chem., 2008, 73,
5015–5021.
18 S. Safe, S. Papineni and S. Chintharlapalli, Cancer Lett., 2008, 269,
326–338.
c
2866 New J. Chem., 2010, 34, 2861–2866 This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010