Preparation of new chlorambucil analogs by bis-SRN1 methodology

Article abstract of DOI:10.1081/SCC-120004080

Three series of chlorambucil analogs were prepared by an original reaction of 1-(3-chloro-2-chloromethylpropenyl)-4-nitrobenzene with various nitronate anions under electron transfer reaction conditions.

Full text of DOI:10.1081/SCC-120004080

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SYNTHETIC COMMUNICATIONS, 32(12), 1859–1865 (2002)
PREPARATION OF NEW
CHLORAMBUCIL ANALOGS BY
BIS-SRN1 METHODOLOGY
Kamel Benakli, Thierry Terme, and Patrice Vanelley
*
Laboratoire de Chimie Organique, CNRS-UMR 6517,
Faculte de Pharmacie, 27 Bd Jean Moulin,
13385 Marseille Cedex 5, France
ABSTRACT
Three series of chlorambucil analogs were prepared by an
original reaction of 1-(3-chloro-2-chloromethylpropenyl)-4-
nitrobenzene with various nitronate anions under electron
transfer reaction conditions.
Chronic lymphocytic leukaemia is the most common form of leukae-
mia in Western countries. Its chemotherapy has been based on the use of
N,N-bis(2-chloroethyl)-p-aminophenylbutyric acid (chlorambucil) for more
than 30 years.[1] Chlorambucil is a bis-alkylating agent that is known to bind
covalently to many types of cellular molecules, such as DNA, RNA, and
proteins.[2] Its mode of action has not, as yet, been entirely clarified.
Previously researchers attributed chlorambucil’s cytotoxicity solely to its
inhibitors effects on DNA synthesis.[3] More recent studies have revealed
*Current address: Department of PharmaceuticalSciences, Wayne State University,
223 Shapero Hall, Detroit, MI 48202.
yCorresponding author. E-mail: patrice.vanelle@pharmacie.univ-mrs.fr
1859
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1860
BENAKLI, TERME, AND VANELLE
that chlorambucil indirectly affects the synthesis of DNA.[4] Biochemical
studies have found that chlorambucil affects other cellular constituents as
well,[5] especially nuclear proteins.[6]
To go further into our survey of bioreductive alkylating agents in
electron transfer reactions[7] and into the development of new analogs of
chlorambucil as anticancer agents, we report herein the synthesis of
a p-nitrobenzyl bis-alkylating agent 6 and the study of its reactivity with
various nitronate anions under SRN1 reaction conditions.
The bis-chloride 6 was prepared in a four-step reaction. Firstly, we
have realized an SRN1 reaction between p-nitrobenzylcholride 1 and the
dioxane salt 2, as described previously,[8] leading to the C-alkylated deriva-
tive 3 in 90% yield. The treatment of the latter compound 3 with sodium
amide induced a nitrous acid elimination to give the ethylenic derivative 4 in
95% yield. Ring opening of compound 4 was easily effected in refluxing
methanolin the presence of an ion exchange resin (Dowex 50x8-50) to
give the corresponding diol 5 in 90% yield.[9] Finally, we obtained the
required bis-alkylating agent 6 in 85% yield by treating the diol 5 with an
excess of thionyl chloride in dimethylformamide at 0ꢀC (Scheme 1).
Scheme 1.

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PREPARATION OF NEW CHLORAMBUCIL ANALOGS
1861
Scheme 2.
The bis-chloride 6 reacted with 5 equivalents of the nitronate anion
7a–c under SRN1 reaction conditions (inert atmosphere, light catalysis) and
in phase-transfer system (40% tetrabutylammonium hydroxide in water and
toluene) for 24 h to give three products: the bis-C-alkylated product 8a–c,
the aldehyde 9a–c and the ketone 10a–c (Scheme 2).
As reported previously in the nitroimidazole series,[10] derivatives 8a–c
resulted from a classical bis-SRN1 mechanism, whereas 9a–c were formed by
a consecutive SRN1 (C-alkylation) and SN2 (O-alkylation) reaction, while
10a–c were obtained by an SRN1 reaction followed by an SN20 and a Michael
addition of nitronate anion.
In conclusion, we have demonstrated an original synthesis of new
analogs of chlorambucil by bis-SRN1 methodology. The study of the anti-
tumor activity of these compounds is under active investigation.
EXPERIMENTAL
Melting points were determined on Buchi B-540 and are uncorrected.
Elemental analyses were performed by the Centre de Microanalyses of
the University of Aix-Marseille 3. Both 1H and 13C NMR spectra were deter-
mined on Bruker ARX 200 spectrometer. The 1H chemicalshifts
were reported as part per million downfield from tetramethylsilane (Me4Si),
and the 13C chemicalshifts were referenced to the sovlent peaks: CDCl
3
(76.9 ppm). The following adsorbent was used for column chromatography:
silica gel 60 (Merck, 230–400 mesh). Thin-layer chromatography was per-
formed with silica gel Merck 60F-254 (0.25 mm layer thickness).

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1862
BENAKLI, TERME, AND VANELLE
2,2-Dimethyl-5-[nitro-(4-nitrophenyl)-methyl]-1,3-dioxane 3, 2,2-di-
methyl-5-(4-nitrobenzylidene)-1,3-dioxane 4 and 2-(4-nitrobenzylidene)pro-
pane-1,3-diol 5 were prepared as previously described.[9] Nitrocyclohexane
was commercially available, nitrocycloheptane was prepared by oxidation
of the corresponding amine with m-chloroperbenzoic acid in refluxing
1,2-dichloroethane by Gilbert and Borden procedure.[11]
1-(3-Chloro-2-chloromethylpropenyl)-4-nitrobenzene (6): Thionylchol r-
ide (5.27 ml, 63 mmol) was added dropwise to a solution of 5 (2.51 g,
12 mmol) in dimethylformamide (50 ml) in a round-bottomed flask equipped
with reflux condenser surmounted by a calcium chloride drying tube. After
stirring at 0ꢀC for 24 h, the reaction mixture was evaporated under reduced
pressure. The residue was dissolved in benzene (25 ml), washed with water
(3 Â 20 ml), dried over MgSO4 and the solvent was removed under reduced
pressure. Recrystallization from ethanol gave 2.51 g (85% yield) of 1-(3-
chloro-2-chloromethylpropenyl)-4-nitrobenzene (6)–pale yellow needles,
m.p. 65ꢀC. H NMR (CDCl3): ꢀ 4.28 (s, 2H), 4.35 (s, 2H), 6.84 (s, 1H),
1
7.52 (d, J ¼ 8.8 Hz, 2H), 8.26 (d, J ¼ 8.8 Hz, 2H). 13C NMR (CDCl3): ꢀ 39.6,
46.4, 123.9, 129.5, 131.7, 137.1, 141.5, 147.3. Anal. calcd for C10H9NO2Cl2:
C, 48.81; H, 3.69; N, 5.69; Cl, 28.81. Found: C, 48.85; H, 3.70; N, 5.75;
Cl, 28.75.
General procedure for bis-SRN1 reaction withaliphatic and cyclic nitro-
nate anions: Under nitrogen atmosphere, a solution of tetrabutylammonium
hydroxide (40% in water, 6.7 mol, 10 mmol) was treated with nitroalkane
(10 mmol) for 1 h. A solution of 1-(3-chloro-2-chloromethylpropenyl)-4-
nitrobenzene 6 (0.50 g, 2 mmol) in toluene (20 ml) was added and the mix-
ture was irradiated with a 300 W sun lamp for 24 h at room temperature
under an inert atmosphere. The organic layer was separated and the aqu-
eous layer was extracted with toluene (3 Â 10 ml). The combined organic
layers were washed twice with water (30 ml), dried over MgSO4 and
removed under reduced pressure. Purification by chromatography on
silica gel eluting with chloroform and recrystallization from isopropanol
led to the corresponding products 8a–c, 9a–c, 10a–c.
1-[4-Methyl-2-(2-methyl-2-nitropropyl)-4-nitropent-1-enyl]-4-nitrobenzene
(8a): White needles, m.p. 80ꢀC. 1H NMR (CDCl3): ꢀ 1.37 (s, 6H), 1.65 (s, 6H),
2.60 (s, 2H), 2.92 (s, 2H), 6.53 (s, 1H), 7.29 (d, J ¼ 8.5 Hz, 2H), 8.20 (d,
J ¼ 8.5 Hz, 2H). 13C NMR (CDCl3): ꢀ 26, 26.2, 40.9, 46.3, 87.6, 88.7, 123.8,
129.6, 133.9, 134.2, 143.5, 146.8. Anal. calcd for C16H21N3O6: C, 54.70; H,
6.02; N, 11.96. Found: C, 54.65; H, 6.04; N, 12.02.
2-(2-Methyl-2-nitropropyl)-3-(4-nitrophenyl)-propenal (9a): White nee-
dles, m.p. 116ꢀC. 1H NMR (CDCl3): ꢀ 1.40 (s, 6H), 3.24 (s, 2H), 7.25 (s, 1H),
7.55 (d, J ¼ 8.2 Hz, 2H), 8.25 (d, J ¼ 8.2 Hz, 2H), 9.60 (s, 1H). 13C NMR
(CDCl3): ꢀ 26, 33.5, 87.5, 124, 129.5, 139.7, 140.4, 148, 150.6, 193.7. Anal.

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PREPARATION OF NEW CHLORAMBUCIL ANALOGS
1863
calcd for C13H14N2O5: C, 56.11; H, 5.07; N, 10.07. Found: C, 56.07; H, 5.12;
N, 10.02.
4-Methyl-2-(2-methyl-2-nitropropyl)-4-nitro-1-(4-nitrophenyl)-pentan-1-one
(10a): White needles, m.p. 134ꢀC. H NMR (CDCl3): ꢀ 1.43 (s, 6H), 1.59 (s,
1
6H), 2.10 (dd, J¼ 4.3 Hz and J¼ 15.2 Hz, 2H), 2.43 (dd, J¼ 7.1 Hz and
J¼ 15.2 Hz, 2H), 3.30 (tt, J¼ 4.3 Hz and J¼ 7.1 Hz, 1H), 8.04 (d, J¼ 8.7 Hz,
2H), 8.33 (d, J¼ 8.7 Hz, 2H). 13C NMR (CDCl3): ꢀ 26, 26.8, 38.2, 43, 87.2,
124.2, 129.6, 140, 150.7, 199.8. Anal. calcd for C16H21N3O7: C, 52.31; H, 5.76;
N, 11.44. Found: C, 52.76; H, 5.95; N, 11.70.
1-Nitro-4-[3-(1-nitrocyclohexyl)-2-(1-nitrocyclohexylmethyl)-propenyl]-
benzene (8b): White needles, m.p. 112ꢀC. 1H NMR (CDCl3): ꢀ 1.20 (m, 6H),
1.30 (m, 2H), 1.45 (m, 2H), 1.60–180 (m, 6H), 2.30 (m, 2H), 2.45 (s, 2H),
2.55 (m, 2H), 2.75 (s, 2H), 6.47 (s, 1H), 7.30 (d, J ¼ 8.2 Hz, 2H), 8.20
(d, J ¼ 8.2 Hz, 2H). 13C NMR (CDCl3): ꢀ 22, 22.3, 24.2, 24.5, 34.5,
41.6, 47.3, 91, 92.3, 123.8, 129.8, 132.9, 133.7, 143.7, 146.7. Anal. calcd
for C22H29N3O6: C, 61.24; H, 6.77; N, 9.74. Found: C, 61.30; H, 6.80;
N, 9.80.
2-(1-Nitrocyclohexylmethyl)-3-(4-nitrophenyl)-propenal (9b): White
needles, m.p. 115ꢀC. 1H NMR (CDCl3): ꢀ 1.60 (m, 6H), 2.40 (m, 4H),
3.20 (s, 2H), 7.40 (s, 1H), 7.60 (d, J ¼ 8.2 Hz, 2H), 8.30 (d, J ¼
8.2 Hz, 2H), 9.70 (s, 1H). 13C NMR (CDCl3): ꢀ 22.1, 24.2, 34.2, 34.4, 90.8,
123.9, 129.5, 139.3, 140.3, 148, 150.8, 193.6. Anal. calcd for C16H18N2O5: C,
60.37; H, 5.70; N, 8.80. Found 60.35; H, 5.72; N, 8.85.
3-(1-Nitrocyclohexyl)-2-(1-nitrocyclohexylmethyl)-1-(4-nitrophenyl)-propan-
1-one (10b): White needles, m.p. 120ꢀC. 1HNMR (CDCl3): ꢀ 1.25–1.45 (m, 8H),
1.50–1.70 (m, 8H), 1.90 (dd, J¼ 4.5 Hz and J¼ 15.1 Hz, 2H), 2.25 (m, 2H), 2.30
(dd, J¼ 6.8 Hz and J¼ 15.2 Hz, 2H), 2.50 (m, 2H), 3.60 (tt, J¼ 4.5 and
J¼ 6.8 Hz, 1H), 8.05 (d, J¼ 8.2 Hz, 2H), 8.35 (d, J¼ 8.2 Hz, 2H). 13CNMR
(CDCl3): ꢀ 22.1, 24.4, 34.3, 34.9, 36.3, 42.8, 90.3, 124.1, 129.6, 139.9, 150.7,
193.2. Anal. calcd for C22H29N3O7: C, 59.05; H, 6.53; N, 9.39. Found: C,
59.07; H, 6.60; N, 9.50.
1-Nitro-4-[3-(1-nitrocycloheptyl)-2-(1-nitrocycloheptylmethyl)-propenyl]-
benzene (8c): White needles, m.p. 96ꢀC. H NMR (CDCl3): ꢀ 1.30–1.50 (m,
1
16H), 1.80 (dd, J ¼ 8.5 Hz and J ¼ 15.3 Hz, 4H), 2.40 (dd, J ¼ 8.5 Hz and
J ¼ 15.3 Hz, 4H), 2.51 (s, 2H), 2.80 (s, 2H), 6.51 (s, 1H), 8.03 (d, J ¼ 8.1 Hz,
2H), 8.32 (d, J ¼ 8.1 Hz, 2H). Anal. calcd for C24H33N3O6: C, 62.73; H, 7.24;
N, 9.14. Found: C, 62.68; H, 7.30; N, 9.20.
2-(1-Nitrocycloheptylmethyl)-3-(4-nitrophenyl)-propenal (9c): White
needles, m.p. 100ꢀC. H NMR (CDCl3): ꢀ 1.30–1.50 (m, 8H), 1.80 (dd, J ¼
1
8.5 Hz and J ¼ 15.3 Hz, 2H), 2.40 (dd, J ¼ 8.5 Hz and J ¼ 15.3 Hz, 2H), 3.20
(s, 2H), 7.40 (s, 1H), 7.50 (d, J ¼ 8.2 Hz, 2H), 8.30 (d, J ¼ 8.2 Hz, 2H), 9.61
(s, 1H). 13C NMR (CDCl3): ꢀ 22.6, 29.3, 34.3, 36.8, 94.8, 123.9, 129.4, 139.8,

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1864
BENAKLI, TERME, AND VANELLE
140.4, 148, 150.4, 193.7. Anal. calcd for C17H20N2O5: C, 61.44; H, 6.07; N,
8.43. Found: C, 61.50; H, 5.92; N, 8.52.
3-(1-Nitrocycloheptyl)-2-(1-nitrocycloheptylmethyl)-1-(4-nitrophenyl)-
propan-1-one (10c): White needles, m.p. 102ꢀC. 1H NMR (CDCl3): ꢀ
1.30–1.61 (m, 16H), 1.90 (dd, J ¼ 8.2 Hz and J ¼ 15.1 Hz, 4H), 1.95 (dd,
J ¼ 4.3 Hz and J ¼ 15.2 Hz, 2H), 2.30 (dd, J ¼ 8.2 Hz and J ¼ 15.1 Hz, 4H),
2.40 (dd, J ¼ 4.3 Hz and J ¼ 15.2 Hz, 2H), 3.50 (tt, J ¼ 4.3 Hz and J ¼ 8.2 Hz,
1H), 8.05 (d, J ¼ 8.1 Hz, 2H), 8.35 (d, J ¼ 8.1 Hz, 2H). 13C NMR (CDCl3): ꢀ
22.7, 29.5, 36.9, 37.5, 37.7, 43.8, 94.6, 124.1, 129.5, 140.2, 150.6, 199.8. Anal.
calcd for C24H33N3O7: C, 60.62; H, 6.99; N, 8.84. Found: C, 60.61; H, 7.04;
N, 8.81.
ACKNOWLEDGMENT
This work has been supported by the Centre Nationalde la Recherche
Scientifique and the Universities of Aix-Marseille. We express our thanks to
1
M. Noailly for H and 13C NMR spectra recording. T. Terme thanks the
President of the Universite de la Mediterranee for his appointment as ATER
at Universite de la Mediterranee.
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PREPARATION OF NEW CHLORAMBUCIL ANALOGS
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Received in the Netherlands June 20, 2001