Total synthesis of (±)-17-norcamptothecin, a novel E-ring modified camptothecin

Article abstract of DOI:10.1016/j.tet.2010.06.003

The first total synthesis of (±)-17-norcamptothecin, a novel camptothecin analog possessing an α-hydroxy-γ-lactone E-ring, has been accomplished by using a short and flexible route. The stability of this new compound in aqueous medium has been evaluated t

Full text of DOI:10.1016/j.tet.2010.06.003

Tetrahedron 66 (2010) 7227e7231
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Total synthesis of (ꢀ)-17-norcamptothecin, a novel E-ring modified camptothecin
Marie Devert, Cyrille Sabot, Pascale Giboreau, Jean-François Constant, Andrew E. Greene,
*
Alice Kanazawa
Département de Chimie Moléculaire, UMR-5250, ICMG FR-2607, Université Joseph Fourier-CNRS, BP 53, 38041 Grenoble Cedex 09, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 April 2010
Received in revised form 28 May 2010
Accepted 1 June 2010
Available online 23 June 2010
The first total synthesis of (ꢀ)-17-norcamptothecin, a novel camptothecin analog possessing an
a-hy-
droxy-g-lactone E-ring, has been accomplished by using a short and flexible route. The stability of this
new compound in aqueous medium has been evaluated through fluorescence spectroscopy.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Total synthesis
Camptothecin analog
17-Norcamptothecin
1. Introduction
A major problem with the C-20 hydroxy d-lactone derivatives of
camptothecin, however, is that they are prone to rapid E-ring-
opening in the bloodstream with attendant loss of therapeutic
efficacy.7 Early attempts to modify the E-ring motif produced de-
creased bioactivity,8e12 which led to the belief that the C-20 hy-
Since the isolation of 20(S)-camptothecin (1, Fig. 1) from the
leaves of the Chinese bush Camptotheca acuminata by Wall et al.,1
a number of analogs of the alkaloid have been prepared and bio-
evaluated;2 the most active of these DNA topoisomerase I in-
hibitors3 are generally substituted on the quinoline part of the
molecule. Among them, topotecan (2, Hycamtin)4 and irinotecan (3,
Camptosar)5 have been approved for clinical use as anticancer
drugs by the FDA. In addition, several analogs are in clinical trials
and are among the most promising cancer chemotherapeutic
agents currently under study.6
droxy
d-lactone motif was essential for biological activity. This
dogma, however, was challenged by homocamptothecin (4, Fig. 2),
a derivative possessing a methylene spacer between C-20 and the
carbonyl group.13 This compound exhibits enhanced stability in
solution and potent antitumoral activity and two analogs, 5 and 6,14
are currently in clinical trials.6 The potential of these new anti-
cancer agents has notably revived interest in lactone-modified
camptothecins,15,16 but surprisingly a synthesis of 17-norcampto-
thecin (7), lacking the E-ring methylene group, has yet to be
reported. This appeared to be a particularly interesting derivative
on the basis of a recent theoretical study reported by Jena and
Figure 1. Camptothecin and analogs.
* Corresponding author. Tel.: þ33 4 76 63 54 32; fax: þ33 4 76 63 57 54; e-mail
address: Alice.Kanazawa@ujf-grenoble.fr (A. Kanazawa).
Figure 2. Structures of homocamptothecins and 17-norcamptothecin.
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.06.003

7228
M. Devert et al. / Tetrahedron 66 (2010) 7227e7231
21
Mishra17 in which it was found that the
planar, in contrast to the d-lactone of camptothecin, and conse-
g
-lactone of compound 7 is
was directly engaged in a Friedlander condensation with o-ami-
nobenzaldehyde. While typical conditions (e.g., PTSA in refluxing
toluene) produced mostly degradation, fortunately, the use of ZnCl2
in refluxing THF22 provided the desired pentacyclic compound 14
in 43% non-optimized yield (two steps).23
€
quently hydrogen bonding between the C-20 hydroxyl and the
carbonyl group might be largely absent. This, according to the
authors, could impart greater chemical stability and enhanced an-
titumor activity to 7 relative to camptothecin. In this paper, we
report an effective, flexible total synthesis of this novel campto-
thecin analog and a study of its hydrolytic stability.
Removal of the PMB protecting group was smoothly and con-
veniently achieved by treatment of 15 with trifluoroacetic acid in
dichloromethane24 to afford, following a non-aqueous workup and
purification, racemic 17-norcamptothecin (7) in 62% yield.25
The topoisomerase I inhibitory activity of compound 7 was
evaluated by using a standard DNA relaxation assay,26 and sur-
prisingly this new analog was found to be completely inactive. It
was postulated that this result could stem from decomposition of 7
under the aqueous conditions of the assay, therefore the stability of
this compound in aqueous medium was next investigated. Thus,
lactone 7 was treated with PBS buffer solutions of different pH
values and the hydrolysis was monitored by fluorescence spec-
troscopy. Since the differences in the fluorescence spectra of the
closed and the opened forms of 7 were particularly pronounced
(Fig. 3),27 this method was well suited for this study.
2. Results and discussion
The strategy envisioned for the preparation of 17-norcampto-
thecin was based on our previously developed efficient, modular
approach to camptothecinoids, which involves a Claisen rear-
18
€
rangement and a Friedlander condensation as the key steps.
The synthesis commenced with etherification of the readily
available hydroxy pyridone 819 with allylic chloride 9 (E/Z mix-
ture) in the presence of cesium carbonate and sodium iodide in
DMF (Scheme 1). The inseparable mixture of allylic ethers 10,
obtained in 72% yield, was then refluxed in chlorobenzene in the
presence of HMDS to promote the Claisen rearrangement. After
acid treatment of the crude mixture and chromatographic puri-
fication, the expected pyridone 11 was isolated in 60% yield. The
450
400
350
300
250
200
150
100
50
g
-lactone motif was next elaborated by ester hydrolysis in 11,
followed by cyclization of the resulting seco acid with EDC and
DMAP in dichloromethane. In order to prevent hydrogenolysis of
p-methoxybenzyl (PMB) group, the vinyl-substituted lactone was
submitted to hydrogenation over Pd/C in ethyl acetate in the
presence of pyridine20 to afford the tricyclic derivative 12 in 50%
overall yield (three steps).
0
350
400
450
500
Wavelength (nm)
550
600
650
700
Figure 3. Fluorescence emission spectra of 7, immediately after treatment with buffer
solutions ( ) and after complete hydrolysis (e), upon excitation at 375 nm.
The fluorescence parameters were then used to calculate the
residual lactone percentage as a function of time by using a pre-
viously described methodology.28 Figure 4 shows the hydrolysis
kinetics of 7 at 20 ꢁC at various pH values. At pH¼7.4, the starting
lactone suffered completely cleavage in less than 5 min (t1/
100
90
80
70
60
50
40
30
20
10
0
Scheme 1. Synthesis of (ꢀ)-17-norcamptothecin.
0
10
20
30
40
50
60
70
t (min)
The transformation of this derivative into ketone 14 was effected
by using a standard protocol of hydroxylation with selenium di-
oxide, followed by DesseMartin oxidation. This unstable ketone
Figure 4. Hydrolysis kinetics of 7 (6: pH¼7.4; ,: pH¼6.4; B: pH¼5.2) and 1 (>:
pH¼7.4).

M. Devert et al. / Tetrahedron 66 (2010) 7227e7231
7229
2<1 min), whereas natural camptothecin displayed no significant
lactone opening under these conditions.29 Hydrolysis of lactone 7
also took place in acid medium, albeit less rapidly.
mixture of diastereoisomers.31 IR (neat): nmax¼2981, 1723, 1640,
1610, 1515, 1246 cmꢂ1. 1H NMR (400 MHz, acetone d6):
d¼7.36e7.34
(m, 3.80H, CArH), 6.95e6.92 (m, 3.80H, CArH), 6.27 (t, 3JHeH¼8.0 Hz,
3
1H, CHCH2Cl), 5.54 (t, JHeH¼8.0 Hz, 0.9H, CHCH2Cl), 4.92 (s, 2H,
3
3. Conclusion
CHCH2O), 4.80 (s, 1.80H, CHCH2O), 4.60 (d, JHeH¼8.0 Hz, 1.80H,
CHCH2Cl), 4.30e4.24 (m, 3.80H, CH2CH3), 3.79 (s, 5.7H, OCH3),
1.34e1.28 (m, 5.7H, CH2CH3). 13C NMR (100 MHz, acetone d6):
In summary, a short and flexible synthesis of (ꢀ)-17-norcamp-
tothecin, a novel E-ring modified camptothecin derivative, has been
developed from the easily accessible hydroxy pyridone 8. The sta-
bility of 7 in aqueous medium, predicted through calculations to be
greater than that of camptothecin, has been shown by using fluo-
rescence spectroscopy to be, in fact, significantly lower. Efforts to
attenuate this phenomenon are planned.
d
¼164.3 (CO2), 164.2 (CO2), 161.7 (CArOCH3), 161.5 (CArOCH3), 149.9
(C]CHCH2Cl), 148.5 (C]CHCH2Cl), 132.2 (CArH), 131.3 (CArH), 130.5
(CArCH2O), 129.9 (CArCH2O), 123.5 (C]CHCH2Cl), 115.6 (CArH), 110.7
(C]CHCH2Cl), 75.4 (CArCH2O), 72.0 (CArCH2O), 62.9 (CH2CH3), 62.8
(CH2CH3), 56.5 (OCH3), 41.8 (CH2Cl), 38.9 (CH2Cl),15.4 (CH2CH3),15.3
(CH2CH3). HRMS (ESI): calcd for C16H25O7NaP 383.1230; found
383.1232.
4. Experimental section
4.1. General
4.1.2. Ethyl 2-(4-Methoxybenzyloxy)-4-(5-oxo-1,2,3,5-tetrahydroin-
dolizin-6-yloxy)but-2-enoate (10). Sodium iodide (50 mg, 0.33
mmol) and
a 4/6 mixture of allylic chlorides 9 (141 mg,
All solvents were dried by standard methods and all reactions
were carried out under an inert atmosphere. Pyridine was distilled
from CaH2. Reactions were monitored by TLC using silica gel 60F254
0.2 mm-thickness plates with visualization by UV (254 nm) and
through staining with a phosphomolybdic acid or KMnO4 solution
in EtOH. For preparative scale chromatography, silica gel 60
0.50 mmol)31 were added to a suspension of pyridone 8 (50 mg,
0.33 mmol) and cesium carbonate (162 mg, 0.50 mmol) in DMF
(0.5 mL). The mixture was stirred at 20 ꢁC for 3 h, whereupon it
was filtered through a pad of silica gel. The solids were rinsed
with EtOAc and then with EtOAc/EtOH (90/10). The filtrate was
concentrated under reduced pressure and the residue was puri-
fied by silica gel column chromatography (EtOAc, then EtOAc/
EtOH, 98/2 to 94/6) to give allylic ether 10 (95 mg, 72%). IR (neat):
nmax¼2955, 1719, 1653, 1597, 1515, 1246, 1220, 1173 cmꢂ1. 1H NMR
(0.04e0.063 mm) was used. Melting points were carried out on
a Büchi B-545 apparatus. A Fourier transform infrared spectrometer
was used to record IR spectra. NMR spectra were recorded at
300 MHz or 400 MHz and referenced to the residual solvent peak.
Unless otherwise stated, CDCl3 was used as the solvent. Two and
three-bond 1He13C connectivities were determined by HMBC ex-
periments and one-bond 1He13C connectivities by HMQC experi-
ments. Mass spectra (MS) were effected using ESI. High resolution
mass spectra (HRMS) were recorded at the LCOSB, Université Pierre
et Marie Curie, Paris.
(300 MHz, CDCl3):
d
¼7.32e7.27 (m, 5H, CArH), 6.89e6.87 (m, 5H,
C
C
ArH), 6.64 (d, 3JHeH¼7.5 Hz, 1H, CPyH), 6.45 (d, 3JHeH¼7.8 Hz, 1.5H,
3
3
PyH), 6.40 (t, JHeH¼6.3 Hz, 1.5H, CHCH2O), 5.96 (d, JHeH¼7.2 Hz,
3
3
1H, CPyH), 5.91 (d, JHeH¼7.5 Hz, 1.5H, CPyH), 5.59 (t, JHeH¼5.4 Hz,
3
1H, CHCH2O), 5.0 (d, JHeH¼5.4 Hz, 2H, CHCH2O), 4.89 (s, 3H,
3
CArCH2O), 4.78 (s, 2H, CArCH2O), 4.53 (d, JHeH¼6.0 Hz, 3H,
CHCH2O), 4.33e4.22 (m, 5H, CH2CH3), 4.15 (m, 5H, NCH2), 3.80 (s,
7.5H, OCH3), 3.0 (m, 5H, CPyCH2), 1.33 (m, 5H, CPyCH2CH2). 13C
4.1.1. Ethyl 4-chloro-2-(4-methoxybenzyloxy)but-2-enoate (9). A
mixture of ethyl 2-diazo-2-diethylphosphonoacetate (2.48 g,
9.93 mmol), 4-methoxybenzyl alcohol (1.65 g, 11.94 mmol), and
rhodium (II) acetate (0.044 g, 0.10 mmol) in toluene (8 mL) was
heated at 100 ꢁC for 1 h, allowed tocoolto20 ꢁC, andfilteredthrough
Celite. The filtrate was concentrated under reduced pressure and the
residue was purified by silica gel column chromatography (Et2O) to
give ethyl 2-(4-methoxybenzyloxy)-2-diethylphosphonoacetate
NMR (75 MHz, CDCl3):
d
¼163.1 (CO2), 162.8 (CO2), 159.6 (CAr
-
OCH3), 159.3 (CArOCH3), 157.2 (NCO), 157.0 (NCO), 146.3 (CAr), 146.1
(CAr), 145.0 (CAr), 144.9 (CAr), 141.1 (CAr), 141.0 (CAr), 130.3 (CArH),
129.0 (CArH), 128.5 (CArCH2O), 127.9 (CArCH2O), 123.7 (C]
CHCH2O), 115.8 (CPyH), 115.7 (CPyH), 113.8 (CAr), 113.7 (CArH), 112.6
(C]CHCH2O), 99.1 (CPyH), 99.0 (CPyH), 73.6 (CArCH2O), 70.2
(CArCH2O), 65.6 (CPyOCH2), 63.2 (CPyOCH2), 61.2 (CH2CH3), 61.1
(CH2CH3), 55.1 (OCH3), 48.6 (NCH2), 30.7 (CPyCH2), 22.0
(CPyCH2CH2), 14.0 (CH2CH3). HRMS (ESI): calcd for C22H25NO6Na
422.1574; found 422.1571.
(3.23 g, 90%). IR (neat):nmax¼2981,1745,1610,1515,1250,1025 cmꢂ1
.
1H NMR (400 MHz, CDCl3):
d
¼7.28 (d, 3JHeH¼8.4 Hz, 2H, CArH), 6.87
3
2
(d, JHeH¼8.4 Hz, 2H, CArH), 4.74 (d, JHeH¼11.2 Hz, 1H, CArCHHO),
2
2
4.52 (d, JHeH¼11.2 Hz, 1H, CArCHHO), 4.33 (d, JHeP¼18.8 Hz, 1H,
CHP), 4.30e4.15 (m, 6H, COCH2, POCH2), 3.80 (s, 3H, OCH3),1.33e1.28
(m, 9H, P(OCH2CH3)2, COCH2CH3). 13C NMR (100 MHz, CDCl3):
4.1.3. (ꢀ)-Ethyl 2-(6-hydroxy-5-oxo-1,2,3,5-tetrahydroindolizin-7-
yl)-2-(4-methoxybenzyloxy)but-3-enoate (11). A solution of allylic
ether 10 (84 mg, 0.21 mmol) in a 1:1 mixture of chlorobenzene and
hexamethyldisilazane (1.5 mL) was heated at reflux for 14 h. After
removal of the solvents under reduced pressure, the resultant crude
trimethylsilyl ether was stirred in a solution of EtOH (1 mL) and 1 N
HCl (0.8 mL) at 20 ꢁC for 2 h. The reaction mixture was extracted
with CH2Cl2 and the organic phase was washed with brine, dried
over Na2SO4, filtered, and concentrated under reduced pressure.
Purification of the residue by silica gel column chromatography
(EtOAc/CH2Cl2, 10/90 to 30/70) gave hydroxy pyridone 11 (50 mg,
60%) as a white solid. Mp 146e148 ꢁC. IR (neat): nmax¼3102, 2976,
d
¼167.2 (CO2), 159.6 (CArOCH3), 130.0 (CArH), 128.0 (CArCH2O), 113.7
1
3
(CArH), 74.5 (d, JCeP¼156.4 Hz, CHPO), 73.6 (d, JC-P¼12.4 Hz,
2
2
C
ArCH2O), 63.5 (d, JCeP¼5.4 Hz, POCH2CH3), 63.4 (d, JCeP¼6 Hz,
POCH2CH3), 61.6 (CO2CH2CH3), 55.1 (OCH3), 16.2 (POCH2CH3), 16.1
(POCH2CH3), 14.0 (CO2CH2CH3). HRMS (ESI): calcd for C16H25O7NaP
383.1230; found 383.1232.
A
solution of ethyl 2-(4-methoxybenzyloxy)-2-diethylphos-
phonoacetate (3.00 g, 8.33 mmol) in THF (20 mL) was added to
a suspension of NaH (60%, 1.00 g, 24.9 mmol) in THF (10 mL) at 0 ꢁC.
After the mixtue was stirred at 0 ꢁC for 15 min and at 20 ꢁC for
45 min, a solution of chloroacetaldehyde (obtained from 17 mL of
50% aqueous solution)30 in THF (2 mL) was added at 0 ꢁC. The re-
action mixture was stirred at 20 ꢁC for 1 h, diluted with Et2O, and
poured into water. The organic phase was then washed with brine,
dried over Na2SO4, filtered, and concentrated under reduced pres-
sure. Purification of the residue by silica gel column chromatography
(EtOAc/pentane, 5/95) gave allylic chloride 9 (1.30 g, 55%) as a 9/10
1740,1653,1588,1510,1250 cmꢂ1.1H NMR (400 MHz, CDCl3):
d¼7.29
(d, 3JHeH¼8.4 Hz, 2H, CArH), 7.12 (s, 1H, OH), 6.86 (d, JHeH¼8.4 Hz,
3
3
3
2H, CArH), 6.40 (dd, JHeHcis¼10.4 Hz, JHeHtrans¼17.2 Hz, 1H, CH]
CH2), 6.36 (s, 1H,
C
PyH), 5.54 (dd, 2JHtranseHcis¼1.6 Hz,
3JHtranseH¼7,6 Hz, 1H, CH]CHtransH), 5.37 (dd, JHciseHtrans¼1.2 Hz,
2
3JHciseH¼10.8 Hz, 1H, CH]CHHcis), 4.72 (d, JHeH¼0.4 Hz, 1H,
3
CArCHHO), 4.32e4.21 (m, 3H, CH2CH3, CArCHHO), 4.12 (t,
3JHeH¼7.2 Hz, 2H, NCH2), 3.79 (s, 3H, OCH3), 2.98 (t, JHeH¼7.6 Hz,
3

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M. Devert et al. / Tetrahedron 66 (2010) 7227e7231
3
2H, CPyCH2), 2.18 (p, J¼7.6 Hz, 2H, CPyCH2CH2), 1.26 (t, 3JHeH¼7.2 Hz,
(400 MHz, CDCl3):
d
¼7.14 (d, JHeH¼8.8 Hz, 2H, CArH), 6.78 (d,
3H, CH2CH3). 13C NMR (100 MHz, CDCl3):
d
¼170.3 (CO2), 159.0 (CAr
3JHeH¼8.8 Hz, 2H, CArH), 6.10 (s, 1H, CPyH), 4.23e4.12 (m, 4H,
-
3
OCH3), 156.8 (NCO), 140.6 (CPyHCPyCPyOH), 138.5 (CPyNCO), 135.2
(CH]CH2), 130.3 (CArCH2), 129.1 (CArH), 127.2 (CPyOH), 116.7 (CH]
CH2), 113.6 (CArH), 99.5 (CPyH), 81.0 (CCO2), 66.7 (CArCH2O), 61.7
(CH2CH3), 55.2 (OCH3), 48.7 (NCH2), 30.8 (CPyCH2), 22.3 (CPyCH2CH2),
14.0 (CH2CH3). HRMS (ESI): calcd for C22H25NO6Na 422.1574; found
422.1572.
CArCH2O, NCH2), 3.73 (s, 3H, OCH3), 3.10 (t, JHeH¼7.6 Hz, 2H,
3
CPyCH2), 2.24 (p, JHeH¼7.6 Hz, 2H, CPyCH2CH2), 2.10e1.92 (m, 2H,
CH2CH3), 0.82 (t, JHeH¼7.6 Hz, 3H, CH2CH3). 13C NMR (100 MHz,
3
CDCl3):
d
¼174.3 (CO2), 159.4 (CArO), 151.4 (NCO), 148.1 (CPyNCO),
140.2 (CPyOH), 134.0 (CPyHCPyCPyO), 129.5 (CArH), 128.5 (CArCH2),
113.6 (CArH), 94.9 (CPyH), 83.6 (CCO2), 68.8 (CArCH2O), 55.1 (OCH3),
49.1 (NCH2), 31.6 (CPyCH2), 30.6 (CH2CH3), 21.8 (CPyCH2CH2), 7.0
(CH2CH3). HRMS (ESI): calcd for C20H21NO5Na 378.1312; found
378.1315.
4.1.4. (ꢀ)-3-Ethyl-3-(4-methoxybenzyloxy)-6,7-dihydrofuro[2,3-f]in-
dolizine-2,9(3H,5H)-dione (12). A solution of LiOH$H2O (107 mg,
2.55 mmol) in water (2.5 mL) was added to a solution of above ester
(200 mg, 0.50 mmol) inTHF (5 mL). The mixture was heated at 80 ꢁC
for 3 h, allowed to cool to 20 ꢁC, and diluted with Et2O (5 mL) and
water (5 mL). The organic phase was separated and the aqueous
phase was treated with 2:1 AcOH/CHCl3 (7 mL) and then extracted
exhaustively with CHCl3. The combined organic extracts were
washed with brine, dried over Na2SO4, filtered, and concentrated
under reduced pressure. The residue was triturated with Et2O to
provide (ꢀ)-2-(6-hydroxy-5-oxo-1,2,3,5-tetrahydroindolizin-7-yl)-
2-(4-methoxybenzyloxy)but-3-enoic acid (160 mg, 86%) as a white
solid. Mp 136e138 ꢁC. IR (neat): nmax¼3263, 2911, 1697, 1532, 1515,
4.1.5. (ꢀ)-3-Ethyl-5-hydroxy-3-(4-methoxybenzyloxy)-6,7-dihy-
drofuro[2,3-f]indolizine-2,9(3H,5H)-dione (13). A mixture of lactone
12 (120 mg, 0.338 mmol) and selenium dioxide (75 mg, 0.68 mmol)
in 1,4-dioxane (freshly distilled from sodium) was refluxed for
10 h.32 After being cooled to 20 ꢁC, the mixture was filtered through
Celite and the solids were rinsed successively with CH2Cl2 and
EtOAc. The filtrate was concentrated under reduced pressure and
the residue was purified by silica gel column chromatography
(EtOAc/CH2Cl2, 10/90 to 50/50) to provide starting material (57 mg)
and an inseparable mixture of diastereomeric alcohols 13 (50 mg,
76% brsm) as an orange solid. Mp 148e160 ꢁC (dec). IR (neat):
1437, 1237 cmꢂ1. 1H NMR (300 MHz, DMSO d6):
d
¼12.80 (br s, 1H,
CO2H), 9.12 (br s, 1H, CPyOH), 7.28 (d, 3JHeH¼7.8 Hz, 2H, CArH), 6.91
nmax¼3341, 2933, 1810, 1671, 1588, 1246, 1033 cmꢂ1
.
1H NMR
(d, 3JHeH¼7.8 Hz, 2H,
C
ArH), 6.34 (dd, 3JHeHcis¼10.8 Hz,
(400 MHz, CD2Cl2):
d
¼7.12e7.15 (m, 4H, CArH), 6.77e6.80 (m, 4H,
3JHeHtrans¼17.4 Hz, 1H, CH]CH2), 6,17 (s, 1H, CPyH), 5.35 (d,
3JHtranseH¼17.4 Hz, 1H, CH]CHtransH), 5.28 (d, 3JHciseH¼10.8 Hz, 1H,
CArH), 6.40 (s, 2H, CPyH), 5.25 (s, 2H, OH) 5.22e5.23 (m, 2H, CHOH),
4.26e4.32 (m, 2H), 4.13e4.20 (m, 4H), 3.96e4.03 (m, 2H),
3.73e3.74 (m, 6H, OCH3), 2.49e2.58 (m, 2H), 2.12e2.19 (m, 2H),
2
CH]CHHcis), 4.56 (d, JHeH¼10.5 Hz, 1H, CArCHHO), 4.20 (d,
2JHeH¼10.5 Hz, 1H, CArCHHO), 3.97 (t, 3JHeH¼6.6 Hz, 2H, NCH2), 3.74
2.08e2.10 (m, 4H, CH2CH3), 0.83 (t, 3JHeH¼5.4 Hz, 6H, CH2CH3). 13
C
(s, 3H, OCH3), 2.95 (t, 3JHeH¼6.6 Hz, 2H, CPyCH2), 2.10e2.06 (m, 2H,
NMR (75 MHz, CD2Cl2):
d
¼174.6 (CO2), 174.5 (CO2), 159.8 (CArO),
CPyCH2CH2). 13C NMR (75 MHz, DMSO d6):
d¼170.8 (CO2H), 158.5
159.7 (CArO), 151.2 (NCO), 150.0 (CPyNCO), 141.5 (CPyO), 141.4 (CPyO),
134.6 (CPyHCPyCPyO), 129.8 (CArH), 128.9 (CArCH2), 128.8 (CArCH2),
113.8 (CArH), 96.1 (CPyH), 96.0 (CPyH), 83.8 (CCO2), 83.7 (CCO2), 73.2
(CHOH), 73.1 (CHOH), 69.1 (CArCH2O), 69.0 (CArCH2O), 55.3 (OCH3),
46.7 (NCH2), 32.4 (CPyCH2), 32.3(CPyCH2), 30.9 (CH2CH3), 30.8
(CH2CH3), 7.0 (CH2CH3). HRMS (ESI): calcd for C20H21NO6Na
394.1261; found 394.1265.
(CArO),156.2 (NCO),140.8 (CPyOH),138.4 (CPyNCO),136.3 (CH]CH2),
130.3 (CArCH2),128.8 (CArH),127.7 (CPyHCPyCPyOH),115.1 (CH]CH2),
113.5 (CArH), 97.7 (CPyH), 80.7 (CCO2H), 65.6 (CArCH2O), 55.0 (OCH3),
48.4 (NCH2), 30.3 (CPyCH2), 21.7 (CPyCH2CH2). HRMS (ESI): calcd for
C20H21NO6Na 394.1261; found 394.1265.
A solution of above carboxylic acid (160 mg, 0.43 mmol), DMAP
(74 mg, 0.61 mmol), and EDC (166 mg, 0.87 mmol) in CH2Cl2 (3 mL)
was stirred at 20 ꢁC for 12 h. The reaction mixture was then diluted
with CHCl3 and washed with 1 N HCl and brine, dried over Na2SO4,
filtered, and concentrated under reduced pressure. The residue was
purified by silica gel column chromatography (EtOAc/CH2Cl2, 10/90
to 30/70) to afford (ꢀ)-3-(4-methoxybenzyloxy)-3-vinyl-6,7-dihy-
drofuro[2,3-f]indolizine-2,9(3H,5H)-dione (89 mg, 58%) as a white
solid. Mp 92e94 ꢁC. IR (neat): nmax¼2955, 1810, 1680, 1597, 1510,
4.1.6. (ꢀ)-3-Ethyl-3-(4-methoxybenzyloxy)-6,7-dihydrofuro[2,3-f]in-
dolizine-2,5,9(3H)-trione (14). A solution of the DesseMartin peri-
odinane (15% in CH2Cl2, 0.282 mL, 0.134 mmol) was added to
a mixture of alcohols 13 (25 mg, 0.07 mmol) and sodium bi-
carbonate (34 mg, 0.40 mmol) in CH2Cl2 (2 mL) at 0 ꢁC. After being
stirred for 1 h, the reaction mixture was diluted with Et2O and
treated with saturated sodium bicarbonate and saturated sodium
thiosulfate (1/2, 3 mL). The organic phase was washed with satu-
rated sodium bicarbonate and brine, dried over Na2SO4, filtered, and
concentrated under reduced pressure to provide ketone 14 (24 mg,
97%) as a white solid. Mp 142e162 ꢁC (dec). IR (neat): nmax¼2933,
1250, 1051 cmꢂ1
.
1H NMR (400 MHz, CDCl3):
d¼7.16 (d,
3
3JHeH¼8.4 Hz, 2H, CArH), 6.79 (d, JHeH¼8.4 Hz, 2H, CArH), 6.09 (s,
3
3
1H, CPyH), 5.98 (dd, JHeHcis¼10.8 Hz, JHeHtrans¼17.2 Hz, 1H, CH]
3
CH2), 5.40 (d, JHciseH¼10.8 Hz, 1H, CH]CHHcis), 5.36 (d,
3JHtranseH¼17.2 Hz, 1H, CH]CHtransH), 4.33 (d, JHeH¼10.0 Hz, 1H,
1823,1736,1680,1606,1241,1189 cmꢂ1. 1H NMR (400 MHz, CD2Cl2):
2
2
3
CArCHHO), 4.27 (d, JHeH¼10.0 Hz, 1H, CArCHHO), 4.18 (t,
d
¼7.13 (d, JHeH¼8.8 Hz, 2H, CArH), 6,85 (s, 1H, CPyH), 6,79 (d,
3JHeH¼7.2 Hz, 2H, NCH2), 3.74 (s, 3H, OCH3), 3.10 (t, JHeH¼8.0 Hz,
3JHeH¼8.8 Hz, 2H, CArH), 4,33 (t, JHeH¼6.4 Hz, 2H, NCH2), 4,23 (d,
3JHeH¼10.4 Hz,1H, CArCHHO), 4.13 (d, 3JHeH¼10.4 Hz,1H, CArCHHO),
3.74 (s, 3H, OCH3), 2.93 (t, 3JHeH¼6.8 Hz, 2H, CH2CO), 2.01e2.12 (m,
2H, CH2CH3), 0.85 (t, 3JHeH¼7.6 Hz, 3H, CH2CH3). 13C NMR (100 MHz,
3
3
2H, CPyCH2), 2.23 (p, JHeH¼7.2 Hz, 2H, CPyCH2CH2). 13C NMR
3
(100 MHz, CDCl3):
d
¼172.2 (CO2), 159.5 (CArO), 151.4 (NCO), 148.2
(CPyNCO), 140.4 (CPyO), 133.5 (CPyHCPyCPyO), 132.8 (CH]CH2), 129.6
(CArH), 128.4 (CArCH2), 120.0 (CH]CH2), 113.6 (CArH), 95.3 (CPyH),
82.6 (CCO2), 68.5 (CArCH2O), 55.1 (OCH3), 49.2 (NCH2), 31.6
(CPyCH2), 21.8 (CPyCH2CH2). HRMS (ESI): calcd for C20H19NO5Na
376.1155; found 376.1142.
CD2Cl2):
d
¼195.5 (CH2COCPy), 173.7 (CO2), 159.9 (CArO), 151.0 (NCO),
147.1 (CPyNCO),137.8 (CPyO),133.4 (CPyHCPyCPyO),129.9 (CArH),128.5
(CArCH2), 113.8 (CArH), 98.3 (CPyH), 83.4 (CCO2), 69.4 (CArCH2O), 55.3
(OCH3), 42.7 (NCH2), 34.0 (CPyCH2), 30.9 (CH2CH3), 7.0 (CH2CH3).
HRMS (ESI): calcd for C20H20NO6 370.1285; found 370.1273.
A mixture of the above lactone (73 mg, 0.21 mmol), 10% Pd/C
(12 mg), and pyridine (0.1 mL, 1.2 mmol) in EtOAc (8 mL) was stir-
red at 20 ꢁC under hydrogen for 1 h. The mixture was then filtered
through Celite and the solids were rinsed with CHCl3. Concentra-
tion of the filtrate under reduced pressure afforded lactone 12
4.1.7. (ꢀ)-O-p-Methoxybenzyl-17-norcamptothecin (15). A 0.5 M
solution of ZnCl2 in THF (0.325 mL, 0.163 mmol) was added to
a mixture of ketone 14 (24 mg, 0.065 mmol), 2-aminobenzaldehyde
(28 mg, 0.23 mmol), and 4 A molecular sieves in dry THF (1 mL).
The resultant mixture was heated at reflux for 5 h, allowed to cool
white solid. Mp 113e115 ꢁC. IR (neat):
ꢀ
(74 mg, 100%) as
a
nmax¼2972, 2937, 1810, 1680, 1601, 1515, 1250, 1046 cmꢂ1. 1H NMR

M. Devert et al. / Tetrahedron 66 (2010) 7227e7231
7231
to 20 ꢁC, and diluted with CHCl3. The organic phase was washed
with saturated sodium bicarbonate and brine, dried over Na2SO4,
filtered, and concentrated under reduced pressure to provide
compound 15 (13 mg, 44%) as a yellow solid. Mp 164e167 ꢁC. IR
4. Kingsburry, W. D.; Boehm, J. C.; Jakas, D. R.; Holden, K. G.; Hetch, S. M.; Gal-
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R. P. J. Med. Chem. 1991, 34, 98e107.
5. (a) Negoro, S.; Fukuoka, M.; Masuda, N.; Takada, M.; Kusunoki, Y.; Matsui, K.;
Takifuji, N.; Kudoh, S.; Niitani, H.; Tagushi, T. J. Natl. Cancer Inst. 1991, 83,
1164e1168; (b) Kawato, Y.; Aonuma, M.; Hirota, Y.; Kuga, H.; Sato, K. Cancer Res.
1991, 51, 4187e4191.
6. Butler, M. S. Nat. Prod. Rep. 2008, 25, 475e516.
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Trans. 1 1974, 1215e1217.
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Mattern, M. R.; Mong, S.-M.; Bartus, J. O.; Johnson, R. K.; Kingdburry, W. D. J.
Med. Chem. 1989, 32, 715e720; (b) Yaegashi, T.; Sawada, S.; Furuta, T.; Yokokura,
T.; Yamaguchi, K.; Miyasaka, T. Chem. Pharm. Bull. 1993, 41, 971e974.
10. (a) Adamovics, J. A.; Hutchinson, C. R. J. Med. Chem. 1979, 22, 310e314; (b)
Sawada, S.; Yaegashi, T.; Furuta, T.; Yokokura, T.; Miyasaka, T. Chem. Pharm. Bull.
1993, 41, 310e313.
11. Nicholas, A. W.; Wani, M. C.; Manikumar, G.; Wall, M. E.; Kohn, K. W.; Pommier,
Y. J. Med. Chem. 1990, 33, 972e978.
12. Snyder, L.; Shen, W.; Bornman, W. G.; Danishefsky, S. J. J. Org. Chem. 1994, 59,
7033e7037.
13. (a) Lavergne, O.; Lesueur-Ginot, L.; Pla Rodas, F.; Bigg, D. C. H. Bioorg. Med. Chem.
Lett. 1997, 7, 2235e2238; (b) Lesueur-Ginot, L.; Demarquay, D.; Kiss, R.;
Kasprzyk, P. G.; Dassonneville, L.; Bailly, C.; Camara, J.; Lavergne, O.; Bigg, D. C. H.
Cancer Res. 1999, 59, 2939e2943.
14. (a) Lavergne, O.; Lesueur-Ginot, L.; Pla Rodas, F.; Kasprzyk, P. G.; Pommier, J.;
Demarquay, D.; Prevost, G.; Ulibarri, G.; Rolland, A.; Schiano-Liberatore, A.-M.;
Harnet, J.; Pons, D.; Camara, J.; Bigg, D. C. H. J. Med. Chem. 1998, 41, 5410e5419;
(neat): nmax¼2920, 1814, 1979, 1606, 1515, 1254, 1232 cmꢂ1. 1H NMR
3
(300 MHz, CDCl3):
d
¼8.41 (s, 1H, CArH), 8.21 (d, JHeH¼8.1 Hz, 1H,
3
3
C
C
ArH), 7.95 (d, JHeH¼8.1 Hz, 1H, CArH), 7.84 (t, JHeH¼8.1 Hz, 1H,
3
ArH), 7.67 (t, JHeH¼8.1 Hz, 1H, CArH), 7.36 (s, 1H, CpyH), 7.21 (d,
3JHeH¼8.7 Hz, 2H, CArH), 6.81 (d, 3JHeH¼8.7H, 2H, CArH), 5.40 (s, 2H,
CH2N), 4.33 (d, 2JHeH¼10.2 Hz, 1H, CArCHHO), 4.28 (d,
2JHeH¼10.2 Hz, 1H, CArCHHO), 3.71 (s, 3H, OCH3), 2.27e2.13 (m, 2H,
CH2CH3), 0.94 (t, JHeH¼7.5 Hz, 3H, CH2CH3). 13C NMR (75 MHz,
3
CDCl3):
d
¼173.9 (CO2), 159.6 (CArO), 152.1 (CAr), 151.1 (CON), 148.9
(CAr), 143.9 (CAr), 142.7 (CAr), 134.9 (CPy), 131.1 (CArH), 130.7 (CArH),
129.8 (CAr), 129.6 (CArH), 128.5 (CAr), 128.3 (CAr), 128.2 (CArH), 127.9
(CArH), 127.8 (CArCH2), 113.8 (CAr), 95.4 (CPyH), 83.7 (CCO2), 69.2
(CArCH2O), 55.2 (OCH3), 50.6 (NCH2), 31.0 (CH2CH3), 7.2 (CH2CH3).
HRMS (ESI): calcd for C27H23N2O5 455.1602; found 455.1603.
4.1.8. (ꢀ)-17-Norcamptothecin (7). Trifluoroacetic acid (1.0 mL,
13.5 mmol) was added to a solution of 15 (24 mg, 0.05 mmol) in
CH2Cl2 (3 mL) at 0 ꢁC and the reaction mixture was stirred for 1 h at
the same temperature. The volatiles were then evaporated under
reduced pressure and the residue was triturated with a small
amount of CH2Cl2 and Et2O to provide 17-norcamptothecin (11 mg,
(b)
Lavergne, O.; Harnett, J.; Rolland, A.; Lanco, C.; Lesueur-Ginot, L.;
Demarquay, D.; Huchet, M.; Coulomb, H.; Bigg, D. C. H. Bioorg. Med. Chem. Lett.
1999, 9, 2599e2602; (c) Lavergne, O.; Demarquay, D.; Bailly, C.; Lanco, C.;
Rolland, A.; Huchet, M.; Coulomb, H.; Muller, N.; Baroggi, N.; Camara, J.; Le
Breton, C.; Manginot, E.; Cazaux, J.-B.; Bigg, D. C. H. J. Med. Chem. 2000, 43,
2285e2289.
62%) as an orange solid. Mp 248e250 ꢁC. 1H NMR (400 MHz, DMSO
3
d6):
d
¼8.72 (s, 1H, CArH), 8.18 (m, 2H, CArH), 7.90 (t, JHeH¼7.2 Hz,
15. (a) Bom, D.; Curran, D. P.; Chavan, A. J.; Kruszewski, S.; Zimmer, S. G.; Fraley, K.
A.; Burke, T. G. J. Med. Chem. 1999, 42, 3018e3022; (b) Du, W.; Curran, D. P.;
Bevins, R. L.; Zimmer, S. G.; Zhang, J.; Burke, T. G. Bioorg. Med. Chem. 2002, 10,
103e110; (c) Bacherikov, V. A.; Tsai, T.-J.; Chang, J.-Y.; Chou, T.-C.; Lee, R.-Z.; Su,
T.-L. Eur. J. Org. Chem. 2006, 4490e4499; (d) Tangirala, R. S.; Antony, S.; Agama,
K.; Pommier, Y.; Anderson, B. D.; Bevins, R.; Curran, D. P. Bioorg. Med. Chem.
2006, 14, 6202e6212; (e) Li, M.; Tang, W.; Zeng, F.; Lou, L.; You, T. Bioorg. Med.
Chem. Lett. 2008, 18, 6441e6443; (f) Giannini, G.; Marzi, M.; Cabri, W.;
Marastoni, E.; Battistuzzi, G.; Vesci, L.; Pisano, C.; Beretta, G. L.; De Cesare, M.;
Zunino, F. Bioorg. Med. Chem. Lett. 2008, 18, 2910e2915; (g) Miao, Z.; Sheng, C.;
Zhang, W.; Ji, H.; Zhang, J.; Shao, L.; You, L.; Zhang, M.; Yao, J.; Che, X. Bioorg.
Med. Chem. 2008, 16, 1493e1510.
1H, CArH), 7.75 (t, 3JHeH¼7.2 Hz, 1H, CArH), 7.33 (s, 1H, CPyH), 6.95 (s,
1H, OH), 5.40 (s, 2H, NCH2), 2.02e2.21 (m, 2H, CH2CH3), 0.84 (t,
3JHeH¼7.6 Hz, 3H, CH2CH3). 13C NMR (75 MHz, DMSO d6):
¼176.2
d
(CO2), 152.2 (CAr), 150.2 (CON), 147.8 (CAr), 143.6 (CAr), 141.0 (CAr),
137.3 (CAr), 131.3 (CArH), 130.3 (CArH), 129.5 (CArH), 128.7 (CArH),
128.4 (CArH), 127.5 (CAr), 127.4 (CArH), 94.3 (CPyH), 76.8 (CCO2), 50.5
(NCH2), 30.0 (CH2CH3), 7.1 (CH2CH3). HRMS (ESI): calcd for
C19H15N2O4 335.1026; found, 335.1019.
16. Recently, it has been reported that non-lactone analogs can also retain anti-
topoisomerase I activity. See, for example: (a) Hautefaye, P.; Cimetière, B.;
Pierré, A.; Léonce, S.; Hickman, J.; Laine, W.; Bailly, C.; Lavielle, G. Bioorg. Med.
Chem. Lett. 2003, 9, 2731e2735; (b) Lansiaux, A.; Léonce, S.; Kraus-Berthier,
L.; Bal-Mahieu, C.; Mazinghien, R.; Didier, S.; David-Cordonnier, M. eH.;
Hautefaye, P.; Lavielle, G.; Bailly, C.; Hickman, J. A.; Pierré, A. Mol. Pharmacol.
2007, 72, 311e319.
Acknowledgements
We thank Dr. J. Einhorn for his interest in our work and
Dr. D. Jouvenot for his kind assistance with the spectrofluorimetric
measurements. Financial support from Université Joseph Fourier,
the CNRS (UMR 5616, FR2607), and the French Ministry of Research
(stipend to M.D.) are gratefully acknowledged.
17. Jena, N. R.; Mishra, P. C. J. Mol. Model. 2007, 13, 267e274.
18. (a) Raolji, G. B.; Garçon, S.; Greene, A. E.; Kanazawa, A. Angew. Chem., Int. Ed.
2003, 42, 5059e5061; (b) Anderson, R. J.; Raolji, G. B.; Kanazawa, A.; Greene, A.
E. Org. Lett. 2005, 7, 2989e2991; (c) Babjak, M.; Kanazawa, A.; Anderson, R. J.;
Greene, A. E. Org. Biomol. Chem. 2006, 4, 407e409.
Supplementary data
19. Padwa, A.; Sheehan, S. M.; Straub, C. S. J. Org. Chem. 1999, 64, 8648e8659.
20. Sajiki, H.; Kuno, H.; Hirota, K. Tetrahedron Lett. 1997, 38, 399e402.
21. Marco-Contelles, J.; Pérez-Mayoral, E.; Samadi, A.; Carreiras, M. C.; Soriano, E.
Chem. Rev. 2009, 109, 2652e2671.
22. This is a slight modification of a reported protocol: (a) McNaughton, B. R.;
Miller, B. L. Org. Lett. 2003, 5, 4257e4259; (b) Dallavalle, S.; Roccheta, D. G.;
Musso, L.; Merlini, L.; Morini, G.; Penco, S.; Tinelli, S.; Beretta, G. L.; Zunino, F.
Bioorg. Med. Chem. Lett. 2008, 18, 2781e2787.
23. This sequence was initially used to obtain the corresponding benzyl derivative.
However, all attempts to remove the benzyl group were unsuccessful.
24. White, J. D.; Amedio, J. C., Jr. J. Org. Chem. 1989, 54, 736e738.
25. This compound was purified by trituration with ether. All attempts to purify it
by silica gel chromatography led to significant decomposition.
1H and 13C NMR spectra of all new compounds and details for
the spectrofluorimetric determinations. Supplementary data asso-
ciated with this article can be found in online version at
doi:10.1016/j.tet.2010.06.003. This data include MOL files and
InChIKeys of the most important compounds described in this
article.
References and notes
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27. The difference between the lmax emission of the closed form and the
corresponding opened form of 7 is greater than 120 nm. For camptothecin, this
difference is ꢃ20 nm (see Supplementary data and Ref. 28)
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tionalized by the better leaving group involved in the cleavage process.
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31. Since the E isomer is less stable to purification, the diastereomeric composition
can vary.
32. This reaction was stopped before the total conversion of the starting material in
order to prevent decomposition of the desired product.
3. Pommier, Y. Chem. Rev. 2009, 109, 2894e2902.