Synthesis of a new structural analogue of (+)-porothramycin

Article abstract of DOI:10.1016/S0040-4020(01)00197-1

A new phosphonate analogue of (+)-porothramycin has been synthesized from (S)-pyroglutaminol. Circular dichroism of diastereomeric intermediates 9 has been studied. The cytostatic activity of the new pyrrolo[2,1-c][1,4]benzodiazepine has been evaluated against human KB cells.

Full text of DOI:10.1016/S0040-4020(01)00197-1

TETRAHEDRON
Pergamon
Tetrahedron 57 $2001) 3389±3395
Synthesis of a new structural analogue of ꢀ1)-porothramycin
Anne Rojas-Rousseau and Nicole Langloisp
Institut de Chimie des Substances Naturelles, CNRS, 91198 Gif-sur-Yvette, France
Received 11 December 2000; revised 12 February 2001; accepted 15 February 2001
AbstractÐA new phosphonate analogue of $1)-porothramycin has been synthesized from $S)-pyroglutaminol. Circular dichroism of
diastereomeric intermediates 9 has been studied. The cytostatic activity of the new pyrrolo[2,1-c][1,4]benzodiazepine has been evaluated
against human KB cells. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
prepared following different chronologies which require
suitable protection and deprotection steps. Among them,
the cyclization of amino thioacetals has signi®cant advan-
tages and was shown to be rather general, but its application
to the synthesis of 9-demethoxyporothramycin 3 failed in
our hands.5 The other methods, including more recent
reduction of azides,6 as well as the cyclization through intra-
molecular aza-Wittig reactions,7 have been mainly applied
to simple PBDs such as DC 81 4 or its O-benzyl derivative.
Our introduction of Raney nickel as catalyst to reduce
aromatic nitro group of PBD precursors8 have already
been extended to the enantioselective synthesis of $1)-9-
demethoxyporothramycin 3 and $1)-porothramycin 5, the
double bond of the C-2 side chain being preserved under
these conditions.9
Several natural pyrrolo[2,1-c][1,4]benzodiazepines $PBDs)
of general formula 1, isolated from various Streptomyces
species, exhibit interesting antibiotic and antitumour
activities. Among them, anthramycin 2 has been the subject
of extensive investigations. These studies have shown a
selective DNA binding of anthramycin, with a preference
for PuGPu sequences and the formation of a covalent adduct
in the minor groove of DNA.1 Therefore, such compounds
could be interesting as potential gene targeted drugs.1,2
In these PBDs, two common structural features are essential
to their biological properties: the S absolute con®guration at
C-11a and the presence of an imine or an equivalent carbi-
nolamine function at N-10±C-11. Indeed, this absolute
con®guration provides these molecules with a twisted
shape, allowing their ®t within the minor groove of DNA
and a nucleophilic attack by the N-2 amino group of a
guanine residue to form an aminal linkage at C-11.3 These
two requirements are also the major problems encountered
in the synthesis of PBDs, owing to frequently observed
racemization at the C-11a position and to the great chemical
sensitivity of the imine function.
Several syntheses of PBDs and structural analogues have
already been described.4 Most of the routes developed for
this are based upon a cyclization of amino-aldehydes,
Keywords: pyrrolo[2,1-c][1,4]benzodiazepines; phosphonate; Horner±
Wadsworth±Emmons reaction; circular dichroism; cytotoxicity.
p
Corresponding author. Tel.: 133-1-69-82-30-68; fax: 133-1-69-07-72-
47; e-mail: nicole.langlois@icsn.cnrs-gif.fr
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020$01)00197-1

3390
A. Rojas-Rousseau, N. Langlois / Tetrahedron 57 -2001) 3389±3395
Scheme 1. Reagents: $a) see Ref. 11; $b) NaH, KI, o-NO2PhCOCl $95%); $c) DIBAL±H, Tol $80%); $d) MeOH, TsOH $100%); $e) Ac2O, Py $98%); $f)
15 mol% QCS, Tol $94%); $g) POCl3±DMF $100%); $h) CH2[P$O)$OMe)2]2, nBuLi $87%); $i) Ba$OH)2, then CO2 $86%); $j) DMSO, COCl2, iPr2NEt $99%);
$k) Raney-Ni, then MeOH, H1 $36%).
We report here the synthesis of 6, an analogue of 3 bearing
an unsaturated phosphonate chain at C-2, according to this
methodology. Indeed, only few modi®cations of C-2 side
chain of synthetic PBDs have been achieved,10 whereas we
described some years ago a very ef®cient method to prepare
an enamido-aldehyde as a good scaffold from which a
variety of unsaturated C-2 side chains could be introduced.
could be explained by the inherent chirality of the chromo-
phore due to non-planarity of the ortho-nitrobenzamide
group. X-Ray analysis of 9a $2S) showed that the nitro
group is practically coplanar with the aromatic ring,
whereas this is almost perpendicular to the amide carbonyl
group.12 The aromatic ring adopts a conformation with the
nitro group pointing on the side opposite to the methoxy
group at C-2, giving an M-helicity for the chirality axis
CO±nitroaryl $Fig. 2). Because of steric factors, the dia-
stereomer 9b $2R) is postulated to adopt a conformation
with the nitro group pointing on the opposite side with a P
2. Results and discussion
The new PBD 6 was synthesized as outlined in Scheme 1.
$5S)-5-$Ethoxy-ethoxymethyl)pyrrolidin-2-one was easily
prepared from $S)-pyroglutaminol.11 After deprotonation,
this compound was treated with o-nitrobenzoyl chloride
affording the imide 7 in 95% yield. The a-hydroxy-ortho-
nitrobenzamides 8 were generated by partial and regio-
selective reduction of 7 with DIBAL±H at 2788C in toluene
$80%), and were quantitatively converted into the more
stable a-methoxy-ortho-nitrobenzamides 9. The mixture
of diastereomers $9a/9b ca. 9:1) was used in the next step
but 9a and 9b have also been separated by column chroma-
tography on silica gel for the purposes of characterization
and checking the validity of the next elimination-step with
1
each diastereomer. The coupling constants observed in H
NMR spectra allowed us to assign the 2,5-cis relative con-
®guration to 9a. The pyrrolidine-rings of these derivatives
adopt a near-envelope conformation with C-3 pointing out
of the plane, on the side opposite to the C-2 methoxy group.
It is interesting to note that the CD curves of 9a and 9b are
mirror images with ®ve Cotton effects alternating in sign,
between 225 and 335 nm, in spite of the same absolute
con®guration of the C-5 centre $Fig. 1). These results
Figure 1. CD curves $MeOH) of 9a $Ð), 9b $±´±), 10a $± ±), 10b $´´´) and
$S)-N-o-nitrobenzoylprolinol [$´´´), l nm $De)]: 255 $11.0), 283 $21.7),
301 $20.5), 330 $22.2).

A. Rojas-Rousseau, N. Langlois / Tetrahedron 57 -2001) 3389±3395
3391
its reduction with NaBH4. The optical rotation of the reduc-
tion product indicated that no racemization had occurred.
The reductive cyclization of 15 with an excess of Raney
nickel, followed by a treatment with methanol and small
amounts of tri¯uoroacetic acid, led to the new
pyrrolo[2,1-c][1,4]benzodiazepine 6 together with two un-
identi®ed minor by-products. The compound 6 could not be
ef®ciently crystallized and was therefore puri®ed by
preparative TLC on silica gel. However, the great reactivity
of the carbinolamine ether functional group under these
conditions explains the modest isolated yield $36%) which
was not optimized owing to the relative cytostatic activity of
6. The con®guration 11R was assigned on the basis of
absence of coupling between 11-H and 11a-H.
Figure 2. X-Ray, general view of 9a.
chirality sense of the helix. Thus, the CD curves of 9a and
9b are virtually of enantiomorphous type since the stronger
perturber of the nitrophenyl chromophore is the CO±N
moiety, approximately perpendicular to the aromatic ring
$N1±C70 ±C10 ±C20ˆ90.98 in 9a). X-Ray structure showed
a hydrogen bond between the hydroxy and the carbonyl
groups in the crystal, and therefore an s-trans conformation
of the amide bond. However, the hydrogen bond is not
essential for this conformation since the CD curves were
recorded in methanol as solvent able to break internal H-
bridges, and the same curves, albeit of somewhat smaller
amplitudes, were obtained, respectively, with the acetates
10a and 10b. It is also worthy of note that $S)-N-o-
nitrobenzoylprolinol $devoid of the a-methoxy group)
gives a CD curve qualitatively similar to that of 9a, indicat-
ing a preferred M-helicity around the CO±nitroaryl bond.
The cytostatic activity of the new phosphonate 6 was
evaluated in vitro using the human KB cell line. The IC50
value $7.5£1027 M), compared to the results obtained with
9-demethoxyporothramycin 3 $IC50ˆ8.6£1028 M), indi-
cated a weaker activity, the compound 6 being atoxic
between 1027 M and 1029 M. Although the studies devoted
to the mechanism of action of PBDs concerned principally
anthramycin 2 $and, more recently, PBD dimers),17 the
biological activities of $1)-porothramycin
5
and
9-demethoxy analogue 3 indicate that the snug ®t within
the minor groove of DNA tolerates the substitution of the
C-2 acrylamide group by two methyl groups.5,18 The 3D
structures of 3 and 6 could explain the difference of their
cytostatic activities. The molecular modelling study shows
an s-trans preferred conformation for the side-chain double
bond in 3 $Eˆ135.2 vs 138.3 kJ/mol), as well as in the
phosphonate analogue 6 $Eˆ113.8 vs 121.6 kJ/mol), as
displayed by the parent anthramycin methyl ether itself,
according to its X-ray structural analysis.19 In the 3D struc-
ture of the most stable conformations of 3 and 6, the carbons
C-1 to C-13 are superimposable and the main difference lies
in the tetrahedral character of the phosphorus atom with, as
a consequence, the pointing of one of the phosphonate
methoxy groups out the general plane of the C-2 side
chain and this steric factor probably could be responsible
for the difference in the ®t to DNA.
The acetates 10 were prepared to protect ef®ciently the
primary alcohol function of 9 during the following step.13
The methoxy groups of the mixture of diastereomers
10a110b were eliminated to form the enamide 11 in
high yield $94%), by heating in toluene in the presence
of quinoleinium camphosulfonate as catalyst.13±15
A
Vilsmeier±Haack reaction converted quantitatively the
compound 11 into the versatile unsaturated aldehyde 12,
provided a large excess of reagent was used to preclude
the formation of dimeric compounds.
This key intermediate, despite its vinylogous imide
structure, gave excellent results in Horner±Wadsworth±
Emmons reactions. Thus, condensation of the anion
obtained by deprotonation of tetramethyl methylene-
diphosphonate with one equivalent of nBuLi at 08C
provided the derivative 13 as a single stereoisomer $87%).
The E geometry of the newly created double bond was
con®rmed by the coupling constants observed in H NMR
between the ethylenic protons H-7 and H-8 $17 Hz).16 The
acetate 13 was saponi®ed with Ba$OH)2 to afford 14 $86%).
3. Conclusions
The total synthesis of the new PBD 6, the phosphonate
analogue of 9-demethoxyporothramycin 3, has been
achieved from inexpensive $S)-pyroglutaminol through a
particularly ef®cient Horner±Wadsworth±Emmons reac-
tion with the enamido-aldehyde 12, to elaborate the side
chain. The compound 6 has been tested in vitro in the
human KB cell line and shown to be almost 10-fold less
cytostatic than 3.
1
Swern oxidation of the primary alcohol 14, with iPr2NEt as
base, led almost quantitatively to the aldehyde 15 $99%).
The aldehyde 15, isolated in a partially hydrated form, could
be used without puri®cation because it gave easily a methyl
acetal when methanol was co-eluent in chromatographic
separations and it could be sensitive to racemization. The
stereogenic centre was preserved in these conditions as
shown by the control of the enantiopurity of 15 through
4. Experimental
4.1. General
Optical rotations were measured on a Perkin±Elmer 241;
the concentrations in CHCl3 solution $unless otherwise indi-
cated) are given in g/100 mL. IR spectra $n cm21, CHCl3)

3392
A. Rojas-Rousseau, N. Langlois / Tetrahedron 57 -2001) 3389±3395
were recorded on a Nicolet 205 $FT). 1H NMR spectra were
obtained $CDCl3 unless otherwise indicated, Me4Si,
dˆ0 ppm) from Bruker AC200, AC250 or AM300;
coupling constant J values are given in hertz $s, d, t, dd
and m indicate singlet, doublet, triplet, doublet of doublets,
and multiplet, respectively). 13C NMR spectra were
recorded on AC250 $62.5 MHz) or AM300 $75.0 MHz).
CD curves were recorded on a Jobin±Yvon dichrographe
V. Mass spectra and high resolution mass spectra were,
respectively, measured on an AEI MS50 or on a Kratos
MS80 spectrometer. Flash chromatography was performed
on silica gel $SDS 230±400 mesh) and preparative thin
layer chromatography on silica gel $Merck HF 2541366).
Usual workup means that the organic layer was dried
over magnesium sulfate, ®ltered and evaporated under
vacuum.
the addition of aqueous Na2CO3 solution $10% w/v)
followed by extraction with CH2Cl2. After usual workup,
the 2-methoxy derivatives 9 were isolated in 100% yield.
The two diastereomers have been separated by chromato-
graphy on silica gel $eluent: CH2Cl2±MeOH 97:3) to be
characterized.
Major diastereomer 9a. [a]Dˆ2230 $cˆ2.15). MS: 249
$M1z2OCH3), 150 $100%). IR: 3500, 2950, 1640. 1H
NMR $400 MHz C6D6), 7.82 $d, 1H, Jˆ8 Hz), 7.29 $d,
1H, Jˆ8 Hz), 30-H and 60-H; 7.09 $dd, 1H, J,8 Hz), 6.92
$dd, 1H, Jˆ8 Hz), 40-H and 50-H; 4.55 $m, 1H, 5-H), 4.22
$1H, 2-H), 4.24 $bd, 1H, 6-Ha), 4.05 $dd, 1H,
J6a,6bˆ11.5 Hz, J5,6bˆ6.5 Hz, 6-Hb), 2.64 $s, 3H, OCH3),
1.87 $m, 1H, 4-Ha), 1.80 $m, 1H, 4-Hb), 1.62 $dd, 1H,
J3a,3bˆ13 Hz, J3,4aˆ7 Hz, 3-Ha), 1.44 $m, 1H, 3-Hb). 13C
NMR $50 MHz, C6D6), 134.0, 130.0, 129.1, 124.5 $CH,
Ar), 91.7 $C-2), 65.4 $C-6), 61.4 $C-5), 54.4 $OCH3), 29.8,
24.9 $C-3, C-4). CD [MeOH, cˆ0.81 mM, l nm $De)], 225
$22.3), 253 $14.5), 282 $25.3), 305 $20.2), 335 $25.8).
Anal.: C13H16N2O5; Calcd: C, 55.71; H, 5.75; N, 10.00.
Found: C, 55.59; H, 5.63; N, 9.98.
4.1.1. ꢀ5S)-5-ꢀ1-Ethoxy-ethoxymethyl)-1-ꢀ2-nitro-benzoyl)-
pyrrolidin-2-one 7. A solution of $5S)-5-$1-ethoxy-ethoxy-
methyl)-pyrrolidin-2-one $5.05 g, 27 mmol) in dry THF
$32 mL) was added dropwise to a suspension of NaH
$50% in oil, 1.30 g, 27 mmol) and potassium iodide
$4.48 g, 27 mmol) in dry THF $32 mL) at 08C under
argon. The mixture was stirred for 1.5 h at room temperature
and a solution of 2-nitrobenzoyl chloride $3.56 mL,
27 mmol) in dry THF $32 mL) was added dropwise. After
being stirred for 10 min at the same temperature, the reac-
tion medium was quenched with a saturated aqueous solu-
tion of ammonium chloride and extracted with ethyl acetate.
After the usual treatment, the crude product $9.0 g) was
puri®ed by column chromatography $eluent: heptane±
EtOAc 1:1) to give $5S)-5-$1-ethoxy-ethoxymethyl)-1-$2-
nitro-benzoyl)-pyrrolidin-2-one 7 $8.65 g, 95%). MS: 290
Minor diastereomer 9b. [a]Dˆ182 $cˆ1.15). MS: 249
$M1z2OCH3), 150 $100%). IR: 3500, 2930, 1640. 1H
NMR $400 MHz, C6D6), 7.87 $d, 1H, Jˆ8 Hz), 7.42 $d,
1H, Jˆ8 Hz), 30-H, 60-H; 7.09 $dd, 1H, Jˆ8 Hz), 6.89 $d,
1H, Jˆ8 Hz), 40-H, 50-H; 4.64 $m, 1H, 5-H), 4.14 $1H,
6-Ha), 4.12 $d, 1H, Jˆ3.5 Hz, 2-H), 4.07 $dd, 1H,
J6a,6bˆ11 Hz, J5,6bˆ4.5 Hz, 6-Hb), 3.62 $OH), 2.46 $s, 3H,
OCH3), 2.11 $m, 1H, 4-Ha), 1.73 $m, 2H, 4-Hb, 3-Ha), 1.50
$dd, 1H, J3a,3bˆ11.5 Hz, J3b,4aˆ7 Hz, 3-Hb). 13C NMR
$50 MHz, C6D6), 168.7 $CO), 146.5, 133.1 $C-10, C-20),
133.7, 129.9, 129.4, 124.1 $CH, Ar), 91.0 $C-2), 64.8
$C-6), 61.0 $C-5), 54.1 $OCH3), 29.4, 25.8 $C-3, C-4). CD
[MeOH, cˆ0.84 mM, l nm $De)], 225 $14.3), 252 $25.9),
282 $14.4), 305 $20.9), 335 $14.4).
$$M1z2NO2), 205, 150 $100%), 73. IR: 2985, 1750, 1682,
1
0
0
1530. H NMR $200 MHz), 8.20 $d, 1H, J3 ,4 ˆ8 Hz) and
7.32 $m, 1H), 30-H, 60-H; 7.70 and 7.55 $2 dd, 2H,
0
0
0
0
0
0
0
0
J3 ,4 ˆJ4 ,5 ˆJ5 ,6 ˆ8 Hz, 4 -H and 5 -H), 4.70 $m, CH±
CH3 and 5-H), 3.95 $m, 1H), 3.55 $m, 2H), 2.75 $m,1H),
2£CH2O), 2.30 $m, 4H, 3-H2 and 4-H2), 1.25 $m, 6H,
CHCH3 and CH2CH3).
4.1.4. ꢀ5S)-5-Acetoxymethyl-2-methoxy-1-ꢀ2-nitro-benzoyl)-
pyrrolidines 10. To a solution of $5S)-5-hydroxymethyl-2-
methoxy-1-$2-nitro-benzoyl)-pyrrolidines 9 $2.34 g, 8.35
mmol) in anhydrous pyridine $55 mL) was added dropwise
acetic anhydride $14 mL). After being stirred at room
temperature for 1 h, the mixture was cooled to 08C, before
the addition of methanol. After additional stirring for
30 min, the solvents were eliminated under reduced pres-
sure. Extraction of the product with EtOAc, washing of the
organic phases with aqueous NaHCO3 $5%) followed by
usual treatment gave $5S)-5-acetoxymethyl-2-methoxy-1-
$2-nitro-benzoyl)-pyrrolidines 10 $2.63 g, 98%).
4.1.2. ꢀ5S)-5-ꢀ1-Ethoxy-ethoxymethyl)-1-ꢀ2-nitro-benzoyl)-
pyrrolidin-2-ols 8. To a stirred solution of $5S)-5-$1-
ethoxy-ethoxymethyl)1-$2-nitro-benzoyl)-pyrrolidin-2-one
$3.50 g, 10.4 mmol) in dry toluene $100 mL), stirred at
2788C under argon, were added a solution of DIBAL±H
in toluene $1.5 M, 12.5 mL, 18.75 mmol) and, after 10 min,
a saturated aqueous solution of ammonium chloride. The
mixture was extracted with CH2Cl2 and treated as usual to
give the crude compound which was puri®ed by column
chromatography $eluent: heptane±ethyl acetate 1:3,
2.82 g, 80%). MS: 321 $$M1z2OH), 249, 226, 150
1
$100%). IR: 3340, 2930, 1683, 1530. H NMR $200 MHz)
Major diastereomer 10a. MS: 291 $M1z2OCH3), 249, 216,
172, 150 $100%). IR: 3530, 2950, 1745, 1650, 1530, 1405,
1350. 1H NMR $250 MHz), 8.13, 7.65 $2d, 2H, 30-H, 60-H),
7.50 $m, 2H, 50-H, 40-H), 4.50 and 4.30 $2m, 5-H and 6-H2),
2.92 $s, 2-OCH3), 2.18 and 1.95 $2m, 3-H2 and 4-H2), 2.07
$s, COCH3). CD [MeOH, cˆ1.24 mM, l nm $De)], 227
$22.7), 255 $13.2), 283 $22.5), 305 $10.9), 335 $22.9).
0
0
8.12 $d, 1H, J3 ,4 ˆ7 Hz, Ar±H), 7.58 $m, 3H, Ar±H), 4.90
$m, 2H, attributed to 2-H and CH±CH3), 4.7±3.5 $5H, 5-H
and 2£CH2O), 2.18 and 1.95 $2m, 4H, 4-H2 and 3-H2), 1.40
$dd, 3H, CHCH3), 1.25 $2t, 3H, Jˆ8 Hz, CH2CH3).
4.1.3. ꢀ5S)-5-Hydroxymethyl-2-methoxy-1-ꢀ2-nitro-ben-
zoyl)-pyrrolidines 9. p-Toluenesulfonic acid $2.14 g,
12.44 mmol) was added slowly to a stirred solution of 8
$4.46 g, 13.2 mmol) in a CH2Cl2±MeOH 9:1 mixture
$15 mL) at 08C. The mixture was stirred for 15 min before
Minor diastereomer 10b. IR: 3475, 2950, 1745, 1660, 1575,
1530, 1485. 1H NMR $250 MHz): 8.20, 7.70 $2d, 2H, 30-H,
60-H), 7.60 $m, 2H, 50-H, 40-H), 4.56 $m, 6-H2), 4.30 $m,

A. Rojas-Rousseau, N. Langlois / Tetrahedron 57 -2001) 3389±3395
3393
1H, 5-H), 4.00 $dd, J2,3aˆ6 Hz, J2,3bˆ2 Hz, 2-H), 2.71 $s,
2-OCH3), 2.17 and 1.88 $2m, 3-H2 and 4-H2), 2.07 $s,
COCH3). CD $MeOH, cˆ1.54 mM, l nm $De)], 222
$12.9), 254 $21.2), 283 $11.0), 305 $20.3), 335 $10.9).
After complete reaction, a saturated aqueous solution of
NH4Cl $10 mL) was added and the mixture was extracted
with ethyl acetate. Usual workup afforded the crude product
which was puri®ed by preparative TLC on silica gel
$eluent: CH2Cl2±MeOH 93:7) to give the $S)-5-acetoxy-
methyl-3-[2-$dimethylphosphono)-ethenyl]-1-$2-nitro-
benzoyl)-2-pyrroline 13 $380 mg, 87%). [a]Dˆ2142
$cˆ0.88). MS: 424 $M1z), 351, 347, 317, 230, 214
$100%), 150, 104. IR: 3003, 2950, 1748, 1669, 1661,
4.1.5.
ꢀS)-5-Acetoxymethyl-1-ꢀ2-nitro-benzoyl)-2-pyr-
roline 11. To a solution of $5S)-5-acetoxymethyl-2-
methoxy-1-$2-nitro-benzoyl)-pyrrolidines 10 $1.45 g, 4.5
mmol) in anhydrous toluene $11 mL) was added
quinoleinium camphosulfonate $0.245 g, 0.675 mmol).
After being stirred under argon at 1108C for 2 h, the solvent
was evaporated under vacuum. The crude product was puri-
®ed by ¯ash column chromatography $eluent: pentane±Et2O
1:3) to afford $S)-5-acetoxymethyl-1-$2-nitro-benzoyl)-2-
pyrroline 11 $1.23 g, 94%). [a]Dˆ2170 $cˆ0.26). MS:
290 $M1z), 249, 230, 150 $100%), 104, 80, 76. IR: 3100,
1
1529, 1416, 1350. H NMR $200 MHz): 8.24, 7.49 $2d,
2H, J,8 Hz, 30-H, 60-H), 7.80, 7.68 $2dd, 2H, Jˆ7 Hz,
H-40, H-50), 7.07 $dd, 1H, JP,Hˆ21 Hz, J7,8ˆ17 Hz, 7-H),
6.21 $s, 1H, 2-H), 5.43 $dd, 1H, JP,HˆJ7,8ˆ17 Hz, 8-H),
5.01 $m, 1H, 5-H), 4.63 $dd, 1H, J6a,6bˆ11 Hz, J6a,5ˆ5 Hz,
6-Ha), 4.34 $dd, 1H, J6a,6bˆ11 Hz, J6b,5ˆ4 Hz, 6-Hb), 3.69
$d, 6H, 2£P$O)OCH3), 3.08 $dd, 1H, J4a,4bˆ16 Hz,
1
2900, 2825, 1730, 1640, 1615, 1520. H NMR $200 MHz),
J4a,5ˆ11 Hz, 4-Ha), 2.66 $dd, 1H, J4a,4bˆ16 Hz, J4b,5ˆ
8.14 $dd, 1H, Jˆ7.5 Hz, J0ˆ1.5 Hz, Ar±H), 7.70±7.37 $m,
3H, Ar±H), 5.83 $m, 1H, 2-H), 5.09 $m, 1H, 3-H), 4,88 $m,
1H, 5-H), 4.39 $m, 2H, 6-H2), 2.98 $m, 1H, J4a,4bˆ17 Hz,
J4a,5ˆ10 Hz, 4-Ha), 2.50 $bd, 1H, J4a,4bˆ17 Hz, 4-Hb), 2.06
$s, 3H, COCH3). Anal.: C14H14N2O5; Calcd: C, 57.93; H,
4.86; N, 9.65. Found: C, 57.68; H, 5.01; N, 9.47.
4 Hz, 4-Hb), 2.09 $s, 3H, COCH3). 13C NMR $62.5 MHz),
170.8 $COCH3), 163.9 $CON), 145.3 $C-20), 141.9 $C-7),
134.7 $C-40), 133.2 $C-2), 131.1 $C-50), 130.9 $C-10), 128.6
$C-60), 124.9 $C-30), 123.1, 122.7 $C-3), 113.2, 110.2 $C-8),
63.5 $C-6), 57.0 $C-5), 52.3 $OCH3), 31.0 $C-4), 20.7
$COCH3).
4.1.6. ꢀS)-5-Acetoxymethyl-3-formyl-1-ꢀ2-nitro-benzoyl)-
2-pyrroline 12. Phosphorus oxychloride $2.05 mL,
22 mmol) was added at 08C under a nitrogen atmosphere
to DMF $1.7 mL, 22 mmol) and the mixture was stirred at
room temperature for 20 min. Excess of POCl3 was
removed by evaporation in the presence of toluene. To a
stirred solution of this reagent in dry dichloromethane
$6 mL) was added at 08C under argon a solution of $5S)-5-
acetoxymethyl-1-$2-nitro-benzoyl)-2-pyrroline 11 $0.481 g,
1.66 mmol) in CH2Cl2 $6 mL). After being stirred for 3.5 h
at room temperature, sodium carbonate was added until pH
14, and the mixture was extracted with CH2Cl2. The crude
product was puri®ed by column chromatography $ether) to
afford $S)-5-acetoxymethyl-3-formyl-1-$2-nitro-benzoyl)-
2-pyrroline 12 $0.529 g, 100%). Mpˆ94±968C $EtOAc±
Et2O). [a]Dˆ2219 $cˆ1.0). MS: 318 $M1z), 258, 150
$100%). IR: 2900, 2825, 1740, 1655, 1605, 1530. 1H
NMR $200 MHz), 9.37 $s, 1H, CHO), 8.21, 7.49 $2d, 2H,
4.1.8. ꢀS)-3-[2-ꢀDimethylphosphono)-ethenyl]-5-hydroxy-
methyl-1-ꢀ2-nitro-benzoyl)-2-pyrroline 14. A saturated
aqueous solution of Ba$OH)2 $2.6 mL) was added under
inert atmosphere to a solution of the acetate 13 $170 mg,
0.40 mmol) in dioxan $5.8 mL). The mixture was stirred at
room temperature until complete reaction and neutralized
by addition of CO2. After ®ltration, the product was
extracted with dichloromethane to give the primary alcohol
14 $131.4 mg, 86%) after usual workup. [a]Dˆ2114
$cˆ0.84). MS: 382 $weak, M1z), 317 $100%), 285, 261,
202, 170, 150. HRMS Calcd for C16H19N2O7P: 382.0930;
Found: 382.0943. IR: 3402, 1649, 1616, 1529, 1416, 1343.
1H NMR $200 MHz): 8.26, 7.49 $2d, 2H, Jˆ8 Hz, 30-H,
60-H), 7.80, 7.72 $2dd, 2H, 40-H, 50-H), 7.03 $dd, 1H,
JP,Hˆ21 Hz, J7,8ˆ17 Hz, 7-H), 6.20 $s, 1H, 2-H), 5.44 $dd,
1H, JP,HˆJ7,8ˆ17 Hz, 8-H), 4.84 $m, 1H, 5-H), 4.03 $bd, 1H,
J6a,6bˆ12, 6-Ha), 3.93 $dd, 1H, J6a,6bˆ12 Hz, J6b,5ˆ5 Hz, 6-
Hb), 3.68 $d, 6H, 2£P$O)OCH3), 3.07 $dd, 1H, J4a,4b
ˆ
Jˆ8 Hz, 30-H, 60-H), 7.79, 7.67 $2 dd, 2H, J3 ,4
ˆ
16 Hz, J4a,5ˆ11 Hz, 4-Ha), 2.65 $dd, 1H, J4a,4bˆ16 Hz,
J4b,5ˆ4 Hz, 4-Hb). 13C NMR $50 MHz), 164.9 $CO), 145.4
$C-20), 142.1 $C-7), 134.8 $C-40), 133.2 $C-2), 131.3 $C-10),
131.0 $C-50), 128.7 $C-60), 125.0 $C-30), 124.0, 123.5 $C-3),
113.8, 110.0 $C-8), 63.8 $C-6), 61.4 $C-5), 52.4 $OCH3),
31.2 $C-4).
0
0
0
0
0
0
0
0
J4 ,5 ˆJ5 ,6 ˆ8 Hz, 4 -H, 5 -H), 6.83 $s, 1H, 2-H), 5.00 $m,
1H, 5-H), 4.62 $dd, 1H, J6a,6bˆ11 Hz and J5,6aˆ5 Hz, 6-Ha),
4.27 $dd, 1H, J6a,6bˆ11 Hz, J5,6b,3 Hz, 6-Hb), 3.08 $dd, 1H,
J4a,4bˆ16 Hz and J4a,5ˆ10 Hz, 4-Ha), 2.79 $dd, 1H,
J4a,4bˆ16 Hz, J4b,5,3 Hz, 4-Hb), 2.07 $s, 3H, COCH3).
13C NMR: 185.7 $CHO), 170.8 $OCO), 164.8 $NCO),
145.4 $C-20), 144.5 $C-2), 134.9, 131.3, 128.6 and 125.0
$CH, Ar), 130.5 $C-10), 126.9 $C-3), 63.4 $C-6), 58.1
$C-5), 28.7 $C-4), 20.5 $COCH3). Anal.: C15H14N2O6;
Calcd: C, 56.60; H, 4.43; N, 8.80. Found: C, 56.52; H,
4.60; N, 8.68.
4.1.9. ꢀS)-3-[2-ꢀDimethylphosphono)-ethenyl]-5-formyl-
1-ꢀ2-nitro-benzoyl)-2-pyrroline 15. To dichloromethane
$2.5 mL) cooled to 2308C under argon was added dropwise
oxalyl chloride $0.11 mL, 1.26 mmol) and a solution of
DMSO $0.18 mL, 2.54 mmol) in CH2Cl2 $2.5mL). After
being stirred at 2308C for 0.3 h, a solution of primary
alcohol 14 $251 mg, 0.657 mmol) in CH2Cl2 $5.0 mL) was
added dropwise. The mixture was stirred at 2308C for 1.5 h,
then iPr2NEt $0.63 mL) was added and the mixture was
stirred for 10 min and at 08C for 20 min before the addition
of citrate±phosphate buffer $pH 5.6), followed by extraction
three times with EtOAc. Each organic phase was washed
three times with small amounts of H2O. Usual treatments
afforded the crude aldehyde 15 $247.1 mg, 99%), pure
4.1.7. ꢀS)-5-Acetoxymethyl-3-[2-ꢀdimethylphosphono)-
ethenyl]-1-ꢀ2-nitro-benzoyl)-2-pyrroline 13. To a solution
of tetramethyl methylenediphosphonate $264 mg, 1.13
mmol) in dry THF $5.0 mL) stirred at 08C under argon
was added nBuLi $1.5 M in hexane, 0.76 mL, 1.13 mmol).
After being stirred for 0.5 h at 08C a solution of $S)-5-acet-
oxymethyl-3-formyl-1-$2-nitro-benzoyl)-2-pyrroline 12
$329 mg, 1.03 mmol) in dry THF $10 mL) was added.

3394
A. Rojas-Rousseau, N. Langlois / Tetrahedron 57 -2001) 3389±3395
enough for the next step. A puri®cation by preparative TLC
$eluent: EtOAc±MeOH 9:1) give 15 $80% yield) containing
some methylacetal form. MS: 380 $M1z), 351, 317, 285,
230, 202, 170, 150 $100%), 94. HRMS: Calcd for
C16H17N2O7P $M1z): 380.0773; Found: 380.0794. IR:
1735, 1655, 1616, 1529, 1416, 1357. 1H NMR
$250 MHz): 9.87 $s, CHO), 8.27, 8.25 $2dd, 1H, Jˆ8 Hz,
J0ˆ1 Hz, Ar±H), 7.83, 7.80, 7.73, 7.70 $2 double dd, 40-H,
50-H), 7.57, 7.52 $1H, Ar±H), 7.05 $2dd, 1H, JP,Hˆ21 Hz,
J7,8ˆ17 Hz, 7-H), 6.35 $bs, 2-H), 6.23 $bs, 2-H, acetal),
5.46 $2dd, 1H, JP,HˆJ7,8ˆ17 Hz, 8-H), 5.23 $dd, Jˆ11 Hz,
J0ˆ5 Hz, 5-H), 4.86 $m, H-5, acetal), 3.70 $d, 6H,
2£P$O)OCH3), 3.50 $2s, OCH3, acetal), 3.2±2.6 $4-H2).
contribution and enthusiastic encouragements in CD
studies. We also thank C. Gaspard $ICSN) for performing
the bioassays and M.-E. Tran Hun Dau for modelization of 3
and 6.
References
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[1,4]benzodiazepine-5-one 6. A solution of aldehyde 15
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Ã
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Â
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1
332.0926; Found: 332.0910. H NMR $300 MHz): 8.01 $d,
1H, 6-H), 7.52 $bs, 1H, 3-H), 7.35 $1H, masked, 12-H), 7.30
$masked, 8-H), 6.87 $dd, 1H, 7-H), 6.63 $d, 1H, 9-H), 5.45
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4.2. Computational procedure
Ten thousand conformations of each compound, i.e. the
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Ã
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Acknowledgements
We thank Dr R. Z. Andriamialisoa for CD curves and we are
particularly indebted to the late Professor G. Snatzke for his
17. Jenkins, T. C.; Hurley, L. H.; Neidle, S.; Thurston, D. E.
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3395
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