Synthesis and biological evaluation of hydrophilic embelin derivatives

Article abstract of DOI:10.1016/j.tet.2012.04.024

In continuance of our search for newer anti-cancer agents we were interested on embelin, a XIAP (X-linked inhibitor of apoptosis protein) inhibitor. This natural benzoquinone bear a lipophilic chain and we report here the synthesis of hydrophilic analogue

Full text of DOI:10.1016/j.tet.2012.04.024

Tetrahedron 68 (2012) 4655e4663
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and biological evaluation of hydrophilic embelin derivatives
Marc Lamblin a, Antoine Sallustrau a, Claude Commandeur a, Thierry Cresteil b, Franc¸ ois-Xavier Felpin c,
,
Jean Dessolin a
*
a
ꢀ
Universite de Bordeaux, CNRS UMR 5248, CBMN, IECB, 2 rue Robert Escarpit, 33607 Pessac Cedex, France
b ICSN e CNRS, UPR 2301, avenue de la Terrasse, 91198 Gif sur Yvette, France
c
ꢀ
ꢁ
Universite de Nantes, UFR des Sciences et des Techniques, CNRS UMR 6230, CEISAM, 2 rue de la Houssiniere, 44322 Nantes Cedex 3, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 March 2012
Received in revised form 29 March 2012
Accepted 4 April 2012
Available online 14 April 2012
In continuance of our search for newer anti-cancer agents we were interested on embelin, a XIAP (X-
linked inhibitor of apoptosis protein) inhibitor. This natural benzoquinone bear a lipophilic chain and we
report here the synthesis of hydrophilic analogues of embelin. To allow a large flexibility in the nature of
the hydrophilic group, three amines with different length of carbon chain bearing a protected benzo-
quinone were prepared. The cytotoxic effects of these derivatives were evaluated on KB cell line.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Benzoquinone
Embelin
Hydrophilic analogues
1. Introduction
opportunity. Such drastic changes in the compound polarity, when
applied to the naphthoquinone scaffold led to enhanced cytotoxic
Embelin (1), a benzoquinone extracted from the Embelia ribes
and pro-apoptotic activity.10 Introduction of a polar group may also
improve water solubility and biodisponibility. We therefore envi-
sioned the preparation of embelin derivatives bearing a long hy-
drophilic chain in order to evaluate the potential of such
modification in the anti-cancer activity. We designed our targets
following the structure depicted in Fig. 2. Indeed, we envisioned the
introduction of an amine function on a short carbon chain for
a further ligation with an amino-acid group. Such modification
would provide useful information on the influence of the polarity of
the side chain for anti-cancer activity.
plant (Myrsinaceae), displays many biological activities known
since the antiquity.1 For instance, embelin showed effects on NF-
kB
signalling (nuclear factor kappa-light-chain-enhancer of activated
B cells)2 and on immunity and inflammation.3 Its capacity to inhibit
XIAP (X-linked inhibitor of apoptosis protein) and thus induce ap-
optosis has been also reported.4 It has been proven that embelin
enhances therapeutic efficacy of ionizing radiation in prostate
cancer.5 These rich biological activities make embelin an interesting
scaffold for medicinal chemists.
Embelin bears a lipophilic chain attached to a hydrophilic ben-
zoquinone moiety. A survey of literature precedents shows that
other benzoquinone based natural products, such as Iilimaquinone
(2)6 and metachromine A (3)7 (Fig. 1) share this common feature
(i.e., a lipophilic chain and a hydrophilic benzoquinone moiety) and
display interesting anti-cancer activities. Many embelin analogues
have been synthesized in the search of an improved anti-tumour
activity.1,8
Our group has been interested for a long time in the synthesis
and the biological evaluation of anti-cancer agents including qui-
none based compounds.9 Considering that modifications reported
in the literature so far, on the embelin scaffold, did not affect the
polarity of the linear chain,8 we were interested in exploring this
l
* Corresponding author. E-mail address: j.dessolin@iecb.u-bordeaux.fr(J. Dessolin).
Fig. 1. Benzoquinone based natural products bearing a lipophilic chain.
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.04.024

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M. Lamblin et al. / Tetrahedron 68 (2012) 4655e4663
Fig. 2. Benzoquinone based natural products bearing a lipophilic chain.
2. Results and discussion
The synthesis of the embelin derivatives involved three com-
mon precursors, 11, 13 and 17, depending on the length of the car-
bon chain, that were prepared from commercially available 2,4,5-
trimethoxybenzaldehyde 1 (Scheme 1). A BaeyereVilliger oxida-
tion of 4 followed by a hydrolysis with potassium hydroxide under
alcoholic conditions furnished the 2,4,5-trimethoxyphenol 5 in 83%
yield.11 Treatment of the phenol with allyl bromide provided 6,
which can be submitted to a Claisen rearrangement upon heating in
a microwave oven at 190 ꢀC in neat conditions to lead to the
allylphenol 7 in 92% yield. To access the two-carbon chain carba-
mate 10, an oxidative cleavage of the olefin should provide an easy
to functionalize aldehyde, thus the phenol function of 7 needed
a suitable protection. The phenol was masked with a TBS group by
treatment of 7 with TBSCl in presence of imidazole. Olefin 8 was
then submitted to a LemieuxeJohnson oxidative cleavage and 9
was obtained in 89% yield. The aldehyde 9 was converted into the
carbamate 10 by a reductive carbamatation with tert-butyl carba-
mate in 89% yield.12 The TBS protecting group was easily removed
by treatment with TBAF to furnish the two-carbon chain carbamate
11 in 90% yield.
Scheme 2. (a) (1) HMTA, TFA, (2) HCl, THF, 47%; (b) TBDMSiH, BocNH2, TFA, CH3CN,
86%; (c) TBSCl, imidazole, DMF, 92%; (d) (Ph)3PþCH2CN,Clꢁ
quantitative.
, NaOH, H2O, DCM,
Alternatively, the phenol function of compound 12 was protected as
a silyl ether and the resulting aldehyde 14 was transformed by
a Wittig reaction to the phenylacrylonitrile 15. Hydrogenation of
compound 15 could give a direct access to the corresponding three-
carbon chain analogues of embelin.
As shown in Scheme 3, the precursors prepared above were
used to prepare a variety of compounds. Carbamates 11 and 13 were
Boc deprotected and the crude resulting amines were directly
coupled with N-Boc protected amino-acids to generate a series of a-
benzyl and
spectively.
a
-phenethylamidocarbamates 16aef and 17aec, re-
a-(Phenyl)propylamidocarbamates 18aec were pre-
pared by hydrogenation of the phenylacrylonitrile 15 followed by
coupling of the resulting amine with N-Boc protected amino-acids
and TBAF deprotection of the phenol.
Scheme 3. Reagents and conditions: (a) (1) TFA, DCM, (2) BocNHCH(R)CO2H, EDC$HCl,
HOBt, DIPEA, DMF, 64e96%; (b) (1) H2, PtO2, EtOH/CHCl3, (2) BocNHCH(R)CO2H,
EDC$HCl, HOBt, DIPEA, DMF, 64e77%.
Generation of the para-quinone cycle was performed by oxida-
tion of phenols 16aef, 17aec and 18aec with (diacetoxyiodo)
benzene (Scheme 4). Hydrolysis of the methoxy of the benzoqui-
nones moieties and Boc deprotection of amines were performed by
hydrochloric acid treatment to furnish a series of embelin de-
rivatives with three different carbon chain lengths and various
terminal amino-acids.
Scheme 1. Reagents and conditions: (a) (1) mCPBA, DCM, (2) KOH, EtOH, 83%; (b) allyl
bromide, K2CO3, acetone, 97%; (c) MW, 190 ꢀC, 30 min, 92%; (d) TBSCl, imidazole, DMF,
98%; (e) OsO4, NaIO4, Et2O/H2O/tBuOH, 89%; (f) TBDMSiH, BocNH2, TFA, CH3CN, 89%;
(g) TBAF, Et3N, THF, 90%.
In order to provide analogues bearing side chain of one- and
three-carbon (Scheme 2), 2-hydroxy-3,5,6-trimethoxybenzal-
dehyde 12 was prepared by a Duff reaction on phenol 5. Sub-
sequently, the aldehyde function was converted into the
corresponding one-carbon chain carbamate 13 by a reductive car-
bamatation with tert-butyl carbamate in 86% yield, to provide the
one-carbon chain carbamate precursor of embelin derivatives.
Compounds 16aef, 17aec, 18aec, 19aef, 20aec, 21aec, 22aef,
23aec and 24aec (Table 1) were evaluated for their cytotoxic effect
on KB cell line, with no activity, while embelin display an IC50 of
5.58 mM under the same conditions. Since none of the new syn-
thesized analogues displayed any cytotoxic activity, we suspect
that changing the polarity of embelin side chain might result in
a poor cellular uptake. Amphiphilic disubstituted compounds,

M. Lamblin et al. / Tetrahedron 68 (2012) 4655e4663
4657
4. Experimental section
4.1. General remarks
All commercial solvents and reagents were used as received
from the Aldrich Chemical Company, Fischer Scientific Ltd, Alfa
Aesar Company or TCI Europe company. All glassware was flame
dried and allowed to cool under a stream of dry argon. Silica gel
(40e63 mm) used in flash column chromatography was obtained
from Merck and was pre-coated with oxalic acid.13 Analytical thin-
layer chromatography (TLC) was performed on silica gel plates
(TLC silica gel 60 F254 purchased from Merck), visualized with
a Spectroline UV254 lamp, and stained with a basic solution of
KMnO4. Solvent systems associated with Rf values and flash col-
umn chromatography are reported as percent by volume values. 1H
Scheme 4. Reagents and conditions: (a) PhI(OAc)2, CH3CN/H2O, 54e77%; (b) HCl,
MeOH, 73e89%.
Table 1
Structures of embelin derivatives and intermediates
Entry
R
Entry
R
Entry
R
16a
16b
16c
16d
eCH3
19a
19b
19c
19d
eCH3
22a
22b
22c
22d
eCH3
eCH2OtBu
eCH2OtBu
eCH2OH
eCH(CH3)OtBu
eCH(CH3)OBn
eCH(CH3)OtBu
eCH(CH3)OBn
eCH(CH3)OtBu
eCH(CH3)OBn
CH2
CH2
CH2
16e
16f
19e
19f
22e
22f
NH
NH
NH
CH2
OtBu
CH2
OtBu
CH2
OH
17a
17b
17c
18a
18b
18c
eCH3
20a
20b
20c
21a
21b
21c
eCH3
23a
23b
23c
24a
24b
24c
eCH3
eCH2OtBu
eCH(CH3)OtBu
eCH3
eCH2OtBu
eCH(CH3)OtBu
eCH3
eCH2OH
eCH(CH3)OH
eCH3
eCH2OH
eCH(CH3)OH
eCH2OtBu
eCH(CH3)OtBu
eCH2OtBu
eCH(CH3)OtBu
bearing both hydrophobic and hydrophilic moiety could be the
key to biological properties.
and 13C NMR, recorded at 300 MHz and 75 MHz, respectively, were
performed on Brucker Advance 300 spectrometer. Proton
chemical shifts were internally referenced to the residual proton
resonance in CDCl3 7.26 ppm), CD3OD ( 3.31 ppm). Carbon
chemical shifts were internally referenced to the deuterated sol-
vent signals in CDCl3 77.2 ppm), CD3OD ( 49.0 ppm). FT-IR
a
(
d
d
3. Conclusion
(
d
d
In summary, we have described the synthesis of a library of
hydrophilic embelin analogues. An efficient diverted synthesis
approach has been developed from the common precursor 5.
Preliminary biological studies showed that our targets did not
display any cytotoxic activity on tumoral cells. Although these
results were disappointing, it provided useful information for the
establishment of a comprehensive structureeactivity relationship
of embelin analogues. In order to improve water solubility and
biodisponibility of embelin, but still maintaining a hydrophobe
side chain required for the pro-apoptotic activity, we are now
working on the preparation of amphiphilic agents. These results
will be disclosed in due course.
spectra were recorded on a Bruker IRFT IFS55 spectrometer with
samples loaded as neat films on ZnSe plates or as a powder mixed
with KBr.
4.2. Experimental procedures
4.2.1. 2,4,5-Trimethoxyphenol (5). mCPBA (9.4 g, 70 wt %,
38.25 mmol, 1.5 equiv) was added dropwise to stirred solution of
2,4,5-trimethoxybenzaldehyde 1 (5 g, 25.5 mmol, 1 equiv) in
50 mL of DCM at 0 ꢀC. After addition was complete, the ice bath
was removed and the mixture allowed warming to room

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M. Lamblin et al. / Tetrahedron 68 (2012) 4655e4663
temperature for 2 h. The reaction mixture was filtered, then the
organic solution was washed with aq NaHCO3 (2ꢂ20 mL), H2O
(20 mL) and brine (20 mL). The solution was then concentrated
giving a dark yellow oil that was dissolved in EtOH (25 mL) and
stirred with 10% KOH (25 mL) at 50 ꢀC for 2 h. The mixture was
acidified to pH 1 with 1 M HCl and extracted with DCM (4ꢂ40 mL).
The combined organic layers were washed with H2O (50 mL),
brine (50 mL) and then dried (MgSO4). The solution was concen-
trated and the residual oil was purified by silica gel column
chromatography (20% EtOAc in hexanes) providing the phenol 5 in
83% yield (3.9 g, 21.2 mmol). The spectroscopic data for these
compounds were identical to those reported in the literature.14
Rf¼0.25 (20% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3)
(ZnSe) n
2860, 1630, 1514, 1460, 1410, 1190, 1079, 890 cmꢁ1; HRMS
(ESI-TOF) calcd for [MþNaþ]: 361.1811; found: 361.1816.
4.2.5. 2-(2-(tert-Butyldimethylsilyloxy)-3,5,6-trimethoxyphenyl)ac-
etaldehyde (9). 3.15 mL (0.157 mmol, 0.025 equiv) of a 0.05 M so-
lution of OsO4 in tBuOH were added to a stirred solution of alkene 8
(2.13 g, 6.3 mmol, 1 equiv) in Et2O (125 mL). The resulting dark
solution was stirred for 10 min prior to the addition of H2O (125 mL)
and finely powdered NaIO4 (2.69 g, 12.6 mmol, 2 equiv). The re-
action mixture was then vigorously stirred at room temperature for
20 h. 3.15 mL (0.157 mmol, 0.025 equiv) of a 0.05 M solution of OsO4
t
in BuOH were added to the reaction and the mixture was further
stirred for 20 h. The organic fraction was separated, then washed
with 1 M Na2S2O4 (50 mL), water (50 mL), brine (50 mL) and then
dried (Na2SO4). The solution was concentrated and the residual oil
was purified on silica gel chromatography (10e20% EtOAc in hex-
anes) to provide 1.78 g (5.23 mmol) of aldehyde 9 in 89% yield.
d
6.61 (1H, s), 6.58 (1H, s), 3.85 (3H, s), 3.84 (3H, s), 3.81 (3H, s); 13
C
NMR (75 MHz, CDCl3)
d 143.7, 143.1, 141.9, 139.5, 100.8, 99.5, 57.0,
56.8, 56.3; mp¼62e63 ꢀC; IR (ZnSe)
n 3415, 3080, 3005, 2940,
2840, 1625, 1525, 1200, 855 cmꢁ1
.
Rf¼0.33 (20% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3)
d 9.65
4.2.2. 1-(Allyloxy)-2,4,5-trimethoxybenzene (6). Freshly distillated
allyl bromide (2.8 mL, 32.2 mmol, 1.5 equiv) and K2CO3 (29.7 g,
215 mmol, 10 equiv) were added to the phenol 5 (3.96 g, 21.5 mmol,
1 equiv) dissolved in dry acetone (300 mL). The reaction mixture
was then refluxed for 20 h. After cooling to room temperature, the
mixture was filtered over a pad of Celite, the precipitate was
washed with acetone (50 mL) and combined organic fractions were
concentrated. The residual oil was chromatographed on silica gel
(10e20% EtOAc in hexanes) to provide 4.66 g (20.8 mmol) of ally-
lated phenol 6 in 97% yield as a white solid. Rf¼0.32 (15% EtOAc in
(1H, t, J¼1.8 Hz), 6.50 (1H, s), 3.85 (3H, s), 3.78 (3H, s), 3.72 (3H, s),
3.71 (2H, d, J¼1.8 Hz), 0.96 (9H, s), 0.16 (6H, s); 13C NMR (75 MHz,
CDCl3)
d 200.1, 146.5, 146.1, 141.4, 137.0, 119.0, 98.0, 60.6, 56.6, 55.3,
39.9, 26.1 (3C), 18.7, ꢁ3.9 (2C); IR (ZnSe)
n 2930, 1727, 1585, 1251,
1083, 912, 840, 780 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]:
363.1604; found: 363.1599.
4.2.6. tert-Butyl-2-(tert-butyldimethylsilyloxy)-3,5,6-trimethoxyphen-
ethylcarbamate (10). TBDMSiH (1.18 mL, 7.3 mmol, 2 equiv) was
added to a stirred solution of aldehyde 9 (1.24 g, 3.65 mmol,1 equiv),
hexanes); 1H NMR (300 MHz, CDCl3)
d
6.64 (1H, s), 6.61 (1H, s), 6.09
tert-butyl carbamate (855 mg, 7.3 mmol, 2 equiv) and TFA (562 mL,
(1H, ddt, J¼17.2, 10.5, 5.5 Hz), 5.43 (1H, dq, J¼17.2, 1.5 Hz), 5.28 (1H,
7.3 mmol, 2 equiv) in CH3CN (15 mL). The solution was stirred at
room temperature for 18 h, then diluted with Et2O (30 mL), washed
with aqueous NaHCO3 (20 mL), brine (20 mL) and dried (MgSO4).
The solution was concentrated and the residual oil was purified on
silica gel chromatography (20% EtOAc in hexanes) to provide 1.47 g
(3.32 mmol) of carbamate 10 in 89% yield. Rf¼0.25 (20% EtOAc in
dq, J¼10.5, 1.3 Hz), 5.07 (2H, dt, J¼5.5, 1.5 Hz), 3.87 (3H, s), 3.86 (3H,
s), 3.84 (3H, s); 13C NMR (75 MHz, CDCl3)
d 144.0, 143.7, 143.0, 141.9,
133.9, 117.7, 103.3, 100.8, 71.6, 57.2, 56.8 (2C); mp¼26e27 ꢀC; IR
(ZnSe)
n 742, 927, 997, 1026, 1124, 1224, 1251, 1454, 1504, 1593,
2835, 2935 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 247.0946;
found: 247.0953.
hexanes); 1H NMR (300 MHz, CDCl3)
d
6.43 (1H, s), 3.85 (3H, s), 3.80
(3H, s), 3.78 (3H, s), 3.33 (2H, q, J¼5.4 Hz), 2.88 (2H, t, J¼6.0 Hz), 1.42
(9H, s), 1.01 (9H, s), 0.19 (6H, s); 13C NMR (75 MHz, CDCl3)
156.0,
146.6, 145.9, 141.4, 136.8, 117.1, 96.9, 78.6, 60.9, 56.5, 55.2, 41.2, 28.4
4.2.3. 2-Allyl-3,4,6-trimethoxyphenol (7). Neat 1-(allyloxy)-2,4,5-
trimethoxybenzene 6 (1 g, 4.45 mmol) was heated on a Biostage
Initiator microwave reactor at 190 ꢀC for 30 min. After cooling, the
dark oil was purified on silica gel chromatography (10e30% EtOAc
in hexanes) to provide 921 mg (4.1 mmol) of product 7 in 92% yield.
The spectroscopic data for these compounds were identical to those
reported in the literature.15 Rf¼0.37 (30% EtOAc in hexanes); 1H
d
(3C), 26.2 (3C), 24.2, 18.8, ꢁ3.8 (2C); IR (ZnSe)
n 3001, 2852, 1682,
1604, 1499, 1392, 1245, 1056, 1032, 970, 851 cmꢁ1; HRMS (ESI-TOF)
calcd for [MþNaþ]: 464.2444; found: 464.2401.
4.2.7. tert-Butyl-2-hydroxy-3,5,6-trimethoxyphenethylcarbamate
(11). TBAF (3.34 mL of a 1 M solution in THF, 3.34 mmol, 2 equiv)
was added to a stirred solution of silylated phenol 10 (717 mg,
NMR (300 MHz, CDCl3)
d
6.48 (1H, s), 6.04 (1H, ddt, J¼17.1, 10.0,
6.1 Hz), 5.34 (1H, br s), 5.11e4.98 (2H, m), 3.89 (3H, s), 3.86 (3H, s),
3.79 (3H, s), 3.48 (2H, dt, J¼6.1, 1.6 Hz); 13C NMR (75 MHz, CDCl3)
1.67 mmol, 1 equiv) and Et3N (700 mL, 5.01 mmol, 3 equiv) in THF
d
145.4, 142.0, 141.5, 137.6, 136.4, 120.3, 114.3, 96.7, 60.7, 56.3, 56.0,
(10 mL). The solution was stirred at room temperature for 1 h
then concentrated and directly loaded on silica gel chromatog-
raphy (50% EtOAc in hexanes) to provide 493 mg (1.5 mmol) of
phenol 11 in 90% yield. Rf¼0.15 (30% EtOAc in hexanes); 1H NMR
28.0; IR (ZnSe)
n 3450, 2830, 1640, 1620, 1510, 1460, 1450, 1410,
1200, 1035, 1000, 915 cmꢁ1
.
4.2.4. (2-Allyl-3,4,6-trimethoxyphenoxy)(tert-butyl)dimethylsilane
(8). TBSCl (978 mg, 6.5 mmol, 1.4 equiv) and imidazole (751 mg,
11,0 mmol, 2.4 equiv) were added to a stirred solution of phenol 7
(1.04 g, 4.6 mmol, 1 equiv) in DMF (4.6 mL) at room temperature.
The mixture was stirred at room temperature for 20 h and parti-
tioned between Et2O (50 mL) and H2O (50 mL). The organic layer
was further washed with H2O (20 mL), brine (20 mL) and then dried
(MgSO4). The solution was concentrated in vacuum and the residual
oil was purified on silica gel chromatography (5e10% EtOAc in
hexanes) to provide 1.54 g (4.5 mmol) of protected phenol 8 in 98%
yield. Rf¼0.69 (10% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3)
(300 MHz, CDCl3) d 6.48 (1H, s), 3.88 (3H, s), 3.85 (3H, s), 3.80
(3H, s), 3.43e3.27 (2H, m), 2.90 (2H, t, J¼7.0 Hz), 1.43 (9H, s); 13C
NMR (75 MHz, CDCl3)
d 156.2, 145.6, 142.3, 142.0, 138.1, 119.9, 97.1,
78.8, 61.1, 56.9, 56.4, 40.7, 28.4 (3C), 24.0; IR (ZnSe)
n 3405 (br s),
2975, 2840, 1694, 1505, 1392, 1366, 1250, 1088, 1029, 974,
862 cmꢁ1; HRMS (ESI-TOF) calcd for [MþHþ]: 328.1760; found:
328.1783.
4.2.8. 2-Hydroxy-3,5,6-trimethoxybenzaldehyde (12). A solution of
phenol 5 (3.6 g, 19.5 mmol, 1 equiv) and HMTA (3.0 g, 21.5 mmol,
1.1 equiv) in TFA (40 mL) under Ar was refluxed for 20 h. The so-
lution was cooled to room temperature and concentrated in vac-
uum. Toluene (20 mL) was added to the residue and the solution
was further concentrated to remove traces of TFA. 20 mL of THF and
20 mL of 2 M HCl were added to the residual oil and the mixture
d
6.42 (1H, s), 6.07e5.91 (1H, m), 5.02e4.92 (2H, m), 3.85 (3H, s),
3.78 (3H, s), 3.77 (3H, s), 3.46 (2H, dt, J¼5.9, 1.7 Hz), 1.00 (9H, s), 0.18
(6H, s); 13C NMR (75 MHz, CDCl3)
146.7, 145.9, 141.4, 137.1, 136.7,
125.7, 114.6, 96.7, 61.0, 56.6, 55.2, 28.9, 26.2 (3C), 18.9, ꢁ3.8 (2C); IR
d

M. Lamblin et al. / Tetrahedron 68 (2012) 4655e4663
4659
was refluxed for 2 h. The solution was cooled to room temperature
and extracted with DCM (4ꢂ50 mL), combined organic layers were
washed with brine (50 mL) and dried (MgSO4). The solution was
concentrated and the residual oil was purified on silica gel chro-
matography (40% EtOAc in hexanes) to provide 1.94 g (9.16 mmol)
of benzaldehyde 12 in 47% yield. Rf¼0.45 (40% EtOAc in hexanes);
784 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 372.1607; found:
372.1611.
4.3. General procedure for deprotection of tert-butyl
carbamates 11 and 13 and peptide coupling, synthesis of 16aef
and 17aec
1H NMR (300 MHz, CDCl3)
d
11.38 (1H, s), 10.31 (1H, s), 6.89 (1H, s),
3.95 (3H, s), 3.90 (3H, s), 3.88 (3H, s); 13C NMR (75 MHz, CDCl3)
TFA (3 mL) was added to a solution of carbamate 11, or 13
(1 mmol, 1 equiv) in DCM (3 mL) at 0 ꢀC. The solution was stirred at
0 ꢀC for 30 min then toluene (6 mL) was added and the solution was
concentrated in vacuum. Toluene (6 mL) was added to the residue
and the solution was further concentrated to remove the residual
TFA providing crude amino salts, which were used without further
purification in peptide coupling. The corresponding amino salt was
dissolved in DMF (10 mL) then the N-protected amino-acid
d
195.4, 146.4, 144.9, 143.8, 143.6, 114.5, 109.5, 62.4, 57.7, 57.0;
mp¼82e83 ꢀC (lit.16 84 ꢀC); IR (ZnSe)
n 3210, 1660, 1605, 1453, 1397,
1326, 1261, 1074, 951, 742, 713 cmꢁ1; HRMS (ESI-TOF) calcd for
[MþNaþ]: 235.0582; found: 235.0581.
4.2.9. tert-Butyl-2-hydroxy-3,5,6-trimethoxybenzylcarbamate
(13). TBDMSiH (873
mL, 5.45 mmol, 2.9 equiv) was added to
a stirred solution of benzaldehyde 12 (400 mg, 1.88 mmol, 1 equiv),
tert-butyl carbamate (640 mg, 5.45 mmol, 2.9 equiv) and TFA
(274 mL, 3.57 mmol, 1.9 equiv) in CH3CN (7.5 mL). The solution was
(1 mmol, 1 equiv), DIPEA (697 mL, 4 mmol, 4 equiv), HOBt
(675 mmol, 5 mmol, 5 equiv) were added. The mixture was cooled
to 0 ꢀC, then EDC$HCl (211 mg, 1.1 mmol, 1.1 equiv) was added. The
mixture was stirred at room temperature overnight, then diluted
with Et2O (60 mL), washed with 1 M NaOH (20 mL), H2O (20 mL),
1 M HCl (20 mL), H2O (20 mL), brine (20 mL) and dried (Na2SO4).
The reaction was concentrated in vacuum providing the product,
which was used pure enough for the next step.
stirred at room temperature for 18 h, then diluted with Et2O
(30 mL), washed with aqueous NaHCO3 (20 mL), brine (20 mL) and
dried (MgSO4). The solution was concentrated and the residual oil
was purified on silica gel chromatography (40% EtOAc in hexanes)
to provide 506 mg (1.61 mmol) of carbamate 13 in 86% yield.
Rf¼0.34 (40% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3)
d 6.53
(1H, s), 4.34 (2H, d, J¼6.4 Hz), 3.87 (3H, s), 3.84 (3H, s), 3.82 (3H, s),
4.3.1. (S)-tert-Butyl-1-(2-hydroxy-3,5,6-trimethoxybenzylamino)-1-
1.43 (9H, s); 13C NMR (75 MHz, CDCl3)
138.9, 120.2, 99.4, 80.1, 61.2, 56.9, 56.7, 34.4, 28.3 (3C); IR (ZnSe)
d
157.5, 145.4, 144.1, 141.3,
oxopropan-2-ylcarbamate (16a). Yield 89%; Rf¼0.41 (80% EtOAc in
n
hexanes); 1H NMR (300 MHz, CDCl3,
d ppm) d 6.53 (1H, s), 4.46
3421 (br s), 2992, 2840, 1701, 1406, 1343, 1275, 1080, 1051, 966,
842 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 336.1423; found:
336.1432.
(2H, d, J¼6.2 Hz), 4.25e4.09 (1H, m), 3.86 (3H, s), 3.83 (3H, s),
3.82 (3H, s), 1.41 (9H, s), 1.33 (3H, d, J¼7.1 Hz); 13C NMR (75 MHz,
CDCl3,
d ppm) d 172.0, 156.3, 146.3, 145.2, 142.2, 139.9, 120.1,
100.5, 81.0, 62.1, 61.3, 57.8, 57.5, 34.5, 29.1 (3C), 19.2; IR (ZnSe)
n
4.2.10. 2-(tert-Butyldimethylsilyloxy)-3,5,6-trimethoxybenzaldehyde
(14). TBSCl (143 mg, 0.95 mmol, 1.4 equiv) and imidazole (111 mg,
1.63 mmol, 2.4 equiv) were added to a stirred solution of phenol 12
(145 mg, 0.68 mmol, 1 equiv) in DMF (1 mL) at room temperature.
The mixture was stirred at room temperature for 20 h and parti-
tioned between Et2O (20 mL) and H2O (20 mL). The organic layer
was further washed with H2O (10 mL), brine (10 mL) and then
dried (MgSO4). The solution was concentrated in vacuum and the
residual oil was purified on silica gel chromatography (20% EtOAc
in hexanes) to provide 204 mg (0.62 mmol) of protected phenol 14
in 92% yield. Rf¼0.34 (20% EtOAc in hexanes); 1H NMR (300 MHz,
3401 (br), 2975, 2942, 1717, 1492, 1366, 1245, 1088, 974,
733 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 407.1794; found:
407.187.
4.3.2. (S)-tert-Butyl-3-tert-butoxy-1-(2-hydroxy-3,5,6-trimethoxy-
benzylamino)-1-oxopropan-2-ylcarbamate
(16b). Yield
93%;
Rf¼0.64 (80% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3,
d
ppm) d 6.52 (1H, s), 4.54e4.36 (2H, m), 4.25e4.10 (1H, br s), 3.84
(3H, s), 3.81 (6H, s), 3.78e3.64 (1H, br s), 3.44e3.22 (1H, br s), 1.42
(9H, s), 1.09 (9H, s); 13C NMR (75 MHz, CDCl3,
ppm) 172.3,
155.4, 145.4, 144.4, 141.5, 139.1, 119.5, 100.0, 80.0, 73.8, 61.7, 61.2,
60.3, 57.0, 56.7, 33.6, 28.2 (3C), 27.2 (3C); IR (ZnSe) 3389 (br),
d
d
CDCl3)
(3H, s), 1.00 (9H, s), 0.18 (6H, s); 13C NMR (75 MHz, CDCl3)
147.71, 147.66, 144.3, 142.1, 123.6, 105.8, 62.9, 58.2, 56.7, 26.7 (3C),
d
10.46 (1H, s), 6.75 (1H, s), 3.87 (3H, s), 3.85 (3H, s), 3.82
n
d
191.0,
2939, 1715, 1661, 1490, 1395, 1360, 1250, 1224, 1132, 1089, 1025,
914, 738 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 479.2369;
found: 479.2383.
19.7, ꢁ3.3 (2C); IR (ZnSe)
n 2930, 1854, 1724, 1549, 1230, 1075, 826,
770 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 349.1447; found:
349.1419.
4.3.3. tert-Butyl-(2S,3R)-3-tert-butoxy-1-(2-hydroxy-3,5,6-
trimethoxybenzylamino)-1-oxobutan-2-ylcarbamate
(16c). Yield
4.2.11. (E)-3-(2-(tert-Butyldimethylsilyloxy)-3,5,6-trimethoxyphenyl)
acrylonitrile (15). To a solution of benzaldehyde 14 (234 mg,
0.71 mmol, 1 equiv) in DCM (13 mL) at 25 ꢀC were added succes-
sively a 30% sodium hydroxide aqueous solution (13 mL) and
94%; Rf¼0.70 (80% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3,
d
ppm)
d
6.51 (1H, s), 4.48 (1H, dd, J¼14.1, 6.3 Hz), 4.37 (1H, dd,
J¼14.1, 6.3 Hz), 4.02e4.15 (1H, m), 3.82 (3H, s), 3.81 (3H, s), 3.80
(3H, s), 3.77e3.79 (1H, m), 1.40 (9H, s), 1.14 (9H, s), 0.95 (3H, d,
(cyanomethyl)triphenylphosphonium
chloride
(383
mg,
J¼6.2 Hz); 13C NMR (75 MHz, CDCl3,
d ppm) d 172.0, 156.4, 146.3,
1.13 mmol, 1.6 equiv). After 30 min stirring, 25 mL of water were
added, the organic layer was decanted, and the aqueous layer was
extracted with DCM. The gathered organic layers were dried over
MgSO4 and evaporated under reduced pressure. The residual oil
was purified on silica gel chromatography (20% EtOAc in hexanes)
to provide 248 mg (0.71 mmol) of cyanostyrene 15 in quantitative
yield. Rf¼0.33 (20% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3)
145.4, 142.3, 139.9, 120.4, 100.9, 80.6, 75.9, 67.8, 62.1, 61.2, 57.8, 57.7,
34.9, 29.2 (3C), 29.1 (3C), 15.0; IR (ZnSe)
n 3407 (br), 2907, 1715,
1496, 1367, 1257, 1079, 863, 737 cmꢁ1; HRMS (ESI-TOF) calcd for
[MþNaþ]: 493.2526; found: 493.2497.
4.3.4. tert-Butyl-(2S,3R)-3-(benzyloxy)-1-(2-hydroxy-3,5,6-
trimethoxybenzylamino)-1-oxobutan-2-ylcarbamate
(16d). Yield
d
7.67 (1H, d, J¼16.9 Hz), 6.59 (1H, s), 6.48 (1H, d, J¼16.9 Hz), 3.87
(3H, s), 3.80 (3H, s), 3.76 (3H, s), 1.01 (9H, s), 0.16 (6H, s); 13C NMR
(75 MHz, CDCl3) 146.7, 143.1, 142.2, 137.9, 119.8, 119.1, 101.3, 100.3,
60.2, 56.8, 55.5, 25.9 (3C), 18.7, ꢁ4.0 (2C); IR (ZnSe) 2927, 2856,
2215, 1612, 1584, 1487, 1434, 1352, 1256, 1229, 1104, 1064, 979, 839,
82%; Rf¼0.57 (80% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3,
d
ppm) d 7.39e7.22 (4H, m), 7.20e7.10 (1H, m), 6.52 (1H, s),
d
4.67e4.04 (6H, m), 3.83 (3H, s), 3.81 (3H, s), 3.75 (3H, s), 1.44
n
(9H, s), 1.15 (3H, dd, J¼6.4, 21.7 Hz); 13C NMR (75 MHz, CDCl3,
d
ppm) d 171.7, 155.8, 145.4, 144.4, 141.4, 139.0, 137.8, 128.4,

4660
M. Lamblin et al. / Tetrahedron 68 (2012) 4655e4663
128.3, 127.9, 127.8, 127.7, 119.2, 99.8, 80.2, 74.6, 71.6, 61.2, 57.8,
56.9, 56.6, 33.8, 28.3 (3C), 15.7; IR (ZnSe) 3418 (br), 2980,
733 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 507.2682; found:
n
507.2687.
2905, 2250, 1718, 1495, 1394, 1365, 1350, 1257, 1087, 970,
737 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 527.2369; found:
527.2373.
4.4. General procedure for peptide coupling from
cyanostyrenes, synthesis of 18aec
4.3.5. (S)-tert-Butyl-1-(2-hydroxy-3,5,6-trimethoxybenzylamino)-3-
(1H-indol-3-yl)-1-oxopropan-2-ylcarbamate
(16e). Yield
88%;
ppm)
A stirred suspension of cyanostyrene 15 (1 mmol, 1 equiv)
in absolute EtOH (5 mL) and CHCl3 (250 mL) containing PtO2
Rf¼0.43 (80% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3,
d
d
7.56 (1H, d, J¼7.8 Hz), 7.29 (1H, d, J¼8.4 Hz), 7.13 (1H, t, J¼7.2 Hz),
(0.1 g%) was placed under H2 at atmospheric pressure and the
mixture was stirred at room temperature for 20 h. The re-
action mixture was then filtered through a Celite pad and
washed with EtOH. Evaporation of solvent afforded the cor-
responded amine, which was directly submitted to peptide
coupling. The amine was dissolved in DMF (10 mL) then the
7.03 (1H, t, J¼7.5 Hz), 6.85 (1H, s), 6.53 (1H, s), 4.48 (1H, br s), 4.33
(2H, br s), 3.84 (3H, s), 3.81 (3H, s), 3.71 (3H, s), 3.35e2.98 (2H, br s),
1.40 (9H, s); 13C NMR (75 MHz, CDCl3,
d ppm) d 173.5, 155.5, 145.3,
144.4, 141.4, 139.1, 136.3, 127.3, 123.6, 121.9, 119.4, 119.2, 118.5, 111.3,
105.7, 99.8, 80.5, 65.8, 61.1, 56.9, 56.7, 33.8, 28.4, 28.2 (3C); IR (ZnSe)
n
3439 (br), 2977, 2943, 1715, 1496, 1390, 1367, 1257, 1248, 1089,
N-protected amino-acid (1.1 mmol, 1.1 equiv), DIPEA (697 mL,
1027, 863, 738 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 522.2216;
4 mmol, 4 equiv), HOBt (675 mmol, 5 mmol, 5 equiv) were
added. The mixture was cooled to 0 ꢀC, then EDC$HCl (211 mg,
1.1 mmol, 1.1 equiv) was added. The mixture was stirred at
room temperature overnight, then diluted with Et2O (60 mL),
washed with 1 M NaOH (20 mL), H2O (20 mL), 1 M HCl
(20 mL), H2O (20 mL), brine (20 mL) and dried (Na2SO4). The
reaction was concentrated in vacuum providing a mixture of
TBS protected and deprotected phenol. Thus, the mixture was
then submitted to TBAF deprotection: TBAF (1 mL of a 1 M
solution in THF, 1 mmol, 1 equiv) was added to a stirred so-
found: 522.2200.
4.3.6. (S)-tert-Butyl-3-(4-tert-butoxyphenyl)-1-(2-hydroxy-3,5,6-
trimethoxybenzylamino)-1-oxopropan-2-ylcarbamate (16f). Yield
92%; Rf¼0.36 (50% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3,
d
ppm)
d
6.93 (2H, d, J¼8.2 Hz), 6.74 (2H, d, J¼8.1 Hz), 6.50 (1H,
s), 4.48e4.21 (3H, m), 3.81 (3H, s), 3.77 (3H, s), 3.68 (3H, s),
3.08e2.76 (2H, m), 1.32 (9H, s), 1.26 (9H, s); 13C NMR (75 MHz,
CDCl3,
131.1, 129.6 (2C), 124.0 (2C), 119.1, 99.7, 79.5, 78.1, 61.1, 56.8, 56.6,
55.5, 37.9, 33.7, 28.6 (3C), 28.2 (3C); IR (ZnSe) 3454, 2975,
2906, 1700, 1667, 1495, 1366, 1247, 1088, 1026, 973, 862,
736 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 555.6156; found:
555.6139.
d ppm) d 172.8, 155.3, 154.1, 145.3, 144.3, 141.3, 139.0,
lution of the mixture and Et3N (278
mL, 2 mmol, 2 equiv) in
n
THF (5 mL). The solution was stirred at room temperature for
1 h then concentrated and directly loaded on silica gel chro-
matography (50% EtOAc in hexanes).
4.4.1. (S)-tert-Butyl-1-(3-(2-hydroxy-3,5,6-trimethoxyphenyl)propy-
4.3.7. (S)-tert-Butyl-1-(2-hydroxy-3,5,6-trimethoxyphenethylamino)-
lamino)-1-oxopropan-2-ylcarbamate (18a). Yield 74%; Rf¼0.51 (80%
1-oxopropan-2-ylcarbamate (17a). Yield 64%; Rf¼0.45 (80% EtOAc in
EtOAc in hexanes); 1H NMR (300 MHz, CDCl3,
d ppm) d 6.46 (1H, s),
hexanes); 1H NMR (300 MHz, CDCl3,
d
ppm)
d
6.43 (1H, s), 4.31e4.11
4.14 (1H, m), 3.88 (3H, s), 3.85 (3H, s), 3.81 (3H, s), 3.18 (2H, m), 2.74
(1H, m), 3.83 (3H, s), 3.79 (3H, s), 3.75 (3H, s), 3.35e3.50 (2H, m), 2.89
(2H, t, J¼6.7 Hz), 1.80 (2H, m), 1.47 (9H, s), 1.37 (3H, d, J¼7.0 Hz); 13C
(2H, t, J¼6.3 Hz),1.40 (9H, s),1.27 (3H, d, J¼7.0 Hz); 13C NMR (75 MHz,
NMR (75 MHz, CDCl3, d ppm) d 172.3, 155.3, 145.7, 142.2, 141.8,137.6,
CDCl3,
d
ppm)
d
172.3,155.3,145.6,142.5,141.6,137.9,119.8, 97.3, 79.6,
121.4, 96.4, 77.2, 61.1, 56.8, 56.4, 37.8, 29.7, 28.4 (3C), 22.6, 20.5,19.0;
65.8, 61.0, 56.9, 56.1, 40.3, 28.3 (3C), 23.2, 18.9; mp¼147e148 ꢀC; IR
IR (ZnSe) n 3368 (br), 2944, 2250, 1706, 1670, 1590, 1490, 1401, 1370,
(ZnSe)
n
3399 (br), 2977, 2937, 1701, 1661, 1493, 1453, 1366, 1351,
1079, 1025, 976, 735 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]:
1248, 1220, 1167, 1089, 974 cmꢁ1; HRMS (ESI-TOF) calcd for
435.2107; found: 435.2107.
[MþNaþ]: 421.1951; found: 421.1947.
4.4.2. (S)-tert-Butyl-3-tert-butoxy-1-(3-(2-hydroxy-3,5,6-trimetho-
xyphenyl)propylamino)-1-oxopropan-2-ylcarbamate (18b). Yield
64%; Rf¼0.19 (50% EtOAc in hexanes); 1H NMR (300 MHz,
4.3.8. (S)-tert-Butyl-3-tert-butoxy-1-(2-hydroxy-3,5,6-trimethoxy-
phenethylamino)-1-oxopropan-2-ylcarbamate (17b). Yield 67%;
Rf¼0.67 (80% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3,
CDCl3,
d ppm) d 6.43 (1H, s), 4.22e4.10 (1H, m), 3.84 (3H, s),
d
ppm)
d
6.42 (1H, s), 4.18e4.04 (1H, m), 3.81 (3H, s), 3.79 (3H,
3.81 (3H, s), 3.78 (3H, s), 3.80e3.75 (1H, m), 3.48e3.36 (1H, m),
3.32e3.18 (1H, m), 3.17e3.02 (1H, m), 2.72 (2H, t, J¼6.8 Hz),
1.76 (2H, t, J¼6.6 Hz), 1.45 (9H, s), 1.16 (9H, s); 13C NMR
s), 3.77 (3H, s), 3.75e3.64 (1H, m), 3.50e3.40 (2H, m),
3.40e3.28 (1H, m), 2.89 (2H, t, J¼6.6 Hz), 1.42 (9H, s), 1.08 (9H,
s); 13C NMR (75 MHz, CDCl3,
d
ppm)
d
172.6, 155.4, 145.6, 142.4,
(75 MHz, CDCl3, d ppm) d 170.4, 155.4, 145.6, 142.2, 141.9, 137.7,
141.8, 138.0, 119.8, 97.3, 79.7, 73.5, 61.8, 61.0, 56.9, 57.5, 56.4,
40.1, 28.3 (3C), 27.2 (3C), 23.4; IR (ZnSe) 3455 (br), 2943,
121.5, 96.6, 79.8, 73.5, 61.9, 61.0, 56.8, 56.3, 54.7, 37.9, 28.6,
28.3 (3C), 27.4 (3C), 20.6; IR (ZnSe) 3469 (br), 2976, 2954,
n
n
2248, 1715, 1668, 1495, 1392, 1366, 1248, 1089, 1024, 974, 912,
2260, 1725, 1668, 1495, 1392, 1367, 1351, 1248, 1227, 1079, 976,
733 cmꢁ1
;
HRMS (ESI-TOF) calcd for [MþNaþ]: 493.5462;
859 cmꢁ1
;
HRMS (ESI-TOF) calcd for [MþNaþ]: 507.5728;
found: 493.5465.
found: 507.5731.
4.3.9. tert-Butyl-(2S,3R)-3-tert-butoxy-1-(2-hydroxy-3,5,6-trime-
4.4.3. tert-Butyl-(2S,3R)-3-tert-butoxy-1-(3-(2-hydroxy-3,5,6-
trimethoxyphenyl)propylamino)-1-oxobutan-2-ylcarbamate
(18c). Yield 77%; Rf¼0.25 (50% EtOAc in hexanes); 1H NMR
thoxyphenethylamino)-1-oxobutan-2-ylcarbamate
(17c). Yield
71%; Rf¼0.70 (80% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3,
d
ppm)
d
6.43 (1H, s), 4.04e4.15 (1H, m), 4.02e3.93 (1H, m),
(300 MHz, CDCl3, d ppm) d 6.45 (1H, s), 4.25e4.12 (1H, m),
3.81 (3H, s), 3.79 (3H, s), 3.77 (3H, s), 3.32e3.58 (2H, m), 2.89
(2H, t, J¼6.3 Hz), 1.43 (9H, s), 1.09 (9H, s), 1.02 (3H, d, J¼6.3 Hz);
4.11e4.02 (1Hm), 3.87 (3H, s), 3.83 (3H, s), 3.80 (3H, s), 3.38e3.14
(2H, m), 2.47 (2H, t, J¼7.1 Hz), 1.79 (2H, q, J¼6.7 Hz), 1.48 (9H, s),
13C NMR (75 MHz, CDCl3,
d
ppm)
d
170.2, 155.6, 145.6, 142.3,
1.27 (3H, s), 1.24 (9H, s); 13C NMR (75 MHz, CDCl3,
d ppm) d 169.8,
141.9, 138.0, 119.7, 97.3, 79.4, 74.5, 66.9, 61.0, 58.9, 56.9, 56.3,
39.8, 28.3 (3C), 28.1 (3C), 23.4, 15.2; IR (ZnSe) 3369 (br), 2976,
2937, 1715, 1666, 1496, 1367, 1248, 1220, 1168, 1089, 1027, 917,
155.6, 145.6, 142.0, 141.9, 137.7, 121.8, 96.5, 79.5, 77.2, 74.7, 69.9,
61.0, 56.9, 56.3, 38.4, 28.4 (6C), 20.9, 18.2, 14.1; IR (ZnSe) 3398
(br), 2951, 2938, 1723, 1659, 1494, 1401, 1366, 1250, 1090, 1026,
n
n

M. Lamblin et al. / Tetrahedron 68 (2012) 4655e4663
4661
974, 735 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 521.5993;
J¼7.8 Hz), 7.13 (1H, t, J¼7.4 Hz), 7.05 (1H, t, J¼7.9 Hz), 7.03 (1H, s),
5.69 (1H, s), 4.44e4.34 (1H, m), 4.31 (1H, d, J¼6.7 Hz), 4.27 (1H, d,
J¼6.7 Hz), 4.05 (3H, s), 3.79 (3H, s), 3.36e3.04 (2H, m), 1.43 (9H, s);
found: 521.6011.
4.5. General procedure for the oxidation of phenols 16aef,
17aec and 18aec to quinones 19aef, 20aec and 21aec
13C NMR (75 MHz, CDCl3,
d ppm) d 183.1, 181.9, 171.1, 158.4, 155.5,
155.3, 136.1, 127.4, 123.5, 123.1, 122.2, 119.7, 118.9, 111.1, 110.7, 105.9,
80.0, 61.9, 56.4, 55.5, 32.2, 28.6 (3C), 28.3; IR (ZnSe) 3354 (br),
n
PhI(OAc)2 (322 mg, 1 mmol, 1 equiv) was added to a stirred
solution of phenol (1 mmol, 1 equiv) in CH3CN (9 mL) and water
(1 mL) at 0 ꢀC. The solution was stirred at 0 ꢀC for 15 min, then
diluted with Et2O (50 mL), washed with brine (10 mL) and dried
(Na2SO4). The solution was concentrated and purified on silica gel
chromatography (60e80% EtOAc in hexanes).
2975, 2929, 2867, 1716, 1668, 1602, 1520, 1453, 1366, 1213, 1166,
1045, 913, 850 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 506.1903;
found: 506.1924.
4.5.6. (S)-tert-Butyl-3-(4-tert-butoxyphenyl)-1-((2,5-dimethoxy-3,6-
dioxocyclohexa-1,4-dienyl)methylamino)-1-oxopropan-2-
ylcarbamate (19f). Yield 63%; Rf¼0.56 (80% EtOAc in hexanes); 1H
4.5.1. (S)-tert-Butyl-1-((2,5-dimethoxy-3,6-dioxocyclohexa-1,4-
dienyl)methylamino)-1-oxopropan-2-ylcarbamate (19a). Yield 61%;
NMR (300 MHz, CDCl3,
d
ppm)
d
7.03 (2H, d, J¼8.4 Hz), 6.83 (2H, d,
J¼8.4 Hz), 5.76 (1H, s), 4.38e4.08 (3H, m), 4.16 (3H, s), 3.82 (3H, s),
Rf¼0.48 (80% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3,
d ppm)
3.05e2.86 (2H, m), 1.40 (9H, s), 1.30 (9H, s); 13C NMR (75 MHz,
d
5.77 (1H, s), 4.31 (2H, d, J¼6.1 Hz), 4.18 (3H, s), 4.14e4.01 (1H, m),
CDCl3,
d ppm) d 183.1, 182.3, 170.6, 158.5, 156.1, 155.1, 154.2, 131.3,
3.81 (3H, s), 1.42 (9H, s), 1.32 (3H, d, J¼7.1 Hz); 13C NMR (75 MHz,
129.6 (2C), 124.3 (2C), 123.7, 106.0, 80.1, 78.3, 62.0, 56.5, 56.0, 38.2,
CDCl3,
d
ppm)
d
183.1, 182.4, 172.2, 158.7, 156.4, 123.8, 105.9, 79.9,
32.2, 28.8 (3C), 28.2 (3C); IR (ZnSe) n 3400 (br), 2939, 1716, 1660,
62.0, 56.5, 50.2, 32.5, 28.3 (3C), 18.5; mp¼133e134 ꢀC; IR (ZnSe)
n
1602, 1455, 1365, 1217, 1149, 1045, 917 cmꢁ1; HRMS (ESI-TOF) calcd
3392 (br), 2976, 2930, 1715, 1667, 1603, 1496, 1366, 1330, 1278, 1166,
for [MþNaþ]: 539.2369; found: 539.2369.
1066, 1023, 951 cmꢁ1
391.1481; found: 391.1467.
;
HRMS (ESI-TOF) calcd for [MþNaþ]:
4.5.7. (S)-tert-Butyl-1-(2-(2,5-dimethoxy-3,6-dioxocyclohexa-1,4-
dienyl)ethylamino)-1-oxopropan-2-ylcarbamate (20a). Yield 64%;
4.5.2. (S)-tert-Butyl-3-tert-butoxy-1-((2,5-dimethoxy-3,6-dioxo-
cyclohexa-1,4-dienyl)methylamino)-1-oxopropan-2-ylcarbamate
(19b). Yield 70%; Rf¼0.50 (80% EtOAc in hexanes); 1H NMR
Rf¼0.37 (80% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3,
d ppm)
d
5.73 (1H, s), 4.15e4.05 (1H, m), 4.11 (3H, s), 3.79 (3H, s), 3.29e3.44
(2H, m), 2.65 (2H, t, J¼6.6 Hz), 1.41 (9H, s), 1.28 (3H, d, J¼7.0 Hz); 13C
(300 MHz, CDCl3,
d
ppm)
d
5.78 (1H, s), 4.38 (1H, dd, J¼6.0,
NMR (75 MHz, CDCl3, d ppm) d 183.1,182.4, 172.8, 158.7, 156.7, 155.3,
14.1 Hz), 4.27 (1H, dd, J¼6.0, 14.1 Hz), 4.17 (3H, s), 4.15e4.01
126.2, 105.6, 79.9, 61.6, 56.4, 50.1, 38.3, 28.3 (3C), 23.1, 18.7;
(1H, br s), 3.81 (3H, s), 3.79e3.69 (1H, s), 3.45e3.28 (1H, s), 1.44
mp¼82e83 ꢀC; IR (ZnSe)
n 3418 (br), 3271, 2939, 1715, 1652, 1600,
(9H, s), 1.16 (9H, s); 13C NMR (75 MHz, CDCl3,
d
ppm)
d
183.2,
1520, 1455, 1367, 1324, 1217, 1167, 1045, 915, 845, 733 cmꢁ1; HRMS
182.2, 170.3, 158.7, 156.3, 124.1, 105.9, 79.9, 73.8, 62.0, 61.8, 56.5,
(ESI-TOF) calcd for [MþNaþ]: 405.1638; found: 405.1623.
54.4, 32.2, 28.3 (3C), 27.3 (3C); mp¼111e112 ꢀC; IR (ZnSe)
n 3351
(br), 2974, 2929, 2873, 1715, 1668, 1602, 1496, 1365, 1234, 1166,
1074, 1023 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 463.2056;
found: 463.2050.
4.5.8. (S)-tert-Butyl-3-tert-butoxy-1-(2-(2,5-dimethoxy-3,6-
dioxocyclohexa-1,4-dienyl)ethylamino)-1-oxopropan-2-ylcarbamate
(20b). Yield 70%; Rf¼0.45 (80% EtOAc in hexanes); 1H NMR
(300 MHz, CDCl3,
d ppm) d 5.72 (1H, s), 4.11 (3H, s), 4.10e4.02 (1H,
4.5.3. tert-Butyl-(2S,3R)-3-tert-butoxy-1-((2,5-dimethoxy-3,6-
dioxocyclohexa-1,4-dienyl)methylamino)-1-oxobutan-2-ylcarbamate
(19c). Yield 68%; Rf¼0.48 (80% EtOAc in hexanes); 1H NMR
s), 3.78 (3H, s), 3.75e3.66 (1H, m), 3.45e3.10 (3H, m), 2.65 (2H, t,
J¼6.5 Hz), 1.42 (9H, s), 1.14 (9H, s); 13C NMR (75 MHz, CDCl3,
d ppm)
d
183.1, 182.2, 170.7, 158.7, 156.6, 126.0, 105.6, 79.8, 73.8, 62.0, 61.7,
(300 MHz, CDCl3,
d
ppm)
d
5.79 (1H, s), 4.44 (1H, dd, J¼6.3, 14.0 Hz),
61.6, 56.4, 54.4, 38.3, 28.3 (3C), 27.3 (3C), 23.1; mp¼55e56 ꢀC; IR
4.24 (1H, dd, J¼6.3, 14.0 Hz), 4.19 (3H, s), 4.16e4.07 (1H, m),
(ZnSe) n 3341 (br), 2976, 2875, 2251, 1652, 1600, 1505, 1392, 1366,
4.06e4.00 (1H, m), 3.83 (3H, s), 1.44 (9H, s), 1.24 (9H, s), 1.01 (3H, d,
1217, 1046, 915, 845, 733 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]:
J¼6.3 Hz); 13C NMR (75 MHz, CDCl3,
d
ppm)
d
183.2, 182.1, 169.6,
477.2213; found: 477.2230.
158.7,156.2, 155.6, 124.2,105.9, 79.5, 75.0, 68.8, 61.9, 58.6, 56.5, 32.1,
28.3 (3C), 28.2 (3C), 17.6; mp¼134e135 ꢀC; IR (ZnSe)
n
3399 (br),
4.5.9. tert-Butyl-(2S,3R)-3-tert-butoxy-1-(2-(2,5-dimethoxy-3,6-
dioxocyclohexa-1,4-dienyl)ethylamino)-1-oxobutan-2-ylcarbamate
(20c). Yield 74%; Rf¼0.61 (80% EtOAc in hexanes); 1H NMR
2976, 1668, 1601, 1520, 1366, 1298, 1212, 1068, 1023, 977, 931, 842,
792 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 477.2213; found:
477.2199.
(300 MHz, CDCl3,
d ppm) d 5.72 (1H, s), 4.11 (3H, s), 4.03e4.10
(1H, m), 3.98 (1H, br s), 3.79 (3H, s), 3.50e3.25 (2H, m), 2.66 (2H,
4.5.4. tert-Butyl-(2S,3R)-3-(benzyloxy)-1-((2,5-dimethoxy-3,6-
dioxocyclohexa-1,4-dienyl)methylamino)-1-oxobutan-2-ylcarbamate
(19d). Yield 68%; Rf¼0.50 (80% EtOAc in hexanes); 1H NMR
t, J¼7.2 Hz), 1.42 (9H, s), 1.20 (9H, s), 1.00 (3H, d, J¼6.2 Hz); 13C
NMR (75 MHz, CDCl3,
d ppm) d 183.1, 182.1, 170.0, 158.7, 156.7,
155.6, 126.0, 105.5, 79.5, 74.9, 66.8, 61.6, 58.6, 56.4, 38.1, 28.3 (3C),
(300 MHz, CDCl3,
d
ppm)
d
7.38e7.21 (4H, m), 7.03e6.85 (1H, m),
28.2 (3C), 23.0, 17.8; mp¼94e95 ꢀC; IR (ZnSe)
n 3391 (br), 2977,
5.74 (1H, s), 4.66e4.45 (2H, m), 4.42e4.11 (4H, m), 4.12 (3H, s), 3.79
2251, 1715, 1667, 1600, 1487, 1367, 1217, 1168, 1067, 964, 845,
733 cmꢁ1; HRMS (ESI-TOF) calcd for [MþNaþ]: 491.2369; found:
491.2374.
(3H, s), 1.44 (9H, s), 1.17 (3H, dd, J¼6.5, 15.5 Hz); 13C NMR (75 MHz,
CDCl3,
d ppm) d 183.1, 182.0, 169.6, 158.6, 156.4, 159.8, 138.0, 128.5,
128.4, 127.9, 127.7, 127.6, 123.9, 105.9, 80.1, 74.7, 71.6, 61.9, 57.9, 56.5,
32.3, 28.3 (3C), 15.7; mp¼111e112 ꢀC; IR (ZnSe)
n
3363 (br), 2977,
4.5.10. (S)-tert-Butyl-1-(3-(2,5-dimethoxy-3,6-dioxocyclohexa-1,4-
2929, 2855, 1715, 1668, 1602, 1497, 1366, 1213, 1166, 1067 cmꢁ1
;
dienyl)propylamino)-1-oxopropan-2-ylcarbamate (21a). Yield 60%;
HRMS (ESI-TOF) calcd for [MþNaþ]: 511.2056; found: 511.2059.
Rf¼0.40 (80% EtOAc in hexanes); 1H NMR (300 MHz, CDCl3,
d ppm)
d
5.75 (1H, s), 4.23e4.06 (1H, m), 4.12 (3H, s), 3.82 (3H, s), 3.34e3.12
4.5.5. (S)-tert-Butyl-1-((2,5-dimethoxy-3,6-dioxocyclohexa-1,4-
dienyl)methylamino)-3-(1H-indol-3-yl)-1-oxopropan-2-ylcarbamate
(19e). Yield 54%; Rf¼0.37 (80% EtOAc in hexanes); 1H NMR
(2H, m), 2.48 (2H, t, J¼7.2 Hz), 1.72e1.56 (2H, m), 1.45 (9H, s), 3.38
(3H, d, J¼7.1 Hz); 13C NMR (75 MHz, CDCl3,
d ppm) d 183.2, 182.5,
172.5, 158.7, 156.2, 155.5, 128.4, 105.5, 77.2, 61.5, 56.4, 38.4, 29.7,
28.3 (3C), 19.9, 18.6, 14.1; IR (ZnSe) n 3379 (br), 2975, 1717, 1659,
(300 MHz, CDCl3,
d
ppm)
d
7.58 (1H, d, J¼7.8 Hz), 7.28 (1H, d,

4662
M. Lamblin et al. / Tetrahedron 68 (2012) 4655e4663
1599, 1526, 1455, 1366, 1228, 1167, 1067, 923 cmꢁ1; HRMS (ESI-TOF)
3331 (br), 3256, 1657, 1595, 1458, 1343, 1249, 1201, 1049,
839 cmꢁ1; HRMS (ESI-TOF) calcd for [MþHþ]: 271.0925; found:
271.0913.
calcd for [MþNaþ]: 419.1794; found: 419.1806.
4.5.11. (S)-tert-Butyl 3-tert-butoxy-1-(3-(2,5-dimethoxy-3,6-dioxo-
cyclohexa-1,4-dienyl)propylamino)-1-oxopropan-2-ylcarbamate
(21b). Yield 77%; Rf¼0.44 (80% EtOAc in hexanes); 1H NMR
4.6.4. (2S,3R)-3-(Benzyloxy)-1-((2,5-dihydroxy-3,6-dioxocyclohexa-
1,4-dienyl)methylamino)-1-oxobutan-2-aminium chloride (22d). Yield
(300 MHz, CDCl3,
d
ppm)
d
5.72 (1H, s), 4.08 (3H, s), 3.79 (3H,
79%; 1H NMR (300 MHz, CD3OD,
d ppm) d 7.40e7.24 (5H, m), 5.95
s), 3.85e3.71 (2H, m), 3.38 (1H, t, J¼7.9 Hz), 3.26e3.14 (2H, m),
(1H, s), 4.65 (1H, d, J¼11.6 Hz), 4.52 (1H, d, J¼11.6 Hz), 4.35 (1H, d,
2.46 (2H, d, J¼7.3 Hz), 1.61 (2H, q, J¼7.1 Hz), 1.43 (9H, s), 1.16
J¼13.8 Hz), 4.18 (1H, d, J¼13.8 Hz), 3.94 (1H, t, J¼6.0 Hz), 3.77 (1H, d,
(9H, s); 13C NMR (75 MHz, CDCl3,
d
ppm)
d
183.2, 182.3, 170.5,
J¼5.6 Hz), 1.29 (3H, t, J¼6.3 Hz); 13C NMR (75 MHz, CD3OD,
d ppm)
158.7, 156.2, 155.3, 128.5, 105.5, 79.9, 73.8, 61.9, 61.7, 61.5, 56.4,
38.5, 28.3 (3C), 28.0, 27.4 (3C), 20.0; IR (ZnSe) 3353 (br),
d
182.5, 180.5, 166.6, 160.1, 155.4, 137.5, 128.0 (2C), 127.64 (2C), 127.56,
n
116.8, 111.9, 73.3, 71.0, 57.6, 31.6, 15.1; IR (ZnSe): n 3361, 3189 (br),
2974, 2929, 1715, 1666, 1602, 1520, 1367, 1355, 1258, 1167,
1653, 1598, 1458, 1387, 1254, 1091 cmꢁ1; HRMS (ESI-TOF) calcd for
1067 cmꢁ1
found: 491.2347.
;
HRMS (ESI-TOF) calcd for [MþNaþ]: 491.2369;
[MþHþ]: 361.1394; found: 361.1417.
4.6.5. (S)-1-((2,5-Dihydroxy-3,6-dioxocyclohexa-1,4-dienyl)methyl-
4.5.12. tert-Butyl-(2S,3R)-3-tert-butoxy-1-(3-(2,5-dimethoxy-3,6-
dioxocyclohexa-1,4-dienyl)propylamino)-1-oxobutan-2-ylcarbamate
(21c). Yield 68%; Rf¼0.50 (80% EtOAc in hexanes); 1H NMR
amino)-3-(1H-indol-3-yl)-1-oxopropan-2-aminium chloride (22e). Yield
82%; 1H NMR (300 MHz, CD3OD,
d
ppm)
d
7.61 (1H, d, J¼7.7 Hz), 7.35
(1H, d, J¼8.1 Hz), 7.20 (1H, s), 7.10 (1H, t, J¼7.9 Hz), 7.03 (1H, t,
J¼7.9 Hz), 5.95 (1Hꢂ0.15, s), 5.86 (1Hꢂ0.85, s), 4.34e4.26 (1H, m),
4.14e4.04 (2H, m), 3.38e3.18 (2H, m); 13C NMR (75 MHz, CD3OD,
(300 MHz, CDCl3,
d ppm) d 5.71 (1H, s), 4.06 (3H, s), 4.16e3.9
(2H, m), 3.78 (3H, s), 3.79 (3H, s), 3.40e3.05 (2H, m), 2.46 (2H, t,
J¼7.3 Hz), 1.42 (9H, s), 1.03 (9H, s), 1.03 (3H, d, J 7.3 Hz); 13C
d
ppm) d 183.0, 168.7, 168.5, 156.6, 156.5, 136.7, 126.9, 124.2, 121.5, 118.9,
NMR (75 MHz, CDCl3,
d
ppm)
d
183.2, 182.2, 169.7, 158.7, 156.1,
117.7, 111.8, 111.2, 106.5, 103.5, 53.6, 31.5, 27.4; IR (ZnSe): n 3221 (br),
155.6, 128.5, 105.5, 79.5, 75.0, 66.9, 61.4, 58.3, 56.4, 38.7, 28.33
(3C), 28.28 (3C), 22.6, 20.3, 14.1; IR (ZnSe) 3351 (br), 2974,
1648, 1591, 1516, 1388, 1255, 1089 cmꢁ1; HRMS (ESI-TOF) calcd for
n
[MþHþ]: 356.1241; found: 356.1237.
2929, 2875, 1715, 1668, 1602, 1496, 1365, 1324, 1217, 1167,
1074 cmꢁ1
found: 505.2548.
;
HRMS (ESI-TOF) calcd for [MþNaþ]: 505.2526;
4.6.6. (S)-1-((2,5-Dihydroxy-3,6-dioxocyclohexa-1,4-dienyl)methyl-
amino)-3-(4-hydroxyphenyl)-1-oxopropan-2-aminium chloride (22f).
Yield 74%; 1H NMR (300 MHz, CD3OD,
d ppm) d 7.03 (2H, t,
4.6. General procedure for Boc deprotection and methoxy
hydrolysis, synthesis of 22aef, 23aec and 24aec
J¼8.0 Hz), 6.71 (1H, d, J¼8.6 Hz), 6.67 (1H, d, J¼8.6 Hz), 5.99 (1H,
s), 4.37 (1H, t, J¼13.5 Hz), 4.13e3.92 (2H, m), 3.00 (2H, t,
J¼7.5 Hz); 13C NMR (75 MHz, CD3OD,
d ppm) d 182.4, 168.02,
167.97, 156.70, 156.66, 155.5, 130.22, 130.20, 124.5, 115.30, 115.26,
The protected quinone was suspended in a 95/5 mixture of
1 M HCl and methanol. The solution was stirred for 48 h at
room temperature resulting in complete dissolution of mate-
rial. The solution was then concentrated and the residual oil
was triturated in diethyl ether to precipitate the product. The
surnatant liquid was removed and the powder was dried under
vacuo.
113.3, 103.5, 54.4, 36.5, 31.2; IR (ZnSe):
n 3221 (br), 1648, 1591,
1516, 1388, 1255, 1089 cmꢁ1; HRMS (ESI-TOF) calcd for [MþHþ]:
333.1081; found: 333.1092.
4.6.7. (S)-1-(2-(2,5-Dihydroxy-3,6-dioxocyclohexa-1,4-dienyl)ethyl-
amino)-1-oxopropan-2-aminium chloride (23a). Yield 82%; 1H
NMR (300 MHz, CD3OD,
d
ppm)
d
5.94 (1Hꢂ0.76, s), 5.82
4.6.1. (S)-1-((2,5-Dihydroxy-3,6-dioxocyclohexa-1,4-dienyl)methyl-
(1Hꢂ0.24, s), 3.94e3.82 (1H, m), 3.53 (1H, q, J¼6.5 Hz), 3.33e3.20
amino)-1-oxopropan-2-aminium chloride (22a). Yield 77%; 1H NMR
(1H, m), 2.65 (2H, t, J¼6.5 Hz), 1.45 (3H, d, J¼6.7 Hz); 13C NMR
(300 MHz, CD3OD,
d
ppm)
d
6.01 (1Hꢂ0.43, s), 5.88 (1Hꢂ0.57, s),
(75 MHz, CD3OD, d ppm) d 182.5, 182.3, 196.5, 160.4, 155.1, 115.3,
4.29 (1H, d, J¼13.8 Hz), 4.23 (1H, d, J¼13.8 Hz), 3.87 (1H, q,
114.0, 103.4, 103.0, 48.9, 37.3, 22.3, 22.2, 16.3; IR (ZnSe): n 3355,
J¼7.0 Hz), 1.47 (3H, d, J¼7.0 Hz); 13C NMR (75 MHz, CD3OD,
d
ppm)
3195, 2855 (br), 1658, 1590, 1551, 1376, 1271, 1203, 1110,
1081 cmꢁ1; HRMS (ESI-TOF) calcd for [MþHþ]: 255.0975; found:
255.0969.
d
182.5, 181.5, 171.1, 169.8, 169.4, 160.4, 156.0, 113.2, 112.2, 104.1,
103.5, 49.0, 31.7, 31.6, 16.5; IR (ZnSe): n 3398, 3262, 3068 (br), 1650,
1598, 1546, 1379, 1245, 1203, 1049, 846 cmꢁ1; HRMS (ESI-TOF) calcd
for [MþHþ]: 241.0819; found: 241.0815.
4.6.8. (S)-1-(2-(2,5-Dihydroxy-3,6-dioxocyclohexa-1,4-dienyl)ethyl-
amino)-3-hydroxy-1-oxopropan-2-aminium chloride (23b). Yield
4.6.2. (S)-1-((2,5-Dihydroxy-3,6-dioxocyclohexa-1,4-dienyl)methyl-
89%; 1H NMR (300 MHz, CD3OD,
d
ppm)
d
5.84 (1Hꢂ0.1, s), 5.84
amino)-3-hydroxy-1-oxopropan-2-aminium chloride (22b). Yield
(1Hꢂ0.9, s), 3.88 (1H, dd, J¼3.9, 14.4 Hz), 3.83 (1H, dd, J¼3.9,
10.5 Hz), 3.72 (1H, dd, J¼6.6, 10.5 Hz), 3.49 (1H, dd, J¼6.6, 10.5 Hz),
3.40e3.30 (2H, m), 2.67 (2H, t, J¼6.6 Hz); 13C NMR (75 MHz, CD3OD,
88%; 1H NMR (300 MHz, CD3OD,
d
ppm)
(1Hꢂ0.27, s), 4.27 (2H, s), 3.96e3.85 (2H, m), 3.77 (1H, dd, J¼7.8,
12.4 Hz); 13C NMR (75 MHz, CD3OD,
ppm) 187.6, 182.3, 170.9,
d
6.01 (1Hꢂ0.73 s), 5.88
d
d
d
ppm)
d 182.5,182.3,166.6,160.4,155.1,115.3,103.0, 60.3, 55.0, 37.4,
166.6, 113.2, 112.0, 103.7, 103.4, 60.3, 54.8, 31.6; IR (ZnSe):
n
3260
22.2; IR (ZnSe): n 3220 (br), 1649, 1592, 1517, 1389, 1254, 1100, 1087,
(br), 1650, 1590, 1547, 1378, 1203, 1088 cmꢁ1; HRMS (ESI-TOF) calcd
830 cmꢁ1; HRMS (ESI-TOF) calcd for [MþHþ]: 271.0925; found:
for [MþHþ]: 257.0768; found: 257.0751.
271.0933.
4.6.3. (2S,3R)-1-((2,5-Dihydroxy-3,6-dioxocyclohexa-1,4-dienyl)
4.6.9. (2S,3R)-1-(2-(2,5-Dihydroxy-3,6-dioxocyclohexa-1,4-dienyl)
methylamino)-3-hydroxy-1-oxobutan-2-aminium chloride (22c).
ethylamino)-3-hydroxy-1-oxobutan-2-aminium chloride (23c). Yield
1
Yield 84%; 1H NMR (300 MHz, CD3OD,
d
ppm)
d
6.02 (1Hꢂ0.29,
89%; H NMR (300 MHz, CD3OD,
d
ppm)
d
5.95 (1H, s), 4.01 (1H, q,
s), 5.89 (1Hꢂ0.71, s), 4.33 (1H, d, J¼13.8 Hz), 4.22 (1H, d,
J¼13.8 Hz), 4.02e3.91 (1H, m), 3.54 (1H, d, J¼7.3 Hz), 1.24 (3H, d,
J¼6.3 Hz), 3.60 (1H, d, J¼6.3 Hz), 3.50e3.32 (2H, m), 2.68 (2H, t,
J¼6.8 Hz), 1.27 (3H, d, J¼6.3 Hz); 13C NMR (75 MHz, CD3OD,
d ppm)
J¼6.3 Hz); 13C NMR (75 MHz, CD3OD,
d
ppm)
d
182.7, 181.7, 167.3,
d
184.7, 184.5, 169.3, 162.7, 157.4, 117.3, 105.2, 68.1, 61.3, 39.7, 24.3,
160.8, 156.3, 113.4, 112.2, 103.9, 66.5, 59.5, 31.9, 19.3; IR (ZnSe):
n
21.2; IR (ZnSe): n 3391 (br), 1652, 1590, 1592, 1547, 1375, 1267, 1209,

M. Lamblin et al. / Tetrahedron 68 (2012) 4655e4663
4663
1097, 745 cmꢁ1; HRMS (ESI-TOF) calcd for [MþHþ]: 285.1081; found:
Coulter). Controls received the same volume of DMSO (1% final
volume). After 72 h exposure, MTS reagent (Celltiter 96Ò AQeous
One, Promega) was added and incubated for 3 h at 37 ꢀC: the ab-
sorbance was monitored at 490 nm and results expressed as the
inhibition of cell proliferation calculated as the ratio [(1ꢁ(OD490
treated/OD490 control))ꢂ100] in triplicate experiments.
285.1099.
4.6.10. (S)-1-(3-(2,5-Dihydroxy-3,6-dioxocyclohexa-1,4-dienyl)pro-
pylamino)-1-oxopropan-2-aminium chloride (24a). Yield 73%; 1H
NMR (300 MHz, CD3OD,
d
ppm)
d
5.93 (1Hꢂ0.75, s), 5.82 (1Hꢂ0.25,
s), 3.97 (1H, q, J¼6.9 Hz), 3.32e3.13 (2H, m), 2.46 (2H, t, J¼7.5 Hz),
1.80e1.62 (2H, m), 1.54 (3H, d, J¼6.9 Hz); 13C NMR (75 MHz, CD3OD,
Acknowledgements
d
ppm) d 182.6, 182.3, 169.5, 160.3, 154.3, 117.5, 116.2, 103.2, 102.8,
49.0, 38.9, 27.2, 19.31, 19.27, 16.4; IR (ZnSe):
n 3250 (br), 3085 (br),
ꢀ
ꢀ
1651, 1595, 1504, 1397, 1268, 1210, 1092 cmꢁ1; HRMS (ESI-TOF)
CNRS, Universite de Bordeaux I, Ligue Contre le Cancer (Comite
ꢀ
calcd for [MþHþ]: 269.1132; found: 269.1119.
de la Dordogne, Comite de la Gironde) and Association pour la
Recherche sur le Cancer, (postdoctoral grant to M.L. and C.C.) are
gratefully acknowledged for financial support.
4.6.11. (S)-1-(3-(2,5-Dihydroxy-3,6-dioxocyclohexa-1,4-dienyl)pro-
pylamino)-3-hydroxy-1-oxopropan-2-aminium chloride (24b). Yield
75%; 1H NMR (300 MHz, CD3OD,
d
ppm)
d
5.94 (1Hꢂ0.36, s), 5.82
References and notes
(1Hꢂ0.64, s), 4.00e3.85 (2H, m), 3.83 (1H, dd, J¼5.4, 7.3 Hz), 3.25
(2H, t, J¼7.1 Hz), 2.48 (2H, t, J¼7.5 Hz), 1.78e1.66 (2H, m); 13C NMR
1. (a) Mahendran, S.; Badami, S.; Ravi, S.; Thippeswamy, B. S.; Veerapur, V. P. Chem.
Pharm. Bull. 2011, 59, 913 and references cited herein; (b) Radhakrishnan, N.;
Gnanamani, A.; Mandal, A. B. Biol. Med. 2011, 3, 1.
2. Ahn, K. S.; Sethi, G.; Aggarwal, B. B. Mol. Pharmacol. 2007, 71, 209.
3. Damgaard, R. B.; Gyrd-Hansen, M. Discov. Med. 2011, 11, 221.
4. (a) Nikolovska-Coleska, Z.; Xu, L.; Hu, Z.; Tomita, Y.; Li, P.; Roller, P. P.; Wang, R.;
Fang, X.; Guo, R.; Zhang, M.; Lippman, M. E.; Yang, D.; Wang, S. J. Med. Chem.
2004, 47, 2430; (b) Hu, R.; Zhu, K.; Li, Y.; Yao, K.; Zhang, R.; Wang, H.; Yang, W.;
Liu, Z. Med. Oncol. 2011, 28, 1584.
(75 MHz, CD3OD,
d ppm) d 183.0, 182.7, 167.0, 154.8, 117.9, 116.5,
103.2, 60.8, 55.4, 39.3, 27.6, 19.6; IR (ZnSe): n 3354, 3056 (br), 1649,
1587, 1503, 1370, 1256, 1203, 1073, 803 cmꢁ1; HRMS (ESI-TOF) calcd
for [MþHþ]: 285.1081; found: 285.1106.
4.6.12. (2S,3R)-1-(3-(2,5-Dihydroxy-3,6-dioxocyclohexa-1,4-dienyl)
propylamino)-3-hydroxy-1-oxobutan-2-aminium chloride (24c). Yield
5. Dai1, Y.; DeSano, J.; Qu, Y.; Tang, W.; Meng, Y.; Lawrence, T. S.; Xu, L. Am. J.
Cancer Res. 2011, 1, 128.
6. Luibrand, R. T.; Erdman, T. R.; Vollmer, J. J.; Scheuer, P. J.; Finer, J.; Clardy, J.
Tetrahedron 1979, 35, 609.
7. Ishibashi, M.; Ohizumi, Y.; Cheng, J. F.; Nakamura, H.; Hirata, Y.; Sasaki, T.;
80%; 1H NMR (300 MHz, CD3OD,
d
ppm)
d
5.93 (1Hꢂ0.71, s), 5.82
(1Hꢂ0.29, s), 4.02 (1H, t, J¼4.8 Hz), 3.63 (1H, d, J¼5.1 Hz), 3.38e3.16
(2H, m), 2.48 (2H, t, J¼5.8 Hz), 1.79e1.63 (2H, m), 1.32 (3H, d,
J¼4.8 Hz); 13C NMR (75 MHz, CD3OD,
d ppm) d 182.3, 182.7, 167.4,
Kobayashi, J. J. Org. Chem. 1988, 53, 2855.
8. (a) Chen, J.; Nikolovska-Coleska, Z.; Wang, G.; Qiu, S.; Wang, S. Bioorg. Med.
160.7, 154.8, 117.9, 116.6, 103.2, 66.4, 59.6, 39.4, 27.6, 19.4; IR (ZnSe):
n
ꢀ
ꢀ
Chem. Lett. 2006, 16, 5805; (b) Viault, G.; Gree, D.; Das, S.; Yadav, J. S.; Gree, R.
Eur. J. Org. Chem. 2011, 7, 1233.
3145 (br), 1651, 1589, 1437, 1386, 1268, 1089 cmꢁ1; HRMS (ESI-TOF)
calcd for [MþHþ]: 299.1238; found: 299.1239.
9. (a) Commandeur, C.; Chalumeau, C.; Dessolin, J.; Laguerre, M. Eur. J. Org. Chem.
2007, 3045; (b) Ventimila, N.; Dupont, P. Y.; Laguerre, M.; Dessolin, J. J. Enzyme
Inhib. Med. Chem. 2010, 25, 152.
10. Depierre G.; Dessolin J.; Laguerre M.; Commandeur C. Patent WO/2007/125196,
PCT/FR2007/000703.
4.7. Biology, cytotoxic assay
11. 43 No pp.Organic Reactions; John Wiley & Sons: Hoboken, NJ, United States,
1993.
12. Dube, D.; Scholte, A. A. Tetrahedron Lett. 1999, 40, 2295.
13. Yamamoto, Y.; Nishimura, K.; Kiriyama, N. Chem. Pharm. Bull. 1976, 24, 1853.
14. Lin, Y. L.; Wu, C. S.; Lin, S. W.; Huang, J. L.; Sun, Y. S.; Yan, D. Y. Bioorg. Med. Chem.
2002, 10, 685.
15. Benbow, J. W.; Katoch-Rouse, R. J. Org. Chem. 2001, 66, 4965.
16. Dean, F. M.; Randell, D. R.; Winfield, G. J. Chem. Soc. 1961, 792.
KB cells were originated from the NCI and grown in D-MEM
medium supplemented with 10% foetal calf serum, in the presence
of penicilline, streptomycine and fungizone in 75 cm3 flasks under
ꢀ
5% CO2. Cells were seeded in 96-well tissue culture plates in 200
medium and treated 24 h later with 2 L stock solution of com-
pounds dissolved in DMSO using a Biomek 3000 (Beckman-
mL
m