Liebeskind-Srogl cross-coupling on γ-carboxyl-γ-butyrolactone derivatives: Application to the side chain of amphidinolides C and F

Article abstract of DOI:10.1016/j.tetlet.2015.04.035

The synthetic approach for the C20-C29 and C20-C34 fragments of amphidinolide F and C was based on an original Liebeskind-Srogl cross-coupling reaction with a glutamic acid-derived building-block. Further highly diastereoselective reduction of the ketone was achieved by using an uncommon Ph₃SiH/TBAF/HMPA system. The amphidinolide C side chain was built through a reductive elimination of chiral epoxide to install the stereogenic center at C29.

Full text of DOI:10.1016/j.tetlet.2015.04.035

Accepted Manuscript
Liebeskind–Srogl Cross-Coupling on γ-Carboxyl-γ-Butyrolactone Derivatives:
Application to the Side Chain of Amphidinolides C and F
Johan Fenneteau, Sara Vallerotto, Laurent Ferrié, Bruno Figadère
PII:
S0040-4039(15)00662-0
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.04.035
TETL 46174
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
3 March 2015
2 April 2015
8 April 2015
Please cite this article as: Fenneteau, J., Vallerotto, S., Ferrié, L., Figadère, B., Liebeskind–Srogl Cross-Coupling
on γ-Carboxyl-γ-Butyrolactone Derivatives: Application to the Side Chain of Amphidinolides C and F, Tetrahedron
Letters (2015), doi: http://dx.doi.org/10.1016/j.tetlet.2015.04.035
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Liebeskind–Srogl Cross-Coupling on γ-
Carboxyl-γ-Butyrolactone Derivatives:
Application to the Side Chain of
Amphidinolides C and F.
Leave this area blank for abstract info.
Johan Fenneteau, Sara Vallerotto, Laurent Ferrié,* Bruno Figadère*
O
O
15
18
Me
Me
1
3
Me
Me
Me
OH
20
[M]
[M]
O
R
11
24
O
SAr
+
OH
OH
O
nBu
9
O
Me
1
O
6
Liebeskind-Srogl
Cross-Coupling
O
Me
OH
4
O
Me
[
M] = Bu3Sn or B(OH)2
R = -Me
OH
Amphidinolide F (1)
Amphidinolide C (2)
Direct introduction of dienic side chain
No protecting group
No epimerisation
nBu
R =

1
Tetrahedron Letters
journal homepage: www.els evier.com
Liebeskind–Srogl Cross-Coupling on γ-Carboxyl-γ-Butyrolactone Derivatives:
Application to the Side Chain of Amphidinolides C and F.
Johan Fenneteau, Sara Vallerotto, Laurent Ferrié, * Bruno Figadère*
Laboratoire de Pharmacognosie, UMR-8076 BioCIS, Université Paris-Sud, CNRS, LERMIT, Faculté de Pharmacie, Rue Jean-Baptiste Clément, 92296
Châtenay-Malabry, France.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
The synthetic approach for the C20-C29 and C20-C34 fragment of amphidinolide F and C was
based on an original Liebeskind–Srogl cross-coupling reaction with a glutamic acid-derived
building-block. Further highly diastereoselective reduction of the ketone was achieved by using
3
an uncommon Ph SiH/TBAF/HMPA system. The Amphidinolide C side chain was built through
Available online
a reductive elimination of chiral epoxide to install the stereogenic center at C29.
2
015 Elsevier Ltd. All rights reserved.
Keywords:
Copper
Stereoselective
Asymmetric epoxidation
Boronic acid
Natural product
Amphidinolides belong to a wide and original family of more
than 30 members of marine macrolactones isolated by Kobayashi
from dinoflagellates Amphidinium sp., which live in symbiosis
with okinawan flatworm Amphiscolops sp. These molecules had
shown important cytotoxicity against solid tumors. In particular,
amphidinolide C is one of the most potent cytotoxic agents of
this family (IC50 = 5.8 and 4.6 ng/mL against murine lymphoma
and human epidermoid carcinoma cells, respectively). Curiously
amphidinolide F (1), which is structurally closely related to
amphidinolide C (2) is however about 1000 fold less active
Figure 1. General structure of amphidinolides F and C.
Our group is currently involved in the total synthesis of some
THF-containing amphidinolides such as amphidinolide
5
3h
N/caribenolide and amphidinolides C and F. Our general
retrosynthesis for these two last molecules rely on a C-
glycosylation to elaborate the C19-C20 bond, followed by a
macrocyclisation of the resulting seco-acid. Here we describe our
synthesis of the C20-C29 and C20-C34 fragment of
amphidinolides F (1) and C (2) through a direct introduction of
the dienic side chain of both congeners. For this purpose, we
suggested to use D-glutamic acid derivative D as a common
precursor for the butyrolactone core, which could react with
metallated-diene E to build those fragments (Scheme 1).
2
(
Figure 1). This intriguing observation suggests an important role
of the side chain, and opens a door for chemical modulations and
the synthesis of analogues. Due to their important cytotoxicity
and their original structures these natural substances has attracted
3
the attention of the scientific community, and recent total
We first studied the synthesis of C20-C29 fragment of
amphidinolide F as it remains a simple and better model to apply
syntheses of these two molecules were reported confirming their
4
3
original structural assignments.
specific methodologies. The addition of sp organo-magnesium, -
manganese, -copper, -cadmium reagents to acyl chloride 3 is well
O
6
2
M2e9
documented; however the addition of sp organometallic to 3
seems more difficult to proceed as no work is reported. Indeed,
we were unable ourselves to perform such a reaction with
metallodienes of type E whatever the metal was: magnesium,
lithium, copper, manganese, zinc or tin under various conditions.
(Scheme 2).
O
1
5
Amphidinolide F (1)
1
8
1
3
Me
Me
Me
OH
20
OH
1
1
24
nBu
O
29
OH
Me
9
O
1
O
Amphidinolide C (2)
6
OH
4
O
A first solution was the installation of dienone by
7
isomerization of a propargylic ketone. Ketone 6 was prepared by
Me
—
——
*
Corresponding authors. Tel.: +33146835598, +33146835592; fax: +33146835399; e-mail: laurent.ferrie@u-psud.fr, bruno.figadere@u-
psud.fr.

2
Tetrahedron Letters
addition of zinc acetylide derived from isovaleraldehyde (5)
onto acyl chloride 3 (70% yield). Isomerization of the triple bond
to conjugated diene under different conditions (Pd(OAc) /PPh
THF, 60 °C or PPh , PhMe, reflux) gave us expected dienic
chloride 3 with the corresponding thiol in the presence of
pyridine. Preliminary experiments between thioester 7a and
phenylboronic acid 8a using conditions described in the literature
2
3
,
3
3 2 3
(CuTC, P(OMe) , Pd (dba) , THF, rt) gave ketone 4b in 52%
ketone 4a in modest yield (55-66%). Unfortunately, under these
reaction conditions, an epimerization of the stereogenic center at
C23 was observed (Scheme 2).
isolated yield (Table 1, entry 1). Vinylic boronic acid 8b also
gave ketone 4c in a similar yield (Table 1, entry 2).
Motivated by these results, catechol boronate
9 was
0
1
OTES
synthesized by hydroboration of 4-methyl-pent-3-enyne with
1
1
1
8
OTMS
catechol borane (CatB-H). Hydrolysis of 9 (H O, 50°C) to the
1
5
2
2
0
1
3
LG
corresponding boronic acid needed extended reaction time and
Me
Me
Me
TBS
1
or
2
O
substantial decomposition was observed. Instability of vinyl
O
24
28
R
11
+
12
boronic acids is well documented, we thus planned an in situ
OTBS
OH
B
Me
9
1
hydrolysis of 9. When crude catechol boronate 9 was treated with
O
6
CO Me
2
thioester 7a in a THF/H O (9/1) mixture (Table 1, entry 3),
This work
2
OTBS
4
coupled product 4a was obtained in 55% yield without
epimerization of the C23 center (98% ee). Slight improvement of
Me
A
the reaction was obtained by using more activated thioester 7b
2
0
O
(
Table 1, entry 4), which gave ketone 4a in 66% yield. The yields
OH
R =
Diene introduction
24
X
O
2
0
nBu
are modest, but this reaction seems to be up to now the only
general method to obtain these chiral conjugated ketones 4a-c in
decent yield.
O
D
+
O
O
24
28
R
or -Me
O
Me
2
8
R
C
[M]
Table 1
Liebeskind–Srogl cross-coupling with γ-arylthiocarbonyl-γ-butyrolactones.
Me
E
CuTC, R-B(OH)
Pd (dba) , P(OMe)
2
O
O
2
3
3
7
7
7
a, Ar = Ph
O
R
Scheme 1. General retrosynthesis for amphidinolides F and C.
O
SAr
b, Ar = p-NO
c, Ar = Tol
2
-Ph
THF, rt
4
a-c
O
Me
O
[
M]
O
O
Me
X
M] = ZnCl, Cu, Li
a
Me
Me
O
Cl
O
Entry
1
Thioester
Boronic acid derivatives
Product
Yield
52%
[
SnBu3, MnCl, MgBr
O
O
3
4a
7a
8a,
8b,
4b
1
2
) PPh3, CBr
CH Cl 0°C
4
2
3
7a
7a
4c
4a
52%
55%
O
Me
Me
O
Me
2
2,
O
) nBuLi, ZnCl
2
then 3
b
Me
9,
THF, -78°C to 0°C
O
6
5
70% (over two steps)
PPh , PhMe
3
reflux, 74%
b
4
7b
9,
4a
66%
O
a
b
Isolated yield. Reaction was performed in THF/H
2
O (9/1) to generate in situ
Epimerisation at C23
during isomerisation process
23
O
Me
Me
the boronic acid by hydrolysis of 9. CuTC = copper (I) thiophene-2-
carboxylate. Tol = Tolyl. Cat = catechol.
O
rac-4a
Table 2
Diastereoselective reduction of ketone 4a
Scheme 2. Efforts toward the introduction of the dienic side chain on acyl
chloride 3.
Reduction
conditions
O
O
At this point, this approach was abandoned and a new
synthesis of 4 has been designed to keep the chiral information.
Acyl chloride 3 was maybe not the most appropriated
electrophile and instead, we turned our attention to thioester
Me
Me
Me
Me
O
O
4
a
O
10
OH
derivatives, which could be ideal substrates through
a
dr
Overall
yield
Product c
Entry
Conditions
a
b
Liebeskind–Srogl cross-coupling. This reaction relies on an
original copper mediated and palladium catalyzed cross-coupling
(syn/anti)
yield (10)
1
2
3
4
5
6
NaBH
NaBH
4
/CeCl
3
, MeOH, 0 °C
, MeOH, 0 °C
61/39
85%
93%
66%
67%
40%
nd
52%
45%
33%
42%
34%
67%
8
between thioesters and boronic acids to afford ketones. This
4
/MnCl
2
48/52
50/50
85/15
90/10
transformation was described as being very chemoselective and
9
as avoiding any epimerization. Moreover, this transformation
LiAlH(OtBu) , THF, -78 °C
3
has the advantage to be very simple to be carried out: room
temperature, strong base free, not strictly dry conditions and easy
available reagents.
L-Selectride, THF, -78 °C
Et
3
SiH/TBAF, HMPA, rt
SiH/TBAF, HMPA, rt
Ph
3
95/5
We decided to evaluate the potential of this transformation for
the direct introduction of dienic moiety of amphidinolide F and
C. Required thioesters 7a-c were synthesized by reaction of acyl
a
b
Determined by HPLC of the crude mixture. Sum of the two isolated syn and
c
anti diastereoisomers. Isolated yield of the syn product. nd = not-determined.

3
I
TMS
tBuOOH
VO(OiPr) (1.5 mol %)
1
2 Me
Pd(PPh3)4
Tl CO /KOH
nBu
3
(S,S)-14 (1.7 mol %)
PPh , CBr4
3
Imidazole
Zn dust
sat. aq.NH Cl
O
O
2
3
nBu
4
nBu
nBu
TMS
TMS
15
O
TMS
16
B
THF/H
6%
2
O
CH
92%, 94% ee
2
Cl2, -20°C
CH Cl2
2
0°C to rt
EtOH, rt
95%
Me
Me
Me
8
OH
OH
Br
11
OH
13
68%
1
) TMS
OH
3 4
CuI, Pd(PPh )
Et NH, rt,
CatB-H
2
nBu
X
2) K
98% (two steps)
2
CO3, MeOH
Me
THF
reflux
OH
OH
OH
NIS
nBu then TBAF
19
nBu
nBu
TMS
I
(RO) B
2
CH
3
CN, 0°C
88%
Me
Me
Me
2
1
17
18
Me
B
Pd
2 3
dba
AsPh
OH
20, R = catechol
23, R = H
N
O
KOH
3
nBu
X
MeOH
O
CPh3
THF, 55°C
2%
O
O
O
Me
Me
B
22
8
N
N
N
O
OH
OH
SnBu
3
O
O
O
(
S,S)-14
CPh3
21
O
Scheme 3. Synthesis of the side chain of amphidinolide C.
Next, we focused our efforts to perform a challenging chemo-
In front of this failure, we envisioned to introduce the boron
atom at the specified position by the mean of N-methyl-
iminodiacetic (MIDA) boronate as a stable boronic acid
surrogate. Use of bis-metalled compound 21 through a
selective Stille cross-coupling finally gave us MIDA boronate 22
in 82% yield. However, cleavage of the MIDA moiety under
and stereo-selective reduction of ketone 4a in order to obtain syn-
alcohol 10. Several reducing agents were screened (Table 2). Use
13
21
22
of Luche’s conditions (Table 2, entry 1) and its manganese
1
4
alternative (Table 2, entry 2) could not furnish any selectivity
despite a decent isolated yield of syn-product 10. Hindered
reducing agent such as LiAlH(OtBu)
3
showed no selectivity and
different reported conditions (1
M
NaOH/THF or
2
3
low yield (Table 2, entry 3) whereas L-Selectride afforded better
selectivity (dr = 85/15) but formation of numerous undetermined
by-products was observed decreasing the yield. Next we turned
NaHCO /MeOH 40 °C) did not furnish desired boronic acid 23,
3
degradations being only observed (Scheme 3). As the generation
of free boronic acid 23 seems to be delicate in our hands, we
decided to modify slightly our original strategy in the synthesis
of the C20-C34 fragment of amphidinolide C as depicted in
Scheme 4.
1
5
our attention to silane reagents as proposed by Hiyama.
Et SiH/TBAF (15 mol%) in HMPA (Table 2, entry 5)
gratifyingly afforded Felkin–Anh product with good
diastereoselectivity (dr = 90/10) albeit in a low yield. Finally, the
use of Ph SiH (Table 2, entry 6) gave the best results in terms of
3
a
Indeed, the utilization of the tin version of Liebeskind–Srogl
3
24
cross coupling could finally allow us to obtain the target
stereoselectivity (dr = 95/5) and yield (67%).
compound as organotin compounds are known to be pretty stable
Having the C20-C29 fragment of amphidinolide F 10 in our
hands, we turned our attention to the synthesis of C20-C34
fragment of amphidinolide C through a similar approach. In order
to reach this objective, we designed a stereoselective synthesis of
boronic acid 23. Installation of the stereogenic center at C29 was
planned by performing a reductive elimination of a chiral epoxi-
alcohol (Scheme 3). Suzuki cross-coupling between boronate
compared to boronic acids. Selective Negishi cross-coupling
25
applied on vinyl iodide 18 with excess of organozinc 24 gave us
desired stannane 25 in 67% yield. To our delight, Liebeskind
cross-coupling of 25 with tolyl-thioester 7c in the presence of
Pd
2
(dba)
3
,
tri-ortho-furyl phosphine (TFP) and copper
26
diphenylphosphinate (CuDPP) allowed us to obtain ketone 4d
in 85% yield. Subsequent reduction of the ketone with
Ph SiH/TBAF in HMPA furnished the C20-C34 fragment of
3
1
6
17
1
1
and vinyl iodide 12 in the presence of Tl
2
CO
3
/KOH
furnished E,Z diene 13 in 86% yield. Application of Sharpless
amphidinolide C (26) in 63% isolated yield and with high
diastereoselectivity (dr > 15:1, Scheme 4).
1
8
epoxidation to 13 afforded epoxide 15 with surprisingly low
enantioselectivity (52% ee). Fortunately, the utilization of
vanadium-catalyzed Yamamoto asymmetric epoxidation of
O
ZnCl
Bu
3
Sn
7c,
CuO PPh2
Pd (dba) , TFP
1
9
OH
2
4
allylic alcohol with bis-hydroxamic ligand (S,S)-14 afforded
finally target product 15 with an excellent enantioselectivity
Pd(Ph3)4
THF, 0 °C to rt
7%
nBu
2
3
1
8
3
Bu Sn
THF, 50 °C
85%
(
94% ee, 92% yield). Reductive elimination of the corresponding
Me
2
5
6
α-bromo-epoxide (16) in the presence of zinc dust afforded
desired alcohol 17, with retention of the chiral information at
C29. Iodolysis of TMS with NIS in acetonitrile gave us E-vinyl
O
O
20
O
OH
Ph
3
SiH
TBAF
O
OH
Me
iodide 18 in 88% yield. Efforts into the preparation of boronate
0 was conducted through two strategies. First, vinyl iodide 18
was coupled with TMS-acetylene through a Sonogashira cross-
coupling followed by TMS cleavage (K CO /MeOH) to yield
nBu
nBu
2
HMPA
63%
dr > 15:1
O
Me
OH
4
d
26
2
3
enyne 19 (98% over two steps). Introduction of boron atom at
C25 was first planned with CatB-H, but, to our dismay, extended
reaction times were required leading only to a complex mixture
of by-products whatever the conditions used (heating, catalysis
with or without TBS protection at C29). (Scheme 3)
Scheme 4. Synthesis of the C20-C34 fragment of amphidinolide C.

4
Tetrahedron
In conclusion, we synthesized both C20-C29 and C20-C34
4. (a) Mahapatra, S.; Carter, R. G. Angew. Chem. Int. Ed. 2012, 51,
7
2
948–7951. (b) Mahapatra, S.; Carter, R. G. J. Am. Chem. Soc.
013, 135, 10792–10803. (c) Valot, G.; Regens, C. S.; O’Malley,
fragments of amphidinolides F and C by using an original
Liebeskind–Srogl cross-coupling as a key step for direct
introduction of their side chain. We showed for the first time not
only the boronic acids but some boronates such as catechol
boronate can be used in this reaction by an in situ hydrolysis. In
case of unstable boronic acid derivatives, the tin version of
Liebeskind–Srogl cross-coupling can be a helpful alternative. We
also found the reduction of unsaturated γ-butyrolactone-γ-ketones
such as 4a and 4d is highly diastereoselective by using
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3
Ph SiH/TBAF in HMPA. Installation of the stereogenic center at
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alcohol. Vanadium-catalyzed Yamamoto epoxidation showed to
be far superior to the classical Sharpless epoxidation on 2,3-
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of this asymmetric reaction toward the synthesis of natural
products.
7
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Acknowledgements
9
.
The Agence Nationale de la Recherche (ANR) through
AMPHICTOT project supported the work. We thank Karine
Leblanc of our internal analysis service for acquisition of HRMS
and HPLC analysis. We gratefully acknowledge Mr. Ron New of
UC Riverside's Analytical Chemistry Instrumentation Facility for
recording LIFDI mass spectra.
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1
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