A straightforward synthesis of the CERT inhibitor (1′R,3′S)-HPA-12

Article abstract of DOI:10.1016/j.tetlet.2015.02.060

A straightforward synthesis of the CERT inhibitor HPA-12, (1′R,3′S)-N-(3-hydroxy-1-hydroxymethyl-3-phenylpropyl)dodecanamide, is reported. The method requires only five synthetic steps from commercially available d-aspartic acid and leads to enantiopure HPA-12 in good overall yields.

Full text of DOI:10.1016/j.tetlet.2015.02.060

Tetrahedron Letters xxx (2015) xxx–xxx
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Tetrahedron Letters
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A straightforward synthesis of the CERT inhibitor (10R,30S)-HPA-12
a
a,b,
José-Luis Abad a, , Iván Armero , Antonio Delgado
⇑
⇑
a Research Unit on BioActive Molecules, Department of Biomedicinal Chemistry, Institute for Advanced Chemistry of Catalonia (IQAC-CSIC), Jordi Girona 18-26, E-08034
Barcelona, Spain
b University of Barcelona (UB), Faculty of Pharmacy, Department of Pharmacology and Medicinal Chemistry, Unit of Pharmaceutical Chemistry (Associated Unit to CSIC), Avga.
Joan XXIII s/n, E-08028 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
A straightforward synthesis of the CERT inhibitor HPA-12, (10R,30S)-N-(3-hydroxy-1-hydroxymethyl-3-
Article history:
Received 31 December 2014
Revised 9 February 2015
Accepted 13 February 2015
Available online xxxx
phenylpropyl)dodecanamide, is reported. The method requires only five synthetic steps from commer-
cially available
D
-aspartic acid and leads to enantiopure HPA-12 in good overall yields.
Ó 2015 Elsevier Ltd. All rights reserved.
Keywords:
Sphingolipids
Ceramide
Transport inhibitor
Chiral pool
Stereoselectivity
Introduction
of the transporter protein.7 However, despite its simplicity, the
structure of HPA-12 has been controversial. Initially assigned as
(10R,30R), the configuration of HPA-12 was carefully reassigned as
(10R,30S),8 and further confirmed by X-ray analysis.9 The interest
of HPA-12 as pharmacological tool has boosted the development
of synthetic approaches to this interesting SL analog since the
first catalytic Mannich-type enantioselective synthesis from
N-acylimino esters reported by Kobayashi and co-workers in
2003.10,11 Based on the wrong initial configurational assignment,
a stereoselective synthesis for HPA-12, based on the use of an
enantiopure sulfoxide as chiral inductor, was reported by
Raghavan et al. in 2004.12 Some years later, Berkes and co-workers
described an efficient and elegant aza-Michael crystallization-
induced asymmetric transformation (CIAT) methodology that led
to the revision of the absolute configuration for HPA-12.8 More
recently, Snowden and co-workers published a tandem approach
from (S)-Wynberg lactone,13 Arenz and co-workers reported a
Sphingolipids (SL) are plasma membrane components that play
key roles in cellular homeostasis and are also implicated in several
pathologies.1 Among the variety of SL, ceramides (Cer) are consid-
ered a metabolic hub in SL metabolism and have been linked to
cancer signaling pathways due to their implication in cell
senescence, apoptosis, cell cycle arrest, and autophagy.2 Cer are
synthesized in the endoplasmic reticulum (ER) and are transported
to the Golgi, either by vesicular traffic (to lead ultimately to
glycosphingolipids, GSL), or by means of a specific ceramide
transporter protein (CERT)3 for their further processing to
sphingomyelins by the action of sphingomyelin synthases (SMS)
(Scheme 1).
In recent years, the modulation of the activity of CERT has been
associated to important cellular events. Thus, downregulation of
this protein has been described to sensitize cancer cells to multiple
cytotoxic agents, potentiating ER stress. Conversely, its expression
is increased in drug-resistant cell lines and in residual tumor
following paclitaxel treatment of ovarian cancer, suggesting that it
could be a target for chemotherapy-resistant cancers.4 In this con-
text, the SL analog HPA-12, already reported in 2001 as an inhibitor
of non-vesicular Cer trafficking,5 has become a well-recognized
CERT inhibitor6 for its ability to interact with the START domain
multistep synthesis from L
-serine as starting material,14 and Kang
and co-workers described the synthesis of (+) and (ꢀ)-HPA-12 by
a Ru-catalyzed asymmetric rearrangement.15,16
Results and discussion
The use of HPA-12 as pharmacological tool for cellular studies
requires the development of efficient synthetic protocols for the
production of the compound. In this Communication, we wish to
report on a straightforward approach that allows the synthesis of
⇑
Corresponding authors. Tel.: +34 934006100; fax: +34 932045904.
E-mail address: delgado@rubam.net (A. Delgado).
http://dx.doi.org/10.1016/j.tetlet.2015.02.060
0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Abad, J.-L.; et al. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.02.060

2
J.-L. Abad et al. / Tetrahedron Letters xxx (2015) xxx–xxx
HPA-12
ER
Golgi
CH3
N
OH
OH
H3C
H3C
O
C13H27
HO
C13H27
CERT
De novo
SMS
HN
R
HN
R
O
O
Ceramides (different acyl chains)
Sphingomyelins
Scheme 1. Biosynthesis of Cer takes place in ER and requires CERT-mediated transport to Golgi for further processing to sphingomyelins.
O
O
O-MPA
L2
HPA-12
a
NH
3 Cl
O
HN
O
C11H23
OH
L1
a
b
OH
Δδ RS > 0 ΔδRS < 0
-0.070
O
1
2
O
O
O
*
H3CO
O
O
OH HN
C11H23
O
HN
C11H23
O
HN
C11H23
OR
OH HN
3' 1'
C11H23
c
b
-0.249
3'
1'
(S)
0.127
OTBDMS
OTBDMS
0.155
O
0.225
-0.235
4
OH
-0.272
-0.145
3a
3b
R = Me 3d
R = Et
3c R = iPr
R = 1-(Me)propyl
R = 2-(Me)propyl
(-)-HPA-12
(1'R,3'S)
3e
Scheme 3. Configurational assignment of C30 in HPA-12 derivative 4. Reagents and
conditions: (a) TBMSCl/DBU/CH2Cl2 (75% yield); (b) EDC/CH2Cl2/DMAP/(R)-(ꢀ)- or
(S)-(+)-MPA/CH2Cl2 (90% yield). Aromatic protons were assigned by HMBC.
Scheme 2. Reagents and conditions: (a) dodecanoyl chloride chloride/NaOH; (b)
BF3ꢁEt2O/ROH (for 3b–3e) or BF3 MeOH (for 3a), (70–75% combined yield for steps a
and b); (c) (i) K-selectride; (ii) LiBEt3H, THF, ꢀ78°, (80% combined yield).
Conclusions
In summary, a straightforward approach to the synthesis of the
CERT inhibitor HPA-12 is described. At a small scale, the method
requires five synthetic steps and two chromatographic purifica-
tions (keto ester 2 and (ꢀ)-HPA-12) from commercially available
enantiomerically pure HPA-12 in only five steps from cheap
starting materials (Scheme 2). Our approach starts from keto
amino acid (1), easily obtained from
and one simple crystallization in 80% combined yield, following a
protocol identical to that reported from enantiomeric -aspartic
D-aspartic acid in two steps
D-aspartic acid to afford the target compound in acceptable overall
L
yields (around 40%). At a larger scale, the major syn isomer can be
isolated by crystallization,11 thus avoiding the use of the final
chromatographic purification. This simple method, amenable to
small to medium scale preparations, challenges the currently
described synthetic protocols for the synthesis of this interesting
pharmacological tool.
acid.17,18 Acylation of 1 with lauric acid under Schotten–Baumann
conditions, followed by esterification with ethanol in the presence
of BF3ꢁEt2O, afforded ethyl ester 3b, which was identical to that
described by the above mentioned Mannich-type enantioselective
approach.10,11 The diastereoselective reduction of the carbonyl
group in 3b with the tandem K-Selectride/LiEt3BH10,11 afforded a
mixture of syn/anti adducts in an approximate 90:10 ratio (by
NMR analysis). Attempts to improve the diastereoselectivity of this
reduction step by modifying the nature of the ester group (esters
3a and 3c–e, Scheme 2) proved fruitless, since similar syn/anti
ratios were obtained in all cases. Likewise, attempts to reduce keto
acid 2 in a diastereoselective fashion under different hydride
sources (LiAlH4, K-selectride or NaBH4/MnCl2, among others) were
unsuccessful. For small to medium scale preparations (typically up
to 25 mmol) the major syn adduct can be easily isolated by flash
chromatography, whereas crystallization11 may be the method of
choice for larger scales.
Acknowledgment
This work was supported by grant SAF2011-22444 (Ministry of
Science and Innovation).
Supplementary data
Supplementary data (general experimental data and detailed
synthetic protocols, compound characterization, and copies of
NMR spectra) associated with this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.tetlet.2015.02.060.
As mentioned above, the configuration of HPA-12 has been a
matter of controversy. In this work, the syn relationship of the
major (10R,30S) HPA-12 diastereomer has been corroborated by
the configurational assignment of the secondary alcohol through
the TBDMS derivative 4, after derivatization to the corresponding
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