Bioorganic & Medicinal Chemistry Letters
Total synthesis of a biotinylated rocaglate: Selective targeting
of the translation factors eIF4AI/II
d
a,
Jennifer M. Chambers a, Lisa M. Lindqvist b,c, , G. Paul Savage , Mark A. Rizzacasa
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a School of Chemistry, The Bio21 Institute, The University of Melbourne, Melbourne, Victoria 3010, Australia
b Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
c Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
d CSIRO Molecular and Health Technologies, Bayview Avenue, Victoria 3168, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
The total synthesis of a biotinylated derivative of methyl rocaglate is described. This compound was
accessed from synthetic methyl rocaglate (2) via formation of the propargyl amide and subsequent click
reaction with a biotin azide. Affinity purification revealed that biotinylated rocaglate (8) and methyl
rocaglate (2) bind with high specificity to translation factors eIF4AI/II. This remarkable selectivity is in
line with that found for the more complex rocaglate silvestrol (3).
Received 17 September 2015
Revised 26 October 2015
Accepted 12 December 2015
Available online 14 December 2015
Ó 2015 Elsevier Ltd. All rights reserved.
Keywords:
Methyl rocaglate
Silvestrol
Biotin tag
eIF4A
Pulldown
Of the more than 100 flavaglines known, about 60 of them are
cyclopenta[b]benzofuran type compounds, with many of these
natural products exhibiting insecticidal and antiproliferative prop-
erties.1,2 The first cyclopenta[b]benzofuran derivative, rocaglamide
(1), was isolated from Aglaia elliptifolia in 1982 and the structure
was solved by single crystal X-ray structural analysis.3 A large
number of other rocaglates have been isolated including aglafoline
(2) from Aglaia elliptifolia in 19924 (see Fig. 1).
Compound 2 was also isolated from Aglaia odorata in 1993 and
given the name (ꢀ)-methyl rocaglate.5 The more complex and
highly active 1,4-dioxane containing rocaglates silvestrol (3) and
the C5000 epimer episilvestrol (4), were isolated by two independent
groups from both Aglaia foveolata and Aglaia leptantha.6–8 Silvestrol
(3) shows potent anticancer activity,9 in particular against CLL,10
and can induce multiple forms of cell death, which varies between
cell types.11
rocaglamide (1) was conjugated to Affi-GelÒ beads and performed
a pull-down assay. Two proteins were found to bind to rocagla-
mide (1) and were identified as prohibitin (PHB) 1 and 2 by
GC–MS and Western blot analysis. It was therefore concluded that
rocaglamide binding to PHB prevented it from interacting with
cRaf, and thus inhibited translation indirectly by blocking the
Raf–MEK–ERK pathway. However, the translation initiation factor
eIF4A was also identified as the primary protein target of rocagla-
mide (1) using a rocaglamide analog.13 Indeed, previous work
suggested that PHB 1/2 is not likely to be involved in the mode
of action of translation inhibition, as rocaglamide compounds have
retained translational activity in cellular extracts, which do not
have a functional Raf–MEK–ERK pathway, which is responsible
for communication between extracellular receptor and the
nucleus.9 We have recently described the total synthesis of a
biotinylated derivative of episilvestrol (4) and demonstrated that
this binds only to eIF4AI/II.14 We now describe the total synthesis
of biotinylated rocaglate and demonstrate that methyl rocaglate
(2) and rocaglamide (1) have a similar selectivity for eIF4AI/II as
episilvestrol.
Two conflicting reports have been published concerning the
protein targets of rocaglate natural products such as rocaglamide
(1). Li-Weber and co-workers found that a rocaglaol derivative
demonstrated similar IC50 and effects on growth inhibition of
Jurkat cells as rocaglamide (1).12 To find the cellular targets,
The synthesis of biotinylated rocaglate began with methyl roca-
glate (2), which was accessed via total synthesis.8b using a [3+2]-
cycloaddition of an oxidopyrylium as pioneered by Porco.15,16
Hydrolysis of 2 with aqueous KOH gave rocagloic acid (5)16e
which was converted into the propargyl amide (6) by coupling
with propargyl amine. A Cu mediated click reaction with the
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Corresponding authors. Tel.: +61 3 9345 2974; fax: +61 3 9347 0852 (L.M.L.);
tel.: +61 3 8344 2397; fax: +61 3 9347 8396 (M.A.R.).
(M.A. Rizzacasa).
0960-894X/Ó 2015 Elsevier Ltd. All rights reserved.