Bioorganic & Medicinal Chemistry Letters 19 (2009) 6319–6325
Bioorganic & Medicinal Chemistry Letters
Syntheses of aminoalcohol-derived macrocycles leading to a small-molecule
binder to and inhibitor of Sonic Hedgehog
Lee F. Peng a,b,c, , , Benjamin Z. Stanton b,c, , Nicole Maloof b,c, Xiang Wang b,c, Stuart L. Schreiber b,c,d,à
*
a GI Unit, Department of Medicine, Massachusetts General Hospital, 55 Fruit Street, Boston MA 02114, United States
b Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, MA 02138, United States
c The Broad Institute, 7 Cambridge Center, Cambridge, MA 02142, United States
d Howard Hughes Medical Institute, Broad Institute of Harvard and MIT, 7 Cambridge Center, Cambridge, MA 02142, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
We report the synthesis and biological activity of a library of aminoalcohol-derived macrocycles from
which robotnikinin (17), a binder to and inhibitor of Sonic Hedgehog, was derived. Using an asymmetric
alkylation to set a key stereocenter and an RCM reaction to close the macrocycle, we were able to syn-
thesize compounds for testing. High-throughput screening via small-molecule microarray (SMM) tech-
nology led to the discovery of a compound capable of binding ShhN. Follow-up chemistry led to a
library of macrocycles with enhanced biological activity relative to the original hit compounds. Differ-
ences in ring size and stereochemistry, leading to alterations in the mode of binding, may account for dif-
ferences in the degree of biological activity. These compounds are the first ones reported that inhibit Shh
signaling at the ShhN level.
Received 28 August 2009
Revised 18 September 2009
Accepted 22 September 2009
Available online 25 September 2009
This article is dedicated to the memory of
Brian L. Gray
Keywords:
Sonic Hedgehog
Robotnikinin
Ó 2009 Elsevier Ltd. All rights reserved.
Macrocycle
Small-molecule microarray
Surface plasmon resonance
Shh-LIGHT2
Ptch1À/À
Polyketide synthase-derived macrolactones are rich in struc-
tural diversity and biological activity. Examples include pikromy-
cin1 and erythromycin2 (inhibitors of bacterial protein synthesis),
enterobactin (inhibitor of bacterial iron transport),3 epothilones
A, B, D (stabilizer of microtubules),4 and FK506 (inhibitor of PP2B
phosphatase via its FKBP12 complex).5–7 We report here a synthe-
sis of macrolactones that has yielded a powerful new small-mole-
cule probe of the Hedgehog signaling pathway, which plays key
roles in development and oncogenesis.
Our synthesis exploits 1,2-aminoalcohols as simple templates
upon which 12-, 13- and 14-membered macrocycles are built
(Scheme 1). The pathway extends previous work, reported by Lee
et al., which also derived macrocyclic scaffolds from aminoalcohol
templates, and yields macrocycles that can be optimized with great
facility when they are identified as hits in small-molecule screens.8
We report herein a new asymmetric alkylation sequence to the
pathway, a modification that installs a stereogenic center bearing
an amide side-chain on the macrocycle scaffold and that resulted
in a new scientific discovery. Starting from commercially available
c
-unsaturated pentenoyl chloride, the Evans oxazolidinone,9 and
readily available chiral 1,2-aminoalcohols, the target macrolac-
tones were synthesized in nine steps. Following an asymmetric
alkylation with a-bromo-tert-butyl acetate, which proceeded with
over 19:1 diastereoselectivity, the tert-butyl ester was cleaved
with TFA. The resulting acid was submitted to standard amine cou-
pling conditions in the presence of a variety of amino alcohols.
In the initial application of the synthetic pathway, we loaded
the resulting alcohol onto polystyrene macrobeads.10 After cleav-
ing the chiral auxiliary under standard conditions, the resulting
acid was coupled with a variety of commercially available 1,2-ami-
noalcohols. Coupling reactions with acids of different chain lengths
bearing terminal olefin groups yielded the acyclic macrolactone
precursors. Ring-closing metathesis reactions (RCMs)11 were used
in the macrocyclization step. Using the (encoded) one macro-
bead/one stock solution approach,12 2070 compounds, including
12-, 13- and 14-membered macrocycles, were synthesized (S.L.S.,
unpublished results).
* Corresponding author. Tel.: +1 617 714 7438; fax: +1 617 714 8943.
These authors contributed equally.
à
Senior Author.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.