Journal of the American Chemical Society
Communication
ORCID
The synthesized molecules were tested in a proliferation
assay against the T-lymphocyte cell line EL4. All three natural
products demonstrated potent inhibition of proliferation, with
IC50 values below 1 μM. When the side chains were alkyl
chains, FR1 with 11 carbon atoms still remained active,
although less potent than FR252921. However, FR2 with only
a methyl group on the side chain completely lost activity even
at 20 μM, the highest concentration tested. Because FR2 was
isolated as a 1.2:1 mixture of (E,E,E) and (E,E,Z) isomers, it
has not yet been possible to fully differentiate the biological
impacts of the methyl side chain versus the alkene geometry in
this case. Nonetheless, since this mixture was completely
inactive under the conditions tested, we can tentatively
conclude that neither of the two compounds possesses
appreciable activity. This result showed that the lipophilic
side chains are important to maintain the activity. Then,
substitution in the macrocycle was evaluated. While C12-
methyl deletion had little influence on the activity (cf.
FR252921 and FR3, Figure 3A,B), further removal of the
C13-hydroxy group rendered analogue FR4 inactive (Figure
3B). Based on these results, several other analogues with
halogenated or arylated side chains were synthesized. Among
them, FR5 with a CF3 substituent was the most potent
inhibitor, with an IC50 of 83 nM surpassing FR252921 by 3-
fold (Figure 3B). Other analogues displayed either inferior
activity or poor solubility. Altogether, these results enabled the
preliminary establishment of an SAR for this family of
compounds as depicted in Figure 3C. The surprisingly strong
modulation of biological activity by side-chain modification is a
valuable vector for development of these molecules.
Present Addresses
⊥Y.C.: Department of Pharmaceutics, Ghent University,
Ghent, Belgium
∥G.C.: Syngenta Crop Protection AG, Monthey, Switzerland
#P.A.: Curium Pharma, Saclay, France
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We are thankful to the ERC (CoG VINCAT), the FWF
(P27194 and Doctoral Program “Molecular Drug Targets”
W1232), and the DFG (Grant MA 4861/3-1) for financial
support of this research. Generous continued support by the
̈
University of Vienna is acknowledged. Dr. H. Kahlig is
acknowledged for expert assistance with structure determi-
nation by NMR. Calculations were partially performed at the
́
Vienna Scientific Cluster (VSC). We thank Prof. L. Gonzalez
(U.Vienna) for generous support, fruitful discussions, and
computational resources. Mr. I. Saridakis (U. Vienna) is
gratefully acknowledged for analytical support.
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
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Experimental, computational, and characterization data,
including Figures S1−S18 and Tables S1−S5 (PDF)
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AUTHOR INFORMATION
Corresponding Author
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J. Am. Chem. Soc. XXXX, XXX, XXX−XXX