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J Am Chem Soc. 2016 Mar 9;138(9):3136-44. doi: 10.1021/jacs.5b13008. Epub 2016 Feb 26.

Ribosome-Templated Azide-Alkyne Cycloadditions: Synthesis of Potent Macrolide Antibiotics by In Situ Click Chemistry.

Author information

1
Department of Chemistry, Temple University , Philadelphia, Pennsylvania 19122, United States.
2
Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
3
Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland , Baltimore, Maryland 21201, United States.
4
Department of Biology, Temple University , Philadelphia, Pennsylvania 19122, United States.
5
Moulder Center for Drug Discovery Research, Temple University School of Pharmacy , Philadelphia, Pennsylvania 19140, United States.
6
Department of Microbiology and Immunology, Temple University School of Medicine , Philadelphia, Pennsylvania 19140, United States.

Abstract

Over half of all antibiotics target the bacterial ribosome-nature's complex, 2.5 MDa nanomachine responsible for decoding mRNA and synthesizing proteins. Macrolide antibiotics, exemplified by erythromycin, bind the 50S subunit with nM affinity and inhibit protein synthesis by blocking the passage of nascent oligopeptides. Solithromycin (1), a third-generation semisynthetic macrolide discovered by combinatorial copper-catalyzed click chemistry, was synthesized in situ by incubating either E. coli 70S ribosomes or 50S subunits with macrolide-functionalized azide 2 and 3-ethynylaniline (3) precursors. The ribosome-templated in situ click method was expanded from a binary reaction (i.e., one azide and one alkyne) to a six-component reaction (i.e., azide 2 and five alkynes) and ultimately to a 16-component reaction (i.e., azide 2 and 15 alkynes). The extent of triazole formation correlated with ribosome affinity for the anti (1,4)-regioisomers as revealed by measured Kd values. Computational analysis using the site-identification by ligand competitive saturation (SILCS) approach indicated that the relative affinity of the ligands was associated with the alteration of macrolactone+desosamine-ribosome interactions caused by the different alkynes. Protein synthesis inhibition experiments confirmed the mechanism of action. Evaluation of the minimal inhibitory concentrations (MIC) quantified the potency of the in situ click products and demonstrated the efficacy of this method in the triaging and prioritization of potent antibiotics that target the bacterial ribosome. Cell viability assays in human fibroblasts confirmed 2 and four analogues with therapeutic indices for bactericidal activity over in vitro mammalian cytotoxicity as essentially identical to solithromycin (1).

PMID:
26878192
PMCID:
PMC4785600
DOI:
10.1021/jacs.5b13008
[Indexed for MEDLINE]
Free PMC Article

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