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Targeting bacteria via iminoboronate chemistry of amine-presenting lipids.

Bandyopadhyay A, McCarthy KA, Kelly MA, Gao J - Nat Commun (2015)

Bottom Line: Here we show that targeted recognition of lipids can be realized by selectively modifying the lipid of interest via covalent bond formation.By targeting phosphatidylethanolamine and lysylphosphatidylglycerol, the two lipids enriched on bacterial cell surfaces, the iminoboronate chemistry allows potent labelling of Gram-positive bacteria even in the presence of 10% serum, while bypassing mammalian cells and Gram-negative bacteria.The covalent strategy for lipid recognition should be extendable to other important membrane lipids.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Merkert Chemistry Center, Boston College, 2609 Beacon Street, Chestnut Hill, Massachuetts 02467, USA.

ABSTRACT
Synthetic molecules that target specific lipids serve as powerful tools for understanding membrane biology and may also enable new applications in biotechnology and medicine. For example, selective recognition of bacterial lipids may give rise to novel antibiotics, as well as diagnostic methods for bacterial infection. Currently known lipid-binding molecules primarily rely on noncovalent interactions to achieve lipid selectivity. Here we show that targeted recognition of lipids can be realized by selectively modifying the lipid of interest via covalent bond formation. Specifically, we report an unnatural amino acid that preferentially labels amine-presenting lipids via iminoboronate formation under physiological conditions. By targeting phosphatidylethanolamine and lysylphosphatidylglycerol, the two lipids enriched on bacterial cell surfaces, the iminoboronate chemistry allows potent labelling of Gram-positive bacteria even in the presence of 10% serum, while bypassing mammalian cells and Gram-negative bacteria. The covalent strategy for lipid recognition should be extendable to other important membrane lipids.

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Synthesis of AB1 and its derivatives(a) Allyl bromide, K2CO3, NaI, acetone, 81%. (b) (CF3SO2)2O, Et3N, DCM, 95%. (c) Cys-OMe, DMPA, MeOH, ~365 nm UV irradiation. (d) Boc anhydride, Na2CO3, THF/H2O, 80% over two steps. (e) Boc-Cys-OtBu, DMPA, MeOH, ~365 nm UV irradiation, 75%. (f) Pd(dppf)Cl2/dppf, B2Pin2, KOAc, dioxane, ~70–80%. (g) 40% TFA in DCM. (h) diethanolamine, 1N HCl, 74% over two steps. (i) 60% TFA in DCM. (j) Fmoc-OSu, Na2CO3, THF/H2O, 81% over two steps.
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Figure 2: Synthesis of AB1 and its derivatives(a) Allyl bromide, K2CO3, NaI, acetone, 81%. (b) (CF3SO2)2O, Et3N, DCM, 95%. (c) Cys-OMe, DMPA, MeOH, ~365 nm UV irradiation. (d) Boc anhydride, Na2CO3, THF/H2O, 80% over two steps. (e) Boc-Cys-OtBu, DMPA, MeOH, ~365 nm UV irradiation, 75%. (f) Pd(dppf)Cl2/dppf, B2Pin2, KOAc, dioxane, ~70–80%. (g) 40% TFA in DCM. (h) diethanolamine, 1N HCl, 74% over two steps. (i) 60% TFA in DCM. (j) Fmoc-OSu, Na2CO3, THF/H2O, 81% over two steps.

Mentions: To test our hypothesis, we have designed and synthesized a novel unnatural amino acid (AB1, Fig. 2) that presents a 2-APBA motif as its side chain. We envisioned that the amino acid scaffold should allow the 2-APBA motif to be readily conjugated to fluorescent labels or other functional peptides. The synthetic route of AB1 is summarized in Fig. 2. Briefly, with 2′,4′-dihydroxy acetophenone 1 as the starting material, regioselective alkylation of the 4′-OH followed by triflate protection of the 2′-OH yielded 3 with an overall 81% yield. By taking advantage of the powerful thiol-ene chemistry,18 compound 3 was conjugated to two cysteine derivatives respectively to give the protected amino acids 4 and 7 in high yields. The key transformation of our synthesis is the Miyaura borylation,19 which converts the triflate to the Bpin moiety. In our hands, rigorous control of temperature was critical to the success of the borylation step: the reaction did not initiate below 95 °C and prolonged heating at higher temperatures caused the complete loss of the Bpin moiety to give the protodeboronated product, a protected AB2.20 With optimized conditions, the Bpin moiety was introduced with 70–80% yield. Fortuitously, with the boronic acid moiety eliminated, AB2 served as a perfect negative control for AB1 in the following membrane binding studies.


Targeting bacteria via iminoboronate chemistry of amine-presenting lipids.

Bandyopadhyay A, McCarthy KA, Kelly MA, Gao J - Nat Commun (2015)

Synthesis of AB1 and its derivatives(a) Allyl bromide, K2CO3, NaI, acetone, 81%. (b) (CF3SO2)2O, Et3N, DCM, 95%. (c) Cys-OMe, DMPA, MeOH, ~365 nm UV irradiation. (d) Boc anhydride, Na2CO3, THF/H2O, 80% over two steps. (e) Boc-Cys-OtBu, DMPA, MeOH, ~365 nm UV irradiation, 75%. (f) Pd(dppf)Cl2/dppf, B2Pin2, KOAc, dioxane, ~70–80%. (g) 40% TFA in DCM. (h) diethanolamine, 1N HCl, 74% over two steps. (i) 60% TFA in DCM. (j) Fmoc-OSu, Na2CO3, THF/H2O, 81% over two steps.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4363082&req=5

Figure 2: Synthesis of AB1 and its derivatives(a) Allyl bromide, K2CO3, NaI, acetone, 81%. (b) (CF3SO2)2O, Et3N, DCM, 95%. (c) Cys-OMe, DMPA, MeOH, ~365 nm UV irradiation. (d) Boc anhydride, Na2CO3, THF/H2O, 80% over two steps. (e) Boc-Cys-OtBu, DMPA, MeOH, ~365 nm UV irradiation, 75%. (f) Pd(dppf)Cl2/dppf, B2Pin2, KOAc, dioxane, ~70–80%. (g) 40% TFA in DCM. (h) diethanolamine, 1N HCl, 74% over two steps. (i) 60% TFA in DCM. (j) Fmoc-OSu, Na2CO3, THF/H2O, 81% over two steps.
Mentions: To test our hypothesis, we have designed and synthesized a novel unnatural amino acid (AB1, Fig. 2) that presents a 2-APBA motif as its side chain. We envisioned that the amino acid scaffold should allow the 2-APBA motif to be readily conjugated to fluorescent labels or other functional peptides. The synthetic route of AB1 is summarized in Fig. 2. Briefly, with 2′,4′-dihydroxy acetophenone 1 as the starting material, regioselective alkylation of the 4′-OH followed by triflate protection of the 2′-OH yielded 3 with an overall 81% yield. By taking advantage of the powerful thiol-ene chemistry,18 compound 3 was conjugated to two cysteine derivatives respectively to give the protected amino acids 4 and 7 in high yields. The key transformation of our synthesis is the Miyaura borylation,19 which converts the triflate to the Bpin moiety. In our hands, rigorous control of temperature was critical to the success of the borylation step: the reaction did not initiate below 95 °C and prolonged heating at higher temperatures caused the complete loss of the Bpin moiety to give the protodeboronated product, a protected AB2.20 With optimized conditions, the Bpin moiety was introduced with 70–80% yield. Fortuitously, with the boronic acid moiety eliminated, AB2 served as a perfect negative control for AB1 in the following membrane binding studies.

Bottom Line: Here we show that targeted recognition of lipids can be realized by selectively modifying the lipid of interest via covalent bond formation.By targeting phosphatidylethanolamine and lysylphosphatidylglycerol, the two lipids enriched on bacterial cell surfaces, the iminoboronate chemistry allows potent labelling of Gram-positive bacteria even in the presence of 10% serum, while bypassing mammalian cells and Gram-negative bacteria.The covalent strategy for lipid recognition should be extendable to other important membrane lipids.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Merkert Chemistry Center, Boston College, 2609 Beacon Street, Chestnut Hill, Massachuetts 02467, USA.

ABSTRACT
Synthetic molecules that target specific lipids serve as powerful tools for understanding membrane biology and may also enable new applications in biotechnology and medicine. For example, selective recognition of bacterial lipids may give rise to novel antibiotics, as well as diagnostic methods for bacterial infection. Currently known lipid-binding molecules primarily rely on noncovalent interactions to achieve lipid selectivity. Here we show that targeted recognition of lipids can be realized by selectively modifying the lipid of interest via covalent bond formation. Specifically, we report an unnatural amino acid that preferentially labels amine-presenting lipids via iminoboronate formation under physiological conditions. By targeting phosphatidylethanolamine and lysylphosphatidylglycerol, the two lipids enriched on bacterial cell surfaces, the iminoboronate chemistry allows potent labelling of Gram-positive bacteria even in the presence of 10% serum, while bypassing mammalian cells and Gram-negative bacteria. The covalent strategy for lipid recognition should be extendable to other important membrane lipids.

Show MeSH
Related in: MedlinePlus