Paper
Organic & Biomolecular Chemistry
used for HPLC analysis. Analysis of the samples was per-
formed by analytical RP-HPLC with a Maisch ReproSil-Pur 120
C18-AQ column (250 × 4.6 mm, 5 μm) and a linear gradient of
0–100% buffer B over 48 minutes at a flow rate of 1 mL min−1
(Buffer A: 95% H2O, 5% MeCN, 0.1% TFA; Buffer B: 5% H2O,
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intact peptide to be calculated based upon the ratio of peak
areas corresponding to the internal standard and the intact
peptides.
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Circular dichroism spectroscopy
A 60 μM solution of each peptide was prepared by dissolving
in 20 mM HEPES buffer (pH 7.4). Samples were measured at
room temperature from 210–250 nm at a scan rate of 20 nm
min−1 and a bandwidth of 0.1 nm. The spectra were converted
to molar ellipticities in units of deg × cm2 dmol−1
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Acknowledgements
We thank Eefjan Breukink for providing authentic daptomycin
and Frederike Müskens for preparing L- and D-kynurenine.
Javier Sastre Toraño is acknowledged for providing HRMS ana-
lysis and Jonas Dörr for assistance in acquiring the CD
measurements. Linda Quarles van Ufford is kindly thanked for
assisting with antibacterial assays. Financial support provided
by The Netherlands Organization for Scientific Research (VIDI
grant to NIM).
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