Total Synthesis of Septocylindrin B and C-Terminus Modified Analogues

<div><p>The total synthesis is reported of the peptaibol Septocylindrin B which is related to the well documented channel forming peptaibol antibiotic Alamethicin. Several analogues were synthesized with a modified <em>C</em>-terminus, to investigate the SAR of the terminal residue Phaol. All these peptides were tested for their membrane perturbation properties by fluorescent dye leakage assay and for their antibacterial activity.</p> </div

Synthetic strategy for the synthesis of ABCD-Phaol-N6 with Z = Cbz.

<p>(i) Cbz-removal with H₂, Pd-C and MeOH followed by coupling via EDC/HOAt. (ii) O<i>t</i>Bu-removal of the <i>C</i>-component with TFA/CH₂Cl₂ and Cbz-removal of the <i>N</i>-component with H₂, Pd-C and MeOH, followed by coupling using EDC/HOAt. (iii) O<i>t</i>Bu removal using ZnBr₂ (iv) Cbz-removal of the <i>N</i>-component with H₂, Pd-C and MeOH, followed by coupling via HOAt/EDC (v) Boc-deprotection using BiCl₃.</p

Release of CF from PC∶Ch (7∶3) liposomes after 20 minutes at different ratios R-1 = [peptide]/[lipid].

<p>Alamethicin F50 is used as a reference.</p

Synthetic strategy for the synthesis of ABCD-ethanolamine with Z = Cbz.

<p>(i) Cbz-removal with H₂, Pd-C and MeOH followed by coupling via EDC/HOAt. (ii) O<i>t</i>Bu-removal with ZnBr₂ .iii) O<i>t</i>Bu-removal of the <i>C</i>-component with TFA/CH₂Cl₂ and Cbz-removal of the <i>N</i>-component with H₂, Pd-C and MeOH, followed by the coupling via EDC/HOAt. (iv) Cbz-removal with H₂, Pd-C and MeOH followed by coupling via PyBOP, followed by deprotection using TBAF.</p

Synthetic strategy for the synthesis of Septocylindrin B with Z = Cbz.

<p>(i) Cbz-removal with H₂, Pd-C and MeOH followed by coupling via EDC/HOAt. (ii) O<i>t</i>Bu-removal of the <i>C</i>-component with TFA/CH₂Cl₂ and Cbz-removal of the <i>N</i>-component with H₂, Pd-C and MeOH, followed by coupling using EDC/HOAt. (iii) O<i>t</i>Bu-removal using ZnBr₂ or TFA and Cbz-removal of the <i>N</i>-component with H₂, Pd-C and MeOH, followed by coupling using EDC/HOAt, after which the peptide is Boc deprotected using ZnBr₂. (iv) aminolysis.</p

Synthetic approach for Septocylindrin B.

<p>A' = residue 2–5, A = residue 1–5, B = 6–13, C = residue 14–17, D = residue 18–20.</p

Phaol [2-{[(2<i>S</i>)-2-amino-3-phenylpropyl]amino}ethanol].

<p>R-Phaol, R = Ac-UPUAUAQUVUGLUPVUUQQ for Septocylindrin B.</p

Antibacterial activity (MIC, µM) of Septocylindrin B and selected analogues.^a

a<p>For HPLC traces of selected analogues see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051708#pone.0051708.s004" target="_blank">Figures S4</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051708#pone.0051708.s005" target="_blank">S5</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051708#pone.0051708.s006" target="_blank">S6</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051708#pone.0051708.s007" target="_blank">S7</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051708#pone.0051708.s008" target="_blank">S8</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051708#pone.0051708.s009" target="_blank">S9</a>.</p>b<p>Data from ref. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051708#pone.0051708-Summers1" target="_blank">[1]</a>.</p>c<p>Not available.</p>d<p>A reduced growth is clearly visible, but no MIC end point ≤100 µM.</p