Fig. 4
Facile synthesis of sterically constrained and labeled cyclic progelators. a Synthetic scheme for unlabeled (route I) and labeled (route II) KLDLCyclic and KFDFCyclic progelators. All self-assembling peptides (SAPs) were cyclized under dilute conditions (500 µM) with 5 eq I2 in a mixture of AcOH/MeOH/H2O to create a soluble progelator. Route I uses N-terminal Fmoc-protected SAPs to improve material separation during chromatographic purification. Fmoc removal generates the intended unlabeled progelators KLDLCyclic and KFDFCyclic. Route II depicts the synthesis of labeled progelators through N-terminal modification with 5(6)-carboxytetramethyl rhodamine prior to cyclization. b, c High-performance liquid chromatography (HPLC) (b) monitored at 214 nm and corresponding electrospray ionization (ESI) spectra (c) of Fmoc-KLDLLinear (red), Fmoc-KLDLCyclic (blue), and KLDLCyclic (green) (835.79 m/z, 787.76 m/z, and 1070.26 m/z, respectively) verify purity and mass of synthetic modifications to KLDL peptides. d, e HPLC (d) monitored at 214 nm and corresponding ESI spectra (e) of Fmoc-KFDFLinear (red), Fmoc-KFDFCyclic (blue), and KFDFCyclic (green) (781.862 m/z, 856.17 m/z, and 1355.66 m/z, respectively) verify purity and mass of synthetic modifications to KFDF peptides. In both KLDL and KFDF systems, macrocyclization causes a slight decrease in polarity and Fmoc-deprotection increases progelator polarity. f KLDLLinear SAP macrocyclization kinetics monitored by liquid chromatography–mass spectrometry (LCMS) at 214 nm reveal complete cyclization after 120 min. g Absorbance spectra of unlabeled (black) and labeled KLDL progelators (pink, λmax = 565 nm for rhodamine signal). h KFDFLinear SAP macrocyclization kinetics monitored by LCMS at 214 nm reveal complete cyclization after 120 min. i Absorbance spectra of unlabeled (black) and labeled KFDF progelators (pink, λmax = 565 nm for rhodamine signal). j Photographs of KLDLLinear precursor as a hydrogel (left) and the resulting KLDLCyclic progelator as a soluble solution (right). k Photographs of KLDLLinear precursor as a hydrogel (left) and the resulting KLDLCyclic progelator as a soluble solution (right)
