Bi-ang Hu

Hydrogels cross-linked by native chemical ligation.

We describe the use of native chemical ligation (NCL) reaction to covalently cross-link soluble polymers into hydrogels. Macromonomers consisting of a four-armed poly(ethylene glycol) (PEG) core end-functionalized with either thioester or N-terminal cysteine peptide were designed and synthesized. Upon mixing aqueous solutions of the thioester and N-terminal cysteine macromonomers, rigid hydrogels formed within minutes. The gelation time was affected by choice of buffer, pH, polymer concentration, reaction temperature, and chemical composition of the N-terminal cysteine conjugate. The kinetics of gel formation and the viscoelastic behavior of selected hydrogels were further studied by oscillatory rheology, which demonstrated a minimum gel formation time of approximately two minutes and the formation of an elastic cross-linked hydrogel via the NCL reaction. A useful feature of this hydrogel strategy is the regeneration of thiol functional groups as a result of the NCL reaction, thereby allowing functionalization of the polymer hydrogel with biomolecules. This was demonstrated by conjugation of a maleimide-GRGDSPG-NH(2) peptide to an NCL hydrogel, permitting the attachment of human mesenchymal stem cells (hMSCs) on the hydrogel. Due to the mild reaction conditions, chemoselectivity, and potential for biological functionalization, our approach may prove useful as a general method for hydrogel formation, including hydrogels intended for biomedical applications.

Protection of 3,4-dihydroxyphenylalanine (DOPA) for Fmoc solid-phase peptide synthesis

Cyclic ethyl orthoformate (Ceof) was utilized as a protecting group to protect the catechol hydroxyl groups of 3,4-dihydroxyphenylalanine (DOPA). This protecting group is stable to strong bases and nucleophiles, and can be removed eAciently by 1 M trimethylsilyl bromide in trifluoroacetic acid in the presence of scavengers at 0C for 60 min. Fmoc-DOPA(Ceof)-OH was synthesized in high yield and applied along with other Fmoc-amino acids to the solid-phase peptide synthesis of a DOPA-containing decapeptide from a mussel adhesive protein. # 2000 Elsevier Science Ltd. All rights reserved.