Three dibenzofuran-based amino acid residues, namely 4-(2-aminoethyl)-6-dibenzofuranpropanoic acid (1), 4-(aminomethyl)-6-dibenzofuranethanoic acid (2), and 4-amino-6-dibenzofuranmethanoic acid (3), were prepared in order to compare their physical properties so as to further understand residue l's ability to nucleate antiparallel 3-sheet formation within small peptides in aqueous solution. FT-IR, variable temperature NMR, and an X-ray crystallography study reveal that amide analogs of 1 and 2 can adopt intramolecularly hydrogen bonded conformations in nonpolar solvents, whereas amides composed of residue 3 cannot. Spectroscopic studies reveal that linear heptapeptides containing 1 are capable of adopting a dynamic antiparallel 3-sheet structure in aqueous solution, whereas residues 2 and 3 are incapable of nucleating a 3-sheet structure in an otherwise identical peptide sequence. The efficacy of residue 1 as a 3-sheet nucleator appears to result from a 15-membered ring intramolecularly hydrogen-bonded hydrophobic cluster conformation which serves as a partial 3-sheet template enabling neighboring residues to be added to the growing sheet with a favorable equilibrium constant. The hydrophobic cluster conformation in these heptapeptides is stabilized by (S-Sheet Formation via Dibenzofuran-Based Amino Acids acid sequence which will adopt a partial /8-sheet structure capable of nucleating a /8-sheet,* 2 **S.*'7 we set out to design an amino acid that will stabilize a partial /8-sheet structure and thus nucleate /3-sheet formation in aqueous solution.8The concept of introducing a conformationally rigid molecule into a peptide to stabilize a single conformation was established by Hirschmann, Veber, Freidinger, Nutt, and their colleagues at Merck.9 Since then and previous to our efforts, several elegant dipeptide and related 8-turn mimetics have been prepared either to control the conformation of peptides and/or as potential pharmaceuticals.10 The ability to design a molecular fragment which nucleates 8-sheet formation was first demonstrated by Kemp by employing the epindolidione nucleus. When the epindolidione ring system is incorporated into an a-amino acid sequence, it serves as an artificial 8-strand and mediates sheet formation via hydrogen bonding between the epindolidione skeleton and the covalently attached peptide chain.10'0'11 The goal of the work described here is to develop an amino acid that is a dipeptide mimetic of the i + 1 and i + 2 residues of a 8-turn in an effort to nucleate 8-sheet folding without significantly perturbing the resulting antiparallel 8-sheet structure. Protein

No abstract

Matrix metalloproteinase (MMP) -activated prodrugs were formed by coupling MMP-cleavable peptides to doxorubicin. The resulting conjugates were excellent in vitro substrates for MMP-2, -9, and -14. HT1080, a fibrosarcoma cell line, was used as a model system to test these prodrugs because these cells, like tumor stromal fibroblasts, expressed several MMPs. In cultured HT1080 cells, simple MMP-cleavable peptides were primarily metabolized by neprilysin, a membrane-bound metalloproteinase. MMP-selective metabolism in cultured HT1080 cells was obtained by designing conjugates that were good MMP substrates but poor neprilysin substrates. To determine how conjugates were metabolized in animals,

The aromatic amino acid residue 4-(2-aminoethyl)-6-dibenzofuranpropanoic acid (1) nucleates antiparallel -sheet folding in tridecapeptides which subsequently self-assemble into fibrils. Residue 1 functions as a folding nucleator by facilitating intramolecular hydrogen bonding between the flanking R-amino acid residues and by favoring the formation of a hydrophobic cluster composed of the dibenzofuran skeleton and the hydrophobic side chains of the flanking R-amino acids. The hydrogen bonded hydrophobic cluster (i.e., -hydrophobic R-amino acid residue-1-hydrophobic R-amino acid residue-) nucleates -sheet folding in relatively small peptides that have a propensity to fold. The R-amino acid sequence design determines the self-association pathway and the resulting molecular architecture. The approach described here takes advantage of template driven hydrophobic clusters and template derived conformational biases to nucleate folding in small peptides, affording -sheets which subsequently self-associate into well-defined quaternary structures. This strategy allows significant R-amino acid sequence variations to be accommodated in the resulting -sheet-based macromolecular assembly without interfering with the folding pathway.Our understanding of -sheet structure lags significantly behind our understanding of R-helical secondary structure due, in part, to the lack of a well-defined peptide model system for studies on -sheet structure. 1 Careful studies on peptide model systems have significantly improved our mechanistic understanding of helical folding. 2 However, it has proven much more difficult to design a peptide that will fold into a monomeric -sheet in aqueous solution. 3 Small peptides having a predominance of -branched residues typically undergo self-association in addition to intramolecular folding, affording heterogeneous aggregated -sheet structures characterized by a mixture of parallel and antiparallel -strand orientations, with a few exceptions. 3 High molecular weight polypeptides composed of a single residue or a repeating dipeptide sequence having a propensity to adopt a -sheet structure also form heterogeneous -sheets. 4 In an effort to nucleate the folding of a structurally well-defined -sheet, we have reported a dibenzofuran-based amino acid residue, namely, 4-(2-aminoethyl)-6-dibenzofuranpropanoic acid (1). This template reverses the polypeptide chain direction by replacing the i + 1 and i + 2 residues of a -turn and facilitates strand-strand interactions in appropriate sequences resulting in -sheet formation. 5 Variable temperature NMR analysis, FT-IR studies, and X-ray crystallographic data demonstrate that residue 1 promotes intramolecular hydrogen bonding between the flanking R-amino acid residues, which appears to be necessary but not sufficient for nucleating -sheet folding in the attached peptide strands. 5 Residue 1 can adopt two different conformations in aqueous solution, as discerned by X-ray crystallographic and 2D-NMR studies, both having the attached R-amino acids intramolecularly hy...