Convergent solid-phase synthesis of symmetrical benzo[b]furan's dimerizer

Peptide-Based Supramolecular Semiconductor Nanomaterials via Pd-Catalyzed Solid-Phase "Dimerizations"

We report a streamlined method for the synthesis of peptides embedded with complex and easily variable π-conjugated oligomeric subunits from commercially available precursors. These modified peptides self-assemble under aqueous conditions to form one-dimensional nanomaterials containing networks of π-stacked conduits, despite the inclusion of π-conjugated oligomers with quadrupoles extended over larger areas. The procedure has circumvented solubility and other synthetic issues to allow for the facile formation of a diverse library of bioelectronic nanomaterials, including a complex sexithiophene-containing peptide whose nanostructures display gate-induced conductivity within field effect transistors.

Amino-terminal dimerization of peptides on the solid support. Synthesis and biological activity of the immunosuppressive HLA-DR fragments linked by poly(ethylene glycol)s

The nonapeptide fragment of the HLA-DR molecule, located in the exposed loop of the beta chain (164-172) and having the sequence VPRSGEVYT, suppresses the immune response. On the basis of the three-dimensional structure of the HLA-DR superdimer, we designed new dimeric analogs in which the VPRSGEVYT peptides are linked through their N-termini by poly(ethylene glycol) linkers of different lengths and are able to mimic the dimeric nature of the immunosuppressive fragments of HLA class II molecules. The analogs were synthesized using standard solid-phase peptide synthesis protocols. The dimerization was achieved by cross-linking the N-terminal positions of the peptides, attached to an MBHA resin, with alpha,omega-bis(acetic acid) poly(ethylene glycol), activated by esterification with pentafluorophenol. Our results demonstrate that the amino-terminal dimerization of the peptide results in enhanced immunosuppressive activity and that the potency of the conjugates depends on the length of the poly(ethylene glycol) linker. MS/MS analysis of the obtained dimeric peptides is also presented.

From solution-phase to solid-phase enyne metathesis: crossover in the relative performance of two commonly used ruthenium pre-catalysts

A crossover in the ability of two distinct ruthenium-based metathesis pre-catalysts to effect the synthesis of dialkenylboronic esters in solution and on the solid-phase was observed. Specifically, while the Grubbs 2nd generation pre-catalyst 3 affords a greater degree of conversion to product than the Hoveyda-Grubbs pre-catalyst 2 in a solution-phase enyne-metathesis reaction, this trend is reversed in the solid-phase variant. Systematic investigation showed this trend to be general, regardless of variations in the homoallylic alcohol and alkynylboronic ester components of the reaction, as well as in the type of solid support employed. Experiments to determine a mechanistic hypothesis for this trend highlighted the significance of the ruthenium remaining bound to the substrate after metathetic rearrangement and found the presence of phosphine ligand to be detrimental to the success of the solid-phase reaction. Therefore, these results suggest an expanded role for phosphine-free pre-catalysts, such as 2, in challenging solid-phase metathesis reactions.

Recent applications of olefin metathesis to combinatorial chemistry

Olefin metathesis has emerged as a versatile technology for the synthesis of combinatorial libraries with regard to both scaffold creation and embellishment. The incessant pursuit of 'next-generation' catalysts continues to raise the bar in terms of efficiency, functional group tolerability, diminished reaction times and temperatures and has helped foster both diversity-oriented and target-directed efforts. This report summarizes recent contributions in the area of olefin cross-metathesis and ring-closing metathesis as applied to combinatorial and parallel synthesis. These examples include generation of dimeric benzo[b]furans as novel probes for protein-protein interaction, a cross-metathesis approach to 'traceless linkers' for azide-containing sugars, stereo-diversified synthesis of 1,4- and 1,5-enediols, a novel mannitol derived combinatorial scaffold, parallel synthesis strategies for aza-sugars, as well as the synthesis of dehydro-Freidinger lactams.

Synthesis of Conformationally Restricted 2,3-Diarylbenzo[b]furan by the Pd-Catalyzed Annulation of o-Alkynylphenols: Exploring a Combinatorial Approach

The palladium/bpy-catalyzed annulation of o-alkynylphenol with various aryl halides to generate diversified 2,3-diarylbenzo[b]furan is herein described. This method provides an efficient synthetic pathway for the combinatorial synthesis of conformationally restricted 2,3-diarylbenzo[b]furan for drug discovery.