Synthesis of Fmoc-Protected Arylphenylalanines (Bip Derivatives) via Nonaqueous Suzuki-Miyaura Cross-Coupling Reactions

A one-step synthesis of Fmoc-protected aryl/heteroaryl-substituted phenylalanines (Bip derivatives) using the nonaqueous palladium-catalyzed Suzuki–Miyaura cross-coupling (SMC) reaction of Fmoc-protected bromo- or iodophenylalanines is reported. This protocol allows for the direct formation of a variety of unnatural biaryl-containing amino acids in good to excellent yield, which can be readily used in subsequent Fmoc solid-phase peptide synthesis. The synthetic utility of this method is also demonstrated by the SMC reaction of bromophenylalanine-containing tripeptides

Ligand-Enabled β‑C(sp³)–H Olefination of Free Carboxylic Acids

An acetyl-protected aminoethyl phenyl thioether has been developed to promote C­(sp³)–H activation. Significant ligand enhancement is demonstrated by the realization of the first Pd­(II)-catalyzed olefination of C­(sp³)–H bonds of free carboxylic acids without using an auxiliary. Subsequent lactonization of the olefinated product via 1,4 addition provided exclusively monoselectivity in the presence of multiple β-C–H bonds. The product γ-lactone can be readily opened to give either the highly valuable β-olefinated or γ-hydroxylated aliphatic acids. Considering the challenges in developing Heck couplings using alkyl halides, this reaction offers a useful alternative

Ligand-Enabled β‑C–H Arylation of α‑Amino Acids Using a Simple and Practical Auxiliary

Pd-catalyzed β-C–H functionalizations of carboxylic acid derivatives using an auxiliary as a directing group have been extensively explored in the past decade. In comparison to the most widely used auxiliaries in asymmetric synthesis, the simplicity and practicality of the auxiliaries developed for C–H activation remains to be improved. We previously developed a simple <i>N</i>-methoxyamide auxiliary to direct β-C–H activation, albeit this system was not compatible with carboxylic acids containing α-hydrogen atoms. Herein we report the development of a pyridine-type ligand that overcomes this limitation of the <i>N</i>-methoxyamide auxiliary, leading to a significant improvement of β-arylation of carboxylic acid derivatives, especially α-amino acids. The arylation using this practical auxiliary is applied to the gram-scale syntheses of unnatural amino acids, bioactive molecules, and chiral bis­(oxazoline) ligands

Combination indices of EI-1 with HCV replication inhibitors.

a<p>NS5A, BMS-790052; NS3, BMS-605339.</p>b<p>Mean of 8 independent experiments.</p>c<p>Loewe combination index at the combined EC₅₀ level.</p

E1 and E2 amino acid changes that emerged during selection with EI-1.

a<p>Fold increase in EC₅₀ compared to wild-type virus. Values represent the mean of ≥3 experiments.</p

Schematic diagram of the HCV E2 protein and sequences of the region encompassing the EI-1 resistance residue.

<p>Previously defined regions of the protein are indicated by the shaded boxes. Numbers correspond to the HCV polyprotein amino acid positions in E2. HVR1, hypervariable region 1. HVR2, hypervariable region 2. pFP₁ and pFP₂, putative fusion peptide regions. igVR, intergenotypic variability region. HR, heptad repeat. TMD, transmembrane domain. The asterisk indicates the position of residue 719 that is involved in EI-1 resistance. The protein sequence alignment from amino acids 709–729 for each of the HCVpp genotype isolates from <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1001086#ppat-1001086-g002" target="_blank">Figure 2</a> is shown. The shaded residues are part of the TMD.</p

EI-1 resistance levels of site-directed changes engineered into HCVcc or HCVpp.

a<p>Fold increase in EC₅₀ compared to wild-type virus. Values represent the mean of ≥3 experiments.</p

Activity of EI-1 in infectious virus assays.

a<p>Mean of ≥4 independent experiments.</p

Effect of EI-1 on HCV cell-to-cell spread.

<p>(A) Huh-7.5 cells were infected with 0.001 ffu/cell HCVcc-1a/2a at 37°C. At 12 hrs post infection, the inoculum was removed and replaced with medium +1% agarose overlay containing EI-1 (0.5 µM) or DMSO and the cultures were incubated at 37°C for 2, 3 or 4 days. Infected cells were labeled by indirect immunofluorescence using an anti-HCV core monoclonal antibody (green) and nuclei were stained with Hoechst 3325 (red). Images were captured using a Nikon Eclipse TE300 inverted epi-fluorescence microscope. (B) The mean number and standard deviation of infected cells/focus was determined from visual counting of infected cells in ≥100 foci for each time point. (C) The mean number and standard deviation of foci/well was determined at 2 and 4 days post infection.</p

Structure-activity-relationship of the EI-1 chemotype.

a<p>Mean of ≥3 independent experiments.</p>b<p>R, aniline ring substituent (<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1001086#ppat-1001086-g001" target="_blank">Fig 1A</a>).</p