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Oxanorbornadienes (ONDs) undergo facile Michael addition with thiols and then fragment by a retro-Diels-Alder (rDA) reaction, a unique two-step sequence among electrophilic cleavable linkages. The rDA reaction rate was explored as a function of the furan structure, with substituents at the 2- and 5-positions found to be the most influential and the fragmentation rate to be inversely correlated with electron-withdrawing ability. Density functional theory calculations provided an excellent correlation with the experimentally measured OND rDA rates.

Virus‐like particles (VLPs) derived from Leviviridae virions contain substantial amounts of cellular and plasmid‐derived RNA. This encapsidated polynucleotide serves as a reservoir for the efficient binding of the intercalating dye thiazole orange (TO). Polyethylene glycol (PEG) molecules and oligopeptides of varying length, end‐functionalized with TO, were loaded into VLPs up to approximately 50 % of the mass of the capsid protein (hundreds to thousands of cargo molecules per particle, depending on size). The kinetics of TO–PEG binding included a significant entropic cost for the reptation of long chains through the capsid pores. Cargo molecules were released over periods of 20–120 hours following simple reversible first‐order kinetics in most cases. These observations define a simple general method for the noncovalent packaging, and subsequent release, of functional molecules inside nucleoprotein nanocages in a manner independent of modifications to the capsid protein. [ABSTRACT FROM AUTHOR]

TheG-protein coupled receptor (C3aR) for human inflammatory proteincomplement C3a is an important component of immune, inflammatory,and metabolic diseases. A flexible compound (N2-[(2,2-diphenylethoxy)acetyl]-l-arginine, 4), known as a weak C3aR antagonist(IC50μM), was transformed here into potent agonists(EC50nM) of human macrophages (Ca2+releasein HMDM) by incorporating aromatic heterocycles. Antagonists werealso identified. A linear correlation between binding affinity forC3aR and calculated hydrogen-bond interaction energy of the heteroatomindicated that its hydrogen-bonding capacity influenced ligand affinityand function mediated by C3aR. Hydrogen-bond accepting heterocycles(e.g., imidazole) conferred the highest affinity and agonist potency(e.g., 21, EC5024 nM, Ca2+, HMDM)with comparable efficacy and immunostimulatory activity as that ofC3a in activating human macrophages (Ca2+, IL1β,TNFα, CCL3). These potent and selective modulators of C3aR,inactivated by a C3aR antagonist, are stable C3a surrogates for interrogatingroles for C3aR in physiology and disease. [ABSTRACT FROM AUTHOR]

We report the total chemical synthesis of human C3a by one-pot native chemical ligation of three unprotected peptide segments, followed by efficient in vitro folding that yielded the anaphylatoxin C3a in high yield and excellent purity. Synthetic C3a was fully active and its crystal structure at 2.1 Å resolution showed 3 helices and a C-terminal turn motif. [ABSTRACT FROM AUTHOR]

Protease-activated receptor 2 (PAR2) is a cell surface protein linked to G-protein dependent and independent intracellular signaling pathways that produce a wide range of physiological responses, including those related to metabolism, inflammation, pain, and cancer. Certain proteases, peptides, and nonpeptides are known to potently activate PAR2. However, no effective potent PAR2 antagonists have been reported yet despite their anticipated therapeutic potential. This study investigates antagonism of key PAR2-dependent signaling properties and functions by the imidazopyridazine compound I-191 (4-(8-( tert -butyl)-6-(4-fluorophenyl)imidazo[1,2- b ]pyridazine-2-carbonyl)-3,3-dimethylpiperazin-2-one) in cancer cells. At nanomolar concentrations, I-191 inhibited PAR2 binding of and activation by structurally distinct PAR2 agonists (trypsin, peptide, nonpeptide) in a concentration-dependent manner in cells of the human colon adenocarcinoma grade II cell line (HT29). I-191 potently attenuated multiple PAR2-mediated intracellular signaling pathways leading to Ca 2+ release, extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, Ras homologue gene family, member A (RhoA) activation, and inhibition of forskolin-induced cAMP accumulation. The mechanism of action of I-191 was investigated using binding and calcium mobilization studies in HT29 cells where I-191 was shown to be noncompetitive and a negative allosteric modulator of the agonist 2f-LIGRL-NH 2 The compound alone did not activate these PAR2-mediated pathways, even at high micromolar concentrations, indicating no bias in these signaling properties. I-191 also potently inhibited PAR2-mediated downstream functional responses, including expression and secretion of inflammatory cytokines and cell apoptosis and migration, in human colon adenocarcinoma grade II cell line (HT29) and human breast adenocarcinoma cells (MDA-MB-231). These findings indicate that I-191 is a potent PAR2 antagonist that inhibits multiple PAR2-induced signaling pathways and functional responses. I-191 may be a valuable tool for characterizing PAR2 functions in cancer and in other cellular, physiological, and disease settings., (Copyright © 2018 by The American Society for Pharmacology and Experimental Therapeutics.)