Fused-ring and bridged-ring tetrahydrofuran scaffolds are found in a number of natural products and biologically active compounds. A new copper-catalyzed intramolecular carboetherification of alkenes for the synthesis of bicyclic tetrahydrofurans is reported herein. The reaction involves Cu-catalyzed intramolecular addition of alcohols to unactivated alkenes and subsequent aryl C-H functionalization provides the C-C bond. Mechanistic studies indicate a primary carbon radical intermediate is involved and radical addition to the aryl ring is the likely C-C bond-forming mechanism. Preliminary catalytic enantioselective reactions are promising (up to 75% ee) and provide evidence that copper is involved in the alkene addition step, likely through a cis-oxycupration mechanism. Catalytic enantioselective alkene carboetherification reactions are rare and future development of this new method into a highly enantioselective process is promising. During the course of the mechanistic studies a protocol for alkene hydroetherification was also developed.

Antibiotic resistance of bacterial pathogens poses an increasing threat to the wellbeing of our society and urgently calls for new strategies for infection diagnosis and antibiotic discovery. The antibiotic resistance problem at least partially arises from extensive use of broad-spectrum antibiotics. Ideally, for the treatment of infection, one would like to use a narrow-spectrum antibiotic that specifically targets and kills the disease-causing strain. This is particularly important considering the commensal bacterial species that are beneficial and sometimes even critical to the health of a human being. In this contribution, we describe a phage display platform that enables rapid identification of peptide probes for specific bacterial strains. The phage library described herein incorporates 2-acetylphenylboronic acid moieties to elicit dynamic covalent binding to the bacterial cell surface. Screening of the library against live bacterial cells yields submicromolar and highly specific binders for clinical strains of Staphylococcus aureus and Acinetobacter baumannii that display antibiotic resistance. We further show that the identified peptide probes can be readily converted to bactericidal agents that deliver generic toxins to kill the targeted bacterial strain with high specificity. The phage display platform described here is applicable to a wide array of bacterial strains, paving the way to facile diagnosis and development of strain-specific antibiotics.

Fundamental questions regarding collagen biosynthesis, especially with respect to the molecular origins of homotrimeric versus heterotrimeric assembly, remain unanswered. Here, we demonstrate that the presence or absence of a single cysteine in type-I collagen’s C-propeptide domain is a key factor governing the ability of a given collagen polypeptide to stably homotrimerize. We also identify a critical role for Ca2+ in non-covalent collagen C-propeptide trimerization, thereby priming the protein for disulfide-mediated covalent immortalization. The resulting cysteine-based code for stable assembly provides a molecular model that can be used to predict, a priori, the identity of not just collagen homotrimers, but also naturally occurring 2:1 and 1:1:1 heterotrimers. Moreover, the code applies across all of the sequence-diverse fibrillar collagens. These results provide new insight into how evolution leverages disulfide networks to fine-tune protein assembly, and will inform the ongoing development of designer proteins that assemble into specific oligomeric forms.

Intracellular procollagen folding begins at the protein’s C-terminal propeptide (C-Pro) domain, which initiates triple-helix assembly and defines the composition and chain register of fibrillar collagen trimers. The C-Pro domain is later proteolytically cleaved and excreted from the body, while the mature triple helix is incorporated into the extracellular matrix. The procollagen C-Pro domain possesses a single N-glycosylation site that is widely conserved in all the fibrillar procollagens across humans and diverse other species. Given that the C-Pro domain is removed once procollagen folding is complete, the N-glycan might be presumed to be important for folding. Surprisingly, however, there is no difference in the folding and secretion of N-glycosylated versus non-N-glycosylated collagen type-I, leaving the function of the N-glycan unclear. We hypothesized that the collagen N-glycan might have a context-dependent function, specifically, that it could be required to promote procollagen folding only when proteostasis is challenged. We show that removal of the N-glycan from misfolding-prone C-Pro domain variants does indeed cause serious procollagen and ER proteostasis defects. The N-glycan promotes folding and secretion of destabilized C-Pro variants by providing access to the ER’s lectin-based chaperone machinery. Finally, we show that the C-Pro N-glycan is actually critical for the folding and secretion of even wild-type procollagen under ER stress conditions. Such stress is commonly incurred during development, wound healing, and other processes in which collagen production plays a key role. Collectively, these results establish an essential, context-dependent function for procollagen’s previously enigmatic N-glycan, wherein the carbohydrate moiety buffers procollagen folding against proteostatic challenge.

Bridged bicyclic rings containing nitrogen heterocycles are important motifs in bioactive small organic molecules. An enantioselective copper-catalyzed alkene carboamination reaction that creates bridged heterocycles is reported herein. Two new rings are formed in this alkene carboamination reaction where N-sulfonyl-2-aryl-4-pentenamines are converted to 6-azabicyclo[3.2.1]octanes using [Ph-Box-Cu](OTf)2 or related catalysts in the presence of MnO2 as stoichiometric oxidant in moderate to good yields and generally excellent enantioselectivities. Two new stereocenters are formed in the reaction, and the C-C bond-forming arene addition is a net C-H functionalization.