Publications

Materials capable of degradation upon exposure to light hold promise in a diverse range of applications including biomedical devices and smart coatings. Despite the rapid access to macromolecules with diverse compositions and architectures enabled by ring-opening metathesis polymerization (ROMP), a general strategy to introduce facile photodegradability into these polymers is lacking. Here, we report copolymers synthesized via ROMP that can be degraded by cleaving the backbone in both solution and solid states under irradiation with a 52 W, 390 nm Kessil LED to generate heterotelechelic low-molecular-weight fragments. To the best of our knowledge, this work represents the first instance of the incorporation of acylsilanes into a polymer backbone. Mechanistic investigation of the degradation process supports the intermediacy of an α-siloxy carbene, formed via a 1,2-photo Brook rearrangement, which undergoes insertion into water followed by cleavage of the resulting hemiacetal.

The catalytic, undirected borylation of alkyl C–H bonds typically occurs at high reaction temperatures or with excess substrate, or both, because of the low reactivity of alkyl C–H bonds. Here we report a new iridium system comprising 2-anilino-1,10-phenanthroline as ligand that catalyzes the borylation of alkyl C–H bonds with little to no induction period and with high reaction rates. This superior activation and reactivity profile of 2-aminophenanthroline catalysts leads to broader scope of the reaction, including those with sensitive reactants, such as epoxides and glycosidic acetals, enhanced diastereoselectivity, and higher yields of borylated products. These catalysts also enable the borylation of alkanes, amines, and ethers at room temperature for the first time. Mechanistic studies imply that facile N-borylation occurs under the reaction conditions, and that iridium complexes containing N-boryl aminophenanthrolines are competent precatalysts for the reaction.

Short-chain acyl-coenzyme A esters serve as intermediate compounds in fatty acid biosynthesis, and the production of polyketides, biopolymers and other value-added chemicals. S. cerevisiae is a model organism that has been utilized for the biosynthesis of such biologically and economically valuable compounds. However, its limited repertoire of short-chain acyl-CoAs effectively prevents its application as a production host for a plethora of natural products. Therefore, we introduced biosynthetic metabolic pathways to five different acyl-CoA esters into S. cerevisiae. Our engineered strains provide the following acyl-CoAs: propionyl-CoA, methylmalonyl-CoA, n-butyryl-CoA, isovaleryl-CoA and n-hexanoyl-CoA. We established a yeast-specific metabolite extraction protocol to determine the intracellular acyl-CoA concentrations in the engineered strains. Propionyl-CoA was produced at 4-9 μM; methylmalonyl-CoA at 0.5 μM; and isovaleryl-CoA, n-butyryl-CoA, and n-hexanoyl-CoA at 6 μM each. The acyl-CoAs produced in this study are common building blocks of secondary metabolites and will enable the engineered production of a variety of natural products in S. cerevisiae. By providing this toolbox of acyl-CoA producing strains, we have laid the foundation to explore S. cerevisiae as a heterologous production host for novel secondary metabolites.

Significance A defining characteristic of living organisms is dynamic alignment of cellular responses to stress through activation of signal transduction pathways essential for fine-tuning of interorgannellar communication. Uncovering these communication signals is one of the prime challenges of biology. We have identified a chloroplast-produced retrograde signal, methylerythritol cyclodiphosphate (MEcPP), as a trigger of unfolded protein response (UPR) required for restoration of protein-folding homeostasis in the endoplasmic reticulum (ER). Increased levels of MEcPP via genetic manipulation or exogenous application potentiate expression of a sub-set of UPR genes, and alter plant’s resistance to the ER stress inducing agent. These findings provide a link between a plastidial retrograde signal and transcriptional reprogramming of ER genes critical for readjustment of protein-folding capacity in stressed cells.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.