Bidirectional Modification of a Alkaloid Identifies Selective Opioid Ligands.

We report a bidirectional diversification and optimization campaign of the newly identified - and -opioid receptor antagonist GB18, a naturally occurring alkaloid. First, we find that replacement of the GB18 piperidine with pyridine alters the pharmacology from antagonism to partial agonism, with reduced potency but markedly higher receptor selectivity for over . Second, we optimize this hit via development of a mutually chemoselective cross-coupling of an alkyl iodide/vinyl triflate pair that leads to a series of low- and sub-nanomolar KOR-selective full agonists, some of which demonstrate bias for G protein activation over β-arrestin2 recruitment.

Palladium Bisphosphine Monoxide Complexes: Synthesis, Scope, Mechanism, and Catalytic Relevance.

Recent studies in transition metal catalysis employing chelating phosphines have suggested a role for partial ligand oxidation in formation of the catalytically active species, with potentially widespread relevance in a number of catalytic systems. We examine the internal redox reaction of Pd(bisphosphine)X (X = Cl, OAc, ) complexes to reveal previously underexplored aspects of bisphosphine monoxides (BPMOs), including evaluation of ligand structure and development of general reaction conditions to access a collection of structurally diverse BPMO precatalysts based on organopalladium oxidative addition complexes. In particular, a series of Pd(BPMO)(R)(X) (R = aryl, alkyl; X = I, Br) oxidative addition complexes bearing 24 different BPMO ligands were characterized by NMR and X-ray crystallography.

Discovery of N-X anomeric amides as electrophilic halogenation reagents.

Electrophilic halogenation is a widely used tool employed by medicinal chemists to either pre-functionalize molecules for further diversity or incorporate a halogen atom into drugs or drug-like compounds to solve metabolic problems or modulate off-target effects. Current methods to increase the power of halogenation rely on either the invention of new reagents or activating commercially available reagents with various additives such as Lewis or Brønsted acids, Lewis bases and hydrogen-bonding activators. There is a high demand for new reagents that can halogenate otherwise unreactive compounds under mild conditions.

Programmable synthesis of well-defined, glycosylated iron(ii) supramolecular assemblies with multivalent protein-binding capabilities.

Multivalency plays a key role in achieving strong, yet reversible interactions in nature, and provides critical chemical organization in biological recognition processes. Chemists have taken an interest in designing multivalent synthetic assemblies to both better understand the underlying principles governing these interactions, and to build chemical tools that either enhance or prevent such recognition events from occurring in biology. Rationally tailoring synthetic strategies to achieve the high level of chemical control and tunability required to mimic these interactions, however, is challenging.

Metal-hydrogen-pi-bonded organic frameworks.

We report the synthesis and characterization of a new series of permanently porous, three-dimensional metal-organic frameworks (MOFs), M-HAF-2 (M = Fe, Ga, or In), constructed from tetratopic, hydroxamate-based, chelating linkers. The structure of M-HAF-2 was determined by three-dimensional electron diffraction (3D ED), revealing a unique interpenetrated -a net topology. This unusual topology is enabled by the presence of free hydroxamic acid groups, which lead to the formation of a diverse network of cooperative interactions comprising metal-hydroxamate coordination interactions at single metal nodes, staggered π-π interactions between linkers, and H-bonding interactions between metal-coordinated and free hydroxamate groups.

Inside polyMOFs: layered structures in polymer-based metal-organic frameworks.

In this report, we explore the internal structural features of polyMOFs consisting of equal mass ratios of metal-coordinating poly(benzenedicarboxylic acid) blocks and non-coordinating poly(ethylene glycol) (PEG) blocks. The studies reveal alternating lamellae of metal-rich, crystalline regions and metal-deficient non-crystalline polymer, which span the length of hundreds of nanometers. Polymers consisting of random PEG blocks, PEG end-blocks, or non-coordinating poly(cyclooctadiene) (COD) show similar alternation of metal-rich and metal-deficient regions, indicating a universal self-assembly mechanism.

Design of metal-mediated protein assemblies via hydroxamic acid functionalities.

The self-assembly of proteins into sophisticated multicomponent assemblies is a hallmark of all living systems and has spawned extensive efforts in the construction of novel synthetic protein architectures with emergent functional properties. Protein assemblies in nature are formed via selective association of multiple protein surfaces through intricate noncovalent protein-protein interactions, a challenging task to accurately replicate in the de novo design of multiprotein systems. In this protocol, we describe the application of metal-coordinating hydroxamate (HA) motifs to direct the metal-mediated assembly of polyhedral protein architectures and 3D crystalline protein-metal-organic frameworks (protein-MOFs).

Anisotropic Dynamics and Mechanics of Macromolecular Crystals Containing Lattice-Patterned Polymer Networks.

The mechanical and functional properties of many crystalline materials depend on cooperative changes in lattice arrangements in response to external perturbations. However, the flexibility and adaptiveness of crystalline materials are limited. Additionally, the bottom-up, molecular-level design of crystals with desired dynamic and mechanical properties at the macroscopic level remains a considerable challenge.

Tunable and Cooperative Thermomechanical Properties of Protein-Metal-Organic Frameworks.

We recently introduced protein-metal-organic frameworks (protein-MOFs) as chemically designed protein crystals, composed of ferritin nodes that predictably assemble into 3D lattices upon coordination of various metal ions and ditopic, hydroxamate-based linkers. Owing to their unique tripartite construction, protein-MOFs possess extremely sparse lattice connectivity, suggesting that they might display unusual thermomechanical properties. Leveraging the synthetic modularity of ferritin-MOFs, we investigated the temperature-dependent structural dynamics of six distinct frameworks.

An Exceptionally Stable Metal-Organic Framework Constructed from Chelate-Based Metal-Organic Polyhedra.

We report the rational design and synthesis of a water-stable metal-organic framework (MOF), Fe-HAF-1, constructed from supramolecular, Fe-hydroxamate-based polyhedra with mononuclear metal nodes. Owing to its chelate-based construction, Fe-HAF-1 displays exceptional chemical stability in organic and aqueous solvents over a wide pH range (pH 1-14), including in the presence of 5 M NaOH. Despite the charge neutrality of the Fe-tris(hydroxamate) centers, Fe-HAF-1 crystals are negatively charged above pH 4.

Constructing protein polyhedra via orthogonal chemical interactions.

Many proteins exist naturally as symmetrical homooligomers or homopolymers. The emergent structural and functional properties of such protein assemblies have inspired extensive efforts in biomolecular design. As synthesized by ribosomes, proteins are inherently asymmetric.

Self-Assembly of a Designed Nucleoprotein Architecture through Multimodal Interactions.

The co-self-assembly of proteins and nucleic acids (NAs) produces complex biomolecular machines (e.g., ribosomes and telomerases) that represent some of the most daunting targets for biomolecular design.

Author Correction: Hyperexpandable, self-healing macromolecular crystals with integrated polymer networks.

Change history: In this Letter, Alexander Groisman should have been listed as an author. This error has been corrected online.

Hyperexpandable, self-healing macromolecular crystals with integrated polymer networks.

The formation of condensed matter typically involves a trade-off between structural order and flexibility. As the extent and directionality of interactions between atomic or molecular components increase, materials generally become more ordered but less compliant, and vice versa. Nevertheless, high levels of structural order and flexibility are not necessarily mutually exclusive; there are many biological (such as microtubules, flagella , viruses) and synthetic assemblies (for example, dynamic molecular crystals and frameworks) that can undergo considerable structural transformations without losing their crystalline order and that have remarkable mechanical properties that are useful in diverse applications, such as selective sorption , separation , sensing and mechanoactuation .

First biochemical and crystallographic characterization of a fast-performing ferritin from a marine invertebrate.

Ferritin, a multimeric cage-like enzyme, is integral to iron metabolism across all phyla through the sequestration and storage of iron through efficient ferroxidase activity. While ferritin sequences from ∼900 species have been identified, crystal structures from only 50 species have been reported, the majority from bacterial origin. We recently isolated a secreted ferritin from the marine invertebrate sp.

A Metal Organic Framework with Spherical Protein Nodes: Rational Chemical Design of 3D Protein Crystals.

We describe here the construction of a three-dimensional, porous, crystalline framework formed by spherical protein nodes that assemble into a prescribed lattice arrangement through metal-organic linker-directed interactions. The octahedral iron storage enzyme, ferritin, was engineered in its C3 symmetric pores with tripodal Zn coordination sites. Dynamic light scattering and crystallographic studies established that this Zn-ferritin construct could robustly self-assemble into the desired bcc-type crystals upon coordination of a ditopic linker bearing hydroxamic acid functional groups.

Halogen interactions in protein-ligand complexes: implications of halogen bonding for rational drug design.

Halogen bonding interactions between halogenated ligands and proteins were examined using the crystal structures deposited to date in the PDB. The data was analyzed as a function of halogen bonding to main chain Lewis bases, viz. oxygen of backbone carbonyl and backbone amide nitrogen.

Novel biotinylated lipid prodrugs of acyclovir for the treatment of herpetic keratitis (HK): transporter recognition, tissue stability and antiviral activity.

Purpose: Biotinylated lipid prodrugs of acyclovir (ACV) were designed to target the sodium dependent multivitamin transporter (SMVT) on the cornea to facilitate enhanced cellular absorption of ACV.

Methods: All the prodrugs were screened for in vitro cellular uptake, interaction with SMVT, docking analysis, cytotoxicity, enzymatic stability and antiviral activity.

Results: Uptake of biotinylated lipid prodrugs of ACV (B-R-ACV and B-12HS-ACV) was significantly higher than biotinylated prodrug (B-ACV), lipid prodrugs (R-ACV and 12HS-ACV) and ACV in corneal cells.

Identification of Novel Nitrosative Stress Inhibitors through Virtual Screening and Experimental Evaluation.

Nitrosative and oxidative stress, associated with the generation of excessive reactive nitrogen and oxygen radical species respectively, are thought to contribute to protein misfolding diseases which represent a group of neurodegenerative disorders that are characterized by protein aggregation and plaque formation. Curcumin, a polyphenolic compound, possesses diverse anti-inflammatory, antitumor, and antioxidant properties. Several studies have revealed that curcumin can reduce the oxidative/nitrosative stress and thereby decrease the neuronal attrition.