Diastereoselective synthesis of cyclopropane amino acids using diazo compounds generated in situ

A simple and high-yielding method for the preparation of cyclopropane amino acids is described. The novel method involves the one-pot cyclopropanation of readily available dehydroamino acids using aryl and unsaturated diazo compounds generated in situ from the corresponding tosylhydrazone salts. It was found that thermal 1,3-dipolar cycloaddition followed by nitrogen extrusion gave the cyclopropane amino acid derivatives with good E selectivity, while reactions in the presence of meso-tetraphenylporphyrin iron chloride gave predominantly the corresponding Z isomers. The synthetic utility of this process was demonstrated in the synthesis of (+/-)-(Z)-2,3-methanophenylalanine [(+/-)-(Z)-1], the anti-Parkinson (+/-)-(E)-2,3-methano-m-tyrosine [(+/-)-(E)-2], and the natural product (+/-)-coronamic acid [(+/-)-3].     

Iron-Catalyzed Halogen Exchange of Trifluoromethyl Arenes**

The facile production of ArCF₂X and ArCX₃ from ArCF₃ using catalytic iron(III)halides is reported, which constitutes the first iron-catalyzed halogen exchange for non-aromatic C−F bonds. Theoretical calculations suggest direct activation of C−F bonds by iron coordination. ArCX₃ and ArCF₂X products of the reaction are synthetically valuable due to their diversification potential. In particular, chloro- and bromodifluoromethyl arenes (ArCF₂Cl, ArCF₂Br respectively) provide access to a myriad of difluoromethyl arene derivatives (ArCF₂R). To optimize for mono-halogen exchange, a statistical method called Design of Experiments was used. Optimized parameters were successfully applied to electron rich and electron deficient aromatic substrates, and to the late stage diversification of flufenoxuron, a commercial insecticide. These methods are highly practical, being run at convenient temperatures and using inexpensive common reagents.     

Reduced field-of-view diffusion-weighted imaging of the brain at 7 T

Ventral and rostral regions of the brain are of emerging importance for the MRI characterization of early dementia, traumatic brain injury and epilepsy. Unfortunately, standard single-shot echo planar diffusion-weighted imaging of these regions at high fields is contaminated by severe imaging artifacts in the vicinity of air–tissue interfaces. To mitigate these artifacts and improve visualization of the temporal and frontal lobes at 7 T, we applied a reduced field-of-view strategy, enabled by outer volume suppression (OVS) with novel quadratic phase radiofrequency (RF) pulses, combined with partial Fourier and parallel imaging methods. The new acquisition greatly reduced the level of artifacts in six human subjects (including four patients with early symptoms of dementia).     

A simple route to derivatives of benzo[j]fluoranthene

3,6,8,11-Tetramethoxybenzo[j]fluoranthene can be made from 1,6-dimethoxynaphthalene in a one-pot ferric chloride oxidation/methanol reduction procedure. The reaction is tolerant of the presence of substituents in the 7-position of the naphthalene nucleus and provides a quick and easy route to these particular benzo[j]fluoranthenes. The reactions presumably proceed through initial formation of a bond between the 4-positions of two naphthalene molecules followed by closure of the five-membered ring. Indeed in one case some 4,4′-binaphthyl was isolated from the reaction mixture and it was generally found that better yields of the benzo[j]fluoranthrenes were obtained starting from the 4,4′-binaphthyl rather than by using the naphthalene as the starting material. In an analogous manner to the ring-closure of the 4,4′-binaphthyls, starting from a hexakisalkoxyphenylnaphthalene, a hexakisalkoxyfluoranthene could be obtained.     

Constraining Cyclic Peptides To Mimic Protein Structure Motifs

Many proteins exert their biological activities through small exposed surface regions called epitopes that are folded peptides of well‐defined three‐dimensional structures. Short synthetic peptide sequences corresponding to these bioactive protein surfaces do not form thermodynamically stable protein‐like structures in water. However, short peptides can be induced to fold into protein‐like bioactive conformations (strands, helices, turns) by cyclization, in conjunction with the use of other molecular constraints, that helps to fine‐tune three‐dimensional structure. Such constrained cyclic peptides can have protein‐like biological activities and potencies, enabling their uses as biological probes and leads to therapeutics, diagnostics and vaccines. This Review highlights examples of cyclic peptides that mimic three‐dimensional structures of strand, turn or helical segments of peptides and proteins, and identifies some additional restraints incorporated into natural product cyclic peptides and synthetic macrocyclic peptidomimetics that refine peptide structure and confer biological properties.     

Glycoconjugated Metallohelices have Improved Nuclear Delivery and Suppress Tumour Growth In Vivo

Monosaccharides are added to the hydrophilic face of a self‐assembled asymmetric Fe^II metallohelix, using CuAAC chemistry. The sixteen resulting architectures are water‐stable and optically pure, and exhibit improved antiproliferative selectivity against colon cancer cells (HCT116 p53^+/+) with respect to the non‐cancerous ARPE‐19 cell line. While the most selective compound is a glucose‐appended enantiomer, its cellular entry is not mainly glucose transporter‐mediated. Glucose conjugation nevertheless increases nuclear delivery ca 2.5‐fold, and a non‐destructive interaction with DNA is indicated. Addition of the glucose units affects the binding orientation of the metallohelix to naked DNA, but does not substantially alter the overall affinity. In a mouse model, the glucose conjugated compound was far better tolerated, and tumour growth delays for the parent compound (2.6 d) were improved to 4.3 d; performance as good as cisplatin but with the advantage of no weight loss in the subjects.