Stereoselective Synthesis of Multisubstituted α-fluoro-β-lactams

β-Lactams, found in β -lactam antibiotics, are the structurally distorted cyclic compounds being subjected to nucleophilic acyl substitution reaction. α-Fluorination of β -lactams is a simple and expedient approach to control the reactivity of β-lactam ring toward nucleophilic attack, which would hopefully lead to the new design of future antibiotics. From the viewpoint of obtaining multisubstituted α -fluoro-β-lactams, α -bromo-α- fluoro-β-lactams are considered as key compounds for structure functionalization, including nucleophilic substitution reaction, aldol-type reaction and metal-catalyzed crosscoupling reaction. All the reactions can be conducted smoothly to afford a variety of multisubstituted α-fluoro-β-lactams. During the course of the examination, chiral α,α-difluoro- β-lactams and α -bromo-β-fluoro-α-lactams are successfully obtained, which are considered potent precursors for making stereocontrolled multisubstituted α-fluoro-β-lactams.

Expressed Protein Ligation Without Intein

Proteins with a functionalized <i>C</i>-terminus such as a <i>C</i>-terminal thioester are key to the synthesis of larger proteins via expressed protein ligation. They are usually made by recombinant fusion to intein. Although powerful, the intein fusion approach suffers from premature hydrolysis and low compatibility with denatured conditions. To totally bypass the involvement of an enzyme for expressed protein ligation, here we showed that a cysteine in a recombinant protein was chemically activated by a small molecule cyanylating reagent at its <i>N</i>-side amide for undergoing nucleophilic acyl substitution with amines including a number of L- and D-amino acids and hydrazine. The afforded protein hydrazides could be used further for expressed protein ligation. We demonstrated the versatility of this approach with the successful synthesis of ubiquitin conjugates, ubiquitin-like protein conjugates, histone H2A with a posttranslational modification, RNAse H that actively hydrolyzed RNA, and exenatide that is a commercial therapeutic peptide. The technique, which is exceedingly simple but highly useful, expands to a great extent the synthetic capacity of protein chemistry and will therefore make a large avenue of new research possible.

Expressed Protein Ligation Without Intein

Proteins with a functionalized <i>C</i>-terminus such as a <i>C</i>-terminal thioester are key to the synthesis of larger proteins via expressed protein ligation. They are usually made by recombinant fusion to intein. Although powerful, the intein fusion approach suffers from premature hydrolysis and low compatibility with denatured conditions. To totally bypass the involvement of an enzyme for expressed protein ligation, here we showed that a cysteine in a recombinant protein was chemically activated by a small molecule cyanylating reagent at its <i>N</i>-side amide for undergoing nucleophilic acyl substitution with amines including a number of L- and D-amino acids and hydrazine. The afforded protein hydrazides could be used further for expressed protein ligation. We demonstrated the versatility of this approach with the successful synthesis of ubiquitin conjugates, ubiquitin-like protein conjugates, histone H2A with a posttranslational modification, RNAse H that actively hydrolyzed RNA, and exenatide that is a commercial therapeutic peptide. The technique, which is exceedingly simple but highly useful, expands to a great extent the synthetic capacity of protein chemistry and will therefore make a large avenue of new research possible.

Photochemical generation of acyl and carbamoyl radicals using a nucleophilic organic catalyst: applications and mechanism thereof

An organic catalyst uses low-energy photons to generate acyl and carbamoyl radicals upon activation of the corresponding chlorides via a nucleophilic acyl substitution path. The synthetic potential and the mechanism of this strategy are discussed.

Crystal structures of two bis-carbamoylmethylphosphine oxide (CMPO) compounds

Two bis-carbamoylmethylphosphine oxide compounds, namely {[(3-{[2-(diphenylphosphinoyl)ethanamido]methyl}benzyl)carbamoyl]methyl}diphenylphosphine oxide, C36H34N2O4P2, (I), and diethyl [({2-[2-(diethoxyphosphinoyl)ethanamido]ethyl}carbamoyl)methyl]phosphonate, C14H30N2O8P2, (II), were synthesized via nucleophilic acyl substitution reactions between an ester and a primary amine. Hydrogen-bonding interactions are present in both crystals, but these interactions are intramolecular in the case of compound (I) and intermolecular in compound (II). Intramolecular π–π stacking interactions are also present in the crystal of compound (I) with a centroid–centroid distance of 3.9479 (12) Å and a dihedral angle of 9.56 (12)°. Intermolecular C—H...π interactions [C...centroid distance of 3.622 (2) Å, C—H...centroid angle of 146°] give rise to supramolecular sheets that lie in the ab plane. Key geometric features for compound (I) involve a nearly planar, trans-amide group with a C—N—C—C torsion angle of 169.12 (17)°, and a torsion angle of −108.39 (15)° between the phosphine oxide phosphorus atom and the amide nitrogen atom. For compound (II), the electron density corresponding to the phosphoryl group was disordered, and was modeled as two parts with a 0.7387 (19):0.2613 (19) occupancy ratio. Compound (II) also boasts a trans-amide group that approaches planarity with a C—N—C—C torsion angle of −176.50 (16)°. The hydrogen bonds in this structure are intermolecular, with a D...A distance of 2.883 (2) Å and a D—H...A angle of 175.0 (18)° between the amide hydrogen atom and the P=O oxygen atom. These non-covalent interactions create ribbons that run along the b-axis direction.

Directed ortho-metalation–nucleophilic acyl substitution strategies in deep eutectic solvents: the organolithium base dictates the chemoselectivity

Organolithium-mediated chemoselectivity in deep eutectic solvents: basicity vs. nucleophilicity.

Exploring the catalytic activity of Lewis-acidic uranyl complexes in the nucleophilic acyl substitution of acid anhydrides

Uranyl(vi) ion is a strongly hard Lewis-acid and plays a catalytic role in the nucleophilic acyl substitution of acid anhydrides.