Preparation of N-Aryl Amides by Epimerization-Free Umpolung Amide Synthesis

Backbone-Determined Antiarrhythmic Structure-Activity Relationships for a Mirror Image, Oligomeric Depsipeptide Natural Product

Cyclic oligomeric depsipeptides (COD) are a structural class within naturally occurring compounds with a wide range of biological activity. Verticilide is a COD (24-membered ring) that was identified by its inhibition of insect ryanodine receptor (RyR). We have since found that the enantiomer of verticilide (ent-verticilide, 1) is a potent inhibitor of mammalian RyR2, a cardiac calcium channel, and therefore a potential antiarrhythmic agent. Oddly, nat-verticilide does not inhibit RyR2. To further develop ent-verticilide as an antiarrhythmic, we explored potential SAR through systematic modification of the ester's functionality to both N-H and N-Me amides. The syntheses of these ent-verticilide-inspired analogs are detailed using a monomer-based platform enabled by enantioselective catalysis. Two analogs among 23 exhibited measurable reduction of calcium sparks in a functional assay of RyR2 activity. These findings illustrate the value of natural product-inspired therapeutic development, but the less-studied approach where the non-natural enantiomeric series harbors important SAR.

Synthesis of Amides via the Amination of Aldehydes with Hydroxylamines Promoted by TBAF·3H2O

A metal-free, mild, and efficient method for the synthesis of amides has been developed from the amination of aldehydes with hydroxylamines promoted by TBAF·3H2O in the presence of KOH. Control experiments showed that the nitrone was the intermediate of this amination. By this method, a series of amides, biologically active compounds bebenil and a COX inhibitor were obtained in moderate to good yields.

Palladium-Catalyzed Chelation-Assisted Aldehyde C-H Bond Activation of Quinoline-8-carbaldehydes: Synthesis of Amides from Aldehydes with Anilines and Other Amines

A palladium-catalyzed chelation-assisted direct aldehyde C-H bond amidation of quinoline-8-carbaldehydes with an amine was developed under mild reaction conditions. A wide range of amides were obtained in good to excellent yields from aldehyde with a variety of aniline derivatives and aliphatic amines. Our methodology was successfully applied to synthesize known DNA intercalating agents and can be easily scaled up to a gram scale.

Nitroalkanes as thioacyl equivalents to access thioamides and thiopeptides

Thioamides are an important, but a largely underexplored class of amide bioisostere in peptides. Replacement of oxoamide units with thioamides in peptide therapeutics is a valuable tactic to improve biological activity and resistance to enzymatic hydrolysis. This tactic, however, has been hampered by insufficient methods to introduce thioamide bonds into peptide or protein backbones in a site-specific and stereo-retentive fashion. In this work, we developed an efficient and mild thioacylation method to react nitroalkanes with amines directly in the presence of elemental sulfur and sodium sulfide to form a diverse range of thioamides in high yields. Notably, this convenient method can be employed for the controlled thioamide coupling of multifunctionalized peptides without epimerization of stereocenters, including the late stage thioacylation of advanced compounds of biological and medicinal interest. Experimental interrogation of postulated mechanisms currently supports the intermediacy of thioacyl species.

Water Complex of Imidogen

Imidogen (NH) is the simplest nitrogen hydride that plays an important role in combustion and interstellar chemistry, and its combination with H₂O is the prototypical amidation reaction of O-H bonds involving a nitrene intermediate. Herein, we report the observation of the elusive water complex of NH, a prereaction complex associated with the amidation reaction in a solid N₂ matrix at 10 K. The hydrogen-bonded structure of NH···OH₂ (versus HN···HOH) is confirmed via IR spectroscopy with comprehensive isotope labeling (D, ¹⁸O, and ¹⁵N) and quantum chemical calculations at the UCCSD(T)/aug-cc-pVQZ level of theory. In line with the observed absorption at 350 nm, irradiation of the complex at 365 nm leads to O-H bond insertion, yielding hydroxylamine NH₂OH.

Organobase-Catalyzed Umpolung of Amides: The Generation and Transfer of Carbamoyl Anion

A novel organobase-catalyzed umpolung reaction of amides was disclosed. This method provides an efficient method to generate and transfer carbamoyl anions. In this transformation, some of the inherent disadvantages of carbamoyl metal were avoided. The mechanistic analysis revealed that the reaction proceeds through polarity inversion of amide, and various carbamoyl anions were applied in the reaction. Moreover, a wide range of substrates was achieved with moderate to excellent yield.