No abstract

A discovery program targeting respiratory syncytial virus (RSV) identified C-nucleoside 4 (RSV A2 EC50 = 530 nM) as a phenotypic screening lead targeting the RSV RNA-dependent RNA polymerase (RdRp). Prodrug exploration resulted in the discovery of remdesivir (1, GS-5734) that is >30-fold more potent than 4 against RSV in HEp-2 and NHBE cells. Metabolism studies in vitro confirmed the rapid formation of the active triphosphate metabolite, 1-NTP, and in vivo studies in cynomolgus and African Green monkeys demonstrated a >10-fold higher lung tissue concentration of 1-NTP following molar normalized IV dosing of 1 compared to that of 4. A once daily 10 mg/kg IV administration of 1 in an African Green monkey RSV model demonstrated a >2-log10 reduction in the peak lung viral load. These early data following the discovery of 1 supported its potential as a novel treatment for RSV prior to its development for Ebola and approval for COVID-19 treatment.

Perhaps the most well-recognized stereogenic elements within chiral molecules are sp3-hybridized carbon atoms possessing four different substituents. However, axes of chirality may also exist about bonds with hindered barriers of rotation, leading to stereoisomers known as atropisomers.1 Understanding the dynamics of these systems can be useful, for example, in the design of single-atropisomer drugs2 or molecular switches and motors.3 For molecules that exhibit a single axis of chirality, rotation about that axis leads to racemization as the system reaches equilibrium. We report here a two-axis system in which an enantioselective reaction that produces four stereoisomers (two enantiomeric pairs) displays a more complex scenario. Following a catalytic asymmetric transformation, we observe a kinetically controlled product distribution that is substantially perturbed from the system’s equilibrium position. Notably, as the system undergoes isomerization, one of the diastereomeric pairs is observed to drift spontaneously to a higher enantiomeric ratio. In a compensatory manner, the other diastereomeric pair also converts to an altered enantiomeric ratio, reduced in magnitude from the initial ratio. These observations occur within a class of unsymmetrical amides that exhibits two asymmetric axes – one defined through a benzamide substructure, and the other implicit with differentially N,N-disubstituted amides. The stereodynamics of these substrates provide an opportunity to observe a curious interplay of kinetics and thermodynamics intrinsic to a system of stereoisomers that is constrained to a situation of partial equilibration.

A century after discovering that the Trypanosoma cruzi parasite is the etiological agent of Chagas disease, treatment is still plagued by limited efficacy, toxicity, and the emergence of drug resistance. The development of inhibitors of the major T. cruzi cysteine protease, cruzain, has been demonstrated to be a promising drug discovery avenue for this neglected disease. Here we establish that a nonpeptidic tetrafluorophenoxymethyl ketone cruzain inhibitor substantially ameliorates symptoms of acute Chagas disease in a mouse model with no apparent toxicity. A high-resolution crystal structure confirmed the mode of inhibition and revealed key binding interactions of this novel inhibitor class. Subsequent structure-guided optimization then resulted in inhibitor analogs with improvements in potency despite minimal or no additions in molecular weight. Evaluation of the analogs in cell culture showed enhanced activity. These results suggest that nonpeptidic tetrafluorophenoxymethyl ketone cruzain inhibitors have the potential to fulfill the urgent need for improved Chagas disease chemotherapy.

We report the enantioselective synthesis of atropisomeric benzamides employing catalytic electrophilic aromatic substitution reactions involving bromination. The catalyst is a simple tetrapeptide bearing a tertiary amine that may function as a Brønsted base. A series of tri- and dibrominations are accomplished for a range of compounds bearing differential substitution patterns. Tertiary benzamides represent appropriate substrates for the reaction since they exhibit sufficiently high barriers to racemization after ortho-functionalization. Mechanism-driven experiments provide some insight into the basis for selectivity. Examination of the observed products at low conversion suggests that the initial catalytic bromination may be regioselective and stereochemistry-determining. A complex between catalyst and substrate is observed by NMR, revealing a specific association. Finally, products of these reactions may be subjected to regioselective metal-halogen exchange and trapping with I2, setting the stage for utility.