Discovery of a potent dual inhibitor of wild-type and mutant respiratory syncytial virus fusion proteins through the modulation of atropisomer interconversion properties.

The development of effective respiratory syncytial virus (RSV) fusion glycoprotein (F protein) inhibitors against both wild-type and the D486N-mutant F protein is urgently required. We recently reported a 15-membered macrocyclic pyrazolo[1,5-a]pyrimidine derivative 4 that exhibited potent anti-RSV activities against not only wild-type, but also D486N-mutant F protein. However, NMR studies revealed that the 15-membered derivative 4 existed as a mixture of atropisomers. An optimization study of the linker moiety between the 2-position of the benzoyl moiety and the 7-position of the pyrazolo[1,5-a]pyrimidine scaffold identified a 16-membered derivative 42c with an amide linker that showed a rapid interconversion of atropisomers. Subsequent optimization of the 5-position of the pyrazolo[1,5-a]pyrimidine scaffold and the 5-position of the benzoyl moiety resulted in the discovery of a potent clinical candidate 60b for the treatment of RSV infections.

Discovery of a Potent Dual Inhibitor of Wild-Type and Mutant Respiratory Syncytial Virus Fusion Proteins.

A novel series of macrocyclic pyrazolo[1,5-a]pyrimidine derivatives as respiratory syncytial virus (RSV) fusion glycoprotein (F protein) inhibitors were designed and synthesized based on docking studies of acyclic inhibitors. This effort resulted in the discovery of several macrocyclic compounds, such as 12b, 12f, and 12h, with low nanomolar to subnanomolar activities against the wild-type RSV F protein A2. In addition, 12h showed a single-digit nanomolar potency against the previously reported drug-resistant mutant D486N. Molecular modeling and computational analyses suggested that 12h binds to the D486N mutant while maintaining a rigid bioactive conformation via macrocyclization and that it interacts with a hydrophobic cavity of the mutant using a new interaction surface of 12h. This report describes the rational design of macrocyclic compounds with dual inhibitory activities against wild-type and mutant RSV F proteins.

Design and Synthesis of 2-(1-Alkylaminoalkyl)pyrazolo[1,5-a]pyrimidines as New Respiratory Syncytial Virus Fusion Protein Inhibitors.

Respiratory syncytial virus (RSV) is one of the most common causes of lower respiratory tract infections and a significant pathogen for both adults and children. Although two drugs have been approved for the treatment of RSV infections, the low therapeutic index of these drugs have led pharmaceutical companies to develop safe and effective small-molecule anti-RSV drugs. The pyrazolo[1,5-a]pyrimidine series of compounds containing a piperidine ring at the 2-position of the pyrazolo[1,5-a]pyrimidine scaffold are known as candidate RSV fusion (F) protein inhibitor drugs, such as presatovir and P3. The piperidine ring has been revealed to facilitate the formation of an appropriate dihedral angle between the pyrazolo[1,5-a]pyrimidine scaffold and the plane of the amide bond for exertion of anti-RSV activity. A molecular-dynamic study on newly designed compounds with an acyclic chain instead of the piperidine ring proposed and demonstrated a new series of pyrazolo[1,5-a]pyrimidine derivatives, such as 9c with a 1-methyaminopropyl moiety, showing similar dihedral angle distributions to those in presatovir. Compound 9c exhibited potent anti-RSV activity with an EC50 value of below 1 nM, which was similar to that of presatovir. A subsequent optimization study on the benzene ring of 9c led to the potent RSV F protein inhibitor 14f with an EC50 value of 0.15 nM. The possibility of improving the biological properties of anti-RSV agents by modification at the 7-position of pyrazolo[1,5-a]pyrimidine is also discussed.