Oxazolyl and thiazolyl amino acids match cyclic glutamine in SARS-CoV-2 Mpro inhibition

The SARS-CoV-2 main protease (Mpro) is a crucial cysteine protease essential for viral replication, making it a prime target for antiviral drug development. Current peptidic inhibitors often utilize a cyclic glutamine derivative as the P1 amino acid subunit, which forms key interactions within the active site. However, this moiety is known for its relatively rapid metabolism, limiting the therapeutic efficacy and pharmacokinetic profile of such drugs. There is a critical need to identify alternative, more metabolically stable P1 surrogates that can maintain potent inhibitory activity against Mpro.

Researchers conducted a structure-activity relationship (SAR) study, synthesizing a series of novel oxazolyl and thiazolyl unnatural amino acids to serve as P1 moieties in potential SARS-CoV-2 main protease inhibitors. This investigation explored various substitution patterns on these heteroaromatic rings, aiming to preserve the critical interactions with active site residues. The primary endpoint was the determination of IC50 values for these newly synthesized compounds against the SARS-CoV-2 main protease in an in vitro biochemical assay, with efficacy compared to established cyclic glutamine derivatives.

The synthesized 2-oxazolyl and 2-thiazolyl amino acid derivatives demonstrated potent inhibitory activity against the SARS-CoV-2 main protease. Specifically, the 2-oxazolyl derivatives achieved an IC50 of 290 nM, while the 2-thiazolyl derivatives exhibited an IC50 of 270 nM. These values indicate that the novel P1 surrogates are similarly effective to compounds incorporating the commonly used cyclic glutamine derivative. This finding is significant as it confirms that these alternative moieties can successfully form the important interactions required within the Mpro active site, providing a foundation for future drug design.

The 2-oxazolyl and 2-thiazolyl derivatives showed IC50 values of 290 nM and 270 nM respectively, demonstrating comparable efficacy to cyclic glutamine derivatives.