conditions(2) SARS-CoV-2(2) 3CL(2) Compound(2) cyclic(2) form(2) methodology(2) agent(2) purification(2) oxime(2) Including(2) Antiviral(2) Glutamine(2) M pro(2) targeting(2) Improved(2) synthesis(2) preparation(2) reagent(2) lack(2) yielding(2) Protease inhibitor(2) Amino acid(2) Alanine(2) analogue(2)