Can ACE2 receptors be syntesized?
The drugs you are referring to are called receptor mimics or peptide inhibitors.  Yes, molecular mimics for human ACE2 can and have been synthesized.  Binding of these mimics to coronavirus spike proteins leads to sequestration or inactivation of viral particles.

Relevant literature:
Romano M, Ruggiero A, Squeglia F, Berisio R. An engineered stable mini-protein to plug SARS-Cov-2 Spikes. bioRxiv. 2020.
Han Y and Král P. Computational Design of ACE2-Based Peptide Inhibitors of SARS-CoV-2. ACS Nano. 2020;14(4): 5143-5147.
Walls AC, Xiong X, Park YJ, et al. Unexpected Receptor Functional Mimicry Elucidates Activation of Coronavirus Fusion. Cell. 2019;176(5):1026-1039.e15.