Coronaviruses Including COVID-19 and Variants

Coronaviruses (CoV) are a large family of viruses that historically have been associated with a wide range of responses, from no symptoms to more severe disease that includes pneumonia, severe acute respiratory syndrome, kidney failure, and death. By targeting the viral replication enzymes and protease, we believe it is possible to develop an effective treatment for all coronaviruses, including COVID-19 and its variants, Severe Acute Respiratory Syndrome (SARS), and Middle East Respiratory Syndrome (MERS). 

We are aggressively pursuing the development of novel antiviral compounds for the treatment of COVID-19 and its variants with multiple routes of administration.

The ability of someone with no symptoms to transmit infection to another person has heightened the public health challenge of COVID-19. We are executing on a multipronged strategy aimed at developing highly potent and safe antiviral therapeutics for SARS-CoV-2 and its variants for hospitalized patients, as well as for those not requiring hospitalization, including for prophylactic use to provide protection to uninfected individuals who may become exposed.

To learn more about coronavirus, please visit the information page at the Center for Disease Control and Prevention (CDC).

Coronavirus Replication and Protease Inhibitor

Program Discovery Preclinical Phase 1 Phase 2a Phase 2b Phase 3
COVID-19 CDI-988 Oral Protease Inhibitor
Discovery Phase complete
Preclinical Phase complete
Phase 1 Phase complete
Phase 2a Phase complete
Phase 2b Phase complete
Phase 3 Phase complete
COVID-19 (Licensed) CDI-45205 Protease Inhibitor
Discovery Phase complete
Preclinical Phase in progress
Phase 1 Phase not started
Phase 2a Phase not started
Phase 2b Phase not started
Phase 3 Phase not started
COVID-19 Replication Inhibitors
Discovery Phase in progress
Preclinical Phase not started
Phase 1 Phase not started
Phase 2a Phase not started
Phase 2b Phase not started
Phase 3 Phase not started


We have identified investigational novel antiviral drug candidate CDI-988 for further development as our oral lead for SARS-CoV-2, the virus that causes COVID-19. This novel protease inhibitor targets a highly conserved region in the active site of SARS-CoV-2 main (3CL) protease required for viral RNA replication. We expect to advance CDI-988 into a Phase 1 study in the first half of 2023.

CDI-988 exhibited superior in vitro potency against SARS-CoV-2 with activity maintained against current variants of concern including Omicron. In preclinical studies, CDI-988 demonstrated a favorable safety profile and pharmacokinetic properties supportive of daily oral dosing. This investigational candidate was specifically designed and developed using Cocrystal’s unique structure-based drug discovery technology platform.


CDI-45205, our novel main protease inhibitor, is being developed as a potential treatment for COVID-19 and its variants via intranasal/pulmonary delivery. An IND-enabling study with CDI-45205 is currently underway.

CDI-45205 showed no cytotoxicity against a variety of human cell lines. This compound has also demonstrated in vitro activity against SARS-CoV-2 and current variants of concern, including Delta and Omicron.  CDI-45205 has a strong synergistic effect with the FDA-approved COVID-19 medicine remdesivir. Additionally, a proof-of-concept animal study demonstrated that daily injection of CDI-45205 exhibited favorable in vivo efficacy in MERS-CoV-2 infected mice. 

In December 2020 we announced the selection of CDI-45205 as our lead coronavirus development candidate among a group of protease inhibitors obtained under an exclusive license agreement with Kansas State University Research Foundation (KSURF).

Novel replication inhibitors

In addition to our two SARS-CoV-2 protease programs, we are pursuing a third COVID-19 program using our unique structure-based drug discovery technology platform to develop novel SARS-CoV-2 inhibitors that block viral replication