This is a multicenter, open-label, Phase 1 a/b dose escalation study of safety, pharmacodynamics, and pharmacokinetics of CG-806 in ascending cohorts (3+3 design) to determine the MTD or recommended dose in patients with relapsed or refractory Acute Myeloid Leukemia (except APML), secondary AML, therapy-related AML, or higher-risk MDS whose disease has relapsed, is refractory or who are ineligible for or intolerant of intensive chemotherapy or transplantation. This is to be followed by a cohort expansion phase.