The goal of this phase 1/2 multicenter, open-label, singe arm dose escalation and expansion study is to assess the safety, tolerability, pharmacokinetic and pharmacodynamic profile of CTX-712 in patients with relapsed/refractory (R/R) acute myeloid leukemia (AML) and higher risk myelodysplastic syndromes (HR-MDS). The phase 1 part of the study consists of sequential standard 3 + 3 dose escalation, where patients will receive ascending doses of CTX-712 to determine the recommended phase 2 dose (RP2D) for further clinical development. This is followed by a confirmatory phase 1 expansion cohort where an additional approximately 10 patients will be treated with CTX-712 at the RP2D to gain further confidence in the selected dose level. After RP2D is determined, Drug-Drug-Interaction cohorts will be started. The phase 2 part of the study will commence after the RP2D has been identified and confirmed and will evaluate therapeutic activity in R/R AML or R/R HR-MDS, in addition to confirmation of the safety profile.