In this research study, the study drug SL-401 will be combined with the standard dose of azacitidine. The goal of this research study is to try and determine the safest, highest dose of study drug, SL-401, in combination with azacitidine that can be given to patients with AML or high-risk MDS. SL-401 works by stopping or slowing the growth of cancer stem cells, which are the undeveloped cells which can develop into cancer cells. The goals of this research study are to look at if this combination works to help treat cancer and if there is any lasting effect of this combination . This study will also look at how the SL-401, in combination with azacitidine, affects certain proteins in the blood and bone marrow. SL-401 has been given to patients with AML and MDS in the past, but this is the first time it will be given in combination with another drug.