I. To determine the maximum tolerated dose (recommended phase II dose, [RP2D]) of 8-chloro-adenosine, when given as a single agent, in patients with relapsed or refractory acute myeloid leukemia. (Phase I) II. To assess tolerability and safety of 8-chloro-adenosine at each dose level by evaluation of toxicities including: type, frequency, severity, attribution, time course and duration. (Phase I) III. To estimate the response rate and to evaluate the antitumor activity of 8-chloro-adenosine, when given as a single agent, as assessed by complete remission rate (complete remission [CR] + complete remission with incomplete blood count recovery [CRi]). (Phase II)