ClAraC (consisting of one dose of clofarabine and ara-C for five days) or FLAMSA (consisting of one dose of fudarabine, amsacrine and ara-C for four days) will be administered followed by reduced-intensity conditioning regimen (RIC) in the setting of allogeneic stem cell transplantation (SCT). The aim of the study is to explore the antileukemic, immunosuppressive effects and toxicity and safety of clofarabine in combination with ara-C in the setting of RIC allogeneic transplantation compared with the FLAMSA-protocol for patients with high-risk acute myeloid leukemia (AML) or advanced myelodysplastic syndrome (MDS).