Four new angucyclin(on)es, 11-deoxylandomycinone (1) and landomycins X-Z (2-4) were isolated from the crude extract of Streptomyces cyanogenus K62 mutant strain, along with the recently reported landomycins S, T and V (5-7) and five other known compounds. The structures of the new compounds 1-4 were elucidated by 1D and 2D NMR studies along with HR-MS analyses. Unique about the structures is that the fourth sugar moiety (sugar D) in landomycins X-Z (2-4) was β-D-amicetose instead of β-D-olivose, usually found in this position. The new angucyclin(on)es were biologically evaluated in comparison with previously known congeners against a small panel of MCF-7 (estrogen responsive) and MDA 231 (estrogen refractory) breast cancer cell lines. 11-deoxylandomycinone (IC(50) 2.1 ± 0.3 and 1.2 ± 0.4 μM) and landomycin Y (IC(50) 1.0 ± 0.1 and 2.0 ± 0.1 μM) showed the highest cytotoxic potencies against both the cell lines.