| Summary: | Four new conjugates, esters of polyhydroxysteroids with long-chain fatty acids (<b>1</b>–<b>4</b>), were isolated from the deep-water Far Eastern starfish <i>Ceramaster patagonicus.</i> The structures of <b>1</b>–<b>4</b> were established by NMR and ESIMS techniques as well as chemical transformations. Unusual compounds <b>1</b>–<b>4</b> contain the same 5α-cholestane-3β,6β,15α,16β,26-pentahydroxysteroidal moiety and differ from each other in the fatty acid units: 5′<i>Z</i>,11′<i>Z</i>-octadecadienoic (<b>1</b>), 11′<i>Z</i>-octadecenoic (<b>2</b>), 5′<i>Z</i>,11′<i>Z</i>-eicosadienoic (<b>3</b>), and 7′<i>Z</i>-eicosenoic (<b>4</b>) acids. Previously, only one such steroid conjugate with a fatty acid was known from starfish. After 72 h of cell incubation, using MTS assay it was found that the concentrations of compounds <b>1</b>, <b>2</b>, and <b>3</b> that caused 50% inhibition of growth (IC<sub>50</sub>) of JB6 Cl41 cells were 81, 40, and 79 µM, respectively; for MDA-MB-231 cells, IC<sub>50</sub> of compounds <b>1</b>, <b>2</b>, and <b>3</b> were 74, 33, and 73 µM, respectively; for HCT 116 cells, IC<sub>50</sub> of compounds <b>1</b>, <b>2</b>, and <b>3</b> were 73, 31, and 71 µM, respectively. Compound <b>4</b> was non-toxic against tested cell lines even in three days of treatment. Compound <b>2</b> (20 µM) suppressed colony formation and migration of MDA-MB-231 and HCT 116 cells.
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