Syntheses of analogue compounds of cortistatin A (1), an anti-angiogenic steroidal alkaloid from Indonesian marine sponge, were investigated by utilizing the CD-ring fragment of vitamin D2. The incidental preparation of a new analogue having CD-cis-fused skeleton and its biological evaluation revealed the importance of the CD-trans-fused structure for the potent and selective antiproliferative activity of 1 against human umbilical vein endothelial cells (HUVECs).
