Novel Epoxidation/Oxygenation Method toward Bioactive Cephalostatins Using Common Alkaline Metals

摘要

Cephalostatins (e. g. cephalostatin 1) are a class of natural products that exert extraordinary antitumor activity with the presence of a significant number of oxygen atoms either in etheric, alcoholic, or epoxydic form. Here, we describe a novel epoxidation method of Delta(14,15) bond of the symmetrical bis-steroidal pyrazine (BSP) (the diketone 2) using only grounded lithium metal in dry THF. This chemo and regioselective method which forms an environmentally begin solved one of the major challenges that overcome the N-oxide formation in BSP's. The epoxidized products underwent a regioselective reduction with sodium borohydride NaBH4 yielding 15 alpha-hydroxy derivatives. Interestingly, the triol derivative 5 was found to exert a powerful activity against the three selected cancer cell lines: K562, MCF-7, and DU-145 using MTT assay (average GI(50)<0.1 mu M). Noteworthy, the BSP 7 (with vicinal-diol functionality) was obtained when the epoxidized derivatives 4 was treated with sodium metal in dry THF.