Total synthesis, structure revision and cytotoxic activity of Sch 53825 and its derivatives

The first total synthesis of Sch 53825 (14) was achieved in 12 steps from 5-hydroxy-1-tetralone in 16% overall yield through N-benzyl cinchoninium chloride-catalyzed asymmetric epoxidation and a Mitsunobu reaction as the key steps. On this basis, the synthesis of palmarumycin B₆ was improved using the same raw material with 6 steps and 32% overall yield. Also, three new analogues with two chlorine atoms were synthesized. Their structures were characterized by ¹H, ¹³C NMR, HR-ESI-MS and X-ray diffraction data. The structure of natural Sch 53825 was revised as an epimer of compound 1 with the anti-hydroxy epoxide at C-4. Their cytotoxic activities against several tumor cell lines (HCT116, U251, BGC823, Huh-7 and PC9) showed that compound 11 exhibited excellent cytotoxicity against above mentioned cancer cell lines with IC₅₀ < 0.5 μM.