合成路线1

The reduction of the carbonyl group of (XLIV) with NaBH4 in THF gives the diol (XLV), which is selectively silylated at the primary OH group with Tbdps-Cl, TEA and DMAP, yielding silyl ether (XLVI). Elimination of the Alloc protecting group with Pd(PPh3)4, PPh3 in THF affords compound (XLVII), which is carefully oxidized at the NH group with MCPBA in dichloromethane, providing the hydroyamine (XLVIII). The reaction of (XLVIII) with Ac2O gives the acetate (XLIX), which is oxidized with DMP to yield the ketone (L). The desilylation of (L) with HF and pyridine affords the hydroxyketone (LI), which by treatment with K2CO3 in methanol undergoes cyclization to the tetracyclic compound (LIII) through the intermediate dihydroxyketone (LII). The reaction of (LIII) with diphosgene and pyridine gives the cyclic carbonate (LIV), which is treated with ammonia in THF, yielding the carbamic ester (LV).