合成路线1

The trichloroethyl ester (X) is treated with concentrated HCl in methanol to eliminate the isopropylidene group, affording the diol (XI). The oxidation of (XI) with sodium periodate, followed by reduction of the resulting aldehyde, gives the primary alcohol (XII). Acetylation of (XII) with acetic anhydride, followed by debenzylation with hydrogen over Pd/C and oxidation with oxalyl chloride, gives the aldehyde (XIII), which is cyclized by treatment with Zn and acetic acid to the tetracyclic alcohol (XIV). The reaction of (XIV) with trimethylsilyl cyanide and ZnCl2 in dichloromethane gives the nitrile (XV), which is treated with trifluoroacetic acid to eliminate the benzyl and the methoxymethyl groups, yielding the primary alcohol (XVI). The methylation of the NH group of (XVI) with formaldehyde and sodium cyanoborohydride in methanol affords the N-methyl derivative (XVII), which is oxidized with CrO3-H2SO4 to the carboxylic acid (XVIII). Elimination of the acetyl group of (XVIII) with NaOH in methanol gives the primary alcohol (XIX), which is finally cyclized by means of AgNO3 in methanol.