Esterification of 16,16-dimethyl-PGF2alpha 11,15-bistetrahydropyranyl ether (I) with diazomethane followed by chlorination with tetrachloromethane and triphenylphosphine in the presence of triethylamine afforded the 9beta-chloro intermediate (II). Deprotection with acetic acid yielded the 11,15 diol (III), which was finally converted to nocloprost by treatment with potassium hydroxide in ethanol-water.