Lubiprostone CAS NO.333963-40-9

Chronic constipation is an affliction affecting 4–5 million Americans alone. When no specific cause is identified, it is classified as idiopathic. Dietary and lifestyle modifications are the first-line conventional approaches followed by the administration of laxatives. Unfortunately, chronic idiopathic constipation is frequently refractory to traditional therapy; thus, the need for novel agents exists. Lubiprostone is a bicyclic fatty acid with a novel mechanism of action. Without affecting sodium and potassium ion concentrations, lubiprostone activates intestinal chloride ion channels, thereby, increasing intestinal water secretion and intestinal fluid chloride ion concentration. In basolateral membranepermeabilized T84 gastrointestinal epithelial cells under chloride gradient conditions, lubiprostone concentration-dependently increased short-circuit current with an EC50 of approximately 20 nM.

Synthesis of lupiprostone started with the tetrahydropyran (THP) protected (-)Corey lactone 30. Desilylation of 30 with TBAF in THF gave free carbinol in 82% yield which was oxidized with oxalyl chloride and DMSO to give corresponding crude aldehyde 31. Aldehyde 31 was condensed with dimethyl 3,3,-difluoro-2-oxoheptylphosphonate (32) in the presence of thallium ethoxide to give unsaturated difluoroketone 33 which was hydrogenated with H2 over Pd/C in ethyl acetate and the resulting ketone was subsequently reduced with sodium borohydride in methanol to give lactone 34 in excellent yield. The lactone 34 was reduced to lactol 35 with DIBAL at -78??C in toluene and the crude lactol 35 was condensed with 4-carboxybutyl triphenylphosphonium bromide (36) in the presence of t-BuOK in THF to yield compound 37. Crude 37 was reacted with benzyl bromide and DBU in dichloromethane (DCM) to give the benzyl ester in 96% yield. Oxidation of the alcohol with Collins reagent and removal of the THP protecting group under acidic conditions gave corresponding prostaglandin E2 benzyl ester 38. Finally, compound 38 was submitted to simultaneous benzyl ester group cleavage and double bond hydrogenation with H2 over Pd/C in ethyl acetate to give lubiprostone (V) in 94% yield.