title: Synthesis of stable isotope-labeled epothilone D using a degradation-reconstruction approach.
abstract: The stabilization of microtubules using epothilones represents a novel mechanism of action to treat Alzheimer's disease. Epothilone D is one such microtubule-stabilizing drug that has been investigated by Bristol-Myers Squibb. An important step in the development process was the synthesis of a stable isotope-labeled analog for use in bioanalytical assays to accurately quantify the concentration of the drug in biological samples. A novel synthetic route to stable isotope-labeled epothilone D is described. The synthetic route was based on a strategy to degrade epothilone B and then use that key intermediate to reconstruct stable isotope-labeled epothilone D. Epothilone B was treated with potassium osmate and sodium periodate. The thiazole moiety in epothilone B was efficiently cleaved to give (1S,3S,7S,10R,11S,12S,16R)-3-acetyl-7,11-dihydroxy-8,8,10,12,16-pentamethyl-4,17-dioxabicyclo[14.1.0]heptadecane-5,9-dione. The epoxide in the macrocyclic ring of that intermediate was cleanly removed by treatment with tungsten hexachloride and n-butyllithium to give the corresponding olefin (4S,7R,8S,9S,16S,Z)-16-acetyl-4,8-dihydroxy-5,5,7,9,13-pentamethyloxacyclohexadec-13-ene-2,6-dione. Bis(triethylsilyl) protection produced (4S,7R,8S,9S,16S,Z)-16-acetyl-5,5,7,9,13-pentamethyl-4,8-bis(triethylsilyloxy)-oxacyclohexadec-13-ene-2,6-dione. This intermediate was coupled to a stable isotope-labeled thiazole using a Wittig reaction as the key step to provide (13)C5, (15)N-labeled epothilone D. In summary, the synthesis was completed in nine total steps, only six of which involved isotopically labeled reagents. A total of 168 mg of (13)C5, (15)N-labeled epothilone D was prepared in an 8% overall yield from (13)C2, (15)N-labeled thioacetamide and (13)C3-labeled ethyl bromopyruvate.
authors.affiliation: Bristol-Myers Squibb Research and Development, Discovery Chemistry Platforms, 5 Research Parkway, Wallingford, CT, 06492, USA.
authors.forename: Richard C
authors.initials: RC
authors.lastname: Burrell
authors.affiliation: Bristol-Myers Squibb Research and Development, Discovery Chemistry Platforms, 5 Research Parkway, Wallingford, CT, 06492, USA.
authors.forename: Wesley A
authors.initials: WA
authors.lastname: Turley
authors.affiliation: Bristol-Myers Squibb Research and Development, Discovery Chemistry Platforms, Route 206 and Province Line Road, Princeton, NJ, 08540, USA.
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Bonacorsi
mesh_terms: D002247:Carbon Isotopes / Q000138:chemical synthesis* / Q000302:isolation & purification*; D004355:Drug Stability; D034261:Epothilones / Q000138:chemical synthesis*; D007553:Isotope Labeling / Q000379:methods*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000302:isolation & purification*
chemical_list: D002247:Carbon Isotopes; D034261:Epothilones; D019275:Radiopharmaceuticals; C114026:desoxyepothilone B
keywords: Alzheimer's disease; degradation of epothilone B; epothilone D; stable isotope labeling