title: Spinosyn g: proof of structure by semisynthesis.
abstract: [reaction: see text] Spinosyn G was isolated in the late 1980s as a minor component from the broth of our potent, fermentation-derived insecticide spinosad. Its structure was then tentatively identified as 5' '-epispinosyn A (3) on the basis of (1)H and (13)C NMR data, but the 4' '-epi compound 4 could not be conclusively ruled out with the data available. Described herein are unambiguous syntheses of both 3 and 4, whereby 3 was proved identical to the natural product. Compound 4 was prepared from intact spinosyn A by a novel F-TEDA-promoted oxidative deamination to the 4' '-ketone 5, stereoselective reduction to the equatorial alcohol 6, and nitrogen incorporation via the axial azide 7. Compound 3 was obtained by coupling spinosyn A 17-pseudoaglycone (9) with the N-protected dihydropyran 16 derived from methyl l-ossaminide (14). This gave an approximately 2:1 mixture of anomeric products 17 with the desired equatorial glycoside predominating, which was then converted to 3 by N-deprotection and methylation.
authors.affiliation: Discovery Research, Dow AgroSciences LLC, 9330 Zionsville Road, Indianapolis, Indiana 46268, USA. prgraupner@dow.com
authors.forename: Paul R
authors.initials: PR
authors.lastname: Graupner
authors.forename: Jacek
authors.initials: J
authors.lastname: Martynow
authors.forename: Peter B
authors.initials: PB
authors.lastname: Anzeveno
mesh_terms: D006027:Glycosides; D007306:Insecticides / Q000138:chemical synthesis / Q000737:chemistry; D018942:Macrolides / Q000138:chemical synthesis; D008968:Molecular Conformation; D013237:Stereoisomerism
chemical_list: D006027:Glycosides; D007306:Insecticides; D018942:Macrolides; C114883:spinosyn A; C500915:spinosyn G