Add time:08/10/2019         Source:sciencedirect.com

Hydrolytically labile ω-chloro-ω-phenylthioglycosides, obtained from the corresponding ω-phenylthioglycosides on treatment with NCS in CCl4, are readily dealkoxyhalogenated with Zn/Ag-graphite in anhydrous solvents affording enantiomerically pure synthons bearing an aldehyde function at the one end and a vinylthioether group at the other end of the ring-opened product. This fragmentation technique turned out to be general and was used for the synthesis of a building block exhibiting the substitution pattern of the C9C14 segment common to all trienomycin-, mycotrienin, and ansatrienin macrolide antibiotics. Zn/Ag-graphite was also used to reductively ring-open the 6-deoxy-6-iodopyranoside 37, easily accessible from D-glucose, to enal 38, which served as central precursor for the synthesis of both the C1C6 as well as C7C13 unit of the polyhydroxylated chain of amphoteronolide B. Combining these two segments 45 and 51 by ketophosphonate/aldehyde coupling afforded enone 54 which is synthetically equivalent to an intermediate of a former total synthesis of this macrolide. Thus, a convergent synthesis of the C1C13 fragment of amphotericin B based upon the hidden C2-symmetry of this target molecule was achieved using metal-graphite promoted ring-opening of carbohydrates in the key step in combination with formal inversion of the configuration of the resulting hex-5-enals.

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