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A stereoselective synthesis of the C(8)-C(20) fragment of premonensin B

✍ Scribed by Philip Kocieński; Sjoerd Wadmana; Kelvin Cooper

Publisher
Elsevier Science
Year
1988
Tongue
French
Weight
212 KB
Volume
29
Category
Article
ISSN
0040-4039

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✦ Synopsis

Two stereoselective Ni(O)-catalysed coupling reactions of MeMgBr with cyclic enol ether intermediates were key steps in the synthesis of the C(8)-C(20) fragment (5s) of Premonensin B. Monensin A (1A) and Monensin B (1B) are pentacyclic polyether ionophores produced by Streptomyces cinnamonensis'. In accord with a general scheme of Cane, Celmer, and Westley 2, Cane3 and Robinson4 have proposed that (1A) and ( 18) are produced by a complex cascade of ring closures involving the triepoxides (2A) and ( 28) which are derived from the trienes Premonensin A (3A) and Premonensin B (3B). Recent attempts to illuminate the late stages of Monensin biosynthesis have focused on the total synthesis of the Premonensin trienes 5,6. We now report a highly stereoselective synthesis of the C(8)-C(20) fragment (5B) which, along with the fragments ( 4) and ( 6), constitute key intermediates in a proposed synthesis of Premonensin 8'.

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