ABSTRACTThere are disclosed novel methods of preparingpentacyclic macrolides having sixteen member lactonerings. Earlier synthetic approaches gave unpredictablevariation of the desired products and hence much reducedbiological activities, attributed to the final steps ofconjugation, deconjugation, and epimerization. Animproved two step route has been devised, involvingepimerization subsequent to deconjugation, yieldingproducts of higher and more consistent purity. The .DELTA.2-isomer is first deconjugated to the 2-epi form which isthen epimerized to the desired end product. Thisprocess is generally applicable to the pentacyclicsixteen member lactone ring macrolides, including theavermectins, milbemycins, and related compounds. Thesecompounds possess broad spectrum antiparasitic activityagainst, e.g., nematodes.
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