摘要：

Compounds of formula (I): ##STR1## [wherein X represents a hydrogen atom or a 2-methylbutyryl group, Y represents a hydrogen atom or a methyl group and Rand Rare the same or different and each represents an oxygen atom or a group of formula N--OR(wherein Rrepresents a hydrogen atom or an alkyl group)], the free hydroxy-carboxylic acids corresponding thereto and salts and esters of said acids may be prepared by oxidizing and, if necessary, oximating a corresponding ML-236A, ML-236B, MB-530A or MB-530B compound, and these compounds have valuable antihypercholesteraemic activity.

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