Machaeric acid, a new triterpene acid recently isolated from the cactus Machaerocereus gummosus, has been shown to have the structure 21-keto-oleanolic acid by appropriate correlation with a 21-dehydro-oleanolic acid derivative obtainable from the triterpene rehmannic acid. Machaerinic acid, a triterpene acid present in trace amounts in the same cactus is one of the two possible isomeric 21-hydroxy-oleanolic acids as demonstrated by sodium borohydride reduction of machaeric acid.These two acids are the first examples of naturally occurring triterpenes with oxygen functions at position 21.
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