Twenty-carbon framework

Research by S. Arseniyadis and co-workers showed that the aldol-annelation-fragmentation strategy could be used for the synthesis of complex structures, which are precursors of a variety of taxoid natural products.This strategy allows the preparation of the twenty-carbon framework of taxanes from inexpensive and simple starting materials. 

Another new skeletal type, this one with twenty carbon atoms, is represented by megastachine (14), isolated from L. megastachyum collected in Madagascar. The structure of (14) was determined by an X-ray crystallographic study of its methiodide. Megastachine contains the sixteen-carbon framework of fawcet-tidine (15) in which the (reduced) oxygen function has been replaced by a (reduced) acetoacetate unit. ... 

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