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Ringing in cortistatin: The pentacyclic core of the cortistatin steroidal alkaloids has been readily assembled in eleven steps from simple building blocks (see scheme; PMB=para-methoxybenzyl, TBS=tert-butyldimethylsilyl). An enyne cycloisomerization and an oxidative dearomatization/cyclization are the key ring-forming steps in this sequence.
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Simmons et al. (2008) studied this question.
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