Recent efforts to construct the B-ring of bryostatins

Among macrocyclic natural products, bryostatins have excellent bioactivities and unique structures that make them highly attractive to synthetic chemists. Particularly challenging for the total synthesis of bryostatins is the B-ring, which features a cis-tetrahydropyran containing a geometrically defined exocyclic Z-methyl enoate. Synthetic chemists have recently displayed great prowess in their efforts to construct this ring, and here we summarize the progress towards this goal.

The total synthesis of C-glycosides with completely resolved seven-carbon backbone polyol stereochemistry: stereochemical correlations and access to L-configured and other rare carbohydrates

The de novo synthesis of a full set of hydroxymethyl C-glycosides from only two precursors is described. The seven-carbon target molecules contain five stereocentres and bridge the stereochemical gap between natural D-configured and non-natural L-configured series of hexoses. Key steps include hydroxylation, differential protection, stereoselective reduction and desymmetrization of 8-oxabicyclo[3.2.1]oct-6-enes. C-Terminus differentiation and C-terminus excision of the seven-carbon polyol backbone lead to hexoses, including those of the L-series. A stereochemical and genetic classification of C-glycosides is presented.

Asymmetric synthesis of the northern half C1-C16 of the bryostatins

Starting from 8-oxabicyclo[3.2.1]oct-6-en-3-one and racemic 2,2-dimethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one, the C1-C16 segment of the bryostatins has been synthesized in 30 steps and 9% overall yield (17 steps longest linear sequence). Fragment coupling by dithiane strategy and protecting group manipulations provided an advanced chemodifferentiated northern half segment.