Synthesis of the C9-C22 fragment of polyene polyol containing macrolactone natural product pentamycin

Total Synthesis of Pentamycin by a Conformationally Biased Double Stille Ring Closure with a Trienyl-bis-stannane

The total synthesis of the potent polyene macrolide antibiotic pentamycin was accomplished by an expedient strategy involving a highly stereoselective assembly of the polyol segment in combination with an adventurous double Stille cross-coupling with a trienyl-bis-stannane closing the macrolactone and installing the sensitive pentaene fragment. Presumably, this remarkable linchpin insertion is enhanced by the linear hydrogen bonding skeleton of the polyol substrate. Further key features include a tailored Rychnovsky alkylation of cyanohydrin acetonides and elaborate Krische couplings to set the characteristic hydroxyl and hydroxymethyl bearing centers with excellent selectivity and yield. The total synthesis unequivocally confirms the full relative and absolute stereochemistry of this polyketide, including a previously uncertain hydroxyl bearing center.

γ-Hydroxy Amides from Tartaric Acid: Versatile Chiral Building Blocks for the Total Synthesis of Natural Products

"Chiral pool" compounds possessing well defined stereocenters and suitable functionality serve as excellent building blocks for the synthesis of natural products and therapeutically important compounds. Tartaric acid is a C₂ -symmetric molecule available in both enantiomeric forms. It was extensively utilized in the synthesis of privileged chiral ligands/catalysts such as TADDOLs, and as a start point in the synthesis of plethora of compounds. The advent of several new C-C bond forming reactions offers opportunity for the development of novel synthetic strategies based on chiral pool compounds. We found that the desymmetrization of the bis-dimethyl amide/Weinreb amide derived from tartaric acid can be accomplished by controlled addition of Grignard /organolithium reagents leading to the mono keto amides, the reduction of which affords the γ-hydroxy amides. This account describes our research efforts of more than a decade on the synthesis and application of diverse γ-hydroxy amides derived from tartaric acid in the total synthesis of structurally simple to complex bio-active natural products.