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A unified enantioselective route to total synthesis of diospongins A and B and their enantiomers is developed by using achiral starting materials. All three stereocenters are described by using catalytic reactions.

Residual dipolar couplings (RDCs), measured in organic solvent media, are used for the precise NMR structural determination of distinct hydrogen-bonded secondary folds in unnatural peptides. The results have shown that the conventional constraints, [super 3][J.sub.HH] and NOE-derived distances have not allowed the accurate structural elucidation even for rigid foldamers and have stressed the need for RDC-based structure validation and refinement for unnatural peptides in small organic molecules.

The design and characterization of short homo-oligomers of a new building block, cis-[beta]-furanoid sugar aminoxy acid is described. They have displayed rigid ribbon-like secondary structures composed of 5/7 bifurcated intramolecular hydrogen bonds.

The heterooligomers composed of alternating conformationally rigid cis-FSA and beta-hGly motifs is synthesized using standard coupling protocols (EDCI/HOBt). The results show that conformationally rigid modified peptides with appropriate functional groups and 14-helical fold have medicinal applications such as disruption of protein-protein interactions.

A study shows that the furanoid cis-beta-sugar amino acid oligomer adopts in solution a well-defined right-handed 14-helix. The functionalization of the conformationally oligomers with defined medicinal properties makes these molecules useful in pharmaceutical applications.

The article focuses on a study related to expanding the conformational pool of cis-β-sugar amino acid. Complex biological functions of biopolymers are due to their inherent property to adopt specific folded conformations, which brings about the appropriate spatial arrangement of the functional groups. The sugar β-amino acids (SAAs) can be considered as a bridge between carbohydrates and protein. The chemical shifts of the amide protons involved in hydrogen bonding were almost invariant, indicating strong hydrogen bonding. The structural data indicate that the mixed peptide heterooligomers comprising alternating cis-FSAA and β-h Gly 1-3 and 5-6 form robust right-handed helical secondary structures in solution.

The present manuscript describes a convenient, mild, and highly stereoselective method for the allylation of δ-hydroxy-α,β-unsaturated ketones having a benzylic hydroxyl group at the δ-position using allyltrimethylsilane mediated by BF 3 ·OEt 2 , leading to 2,4-diallyl-2-methyl-6-aryltetrahydro-2 H -pyran ring systems with quaternary carbon stereogenic centers. This represents the first example of a tandem isomerization followed by one C-O and two C-C bond-forming reactions in one pot. The isolation of TMS-protected lactol as an intermediate from the reaction strongly supports the proposed mechanistic pathway.

A first total synthesis of acortatarins A, B, and an enantiomer of the proposed structure of acortatarin B is described by using readily available d-sugars. This convergent total synthesis revealed the revision of the absolute configuration of acortatarin A and structural revision of acortatarin B. The key steps involved are regioselective epoxide opening with deprotonated 2,5-disubstituted pyrrole and spiroketalization., (© 2011 American Chemical Society)