The isolation and synthesis of neodolastane diterpenoids.

The neodolastane diterpenoids comprise a group of 44 compounds including guanacastepenes, heptemerones, plicatilisins, radianspenes, 2,15-epoxy-5,13-dihydroxyneodolast-3-en-14-one and sphaerostanol. These fungal and marine natural products are characterized by a tricyclic neodolastane skeleton that consists of fused five-, seven- and six-membered rings. Their reported antibiotic activities against antibiotic-resistant bacteria together with strong antifungal and anticancer activities and their novel structures render these compounds interesting synthetic targets. The aim of this account is to summarise the progress in the isolation, characterisation and synthesis of these diterpenoids as well as to review their biogenetic origins and diverse biological activities since their discovery in 2000.

Synthesis and conformational analysis of (alpha-D-galactosyl)phenylmethane and alpha-,beta-difluoromethane analogues: interactions with the plant lectin viscumin.

(Alpha-D-galactosyl)phenylmethane (1), (alpha- and beta-D-galactosyl)(difluoro)phenylmethane (2 and 3) have been prepared and their conformations in solution were described by using a combination of force-field calculations and NMR spectroscopic studies. Galactoside 1 adopts a (4)C(1) chair conformation and an exo anomeric orientation, as is the case for natural alpha-galactosides. The X-ray crystal structure of its difluoromethylene derivative 2 similarly shows a (4)C(1) chair conformation. Surprisingly, compound 2 exhibits a different equilibrium between (1)C(4) chair and (1)S(3) skew boat conformations and significant flexibility around the pseudoglycosidic linkage when in solution. The beta-stereoisomer 3 adopts a major (4)C(1) chair conformation. Interestingly, C-galactosides 1, 2, and 3 bind to viscumin (VAA), a galactoside-specific lectin, which is confirmed by NMR experiments and docking calculations.