An efficient synthesis of synargentolide A from d-mannitol

Recent Advances in the Stereoselective Total Synthesis of Natural Pyranones Having Long Side Chains

Pyranone natural products have attracted great attention in recent years from chemists and biologists due to their fascinating stereoisomeric structural features and impressive bioactivities. A large number of stereoselective total syntheses of these compounds have been described in the literature. The natural pyranones with long side chains have recently received significant importance in the synthetic field. In the present article, we aim to review the modern progress of the stereoselective total syntheses of these natural pyranones containing long-chain substituents.

DFT 1H-1H coupling constants in the conformational analysis and stereoisomeric differentiation of 6-heptenyl-2H-pyran-2-ones: configurational reassignment of synargentolide A

Density functional theory (DFT) (1) H-(1) H NMR coupling constant calculations, including solvation parameters with the polarizable continuum model B3LYP/DGDZVP basis set together with the experimental values measured by spectral simulation, were used to predict the configuration of hydroxylated 6-heptenyl-5,6-dihydro-2H-pyran-2-ones 1, 2, 4, and 7, allowing epimer differentiation. Modeling of these flexible compounds requires the inclusion of solvation models that account for stabilizing interactions derived from intramolecular and intermolecular hydrogen bonds, in contrast with peracetylated derivatives (3, 5, and 6) in which the solvation consideration can be omitted. Using this DFT NMR integrated approach as well as spectral simulation, the configurational reassignment of synargentolide A (8) was accomplished by calculations in the gas phase among four possible diastereoisomers (8-11). Calculated (3) JH,H values established its configuration as 6R-[4'S,5'S,6'S-(triacetyloxy)-2E-heptenyl]-5,6-dihydro-2H-pyran-2-one (8), in contrast with the incorrect 6R,4'R,5'R,6'R-diastereoisomer previously proposed by synthesis (12). Application of this approach increases the probability for successful enantiospecific total syntheses of flexible compounds with multiple chiral centers.

Coibacins A and B: total synthesis and stereochemical revision

The interface between synthetic organic chemistry and natural products was explored in order to unravel the structure of coibacin A, a metabolite isolated from the marine cyanobacterium cf. Oscillatoria sp. that exhibits selective antileishmanial activity and potent anti-inflammatory properties. Our synthetic plan focused on a convergent strategy that allows rapid access to the desired target by coupling of three key fragments involving E-selective Wittig and modified Julia olefinations. CD measurements and comparative HPLC analyses of the natural product and four synthetic stereoisomers led to determination of its absolute configuration, thus correcting the original assignment at C-5 and unambiguously establishing those at C-16 and C-18. Additionally, we synthesized coibacin B on the basis of the assignment of configuration for coibacin A.