Enantioselective Syntheses and Absolute Configurations of Viridiene and Aucantene, Two Constitutents of Algae Pheromone Bouquets

Abstract

Key synthons to the title compounds are optically active y -lactones with known or experimentally determined absolute configurations. Horse liver alcohol dehydrogenase, which catalyses the oxidation of mesoand racemic non-meso diols to chiral lactones, and pig-liver esterase, which catalyzes the saponification of meso-diesters to chiral half-esters, were utilized for the asymmetric synthesis of such precursors. The racemic non-meso diol rac-l is converted to the two stereoisomeric y-lactones (+)-2 and (+)-3 which are readily separated. meso-Diol 12 is oxidized to the chiral y-factone (-)-11. Its enantiomer (+)-11 is obtained by enantioselective saponification of the meso-diester 9 with pig-liver esterase. Appropriately designed syntheses lead from these chiral intermediates to both enantiomers (+)-and (-)-6 of viridiene and (+)-and (-)-I8 of aucantene. In addition, kinetically controlled reduction of the racemic aldehydes racda and rac-15 with horse liver alcohol dehydrogenase offers a convenient alternative to the enantioselective preparation of the enantiomers of the two hydrocarbons 6 and 18. Chromatography of 6 on triacetylated cellulose as a stationary chiral phase confirms the enantiospecificity of the synthetic routes designed.

Marine natural products

“…Nuclear magnetic resonance spectral data of acetoxypachydiol (48) indicate that the tenmembered ring is conformationally mobile at 25 "C but not at (53), which is the C-14 epimer of the known metabolite dictytriol (54),67 has been isolated from Dictyota dichotoma. 68 The structure of isodictytriol (53) was determined by X-ray analysis. Four new 'crenulides' have been isolated from members of the D i c t y ~t a c e a e .…”

Biocatalysis Applied to the Synthesis of Pheromones

“…In this context, the use of enzymatic or microbiologically mediated transformations is a promising new strategy for the synthesis of several algae pheromones [187,188]. In many species of marine brown algae, for example, female gametes secrete a complex bouquet of olefinic C11 hydrocarbons as chemical signals to stimulate and attract male gametes and thereby initiate the sexual fusion [189].…”

Chiral Stationary Phases for Preparative Enantioselective Chromatography

“…Although a number of theoretical investigations have been carried out on the interaction mechanism of CTA I with chiral molecules [47][48][49], the real mode of complexation is still not elucidated because of the complex structure of the polymer which seems to be characterised by the presence of multiple 'interaction sites' [50,51]. Moreover, the critical influence of the size of resolved structures [50,52] and the possibility to separate enantiomers of totally apolar molecules [53,54] point to the large contribution of a mechanism involving an intercalation of the solutes between the polymeric chains (shape-selective adsorption or inclusion chromatography). This explanation does not exclude the possibility that very large molecules that cannot penetrate the polymer matrix or that are very polar interact by simple adsorptive interaction on the surface.…”