88. Synthesis of the Brentonins, Polyolefinic Esterified Glyceryl Ethers of an Unidentified Sponge from the North-Brittany Sea: Absolute Configuration and Novel Structure Assignment

Article abstract of DOI:10.1002/hlca.19910740504

The absulute configurations of acetylated bretonin A (= (+)-(R)-1-<(acetoxy)methyl>-2-<<(4E,6E,8E)-dodeca-4,6,8-trienyl>oxy>ethyl 4-acetoxybenzoate; (-)-1b) and isobretonin A (= (+)-(S)-3-<<(4E,6E,8E)-dodeca-4,6,8-trienyl>oxy>-2-hydroxypropyl 4-hydroxybenzoate; (+)-2), previously isolated from an undetermined sponge of the North Brittany sea, were established by comparison with synthetic (+)-1b and (+)-2, obtained from the condensation of commercial (-)-(R)-2,2-dimethyl-1,3-dioxolan-4-yl p-toluenesulfonate ((-)-(R)-15) with a mixture of (4E,6E,8E)- (14e) and (4E,6Z,8E)-dodeca-4,6,8-trien-1-ol (14z).This also allowed confirming the structure and configuration of bretonin B (= (S)-2-<<(4E,6Z,8E)-dodeca-4,6,8-trienyl>oxy>-1-(hydroxymethyl)ethyl 4 hydroxybenzoate; 3) which was also isolated from the same sponge, albeit in a too small amount for a complete study.As concerns the glyceryl ethers precursers of the bretonins, co-occurene of the usual (S)-configuration (from 1a) with the unusual (R)-configuration (from (+)-2) poses intriguing biogenetic problems.