Synthesis, properties, and identification of epimeric hepoxilins (−)-(10R)-B3 and (+)-(10S)-B3

To characterize the individual epimers of hepoxilin B3, a new total synthesis procedure was developed consisting of subsequent condensations of enentiomerically pure (2R,3S)-epoxy-5-undecynal with LiCCCH2Cl and HCC(CH2)3COOMe, followed by Lindlar hydrogenation, and finally epimer separation. Derivatives of hepoxilin syn -(10R,11R,12S)-B3 (free acid, methyl ester and acetate of methyl ester) are more polar on silica gel, have negative optical rotations [α]25D −60.6°, −62.6°, −25.2°, respectively, and in 1H NMR spectra have the larger splitting of carbinolic H-10 signal (J10,11 5.0–6.1 Hz). Corresponding values for less polar hepoxilin anti -(10S,11R,12S)-B3 derivatives are: [α]25D +73.5°, +61.9°, and −2.0°; J10–11 2.95–3.3 Hz. These data suggest that an epimer of hepoxilin B3 recently isolated by W.H.Gerwick et al. from red algae is syn -(10R,11R,12S)-B3.