抄録
Omaezallene (1) was isolated from Laurencia sp. by Okino and showed strong antifouling activity against the larvae of the barnacle amphitrite. Although organotin compounds, such as tributyltin (TBT), had been widely used as a fouling inhibitor, the use of TBT was prohibited by IMO in 2008 due to its toxicity. Therefore, the development of the potent nontoxic fouling inhibitor is desired strongly, and 1 is expected to be a lead compound as the fouling inhibitor. Although the relative and absolute structure of 1 was assumed using 1D-and 2D-NMR experiments, the relative configurations have not been determined completely. To determine the relative configurations as well as the absolute configuration, the synthetic study toward 1 was started. The synthesis commenced with the known aldehyde 5, derived from D-glucose in 5 steps, which was transformed into the unsaturated ester 12 with E geometry. The ester 12 was next converted to the hemiacetal 14 in 3 steps. The treatment of ethynylmagnesium bromide to 14 afforded the desired propargy alcohol 6 as a major diastereomer. Cyclization of 6 with NBS furnished the construction of the two contiguous stereocenters to give the bromoether 15 in a highly stereoselective manner, which was then derived to the aldehyde 8 in 4 steps. Coupling reaction between 8 and the tribromoolefin 10 synthesized from E-olefin 9 afforded the propargyl alcohol 24. Final two steps successfully furnished the diol 25, of which 11-1-NMR spectrum was almost corresponding to that of natural 1.
