95(P-26) ヘミブレベトキシンBの収束的全合成研究(ポスター発表の部)

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Hemibrevetoxin B (1), isolated from the red tide dinoflagellate Gymnodinium breve by Shimizu group, is a trans-fused tetracyclic ether. To date, many research groups reported total synthesis of 1. Notably, most of them adopted a linear strategy, though a convergent strategy would have comparable efficiency with linear one even in the synthesis of such small polyether. In this context, we planned to synthesize 1 through a convergent strategy that would allow the large-scale preparation. During our studies, Holton group reported first convergent total synthesis of 1 very recently, where the ABCD ring part was constructed in 15 steps after connection of the cyclic A-ring part with the acyclic C12-C21 (BCD-ring) segment. Here, we disclose alternate successful convergent construction of the ABCD ring system 2 of 1 from the A- and D-ring segments (5 and 6, respectively). Previously, we developed an effective convergent method for the synthesis of trans-fused tetracyclic ethers adopting coupling reaction of an acyl anion equivalent with an aldehyde followed by reductive cyclization reactions. Therefore, dimethyldithioacetal mono-S-oxide 5 and aldehyde 6 were selected as A- and D-ring segments, respectively, in our synthetic plan for 1. The segment 5 was prepared in 14 steps from 2,4,6-tri-O-acetyl-D-glucal 7 in 14% total yield. The aldehyde 6 was synthesized in 19 steps from γ-butyrolactone 14 in 11% total yield. Coupling reaction of deprotonated 5 with 6 followed by simultaneous removal of TBS and dithioacetal groups afforded ketodiol 4, which was subjected to reductive cyclization, oxidation, and deprotection to give 3. Formation of cyclic S,O-acetal 34 from 3 followed by oxidation with mCPBA and in situ treatment with AlMe_3 produced tetracyclic 2. Thus, the ABCD-ring part 2 was successfully constructed in 7 steps from 6 in 12% total yield.
天然有機化合物討論会の論文
2003-09-01

95(P-26) ヘミブレベトキシンBの収束的全合成研究(ポスター発表の部)

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