96(P-40) ピンナトキシンAの全合成研究(ポスター発表の部)

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Pinnatoxin A (1) was isolated by Uemura and co-workers from the Pinna muricata in 1995. While 1 is partly responsible for food poisoning in China and Japan, 1 shows significant Ca^<2+> channel activity. Structure of 1 features: 1) a spirocyclic imine (A-ring), 2) a bis-spiroacetal (BCD-ring), and 3) a 27-membered macrocarbocycle. We describe herein our progress toward the convergent total synthesis of 1. The macrocarbocycle 1 was divided into two fragments, the BCD-ring fragment 4 and the AEFG-ring fragment 5. After the two fragments are linked, the macrocarbocycle will be constructed by using RCM reaction. Starting from the allylic alcohol 8, ketone 10 was synthesized through consecutive asymmetric oxidations. By tratment 10 with CSA in MeOH and then changing the solvent to toluene, the desired bis-spiroacetal 11 was selectively obtained, which was then converted to 4. On the other hand, 5 was synthesized from the aldehyde 12, that was derived from D-glucose in 8 steps. Grignard reaction of 12 and 14 gave an alcohol in high yield, which was then converted to the nitrile 15. KN(TMS)_2 mediated cyclization of 15 successfully gave 16 as a single isomer. Manipulation of protecting groups and introduction of the methyl group at C27 as well as an allyl group afforded 5. Both fragments 4 and 5 in hand were linked using t-BuLi in the presence of HMPA. After selective desilylation, treatment of 22 with the highly active Grubbs catalyst 19 produced the desired 27-membered carbocycle 23 in high yield. Hydrolysis of the dithioacetal 23 followed by acid treatment with TFA in MeOH successfully formed the EF-ring. Introduction of the exo methylene (C10), ketone (C6) and azide groups (C1) gave the carboxylic acid 27. The total synthesis of 1 is actively under progress in our research group.
天然有機化合物討論会の論文
2002-09-01

96(P-40) ピンナトキシンAの全合成研究(ポスター発表の部)

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