89(P02) 光学活性4-ブロモトリプトファンを利用した麦角アルカロイドChanoclavine-Iの全合成(ポスター発表の部)

DOI

書誌事項

タイトル別名
  • 89(P02) Total Synthesis of Ergot Alkaloid Using Optically Active 4-Bromotryptophan. The Synthesis of Chanoclavine-I

抄録

We have already demonstrated the aromatic C-H/olefin coupling reaction with the aid of Pd (II) complex. These include the preparation of 4-bromodehydrotryptophan 2 as a building block for the synthesis of indole alkaloids. Here we would like to report an asymmetric synthesis of chanoclavine-I(3), an ergot alkaloid, which utilizes 4-bromodehydrotryptophan 2 via a Pd (II)-mediated C-H/olefin coupling reaction. Our design is outlined in scheme 2. Treatment of 4-bromoindole 1 with a stoichiometric amount of Pd (II) complex was expected to give intermediate 1A (via route A) without affecting the C-Br bond. Insertion of olefin to 1A followed by syn-β-H elimination was then anticipated to generate 4-bromodehydrotryptophan 2, a compound which was expected to be amenable to further functionalization. As shown in scheme 3, treatment of 4-bromoindole 1 and enamide 4 with Pd(OAc)_2 (1 equiv), NaHCO_3, and chloranil as an additive in 1,2-dichloroethane provided 4-bromodehydrotryptophan 2 in 87% yield. Having completed the synthesis of 4-bromodehydrotryptophan 2, we applied it to the syntesis of (-)-chanoclavine-I (3). Retrosynthetic analysis of (-)-chanoclavine-I (3) suggested that 4-bromodehydrotryptophan 2 might be a good precursor (scheme 5). The key step in the conversion of 4-bromodehydrotryptophan 2 into (-)-chanoclavine-I (3) involves the intramolecular cyclization of 12 (12→11). As shown in Scheme 6, attempts to cyclize 12 to 11 under radical conditions led to disappointing results. On the other hand, Heck cyclization of 12 gave the cyclized product 14. Ultimately, compound 18 was reached (see scheme 7). Not unexpectedly, a variety of attempts to achieve the deprotection of N-Boc group in 18 to complete the synthesis of (-)-chanoclavine-I (3) failed. An alternative route (scheme 8) to (-)-chanoclavine-I (3) required preparation of 22, a key intermediate in Oppolzer's synthesis of (±)-chanoclavine-I. As shown in scheme 8, 14 was converted to the key intermediate 22. This intermediate was further converted to (-)-chanoclavine-I (3) according to Oppolzer's route. As both synthetic sample and natural product have negative optical rotations, the absolute configuration of (-)-chanoclavine-I (3) has been assigned to be the one shown in scheme 8. We wish to add that no racemization occurred in our synthetic route.

収録刊行物

詳細情報 詳細情報について

  • CRID
    1390001206078481920
  • NII論文ID
    110006679817
  • DOI
    10.24496/tennenyuki.38.0_529
  • ISSN
    24331856
  • 本文言語コード
    ja
  • データソース種別
    • JaLC
    • CiNii Articles
  • 抄録ライセンスフラグ
    使用不可

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