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. 2012 Oct 19;14(20):5350-3.
doi: 10.1021/ol302535r. Epub 2012 Sep 28.

Synthesis of the pentacyclic skeleton of the indole alkaloid arboflorine

Raul A Leal  1 , Danial R Beaudry, Saeed K Alzghari, Richmond Sarpong
Affiliations

Synthesis of the pentacyclic skeleton of the indole alkaloid arboflorine

Raul A Leal et al. Org Lett. .

Abstract

An effective synthesis of the pentacyclic core of the unusual Kopsia alkaloid arboflorine is reported. The success of the synthetic route rested on the use of a borylative C-H functionalization reaction, a convergent Suzuki cross-coupling to a C(2) halogenated indole, and an unprecedented transannular dehydrogenative C-N bond forming reaction.

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Figures

Figure 1
Figure 1
Structure of the Kopsia indole alkaloid arboflorine (1)
Scheme 1
Scheme 1
Retrosynthetic analysis of arboflorine
Scheme 2
Scheme 2
Synthesis of borylated methoxypicoline 10
Scheme 3
Scheme 3
Synthesis of macrocycle 3
Scheme 4
Scheme 4
Attempted reduction of methoxypicoline moiety of 14
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References

    1. Awang K, Svenet T, Pais M. Nat. Prod. 1993;56:1134–1139.
    1. Lim K-H, Kam T-S. Org. Lett. 2006;8:1733–1735. - PubMed

    1. Other Kopsia indole alkaloids that possess three nitrogen atoms include the mersingines and lahadinines, see: Kam TS, Yoganathan K, Chen WJ. Nat. Prod. 1996;59:1109–1112. Kam TS, Yoganathan K. Phytochemistry. 1997;46:785–787.

    1. Bioactivity including cytotoxicity toward KB and Jurkat cells and reversal of multi-drug resistance of KB cells have been noted for other alkaloids isolated from K. arborea. For example, see: Lim K-H, Hiraku O, Komiyama K, Koyano T, Hayashi M, Kam T-S. J. Nat. Prod. 2007;70:1302–1307.

    1. Johansen MB. Ph.D. Dissertation. The University of Western Ontario; London, ON, Canada: 2010. Part I: Synthesis of Pyrrolo[1,2-A]indoles Part II: Studies Towards Arboflorine.

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