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Hee Yoon Lee

Other affiliations: Columbia University
Bio: Hee Yoon Lee is an academic researcher from KAIST. The author has contributed to research in topics: Digitoxigenin & Wieland–Miescher ketone. The author has an hindex of 1, co-authored 1 publications receiving 75 citations. Previous affiliations of Hee Yoon Lee include Columbia University.

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TL;DR: In this article, the tricyclic enone 2 was constructed via an intramolecular [4 + 2] cycloaddition, as schematized in Figure 1.
Abstract: It has been said that the active components in the Digitalis extracts have been “the most ingested drugs in medicine”.1 These substances, usually called cardenolides, differ from ordinary steroids in three major respects: the C/D ring system is cis rather than trans fused, there is a tertiary hydroxyl at C-14, and the substituent at C-17 (a butenolide) is in the thermodynamically less stable â orientation.2 As might be expected, many partial syntheses of cardenolides have been described starting with readily available steroids.3,4 We now report the total synthesis of natural (+)-digitoxigenin (1), the biologically active cardenolide which, as its trisaccharide derivative digitoxin, is one of the most frequently used of the active principles isolated from Digitalis species. We divided the synthesis, which we carried out both to racemic and to natural (+)-digitoxigenin, in three parts: synthesis of the tricyclic enone 2; elaboration of the fused 5-membered ring D to produce a tetracyclic system bearing both a 14-â-hydroxy substituent and a substituent at C-17 capable of further transformation; and, finally, elaboration of that substituent to the â-oriented butenolide system. We chose to approach the construction of the tricyclic enone 2 via an intramolecular [4 + 2] cycloaddition, as schematized in Figure 1. We initiated the synthesis from the monoketal (-)-3, prepared by applying to the readily available (S)-enantiomer of the Wieland Miescher ketone,5 the sequence previously described6 using its racemate. Ozonolysis of the trimethylsilyl enol ether of 3 gave, in a not unprecedented reaction,7 a mixture of R-hydroxy ketones which was reduced (NaBH4) to the corresponding glycols, followed by cleavage with periodate to the dialdehyde 4 (71% overall yield from 3). The two aldehyde groups in 4 now had to be differentially elaborated.

78 citations


Cited by
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TL;DR: In this paper, the authors are grateful to the Spanish Ministerio de Educación y Ciencia, as well as to Generalitat Valenciana and University of Alicante, for their continuous financial support.
Abstract: We are grateful to the Spanish Ministerio de Educacion y Ciencia, as well as to Generalitat Valenciana and University of Alicante, for their continuous financial support.

366 citations

Journal ArticleDOI
TL;DR: In this article, the union of sodium borohydride and carboxylic acids has yielded an amazingly versatile and efficient set of reducing reagents, including acyloxyborohydride species.
Abstract: The union of sodium borohydride and carboxylic acids has yielded an amazingly versatile and efficient set of reducing reagents. These acyloxyborohydride species reduce and N-alkylate indoles, quinolines, isoquinolines, related heterocycles, imines, enamines, oximes, enamides, and similar functional groups. They reduce amides and nitriles, aryl alcohols and ketones, aldehydes in the presence of ketones, and β-hydroxyketones to 1,3-diols stereoselectively. This reagent is also extraordinarily useful for the N-alkylation of primary and secondary amines with aldehydes and ketones in a novel reductive amination process.

250 citations

Journal ArticleDOI
TL;DR: In this article, the authors stellten die Frage, welchen Stand die Totalsynthese von Naturstoffen erreicht hat, und geschildert, wie viel wir in der Wissenschaft der Totalsynthesis schon erreich haben, aber also, dass dieses Forschungsgebiet den Kinderschuhen gerade erst entschlupft.
Abstract: Ein neues Jahrtausend hat begonnen – Grund genug, sich die Frage zu stellen, welchen Stand die Totalsynthese von Naturstoffen erreicht hat. Dieser Aufsatz mochte eine Antwort geben, indem er die Entwicklung dieser chemischen Disziplin, die Aspekte von exakter Wissenschaft und schoner Kunst in sich vereint, von Anbeginn bis in die heutige Zeit beschreibt; es wird geschildert, wie viel wir in der Wissenschaft der Totalsynthese schon erreicht haben, aber auch, dass dieses Forschungsgebiet den Kinderschuhen gerade erst entschlupft.

112 citations