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Concept
Strychnine total synthesis
Résumé
Strychnine total synthesis in chemistry describes the total synthesis of the complex biomolecule strychnine. The first reported method by the group of Robert Burns Woodward in 1954 is considered a classic in this research field.
At the time it formed the natural conclusion to an elaborate process of molecular structure elucidation that started with the isolation of strychnine from the beans of Strychnos ignatii by Pierre Joseph Pelletier and Joseph Bienaimé Caventou in 1818. Major contributors to the entire effort were Sir Robert Robinson with over 250 publications and Hermann Leuchs with another 125 papers in a time span of 40 years. Robinson was awarded the Nobel Prize in Chemistry in 1947 for his work on alkaloids, strychnine included.
The process of chemical identification was completed with publications in 1946 by Robinson and later confirmed by Woodward in 1947. X-ray structures establishing the absolute configuration became available between 1947 and 1951 with publications from Johannes Martin Bijvoet and J. H. Robertson
Woodward published a very brief account on the strychnine synthesis in 1954 (just 3 pages) and a lengthy one (42 pages) in 1963.
Many more methods exist and reported by the research groups of Magnus, Overman, Kuehne, Rawal, Bosch, Vollhardt, Mori, Shibasaki, Li, Fukuyama Vanderwal and MacMillan. Synthetic (+)-strychnine is also known. Racemic synthesises were published by Padwa in 2007 and in 2010 by Andrade and by Reissig.
In his 1963 publication Woodward quoted Sir Robert Robinson who said for its molecular size it is the most complex substance known.
The C21H22N2O2 strychnine molecule contains 7 rings including an indoline system. It has a tertiary amine group, an amide, an alkene and an ether group. The naturally occurring compound is also chiral with 6 asymmetric carbon atoms including one quaternary one.
The synthesis of ring II was accomplished with a Fischer indole synthesis using phenylhydrazine 1 and acetophenone derivative acetoveratrone 2 (catalyst polyphosphoric acid) to give the 2-veratrylindole 3.
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