Use of natural aminoacids as efficient green catalyst in the synthesis of thiosemicarbazones

Author : Urbain C. Kassehin, Odilon Q. ASSAN, Fernand A. Gbaguidi, Julien R. C. Prevost, Raphael Frederick, and Jacques H. Poupaert

In an effort to find improved conditions for the synthesis of medicinally relevant thiosemicarbazones basing our approach on green chemistry approach, we used ten natural alpha aminoacids as nucleophilic catalysts.We therefore hypothetized that aminoacid acid being amphoteric reagent, should be able to boost a reaction submitted to general acid-base catalysis. Using cyclohexanone 4-phenylthiosemicarbazone as target compound for our benchmark reaction, we were able to demonstrate the validity of our hypothesis. A plot of “hydrophobicity/lipophilicity” balance as reflected by logP and the net actual yield does not show any significant correlation, however it is remarkable to note that while L-phenylalanine shows opposite behavior in water (94%) and methanol (24%), glycine – the most concise alpha-amino-acid – performs equally very well in both solvents (95% and 90%, respectively). These green catalysts and specially glycine may be useful in the elaboration of a compound library.

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