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Short Paper | Regular issue | Vol 94, No. 1, 2017, pp.122-130
Published online, 5th December, 2016
DOI: 10.3987/COM-16-13606
One-Pot Palladium-Catalyzed Racemization of (S)-Praziquanamine: A Key Intermediate for the Anthelmintic Agent (R)-Praziquantel

Zhezhou Yang, Xiang Guo, Shanghu Xu, Huirong Jiao, Zhinmin Tan, and Fuli Zhang*

*Shanghai Institute of Pharmaceutical Industry, China State Institute of Pharmaceutical Industry, 285 Gebaini Road, Shanghai 201203, China

Abstract

An one-pot palladium-catalyzed procedure for racemization of (S)-praziquanamine, which is the undesired enantiomer and produced during the resolution step for preparing the anthelmintic drug (R)-praziquantel, has been developed through dehydrogenation of (S)-praziquanamine into 6,7-dihydro-4H-pyrazino[2,1-a]isoquinolin-4-one and then hydrogenation of the double bonds. And a superior racemization method was also developed that (S)-praziquanamine was directly treated with Pd/C under H2 atmosphere to obtain a racemic mixture in quantitative yield with 95% chemical purity. Such a concise and efficient approach to the racemization of (S)-praziquanamine can be useful to recycle the waste enantiomer into the resolution process to obtain the (R)-enantiomer on a large scale.