Recrystallization of PZQ

Published by RyanPakula on 20 October 2009 - 2:34am

This page details attempts to optimise the recrystallization of praziquantel. Anybody can add to/edit this page.
1. This patent (US patent 4,523,013) recrystallizes PZQ from "a mixture of petroleum ether and acetone," obtaining a 95% yield on the reaction.
2. This paper recrystallizes from ethyl acetate and hexanes to obtain a 70% yield on the reaction.
The best system the Todd lab has observed for the recrystallization of racemic praziquantel, as of Oct. 26, 2009, is the following:
Praziquantel is dissolved in a minimal amount of 50 ± 2ºC ethanol (solubility ca. 190 mg/mL; some results as high as 240 mg/mL; comfortably, 200 mg PZQ/mL 50ºC EtOH). This solution is allowed to cool to rt, and is left at 5ºC overnight before filtration, rinsing the crystals minimally with 5ºC EtOH. After drying under high vacuum, purity can be determined by melting temperature (138-139ºC, ref. RyanPakula blog, supporting NMR spectra coming soon) and proton NMR spectroscopy (CDCl3 works well).


quintus's picture

This is a very insoluble compound in ethanol. Is this absolute ethanol or denatured? How many polymorphs have you observed? For the FDA MPt is not a criteria of purity, you will need a HPLC system.
The variation in solubility may suggest some impurity, therefore a hot filtration should be included.