Racemic Resolution of Praziquantel and Praziquanamine

 

Preparation of starting material for a scaled-up racemic resolution of PZQamine

Following the optimized conditions for rac-PZQ: see Optimizing the acid cleavage conditions II



Hazard and Risk Assessment:
Data: HIRAC MW2

Start time: 3:30 PM 3/11/2010
End time: 9:15 AM 4/11/2010


Procedure:
rac-PZQ (20.0 g, 64.0 mmol) was dissolved in a mixture of EtOH (150 mL) and 1N HCl (600 mL, 53.0 mL of 11.3 N HCl solution (35%) in 547 mL water) and heated to reflux for 18 h. Reaction monitored by TLC showed a complete consumption of PZQ (TLC, EA/hexane 1:1, Rf = 0.15 for PZQ)

work-up: cooled solution basified NaOH solution (5 N) to ph 13, extracted with DCM (4 x 30 mL), washed with brine, dried over NaSO4, evaporated.
Crude Yield: 16.2 g (80.1 mmol, 125%) pale yellow liquid - dry it in high vac.

Notes:
Reaction time can be reduced to 8-10 h under reflux conditions. TLC spot which has a similar Rf value as the starting material comes from a side product.
The main side product is ethyl cyclohexanecarboxylate with has an odor of pineapple and can be removed by an extraction (with EtOAc or DCM) of the acidic aq. solution, also most of the yellow stain can be removed in this extraction step.
Colorless PZQamine stains yellow after standing a while in the light at room temperature.