Racemic Resolution of Praziquantel and Praziquanamine

 

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



Hazard and Risk Assessment:


Procedure:
rac-PZQ (13.0 g, 41.6 mmol) was dissolved in a mixture of EtOH (80 mL) and 1M HCl (420 mL(85 mL in 1 L)) and heated to reflux for 15 h. The solution was allowed to cool to room temperature then cooled in an ice bath, basified with NaOH pellet (approx 22 g, pellets used to minimise volume of aqueous material) to pH 12-13 and extracted with DCM (4 x 150 mL). The organic fractions were combined, dried over magnesium sulphate, filtered and concentrated under reduced pressure to give a clear oil which was placed on the high vac for 4 hours by which time the oil had crystallized into white crystals.

* something went wrong with the reaction during the night. Power had tripped in the fumehood. By the looks of things, I'd say the heating mantle has overheated and the reaction has bumped (quiet violently) out the top of the condenser (which had an additional air condenser on top) and water has tripped the power on coming in contact with the mantle. It's unclear how much material has been lost but there was a sticky residue all over the base of the fumehood. This is unusal as the reaction had been monitored for 5 hours before leaving the lab for the night.

Crude - 6.675 g, 79 %

Recrystallized in toluene:hexane (60:6 mL) and left in the freezer overnight. Crystals filtered off in the morning and washed with hexane.

Off white/pale orange crystals:- 5.372 g, 64 %

1H NMR MNR7-5

The washing were concentrated and allowed to crystallise in the freezer over the weekend.