Racemic Resolution of Praziquantel and Praziquanamine

 

RXN 013 - Enantiopure R-PZQamine (MNR3-2) is converted to R-PZQ (MNR1-3).




Hazard and Risk Assessment:

As for MNR1-1

To a cooled solution of R-Praziquanamine (MNR3-2, 3.88 g, 18.99 mmol) in DCM (95 mL) at 0°C was added triethylamine (3.97 mL, 28.48 mol) and cyclohexanecarbonyl chloride (2.79 mL, 20.89 mmol). The solution was stirred overnight at room temperature.

The solution was quenched with water (25 mL) and stirred for a further 30 min. The layers were separated and the organic layer was washed with saturated sodium carbonate solution (50 mL), 0.5 M HCl (50 mL) and brine (50 mL). Dried over magnesium sulfate, filtered and concentrated under reduced pressure.

Crude as a yellow oil; 4.61 g.

The crude oil was purified by FCC (30-100% EtOAc/hexane) to give a pale yellow oil that turned into a foam under high vacuum. The foam was recrystallized in 50% acetone/hexane and crystals were filtered off and rinsed with hexane after standing in the freezer overnight.

1H NMR MNR9-1 in CDCl3
1H NMR MNR9-1 in MeOD
VT NMR of MNR9-1 in CDCl3 Improved resolution in areas but loss in other areas with temperature.


**ee determined by chiral HPLC, 99.9 %

HPLC trace for MNR9-1



HPLC trace for rac-PZQ



HPLC trace for MNR1-3 :- N-Cyclohexanoyl-protection of MNR2-3 to give S-PZQ (MNR1-3)



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Checking the purity of the samples after sitting in the fridge for over 1 year.

HPLC conditions - Chiralcel OD-H column, IPA:Hex:TEA (40:60:0.1), flow rate 0.6 ml/min

Note - the conditions have changed slightly from above as the HPLC has had a new pump fitted as the previous one was giving unreliable flow rates.

rac-PZQ - the peak at 12.8 mins is some contaminant in the system as it was showing up on blank runs and was much larger on early runs. multiple blanks runs reduced the peak to what is seen here.



MNR9-1 - ee 99%