Racemic Resolution of Praziquantel and Praziquanamine

 

Preparation of MNR34-1 - Step 1 in the alternative route to MNR26





Hazard and Risk Assessment:
MNR35

Procedure

To a solution of MNR34-1 (8.0 g, 31.04 mmol) in toluene (75 ml) was added 2,2-Diethoxyethylamine (7.61 mL, 62.09 mmol), and the mixture was heated to reflux for 2 hours during which time the reaction mixture turned black.

TLC after 2 hours at reflux, ran in 100% EtOAc. Spot at same rf as SM but it appeared to stain differently.

The reaction was then cooled to 0 °C - no solid formed as in the literature so the organic layer was washed with water (50 mL x3,)dried, filtered and concentrated to give the crude amine as a dark brown oil

3.932 g

The aqueous layer was then back extraced with EtOAc (100 mL x 3), the organic layers combined, dried, filtered and concentrated to give more crude amine as the NMR's were identical.

5.47 g

Total recovered - 9.402 g.

The crude was then taken up in DCM (50 mL) and treated with HCl.Et2O. A brown sticky solid (like vegemite) formed which was a total nightmare to deal with. No white salt formed.

Everything left overnight.

Everything was concentrated to dryness to give the dark brown sticky oil that was insolubale in almost everything. EtOAc (100 ml) was added and NaOH (6M) (75 mL). Most of the oil went into solution and the layers were separated. The aqueous layer was then extracted with EtOAc (100 mL x 4) then the organic layers were combined, dried, filtered and concentrated.

Column chromatography of this 20% MeOH/EtOAc + 0.5 % TEA

Frac 7- 13 - 2.238 g as a yellow/off white foam

Frac 26-45