Pictet-Spengler route to Praziquantel

 

Mnr: 1-10




Hazard and Risk Assessment:


Procedure:

To a stirring suspension of paraformaldehyde (2.73 g, 91.0 mmol), 2,2-dimethoxyethylamine (13.2 mL, 91.0 mmol) and benzoic acid (11.11 g, 91.0 mmol) in methanol (90 mL) at 0 °C was added 2-(3,4-Dimethoxyphenyl)ethyl isocyanide MNR4-2 (17.4 g, 91.0 mmol) dropwise and stirred at room temperature for 40 hours.

The reaction was concentrated and dissolved in EtOAc (150 mL) then washed with water (75 mL) and brine (75 mL) then dried over magnesium sulfate, filtered and concentrated under reduced pressure to give the crude as a yellow oil.

Crude :- 46.856 g

Column :- 50-100 % EtOAc/Hex

Frac 3-8 :- 36.126 g, 78.78 mmol, 87 %

Characterisation



As a 50:50 mixture of rotamers. Peaks not fully resolved at 300 K

1H NMR (500 MHz, CDCl3): d = 7.44-7.99 (m, 5H), 7.25 (br, NH), 6.84-6.66 (m, ,3H), 5.03 (br, 1H), 4.49 (br, 1H), 4.20 (br, 1H), 3.96 (br, 1H), 3.84 (s, 3H), 3.83 (s, 3H), 3.66-3.15 (m, 8H), 2.85-2.72 (m, 2H), 1.23-1.03 (m, 6H).



13C NMR (125 MHz, CDCl3): d= 173.1, 168.9, 168.7, 149.1, 147.7, 135.4, 131.3, 130.3, 129.8, 128.5, 128.2, 127.0, 126.8, 120.7, 111.9, 111.4, 101.0, 100.5, 64.0, 63.4, 62.0, 55.9, 55.9, 55.4, 55.3, 53.4, 53.3, 51.4, 51.2, 40.7, 35.2, 15.4


______________________________________________________________________
23/08/12
MNR10-3

Procedure:

To a stirring suspension of paraformaldehyde (3.38 g, 112.43 mmol), 2,2-dimethoxyethylamine (16.4 mL, 112.43 mmol) and benzoic acid (13.73 g, 112.43 mmol) in methanol (90 mL) at 0 °C was added 2-(3,4-Dimethoxyphenyl)ethyl isocyanide MNR4-5 (21.5 g, 112.43 mmol) in methanol (20 mL) dropwise and stirred at room temperature for 41 hours.

The reaction was then concentrated and taken up in EtOAc (200 mL) then washed with water (150 mL) and brine (150 ml) then dried over magnesium sulfate, filtered and concentrated under reduced pressure to give the crude as a yellow oil (49.47 g, 96%)

Due to the crude recovered being less than 100% the aqueous fractions were extraced again with EtOAc (200 mL), dried over magnesium sulfate, filtered and concentrated under reduced pressure to give more crude as a yellow oil (1.364 g, 2.87 mmol, 3%)

Total crude recovered - 50.834 g, 110.86, 99%

TLC of crude mixture run in 50% and 100% EtOAc/Hex


Crude taken on without further purification.