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Racemization of PZQ and PZQamine
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17th January 2011 @ 03:59
Racemization experiments of enantioenrichend S-(+)-PZQamine with Pd/C obtained from Multigram-scale racemic resolution of praziquanamine with (-)-Dibenzoyl-L-tartaric acid (MW49-13)

Scheme MW50-1.png

See also:
Racemization of S-(+)-PZQamine with Pd/C (MW50-4)
Racemization of S-(+)-PZQamine with Pd/BaSO4 (MW50-5)
Racemization of S-(+)-PZQamine with Raney Nickel (MW50-6, MW50-7)
Thiyl radical-mediated racemization of S-(+)-PZQamine (MW50-8)

Hazard and Risk Assessment:
HRAF MW50.pdf

Start time: 3:50 PM 17/01/2011
End time: 1:40 PM 18/01/2011

To a solution of S-(+)-PZQamine (50 mg, 248 µmol, MW: 202.3 g/mol) in toluene (5 mL) was added Pd/C (for 1% Pd: 2.62 mg, 2.48 µmol; for 5% Pd: 13.1 mg, 12.4 µmol; 10% Pd on charcoal, M.W. (Pd) 106.4 g/mol) and heated to 70°C for 3 / 22 h.
The catalyst was filtered off by a filter paper and the solvent was evaporated.

- almost complete amount of starting material was reisolated
- color of the starting material turned from pale yellow to yellow

Starting material S-(+)-PZQamine
[α]D20 = +170° (c=1, DCM)

1% Pd, 3 h
[α]D20 = +156° (c=1, DCM)

5% Pd, 3 h
[α]D20 = +131° (c=1, DCM)
Data: 1H NMR MW50-2.pdf
-> no decomposition / side reaction of the starting material

1% Pd, 2 h
[α]D20 = +152° (c=1, DCM)

- slow racemization of S-(+)-PZQamine with 1% Pd/C under the conditions stated above
-> increase of temperature and catalyst loading (5% Pd)

[1] "Fast racemization and dynamic kinetic resolution of primary benzyl amines", Y. Kim, J. Park and M.-J. Kim, Tetrahedron Letters 2010,51, 42, 5581-5584, (

[2] "Lipase/Palladium-Catalyzed Asymmetric Transformations of Ketoximes to Optically Active Amines", Y. K. Choi, M. J. Kim, Y. Ahn, and M.-J. Kim, Org. Lett. 2001, 3, 25, 4099–4101;
DOI: 10.1021/ol0168622
Attached Files
Scheme MW50-1.png
HRAF MW50.pdf
1H NMR MW50-2.pdf