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18th January 2011 @ 04:47
Varying conditions of the previous experiment Racemization of S-(+)-PZQamine with Pd/C (MW50-1 to MW50-3)

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 (MW50-1 to MW50-3)
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: 4:20 PM 18/01/2011
End time: 4:50 PM 19/01/2011

To a solution of S-(+)-PZQamine (50 mg, 248 µmol, MW: 202.3 g/mol) in toluene (5 mL) was added Pd/C (13.1 mg, 12.4 µmol, 0.05 eq.; 10% Pd on charcoal, M.W. (Pd) 106.4 g/mol) and heated to 90°C for 24 h.
The catalyst was filtered off by a filter paper and the solvent was evaporated.

Yield: 47 mg of a yellow solid reisolated
[α]D20 = +146° (c=1, DCM)

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

Results:
- slow racemization of S-(+)-PZQamine even with 5% Pd/C

-> Pd/C is not a suitable catalyst for the racemization of PZQamine
-> screening other catalysts like Pd/BaSO4, Pd/CaCO3, Raney nickel



References:
[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, (http://dx.doi.org/10.1016/j.tetlet.2010.08.050)
[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