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7th April 2011 @ 09:19
Racemization experiments on enantioenrichend (S)-(+)-PZQamine with Rhodium on charcoal

Scheme MW50-8.png

See also:
Racemization of S-(+)-PZQamine with Pd/C (MW50-1 to MW50-3)
Racemization of S-(+)-PZQamine with Pd/C (MW50-4)
Racemization of S-(+)-PZQamine with Raney Nickel (MW50-6, MW50-7)
Thiyl radical-mediated racemization of S-(+)-PZQamine (MW50-8)
Racemization of S-(+)-PZQamine (MW50-9) and (R) -(-)-PZQ (MW55-5) with sodium naphthalide
Repetition: Racemization of S-(+)-PZQamine (MW50-10) and R -(-)-PZQ (MW55-6) with sodium naphthalide
Racemization of S-(+)-PZQamine with Raney Nickel under high pressure and high temperature (MW50-11)

Hazard and Risk Assessment:
HRAF MW50.pdf

Start time: 7:00 PM 7/04/2011
End time: 10:00 AM 11/04/2011

To a solution of enantioenrichend (S)-PZQamine (20 mg, 98.9 µmol, MW: 202.3 g/mol) in toluene (2 mL) was added Rhodium/Charcoal (10.2 mg, 9.89 µmol, 0.1 eq.; 10% Rh on C, M.W. (Rh) 102.9 g/mol) and heated to 70°C for 4 days.
The mixture was filtered and evaporated under reduced pressure to give 18.8 mg of PZQamine.

TLC (ethyl acetate/methanol/triethylamine, 1:1:0.02, stain: ninhydrin)
TLC MW50-12.jpg

Data: 1H NMR MW50-12.pdf: PZQamine /no side products visible
[α]D20 = +98° (c=1, DCM)

-> Racemization ?! (it's not clear if the lower [α] is a result of a reacemization or lower concentration of (S)-PZQamine caused by solvent impurities/ other impurities)

-> Repeat a scaled-up reaction with an higher catalyst load, longer reaction time and higher temperature, see: Repetition: Racemization of (S)-PZQamine (MW50-13) with Rh/C
Attached Files
Scheme MW50-8.png
1H NMR MW50-12.pdf
1H NMR MW50-12 JCAMP-DX.dx
TLC MW50-12.jpg