InChI is great and all, but today while exploring, I found two issues that bugged me. The first arose from my simple double-checking exercise: I drew praziquantel at http://pubchem.ncbi.nlm.nih.gov/edit/ then took the InChI returned and plugged it into chemspider.com to see if it would bring up the appropriate page for PZQ (which I already knew existed). I made the mistake of leaving one of the amide nitrogens as a carbon, so my search on chemspider returned that there were no hits at all. Now, in this case that's fine, cause I messed u
The sulfur melt dehydrogenation,
was carried out, with 9.5% isolated yield of the desired product and 69.3% recovered starting material. Other products (observed by TLC) were not found after the column.
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Trying to dehydrogenate PZQ using elemental sulfur.
Total yields including second batch of recrystallization are 86.4%, 74.34% (no second batch), 78.7%, and 80.1%, respective to 0x, 0.5x, 1x, and 2.5x hexanes volume to ethanol volume.
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Methods for the purification of PZQ can be collated here.
Literature
1. This paper describes the purification of enantiopure PZQ using "chloroform/methanol 0–0.3% MeOH as a solvent system."
2. This paper uses 1:1 EtOAc/petroleum ether ramping to pure EtOAc.
3. This paper uses "thick layer preparative chromatography [prep TLC] benzene/ethyl acetate 1/1, silica gel."
This page details attempts to optimise the recrystallization of praziquantel. Anybody can add to/edit this page.
Literature
1. This patent (US patent 4,523,013) recrystallizes PZQ from "a mixture of petroleum ether and acetone," obtaining a 95% yield on the reaction.
2. This paper recrystallizes from ethyl acetate and hexanes to obtain a 70% yield on the reaction.
EtOH with hexanes had wispy crystals; recovery was 43.98%; pure by NMR; Tm = 138.2-138.8ºC. No crystals had formed from benzene sl'n nor toluene, so hexanes were added, and vials left at 5ºC. Began EtOH with varying amounts of hexanes recrystallizations.
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1 mL hexanes was added to the solution of benzene (1.4 mL), and 2 mL hexanes were added to the toluene solution (3 mL). After a few hours at 5ºC, crystals have begun to form.
59.27% PZQ was recovered from ethanol heated to 50 ± 2ºC. NMR was clean, Tm = 138.3 - 138.6ºC.
Began recrystallizations with water, ethanol, 50/50 water/ethanol, toluene, and benzene.
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Toluene worked less-than-nicely for recrystallization, and a column to isolate the yellow/brown product failed. This is likely due to the fact that a crude NMR of this product looks 99% identical to PZQ from the bottle.
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