Puzzled over MS

27 Dec
Published by KatB

Subject 

Rants, Miscellaneous

Background
Relevant experiment.  Basically, the Pictet-Spengler to form 3 PZQ analogues and PZQ itself.
The mass spec is of a by-product of the acid mediated PS cyclisation of MNR10-1 to form KAB8-1, aka the dimethoxy N-benzoyl PZQ analogue.

 There was a significant amount of it (~700 mg).  It went from red goop to red crystals after I'd left it alone in the flask for 20 minutes or so - this was during the work up of KAB8-1.
 
Problem
The identity of the peak at  m/z = 441 has been eluding me for the last couple of weeks.  I've tried combinations of known intermediates(?) of the PS reaction, such as these three: 
 

 
I've been focussing on 441, because it's so close to the expected m/z of M + Na of 389.4 (peak at 921, dimer?).  Note: the hemiaminal (3rd from the left) with Na is 407.4 and I think that's the closest I could get. 
 
Any help would be much appreciated!

Comments

MatTodd's picture

Hmm. Make it simple for us. Edit your diagram of possibles to include the m/z expected for each of those species with H+, Na+ and K+ in turn. What's the expected mass - include that too? But you think that this red stuff is not product? It's different from product by TLC? And what have you considered for the big dimer-looking peak?
 
AND, what have the mass specs looked like of similar molecules? If you take a MS of PZQ or a different analog, does it behave similarly? Do you have an NMR spectrum? IR?