[91jga1612]

I have been attempting to synthesise a sensor compound containing cyclen ( 1,3,7,10 tetraazododecane) coupled to a pyrene unit through a methylene bridge.

To do the reductive amination of pyrenecarboxaldehyde and cyclen, three of the nitrogens need to be protected, so I use Boc gorups through a protection step. After the coupling, and purification through silica column, a deprotection step is undertaken.

The deprotection step is carried out in a 1:1 mix of TFA and DCM. Upon stirring for 5/10 mins, a green/brown precipitate forms (suspected TFA salt with product) which is entirely insoluble in DCM, MeOH, H2O, MeCN or DMSO. I have tried a base wash, Et3N and NaOH in turn, still no luck in becoming more soluble. It is the product, as a tiny bit was NMR'd after sonication in CDCl3 for over two hours.

I have tried other methods for deprotection, MeOH/HCl but it seems to create a mess in the NMR.

Has anyone got any ideas on the reason for insolubility of this cyclen moiety?

Thanks