Dear All,
This is my very first post to research gate, I hope to have a good journey with the experts.
I am trying to form a link (bond) between my biopolymer containing amine (positive charged) as lysine with the aldehyde (negative charged) group of another polysacchride by using cyanoborohydride as a catalyst.
My polysacchride contains another negatively charged SO3H group, and I fear during the reaction SO3H form interaction with amine of lysine.
condition of my reactions are acidic.
I am not sure whether the charge interaction between sulfonic group and amine is possible. and if it is, how can i avoid it?
From what you describe it sounds like you are actually doing a reductive amination between amine and aldehyde - imine (Schiff base) formation is the first step of this, but by adding the cyanoborohydride you reduce the imine to an amine. It's not purely based on charge interaction, but a nucleophilic attack of the amine on the partially positively charged center on the aldehyde. So your sulfonate group shouldn't interfere with it. If you only apply the borohydride in catalytic amounts, it will not work though. You need at least a little excess. In addition, your reaction conditions should only be mildly acidic to activate the carbonyl group but not completely protonate the amines (which would render them non-nucleophilic).
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Christina Nadler Thanks.
You got it right about the reductive amination. Since my biopolymer is insoluble in organic solvent, I had to use aqueous buffer of citrate-phospahte of pH=3. Use of higher pH, even 4, makes it difficult to dissolve my polymer.
What if I decrease the concentration of polymer solution to make it soluble at pH=4. Will it have any effect on my reaction.
" imine (Schiff base) formation is the first step of this, but by adding the cyanoborohydride you reduce the imine to an amine"
When should I add sodium cyanoborohydride if not in the beginning.
Thanks again for your support.
Cyanoborohydride is normally added from the beginning, I meant "because you add..." with "by adding...". Generally it is adviced to have a pH between 4 and 5, but it depends on your amine and aldehyde. A quick search showed that it seems to be possible to do it on lysines around pH 3 as well as at basic pH, as in attached paper. In this paper they are trying to push towards N-terminal amine preference over side chain lysine though, but it might be still interesting for you.
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