What are the rough pKa values of the two amine groups in carbidopa?  Do these amines form a diamine or are they seperate aliphatic amines?  I presumed they would have average pKa values for primary (9.4) and secondary amines (10.7), however drugbank says the most basic group in carbidopa has a pKa of around 5.6.  I am not sure how either of the amines have a pKa value of around this unless both of them being bonded has an effect.

Any responses would be greatly appreciated as this is help for an assignment due very soon.  Many thanks,

Tom.

I fear my answer might come to late for your assigment, but I will post it anyways in case you still need it or anyone else is interested in the answer. I guess the pka you got from drugbank is right, as you have to see the drug as a hydrazine, not as a amine. Hydrazine is a weaker base (and therefore a stronger acid) than ammonia because of the nitrogens -I-Effect on each other.