[uglepik]

I got my hand on this little amino acid and wanted to couple it to my growing peptide. However, it behaved oddly, dissolved poorly in DMF and after a 1 hour coupling (having dissolved the amino acid, HBTU/HOBt and DIPEA in DMF:DCM 2:1) I got a highly positive Kaiser test. I don't get it. So, if any one of you guys have experience with coupling of this amino acid in regular Fmoc SPPS, I have a few questions.

1. Why is it supplied as the CHA (cyclohexaneamino) salt and not as the free acid?

2. Which solvent do you use for coupling?

3. Are certain coupling reagents better suited than other for this AA?

4. I read somewhere that boc-protecting group on the imidazole side-chain is labile to prolonged exposure to piperidine. What's your experience?

All advice on this is very welcome!