In relation to my previous question on cysteine, I would like to thank everyone for answers.
However, it seems unfortunately that I'll have to protect the acid and the thiol in Cys also. Is anyone familiar with some procedure I could use to methylate both the acid and thiol in one shot?
I checked some examples on SciFinder, there were conversions of acid to methyl ester (with SOCl2 in MeOH). However, all the examples were aminoacids without thiol, including some unnatural ones - would the thiol also undergo alkylation if it was present?
I even found the method where CH3I is used with tetramethylguanidine in order to selectively alkylate only the thiol, but in that case the acid remains intact.
Could anyone give some suggestion? I'm considering using plain and simple CH3I with K2CO3 in MeOH or THF, but since I didn't find a single example, I'm really skeptical...
Would it be better to alkylate -COOH and -SH with previously Boc-protected Cys or do it on unprotected Cys instead?