What are you hoping to protect with? Are you using a Fmoc or Boc stategy? Is this for solid phase synthesis?

One strategy would be to simply purchase something like Fmoc-Gln(Trt)-OH, which is orthogonally protected, where the alpha amine is protected with base labile Fmoc, and the R-group amine is protected with the acid labile trityl group. A perfunctory search shows that the above protected amino acid goes for about $50 / 5g to $260 / 100g. 

Dear Grant Simpson,

Thanks a lot for your response. Actually, I want to convert alpha amine into isonitrile group. but while this process R-group amine gets convert in nitrile simultaneously. I will try with Trt protected glutamine. Thanks for your suggestion.