Selective Esterification of Amino Acid

I am going to prepare tert-butyl protected threonine. I was going for the classic esterification methodology which is acid catalyzed (sulfuric acid) esterification under reflux of tert butyl alcohol + threonine. My worry is that the -OH r group of threonine will also be esterified. My lab has very few reagents. We don't have TMSCI, silicone, amberlyst or carbodiimide. Does any of you have any suggested methods using tert butyl alcohol? 


Thank you!


