The esters are generally more labile than amides and could be hydrolized with mild reaction conditions and low temperature.

The NH is the amine you want to acylate?

If it is, a possible solution as suggested by Alessandro is to acylate the NH, OH and carboxylic group and hydrolyse with a base (e.g. LiOH in THF/H2O) at rt, this conditiion should not affect the amide. The anhydride from the carboxylic acid may not even be stable to be isolated.

If it is not, then a lot more work is needed to distinguish the different amines.

Thanks Alessandro and Eugene 

Yes I want to acylate the NH group only 

Can I use stirring with dilute sodium hydroxide at room temperature?

NaOH will work too but usually you will need a water miscible organic solvent (THF, MeOH etc) to dissolve the reactant and water for the inorganic base.

K2CO3 will work with simple acetates too, it depends on the acylating group.

Carry this reaction in Dichloromethane-water,  preferably around 15deg, in the presence of Na2CO3.     

I would suggest you run the acylation in DCM-sodium carbonate solution, use about 1.2-1.4 eq of either acetyl chloride or anhydride  and 2-3 eq sodium carbonate. Acylation at NH is much favoured over OH, especially if it is phenolic, so you are unlikely to form much ester. Any ester will be hydrolysed in the reaction mixture anyway

Look for the Schotten–Baumann -method in phase transfer conditions. I don't remember the exact receipe but with the following system you could get an easy workup: Use toluene/water with calcium carbonate as base and a small amount of phase transfer catalyst. Mix with a magnetic stirrer and add the acyl chloride slowly. After the reaction has completed you can separate the layers simply by pipetting the lower aqueous layer off. If you distill off the toluene you get a dry target material.

http://www.tandfonline.com/doi/abs/10.1081/SCC-100000582

Other usefull way is ethylacetate / saturated NaHCO3 solution.

Potassium triphosphate will work perfect as it's not too strong base, yet enough to proceed the reaction in forward direction