Synthesis Communications, Oct, 1978 p. 766
Reactions of Sodium Borohydride in Acidic Media; N-alkylation of aliphatic secondary amines with carboxylic acids
By Gribble, Jasinsky, Pellicone, Panetta @ Dartmouth College
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Uses NaBH4 to repace the OOH if COOH with a secondary amine. Seemed like it might be useful if it hasnt been posted here before...

There is some info about that to be found in

https://www.thevespiary.org/rhodium/Rhodium/pdf/nabh4.carboxylic.acids.pdf