tree sap

[bimapras]

it will work.

[Musikmann]

There are 2 considerations: 1) What is the appropriate solvent and 2) Will it harm the leather.

Since sap is an organic substance (solute), you probably need an organic solvent. Try to identify the tree, and reseach it's sap. Once you find out a little about that, look for the proper solvent. Then, as already suggested, test it on an inconspicuous leather area.

I also agree the isoproanol is probably NOT a good choice. For one thing, it is polar, and I think you need a non-polar substance for an organic compound.