Is it a plant compound or a synthetic one? Depends a lot. If you have a plant isolated compound, you can do preliminary screening and find out the nature of that compound through qualitative chemical tests.Then you can plan whether you really need to do a HPLC analysis or other techniques like TLC, HPTLC or spectroscopic structural determination would be better. And if you have synthesized a new compound from some other methods like organic synthesis, then a lot depends on the reactants and the product you are expecting out of the reaction.