Disclosed is a method of preparing a thiohydrazide product compound from a hydrazide starting compound. The hydrazide starting compound is represented by Structural Formula (I): The thiohydrazide product compound is represented by Structural Formula (II): In Structural Formulas (I)-(II), R1 and R2 are independently an aliphatic group, a substituted aliphatic group, an aryl group or a substituted aryl group, or R1 and R2 taken together with the carbon and nitrogen atoms to which they are bonded, form a non-aromatic heterocyclic ring optionally fused to an aromatic ring. When R2 is an aryl group or a substituted aryl group, then R5 is a hydrazine protecting group; and when R2 is an aliphatic or substituted aliphatic group, then R5 is —H or a hydrazine protecting group. R10 is —H or a substituted or unsubstituted alkyl group. The method comprising the step of reacting the starting compound with a thionylating reagent.