Phenyl 2-Hydroxy-4-methoxy-5-sulfobenzoate-d5 is the isotope labelled analog of Phenyl 2-Hydroxy-4-methoxy-5-sulfobenzoate. Phenyl 2-Hydroxy-4-methoxy-5-sulfobenzoate is synthesized from 4-Methoxysalicylic acid which is a reagent for chloropyridine oxadiazoles as potential antitumor agents.