4-Hydroxy-3-methoxy-5-nitrobenzaldehyde (aka 5-Nitrovanillin, Isonitrovanillin) is a pharmaceutical intermediate that typically used in the preparation of Entacapone as a selective and reversible inhibitor of the enzyme catechol-O-methyltransferase (COMT) for the treatment of Parkinson's disease.
Biochemical and pharmacological properties of a peripherally acting catechol-O-methyltransferase inhibitor entacapone. 
Entacapone increases and prolongs the central effects of L-DOPA in the 6-hydroxydopamine-lesioned rat. 
Synthesis and antitumor activity of feruloyl and caffeoyl derivatives. 
Effect of entacapone on colon motility and ion transport in a rat model of Parkinson’s disease.