to give the isoquinoline rather than requiring a separate reaction to convert a dihydroisoquinoline intermediate. In a Pictet–Spengler reaction, a condensation of a β-phenylethylamine and an aldehyde forms an imine, which undergoes a cyclization to form a tetrahydroisoquinoline instead of the dihydroisoquinoline. In enzymology, the (S)-norcoclaurine synthase () is an enzyme that catalyzes a biological Pictect-Spengler synthesis: Intramolecular aza Wittig reactions also afford isoquinolines. Applications of derivatives Isoquinolines find many applications, including: anesthetics; dimethisoquin is one example (shown below). antihypertension agents, such as quinapril and debrisoquine (all derived from 1,2,3,4-tetrahydroisoquinoline). antiretroviral agents, such as saquinavir with an isoquinolyl functional group, (shown below). vasodilators, a well-known example, papaverine, shown below. Bisbenzylisoquinolinium compounds are compounds similar in structure to tubocurarine. They have two isoquinolinium structures, linked by a carbon chain, containing two ester linkages. In the human body Parkinson's disease, a slowly progressing movement disorder, is thought to be caused by certain neurotoxins. A neurotoxin called MPTP (1[N]-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), the precursor to MPP+, was found and linked to Parkinson's disease in the 1980s. The active neurotoxins destroy dopaminergic neurons, leading to parkinsonism and Parkinson's disease. Several tetrahydroisoquinoline derivatives have been found to have the same neurochemical properties as MPTP. These derivatives may act as precursors to active neurotoxins. Other uses Isoquinolines are used in the manufacture of dyes, paints, insecticides and antifungals. It is also used as a solvent for the extraction of resins and terpenes, and as a corrosion inhibitor. See also Eletefine (1998), an isoquinoline alkaloid. Naphthalene, an analog without the nitrogen atom. References External links Simple aromatic rings