Three Dimensional modelled molecular structure of Sildenafil
Sildenafil, trade name
VIAGRATM, chemical name
5-[2-ethoxy-5-(4-methylpiperazin-1-ylsulfonyl)phenyl]-1-
methyl-3-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one, formula
C22H30N6O4S, was discovered
through a rational drug design programme by the pharmaceutical company
Pfizer. It is a potent selective inhibitor of the enzyme phosphodiesterase (PDE-5), which destroys cyclic guanosine monophosphate (cGMP), itself a
dilator of blood vessels in the body. Viagra thus allows cyclic GMP to
persist and this property has led to its use for the oral treatment of male
erectile dysfunction (N. K. Terrett, A. S. Bell, D. Brown, P. Ellis
Bioorganic & Medicinal Chem. Lett., 1996, 6,
pp.1819-1824). It is adminstered as the citrate.
The structures below were modelled using a program called Chem3D from CambridgeSoft, using molecular
mechanics (MM2) and quantum mechanics (AM1, PM3) methods. In all cases, the
6-H tautomer was found to be lower in energy than the 4-H isomer by about 4-8 kcal/mol. To view these
models, you will need to install a browser plug-in such as Chime or Chem3D Net.
(c) H. S. Rzepa, May 4, 1998. All rights reserved.