開了一下超距離搜索雷達, 探測到幾個可能的目標.

competitive inhibitors of PDE5
http://en.wikipedia.org/wiki/Sildenafil
http://en.wikipedia.org/wiki/Vardenafil
http://en.wikipedia.org/wiki/Tadalafil

http://en.wikipedia.org/wiki/CGMP_s...esterase_type_5
Action of PDE5

PDE5 is an enzyme that accepts cGMP and breaks it down. The kinetics of binding [3H]sildenafil and [3H]tadalafil to the catalytic site of PDE5.

Both inhibitors bind with high affinity and specificity, and cGMP binding to the allosteric sites stimulates binding of PDE5 inhibitors at the catalytic site. The kinetics of inhibitor binding and inhibition of catalysis imply the existence of two PDE5 conformers, and results of native gel electrophoresis reveal that PDE5 exists in two apparently distinct conformations, i.e., an extended conformer and a more compact conformer.

PDE5 activity is modulated by a rapidly reversible redox switch. Chemical reduction of PDE5 relieves autoinhibition of enzyme functions; allosteric cGMP-binding activity is increased 10-fold, and catalytic activity is increased ~3-fold. The redox effect on allosteric cGMP-binding occurs in the isolated regulatory domain. A change in the state of reduction of PDE5 or the isolated regulatory domain is associated with an apparent conformational change similar to that caused by phosphorylation.

PDE5 is expressed in human colonic cells and in intestinal tissue and its activity is regulated by intracellular cGMP levels in these cells that increase on GCC activation. This presumably occurs through binding of cGMP to the GAF domains in the N-terminus of PDE5, resulting in allosteric activation of the enzyme.

The mechanism of action of E4021 on both the nonactivated and activated forms of rod PDE6 because both states are relevant to understanding how PDE5-selective inhibitors may alter signal transduction pathways in photoreceptor cells. PDE5-selective inhibitors may show good discrimination of PDE5 from most other PDE isoforms.

PDE5 Inhibiting Drugs
There are now three oral ED drugs; Viagra, (sildenafil) by Pfizer; Levitra (vardenafil) by Bayer Pharmaceutical and Glaxo-Smith-Kline-Beecham/ Schering Plough; and Cialis (tadalafil) by LillyICOS.

The dilemma: which drug to choose and why.
For all practical purposes, these drugs including Viagra, Levitra, and Cialis are the first line of oral treatment for males with erectile dysfunction. In certain circumstances in which the males are young, no comorbidities are recognized, and laboratory tests are normal one should look for the etiology of their erectile dysfunction before instituting treatment since the disease process may be more serious than the symptoms, i.e., the ED itself. In some cases, treatment of the primary disease may in fact resolve the sexual dysfunction. However, most men have a cause for their ED as noted by the history and physical examination and the laboratory tests and PDE-5 inhibitors are the first line of choice.


http://en.wikipedia.org/wiki/Phosphodiesterase
The cyclic nucleotide phosphodiesterases (PDE) comprise a group of enzymes that degrade the phosphodiester bond in the second messenger molecules cAMP and cGMP. They regulate the localization, duration, and amplitude of cyclic nucleotide signaling within subcellular domains. PDEs are therefore important regulators of signal transduction mediated by these second messenger molecules.

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