Sildenafil

phenylsulfonyl]-4-methylpiperazine 1-[4-ethoxy-3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo4,3-dpyrimidin-5-yl)
Sildenafil citrate, sold as Viagra, Revatio and under various other trade names, is a drug used to treat erectile dysfunction and pulmonary arterial hypertension (PAH). It was originally developed by British scientists and then brought to market by the US-based pharmaceutical company Pfizer. It acts by inhibiting cGMP-specific phosphodiesterase type 5, an enzyme that delays degradation of cGMP, which regulates blood flow in the penis. Since becoming available in 1998, sildenafil has been the prime treatment for erectile dysfunction; its primary competitors on the market are tadalafil (Cialis) and vardenafil (Levitra).
PDE5 Inhibitors 
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PDE5 Inhibitor 
 

Tadalafil

(6R-trans)-6-(1,3-benzodioxol-5-yl)- 2,3,6,7,12,12a-hexahydro-2-methyl-pyrazino 2':1,6 pyrido3,4-bindole-1,4-dione
Tadalafil is a PDE5 inhibitor, currently marketed in pill form for treating erectile dysfunction (ED) under the name Cialis; and under the name Adcirca for the treatment of pulmonary arterial hypertension. It initially was developed by the biotechnology company ICOS, and then again developed and marketed world-wide by Lilly ICOS, LLC, the joint venture of ICOS Corporation and Eli Lilly and Company. Cialis tablets, in 5 mg, 10 mg, and 20 mg doses, are yellow, film-coated, and almond-shaped. The approved dose for pulmonary arterial hypertension is 40 mg (two 20-mg tablets) once daily. Tadalafil is also manufactured and sold under the name of Tadacip by the Indian Pharmaceutical company Cipla in doses of 10 mg and 20 mg. On November 21, 2003 the Food and Drug Administration approved tadalafil (as Cialis) for sale in the United States as the third ED prescription drug pill. Cialis's 36-hour effectiveness earned it the nickname, "The Weekend Pill"; like sildenafil and vardenafil, tadalafil is recommended as an 'as needed' medication. Cialis is the only one of the three that is also offered as a once-daily medication. Moreover, tadalafil was approved in May 2009 in the United States for the treatment of pulmonary arterial hypertension and is currently under regulatory review in other regions for this condition. In late November 2008, Eli Lilly sold the exclusive rights to commercialize tadalafil for pulmonary arterial hypertension in the United States to United Therapeutics for an upfront payment of $150 million.
fast-acting PDE5 Inhibitor 
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Vardenafil

4-2-Ethoxy-5-(4-ethylpiperazin-1-yl)sulfonyl-phenyl-9-methyl-7-propyl-3,5,6,8-tetrazabicyclo4.3.0nona-3,7,9-trien-2-one
Vardenafil is a PDE5 inhibitor used for treating impotence that is sold under the trade name Levitra.

Udenafil

new PDE5 Inhibitor 
PDE5 Inhibitors and ED 
PDE5 Inhibitor drugs

3-(1-methyl-7-oxo-3-propyl-4,7-dihydro-1H-pyrazolo4,3-dpyrimidin-5-yl)-N-2-(1-methylpyrrolidin-2-yl)ethyl-4-propoxybenzenesulfonamide
Udenafil is a drug used in urology to treat erectile dysfunction. It belongs to a class of drugs called PDE5 inhibitor, which many other erectile dysfunction drugs such as sildenafil, tadalafil, and vardenafil also belong to. It was developed by Dong-A Pharmaceutical and is marketed under the trade name Zydena. It is not approved for use in the United States by the U.S.Food and Drug Administration.

Avanafil

2-(hydroxymethyl)-1-pyrrolidinyl-N-4-(3-Chloro-4-methoxybenzyl)amino-2-(2-pyrimidinylmethyl)-5-pyrimidinecarboxamide
Avanafil (dubbed as "Son of Viagra") is a PDE5 inhibitor being developed for erectile dysfunction. Avanafil currently has no trademarked term associated with it but it is being developed by Vivus Inc. It acts by inhibiting a specific phosphodiesterase type 5 enzyme which is found in various body tissues, but primarily in the corpus cavernosum penis, as well as the retina. Other similar drugs are sildenafil, tadalafil and vardenafil.

Sulfoaildenafil

5-(5-(((3R,5S)-3,5-Dimethylpiperazin-1-yl)sulfonyl)-2-ethoxyphenyl)-1-methyl-3-propyl-1H-pyrazolo4,3-dpyrimidine-7(4H)-thione
.Sulfoaildenafil (thioaildenafil) is a synthetic chemical compound that is a structural analog of sildenafil (Viagra). It was first reported in 2005, and it is not approved by any health regulation agency. Like sildenafil, sulfoaildenafil is a phosphodiesterase type 5 inhibitor. Sulfoaildenafil has been found as an adulterant in a variety of supplements which are sold as "natural" or "herbal" sexual enhancement products. A range of designer analogues of USA FDA-approved inhibitors of type-5 cGMP-specific phosphodiesterase (PDE5), such as sildenafil and vardenafil, have been detected in recent years as adulturants in over-the-counter herbal aphrodisiac products and dietary supplements, in an apparent attempt to circumvent both the legal restrictions on sale of erectile dysfunction drugs, which are prescription-only medicines in most Western countries, and the patent protection which prevents sale of these drugs by competitors except under license to their inventors. These compounds have been demonstrated to display PDE5 inhibitory activity in vitro and presumably have similar effects when consumed, but have undergone no formal testing in either humans or animals, and as such represent a significant health risk to consumers of these products due to their unknown safety profile. Some attempts have been made to ban these drugs as unlicensed medicines, but progress has been slow so far, as even in those jurisdictions which have laws targeting designer drugs, the laws are drafted to ban analogues of illegal drugs of abuse, rather than analogues of prescription medicines. However at least one court case has resulted in a product being taken off the market. In December 2010, the United States Food and Drug Administration (FDA) issued a warning to consumers about such products stating, "The FDA has found many products marketed as dietary supplements for sexual enhancement during the past several years that can be harmful because they contain active ingredients in FDA-approved drugs or variations of these ingredients."

Aildenafil

5-(5-(((3R,5S)-3,5-Dimethylpiperazin-1-yl)sulfonyl)-2-ethoxyphenyl)-1-methyl-3-propyl-1H-pyrazolo4,3-dpyrimidin-7(4H)-one
Aildenafil (methisosildenafil) is a synthetic chemical compound that is a structural analog of sildenafil (Viagra). It was first reported in 2003, and it is not approved by any health regulation agency. Like sildenafil, aildenafil is a phosphodiesterase type 5 inhibitor. Aildenafil has been found as an adulterant in a variety of supplements which are sold as "natural" or "herbal" sexual enhancement products. The United States Food and Drug Administration has warned consumers that any sexual enhancement product that claims to work as well as prescription products is likely to contain such a contaminant.

Lodenafil

bis-(2-{4-[4-ethoxy-3-(1-methyl-7-oxo-3-propyl-6,7-dihydro-1H-pyrazolo4,3-dpyrimidin-5-yl)-benzenesulfonyl]piperazin-1-yl}-ethyl)carbonate
Lodenafil is a drug belonging to a class of drugs called PDE5 inhibitor, which many other erectile dysfunction drugs such as sildenafil, tadalafil, and vardenafil also belong to. Like udenafil and avanafil it belongs to a new generation of PDE5 inhibitors. Lodenafil is formulated as a dimer, lodenafil carbonate, which breaks down in the body to form two molecules of the active drug lodenafil. This formulation has higher oral bioavailability than the parent drug. It is manufactured by Cristália Produtos Químicos e Farmacêuticos in Brazil and sold there under the brand-name Helleva . It has undergone Phase III clinical trials, but is not yet approved for use in the United States by the U.S. Food and Drug Administration..

Acetildenafil

5-[2-Ethoxy-5-2-(4-ethyl-piperazin-1-yl)-acetyl-phenyl]-1-methyl-3-propyl-1,6-dihydro-pyrazolo4,3-dpyrimidin-7-one
Acetildenafil (Hongdenafil) is a drug which acts as a phosphodiesterase inhibitor. It is a structural analogue of sildenafil (Viagra) which has been detected in numerous different brands of supposedly “herbal” aphrodisiac products sold to boost libido and alleviate erectile dysfunction. A range of designer analogues of legitimate PDE5 inhibitors such as sildenafil and vardenafil have been detected in recent years in over-the-counter herbal aphrodisiac products, in an apparent attempt to circumvent both the legal restrictions on sale of erectile dysfunction drugs, which are prescription-only medicines in most Western countries, and the patent protection which prevents sale of these drugs by competitors except under license to their inventors. These compounds have been demonstrated to display PDE5 inhibitory activity in vitro and presumably have similar effects when consumed, but have undergone no formal testing in either humans or animals, and as such may represent significant health risks to consumers of these products due to their unknown safety profile. Some attempts have been made to ban these drugs as unlicensed medicines, but progress has been slow so far, as even in those jurisdictions which have laws targeting designer drugs, the laws are drafted to ban analogues of illegal drugs of abuse, rather than analogues of prescription medicines. However at least one court case has resulted in a product being taken off the market.

Zaprinast

5-(2-Propoxyphenyl)-1H-1,2,3triazolo4,5-dpyrimidin-7(4H)-one
Zaprinast was an unsuccessful clinical drug candidate that was a precursor to the chemically-related PDE5 inhibitors, such as sildenafil (Viagra), which successfully reached the market. It is a phosphodiesterase inhibitor, selective for the subtypes PDE5, PDE6, PDE9 and PDE11. IC50 values are 0.76, 0.15, 29.0, and 12.0 μM, respectively.

Icariin

5-hydroxy-2-(4-methoxyphenyl)-8-(3-methylbut-2-enyl)-7-(2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yloxy-3-(2S,3R,4R,5R,6S)-3,4,5-trihydroxy-6-methyloxan-2-yloxychromen-4-one
Icariin is a flavonol, a type of flavonoid. It is the prenyl acetylation of kaempferide 3,7-O-diglucoside. The compound is derived from several species of plants in the Epimedium family, which are commonly known as Horny Goat Weed or Yin Yang Huo. Extracts from these plants are reputed to produce aphrodisiac effects, and are commonly used in Chinese herbal medicine to enhance erectile function, as well as for several other indications. It is thought that icariin is likely to be the primary active component of Epimedium extracts, as it has been shown to share several mechanisms of action with compounds used in Western medicine to treat impotence and improve sexual function. In particular, icariin has been demonstrated to act as a PDE5 inhibitor and to enhance the production of bioactive nitric oxide, as well as mimicking the effects of testosterone. It also shows antioxidant, antidepressant and nootropic effects in animal studies, as well as stimulating osteoblast activity in bone tissue which has been linked to a possible therapeutic role in the treatment of osteoporosis..

Mirodenafil

5-Ethyl-3,5-dihydro-2-[5-(4-(2-hydroxyethyl)-1-piperazinylsulfonyl)-2-propoxyphenyl]-7-propyl-4H-pyrrolo3,2-dpyrimidin-4-one
Mirodenafil is an experimental drug belonging to a class of drugs called PDE5 inhibitors, which many other erectile dysfunction drugs such as sildenafil, tadalafil, and vardenafil also belong to. Like udenafil, lodenafil and avanafil it belongs to a new generation of PDE5 inhibitors. It is not currently approved for use in the United States by the U.S. Food and Drug Administration, but clinical trials are being conducted..