Sep 012017


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Route to Benzimidazol-2-ones via Decarbonylative Ring Contraction of Quinoxalinediones: Application to the Synthesis of Flibanserin, A Drug for Treating Hypoactive Sexual Desire Disorder in Women and Marine Natural Product Hunanamycin Analogue

 Division of Organic Chemistry, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
 Academy of Scientific and Innovative Research (AcSIR), New Delhi 110 025, India
ACS Omega, 2017, 2 (8), pp 5137–5141
DOI: 10.1021/acsomega.7b00819
*E-mail: Phone: +91-20-2590 2445 (D.S.R.).

ACS AuthorChoice – This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.


Benzimidazol-2-ones 1 are an important class of heterocycles and a privileged scaffold in medicinal chemistry. They consist of cyclic urea fused with the aromatic backbone, which can potentially interact in a biological system by various noncovalent interactions such as hydrogen bonding and π stacking. Benzimidazolone derivatives exhibit a wide range of biological activities, and they are useful in treating various diseases including cancer, type II diabetes, central nervous system disorders, pain management, and infectious disease.1 Selected compounds embedded with a benzimidazol-2-one moiety along with their use are captured in Figure 1. It is worth mentioning that oxatomide drug with a benzimidazol-2-one core was approved for marketing a few years ago.2a Very recently, US Food and Drug Administration approved a new drug called flibanserin for the treatment of hypoactive sexual desire disorder (HSDD) in females, which contains benzimidazol-2- one motif.2b


We have developed a mild and new protocol for the synthesis of benzimidazol-2-ones from quinoxalinediones through decarbonylation. The present methodology can be an addition to the toolbox to prepare benzimidazolones, and it will be useful in medicinal chemistry, particularly, late-stage functionalization of natural products, drug scaffolds, or an intermediate containing quinoxaline-2,3-diones. As direct application of this method, we have successfully developed a new route for the synthesis of recently approved drug flibanserin and a urea analogue of antibiotic natural product hunanamycin A. Later application demonstrates the utility of the present method in late-stage functionalization


Synthesis of 1-(2-(4-(3-(trifluoromethyl)phenyl)piperazin-1-yl)ethyl)-1,3-dihydro-2Hbenzo[d]imidazol-2-one (Flibanserin)

Flibanserin hydrochloride as white solid.

1H NMR (400MHz ,DMSO-d6)  11.06 (s, 1 H), 10.93 (br. s., 1 H), 7.54 – 7.41 (t, J = 7.9 Hz, 1 H), 7.36 – 7.22 (m, 3 H), 7.15 (d, J = 7.6 Hz, 1 H), 7.09 – 7.01 (m, 3 H), 4.30 (t, J = 6.7 Hz, 2 H), 4.01 (d, J = 11.6 Hz, 2 H), 3.75 (d, J = 10.4 Hz, 2 H), 3.54 – 3.43 (d, J = 4.2 Hz 2 H), 3.31 – 3.10 (m, 4 H);

HRMS (ESI): m/z calculated for C20H22ON4F3[M+H]+ 391.1740 found 391.1743;



Scheme 4. Synthesis of Flibanserin through Ring Contraction

The same methodology was applied for the synthesis of flibanserin, also known as “female viagra”, which is the first approved medication for treating HSDD in women and is classified as a multifunctional serotonin agonist antagonist.(14, 15) Our synthesis of flibanserin commenced with 1-benzyl-1,4-dihydroquinoxaline-2,3-dione 36,(16) which was reacted with known chloride 37(17) under the basic condition in DMF to give the desired product 38 in good yield. Compound 38 was subjected for the decarbonylative cyclization under the optimized condition to afford the product 39 in 59% yield. Finally, the benzyl group was deprotected using trifluoromethanesulfonic acid in toluene under microwave irradiation,(8b, 18) which gave flibanserin in excellent yield (Scheme 4). The final product was isolated as HCl salt, and all of the spectral data are in agreement with the published data.(15c)

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Rahul D. Shingare completed his M.Sc  (Chemistry) from Fergusson College,  Pune  in 2008. He worked as a research associate in Ranbaxy and Lupin New drug discovery center, Gurgaon and Pune respectively until 2012 and currently pursuing his doctoral research in NCL – Pune from 2012.

Current Research Interests: Antibacterial Natural Product Hunanamycin A: Total Synthesis, SAR and Related Chemistry.









Akshay Kulkarni completed his M.Sc. from Ferguson College, Pune University in the year 2015 and joined our group as a Project Assistant in the month of October, 2015.

Current research interest: Synthesis of silicon incorporated biologically active antimalerial compounds.

e-mail :

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Dr.D. Srinivasa Reddy
Organic Chemistry Division
CSIR-National Chemical Laboratory

  1. 14.

    StahlS. M. Mechanism of action of Flibanserin, A multifunctional serotonin agonist and antagonist (MSAA), in hypoactive sexual desire disorder CNS Spectrums 2015201 DOI: 10.1017/s1092852914000832

  2. 15.

    See, previous synthesis of Flibanserin:

    (a) BiettiG.BorsiniF.TurconiM.GiraldoE.BignottiM. For treatment of central nervous system disorders. U.S. Patent 5,576,318, 1996.

    (b) MohanR. D.ReddyP. K.;ReddyB. V. Process for the preparation of Flibanserin involving novel intermediates. WO2010128516 A2,2010.

    (c) YangF.WuC.LiZ.TianG.WuJ.ZhuF.ZhangJ.HeY.ShenJ. A Facile route of synthesis for making Flibanserin Org. Process Res. Dev. 2016201576 DOI: 10.1021/acs.oprd.6b00108

  3. 16.

    JarrarA. A.FataftahZ. A. Photolysis of some quinoxaline-1,4-dioxides Tetrahedron 1977332127 DOI: 10.1016/0040-4020(77)80326-8

  4. 17.

    XueongX. Preparation method of Flibanserin. CN104926734 A, 2015.

  5. 18.

    RomboutsF.FrankenD.Martínez-LamencaC.BraekenM.ZavattaroC.ChenJ.TrabancoA. A.Microwave-assisted N-debenzylation of amides with triflic acid Tetrahedron Lett. 2010514815 DOI: 10.1016/j.tetlet.2010.07.022




FDA approves flibanserin first treatment for sexual desire disorder

 Uncategorized  Comments Off on FDA approves flibanserin first treatment for sexual desire disorder
Aug 192015



FDA approves first treatment for sexual desire disorder
Addyi approved to treat premenopausal women


The U.S. Food and Drug Administration today approved  to treat acquired, generalized hypoactive sexual desire disorder (HSDD) in premenopausal women. Prior to Addyi’s approval, there were no FDA-approved treatments for sexual desire disorders in men or women.


August 18, 2015


The U.S. Food and Drug Administration today approved Addyi (flibanserin) to treat acquired, generalized hypoactive sexual desire disorder (HSDD) in premenopausal women. Prior to Addyi’s approval, there were no FDA-approved treatments for sexual desire disorders in men or women.

“Today’s approval provides women distressed by their low sexual desire with an approved treatment option,” said Janet Woodcock, M.D., director of the FDA’s Center for Drug Evaluation and Research (CDER). “The FDA strives to protect and advance the health of women, and we are committed to supporting the development of safe and effective treatments for female sexual dysfunction.”

HSDD is characterized by low sexual desire that causes marked distress or interpersonal difficulty and is not due to a co-existing medical or psychiatric condition, problems within the relationship, or the effects of a medication or other drug substance. HSDD is acquired when it develops in a patient who previously had no problems with sexual desire. HSDD is generalized when it occurs regardless of the type of sexual activity, the situation or the sexual partner.

“Because of a potentially serious interaction with alcohol, treatment with Addyi will only be available through certified health care professionals and certified pharmacies,” continued Dr. Woodcock. “Patients and prescribers should fully understand the risks associated with the use of Addyi before considering treatment.”

Addyi can cause severely low blood pressure (hypotension) and loss of consciousness (syncope). These risks are increased and more severe when patients drink alcohol or take Addyi with certain medicines (known as moderate or strong CYP3A4 inhibitors) that interfere with the breakdown of Addyi in the body. Because of the alcohol interaction, the use of alcohol is contraindicated while taking Addyi. Health care professionals must assess the likelihood of the patient reliably abstaining from alcohol before prescribing Addyi.

Addyi is being approved with a risk evaluation and mitigation strategy (REMS), which includes elements to assure safe use (ETASU). The FDA is requiring this REMS because of the increased risk of severe hypotension and syncope due to the interaction between Addyi and alcohol. The REMS requires that prescribers be certified with the REMS program by enrolling and completing training. Certified prescribers must counsel patients using a Patient-Provider Agreement Form about the increased risk of severe hypotension and syncope and about the importance of not drinking alcohol during treatment with Addyi. Additionally, pharmacies must be certified with the REMS program by enrolling and completing training. Certified pharmacies must only dispense Addyi to patients with a prescription from a certified prescriber. Additionally, pharmacists must counsel patients prior to dispensing not to drink alcohol during treatment with Addyi.

Addyi is also being approved with a Boxed Warning to highlight the risks of severe hypotension and syncope in patients who drink alcohol during treatment with Addyi, in those who also use moderate or strong CYP3A4 inhibitors, and in those who have liver impairment. Addyi is contraindicated in these patients. In addition, the FDA is requiring the company that owns Addyi to conduct three well-designed studies in women to better understand the known serious risks of the interaction between Addyi and alcohol.

Addyi is a serotonin 1A receptor agonist and a serotonin 2A receptor antagonist, but the mechanism by which the drug improves sexual desire and related distress is not known. Addyi is taken once daily. It is dosed at bedtime to help decrease the risk of adverse events occurring due to possible hypotension, syncope and central nervous system depression (such as sleepiness and sedation). Patients should discontinue treatment after eight weeks if they do not report an improvement in sexual desire and associated distress.

The effectiveness of the 100 mg bedtime dose of Addyi was evaluated in three 24-week randomized, double-blind, placebo-controlled trials in about 2,400 premenopausal women with acquired, generalized HSDD. The average age of the trial participants was 36 years, with an average duration of HSDD of approximately five years. In these trials, women counted the number of satisfying sexual events, reported sexual desire over the preceding four weeks (scored on a range of 1.2 to 6.0) and reported distress related to low sexual desire (on a range of 0 to 4). On average, treatment with Addyi increased the number of satisfying sexual events by 0.5 to one additional event per month over placebo increased the sexual desire score by 0.3 to 0.4 over placebo, and decreased the distress score related to sexual desire by 0.3 to 0.4 over placebo. Additional analyses explored whether the improvements with Addyi were meaningful to patients, taking into account the effects of treatment seen among those patients who reported feeling much improved or very much improved overall. Across the three trials, about 10 percent more Addyi-treated patients than placebo-treated patients reported meaningful improvements in satisfying sexual events, sexual desire or distress. Addyi has not been shown to enhance sexual performance.

The 100 mg bedtime dose of Addyi has been administered to about 3,000 generally healthy premenopausal women with acquired, generalized HSDD in clinical trials, of whom about 1,700 received treatment for at least six months and 850 received treatment for at least one year.

The most common adverse reactions associated with the use of Addyi are dizziness, somnolence (sleepiness), nausea, fatigue, insomnia and dry mouth.

The FDA has recognized for some time the challenges involved in developing treatments for female sexual dysfunction. The FDA held a public Patient-Focused Drug Development meeting and scientific workshop on female sexual dysfunction on October 27 and October 28, 2014, to solicit perspectives directly from patients about their condition and its impact on daily life, and to discuss the scientific challenges related to developing drugs to treat these disorders. The FDA continues to encourage drug development in this area.

Consumers and health care professionals are encouraged to report adverse reactions from the use of Addyi to the FDA’s MedWatch Adverse Event Reporting program at or by calling 1-800-FDA-1088.

Addyi is marketed by Sprout Pharmaceuticals, based in Raleigh, North Carolina.









fliban chemspider image

13C NMR DB GRAPH 13C NMR DB VAL fliban chemspider image



COSY NMR prediction (27)


Addyi, flibanserin, fda 2015, sexual desire disorder



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