Synthesis and Modeling Studies of Furoxan Coupled Spiro-Isoquinolino Piperidine Derivatives as NO Releasing PDE 5 Inhibitors

An overview on pharmaceutical applications of phosphodiesterase enzyme 5 (PDE5) inhibitors

Phosphodiesterase enzyme 5 (PDE5) inhibitors have emerged as one of the leading molecules for the treatment of erectile dysfunction (ED). PDE5 inhibitors are categorized structurally into several classes. PDE5 inhibitors have been a multidisciplinary endeavor that attracts the attention of researchers because of their multiple pharmaceutical applications. Beyond their action on ED, PDE5 inhibitors are widely used in treatment of benign prostatic hypertrophy (BPH), Eisenmenger's syndrome, Raynaud's Disease, Intrauterine growth retardation (IUGR), Mountain sickness, Bladder pain syndrome/interstitial cystitis (BPS/IC), pulmonary arterial hypertension and type II diabetes (insulin resistance). In addition, PDE5 inhibitors also show promising antiproliferative activity, anti-Alzheimer and COX-1/COX-2 inhibitory activity (anti-inflammatory). Pharmacokinetics, Pharmacogenetics and toxicity of PDE5 inhibitors were finally explored. The diverse therapeutic applications, the high feasibility of structural modification and the appropriate pharmacokinetic properties of PDE5 inhibitors have motivated researchers to develop new scaffolds that have been either under clinical trials or approved by FDA and utilize them to overcome some recent global concerns, such as COVID-19.

Organocatalyzed Enantioselective [3+2] Cycloaddition Reactions for Synthesis of Dispiro[benzothiophenone-indandione-pyrrolidine] Derivatives

An organocatalytic enantioselective [3+2] cycloaddition reaction involving 2-arylidene-1,3-indandiones and N-2,2-difluoroethylbenzothiophenone imines was developed. This approach efficiently afforded dispiro[benzothiophenone-indandione-pyrrolidine]s, featuring three stereocenters, in 84-98% yields with 3-93% ee and 9:1->20:1 dr. Notably, the method maintained its yield and enantioselectivity integrity even in a gram-scale amplification experiment. For example, the product with substituents on aromatics were obtained in 90% yield with 91% ee and >20:1 dr. Its absolute configuration was established through X-ray single-crystal diffraction analysis, and a plausible reaction mechanism was proposed.

Recent Advances in the Synthesis and Biomedical Applications of Heterocyclic NO-Donors

Nitric oxide (NO) is a key signaling molecule that acts in various physiological processes such as cellular metabolism, vasodilation and transmission of nerve impulses. A wide number of vascular diseases as well as various immune and neurodegenerative disorders were found to be directly associated with a disruption of NO production in living organisms. These issues justify a constant search of novel NO-donors with improved pharmacokinetic profiles and prolonged action. In a series of known structural classes capable of NO release, heterocyclic NO-donors are of special importance due to their increased hydrolytic stability and low toxicity. It is no wonder that synthetic and biochemical investigations of heterocyclic NO-donors have emerged significantly in recent years. In this review, we summarized recent advances in the synthesis, reactivity and biomedical applications of promising heterocyclic NO-donors (furoxans, sydnone imines, pyridazine dioxides, azasydnones). The synthetic potential of each heterocyclic system along with biochemical mechanisms of action are emphasized.

4,6-Dinitro-7-(thiazol-2-ylamino)benzo[c][1,2,5]oxadiazole 1-oxide

4,6-Dinitro-7-(thiazol-2-ylamino)benzo[c][1,2,5]oxadiazole 1-oxide was synthesized by a SNAr reaction between 7-chloro-4,6-dinitrobenzofuroxan and 2-aminothiazole. The structure of the newly synthesized compound (45% yield) was elucidated based on 1H-NMR, 13C-NMR, NOESY-1D, ESI-MS, UV-Vis, and FT-IR techniques.

Potential of NO donor furoxan as SARS-CoV-2 main protease (Mpro) inhibitors: in silico analysis

The sharp spurt in positive cases of novel coronavirus-19 (SARS-CoV-2) worldwide has created a big threat to human. In view to expedite new drug leads for COVID-19, Main Proteases (M^pro) of novel Coronavirus (SARS‐CoV‐2) has emerged as a crucial target for this virus. Nitric oxide (NO) inhibits the replication cycle of SARS-CoV. Inhalation of nitric oxide is used in the treatment of severe acute respiratory syndrome. Herein, we evaluated the phenyl furoxan, a well-known exogenous NO donor to identify the possible potent inhibitors through in silico studies such as molecular docking as per target analysis for candidates bound to substrate binding pocket of SARS-COV-2 M^pro. Molecular dynamics (MD) simulations of most stable docked complexes (M^pro-22 and M^pro-26) helped to confirm the notable conformational stability of these docked complexes under dynamic state. Furthermore, Molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) calculations revealed energetic contributions of key residues of M^pro in binding with potent furoxan derivatives 22, 26. In the present study to validate the molecular docking, MD simulation and MM-PBSA results, crystal structure of M^pro bound to experimentally known inhibitor X77 was used as control and the obtained results are presented herein. We envisaged that spiro-isoquinolino-piperidine-furoxan moieties can be used as effective ligand for SARS-CoV-2 M^pro inhibition due to the presence of key isoquinolino-piperidine skeleton with additional NO effect.

Communicated by Ramaswamy H. Sarma