LC and NMR Studies for Identification and Characterization of Degradation Byproducts of Olmesartan Acid,Elucidation of Their Degradation Pathway and Ecotoxicity Assessment

The discovery of various sartans, which are among the most used antihypertensive drugs in the world, is increasingly frequent not only in wastewater but also in surface water and, in some cases, even in drinking or groundwater. In this paper, the degradation pathway of olmesartan acid, one of the most used sartans, was investigated by simulating the chlorination process normally used in a wastewater treatment plant to reduce similar emerging pollutants. The structures of nine isolated degradation byproducts (DPs), eight of which were isolated for the first time, were separated via chromatography column and HPLC methods, identified by combining nuclear magnetic resonance and mass spectrometry, and justified by a proposed mechanism of formation beginning from the parent drug. Ecotoxicity tests on olmesartan acid and its nine DPs showed that 50% of the investigated byproducts inhibited the target species Aliivibrio fischeri and Raphidocelis subcapitata, causing functional decreases of 18% and 53%, respectively.     

Original loading and Suzuki conditions for the solid-phase synthesis of biphenyltetrazoles. Application to the first solid-phase synthesis of irbesartan

Biphenyltetrazoles are recognized privileged structures. Among them, the therapeutically important class of sartans displays antagonistic activity on AT1 receptors. We have developed a method for anchoring tetrazole derivatives via the heterocycle on a hydroxylated resin using zinc triflate. New Suzuki-Miyaura cross-coupling conditions are developed for the quantitative formation of the phenyl-phenyl bond. Our straightforward synthesis scheme, starting from the conserved phenyltetrazole moiety and ending with the appending of the structurally variable moiety, is well suited to the preparation of sartans and their analogues at a laboratory scale. We thus describe here the first solid phase synthesis of irbesartan, a marketed AT1 antagonist.     

Novel paramagnetic AT1 receptor antagonists

Novel paramagnetic selective angiotensin AT(1) receptor antagonists (sartans) bearing nitroxides (3, 4) have been prepared and their pharmacology evaluated in vitro as well as in vivo. Compounds 3, 4 proved to be effective sartans with pK(B) estimates in the range 6.2-9.1. In addition, the sodium salt (11) of 4 (R = Bu) is able to protect against vascular injury in hypertensive rats as determined by its ability to attenuate the development of intimal thickening caused by balloon injury of the carotid artery.     

Fragmentation studies of sartans by electrospray ionization mass spectrometry

Sartans and related analogues with 5‐oxo‐l, 2, 4‐oxadiazole ring and tetrazole ring are investigated in detail using collision‐induced dissociation (CID) method in positive ion mode by electrospray ionization tandem mass spectrometry (ESI‐MSⁿ). It is found that the protonated sartans and related analogues tend to form the N‐substituted‐3‐substituted phenanthridin‐6‐amine ion which has a large conjugative structure. The possible fragmentation pathways were proposed for the first time, and the key structure of product ions was confirmed by high resolution tandem mass spectrometry and theoretical calculation. It is very helpful for understanding the intriguing roles of sartans analogues in fragmentation reactions and enriching the knowledge of the gas‐phase chemistry of the oxadiazole and tetrazole ring. Copyright © 2017 John Wiley & Sons, Ltd.     

Application of Validated TLC—Densitometric Method for Simultaneous Identification and Determination of Losartan Potassium,Telmisartan, and Valsartan in Tablets

JPC – Journal of Planar Chromatography – Modern TLC - The antihypertensive effect of sartans is a result of inhibition of the binding of angiotensin (AT) II to the AT1 receptor in...     

Actions of Novel Angiotensin Receptor Blocking Drugs,Bisartans, Relevant for COVID-19 Therapy: Biased Agonism at Angiotensin Receptors and the Beneficial Effects of Neprilysin in the Renin Angiotensin System

Angiotensin receptor blockers (ARBs) used in the treatment of hypertension and potentially in SARS-CoV-2 infection exhibit inverse agonist effects at angiotensin AR1 receptors, suggesting the receptor may have evolved to accommodate naturally occurring angiotensin ‘antipeptides’. Screening of the human genome has identified a peptide (EGVYVHPV) encoded by mRNA, complementary to that encoding ANG II itself, which is an inverse agonist. Thus, opposite strands of DNA encode peptides with opposite effects at AR1 receptors. Agonism and inverse agonism at AR1 receptors can be explained by a receptor ‘switching’ between an activated state invoking receptor dimerization/G protein coupling and an inverse agonist state mediated by an alternative/second messenger that is slow to reverse. Both receptor states appear to be driven by the formation of the ANG II charge-relay system involving TyrOH-His/imidazole-Carboxylate (analogous to serine proteases). In this system, tyrosinate species formed are essential for activating AT1 and AT2 receptors. ANGII is also known to bind to the zinc-coordinated metalloprotease angiotensin converting enzyme 2 (ACE2) used by the COVID-19 virus to enter cells. Here we report in silico results demonstrating the binding of a new class of anionic biphenyl-tetrazole sartans (‘Bisartans’) to the active site zinc atom of the endopeptidase Neprilysin (NEP) involved in regulating hypertension, by modulating humoral levels of beneficial vasoactive peptides in the RAS such as vasodilator angiotensin (1–7). In vivo and modeling evidence further suggest Bisartans can inhibit ANG II-induced pulmonary edema and may be useful in combatting SARS-CoV-2 infection by inhibiting ACE2-mediated viral entry to cells.     

Method for trace determination of N-nitrosamines impurities in metronidazole benzoate using high-performance liquid chromatography coupled with atmospheric-pressure chemical ionization tandem mass spectrometry

Genotoxic impurity control has been a great concern in the pharmaceutical industry since the recall of the large round of sartans worldwide in 2018. In these sartans, N-nitrosamines were the main contaminants in active pharmaceutical ingredients and formulations. Numerous analytical methods have been developed to detect N-nitrosamines in food, drugs, and environmental samples. In this study, a sensitive method is developed for the trace determination of N-nitrosamine impurities in metronidazole benzoate pharmaceuticals using high-performance liquid chromatography/atmospheric-pressure chemical ionization tandem mass spectrometry in the multiple reaction monitoring mode. The method was validated regarding system suitability, selectivity, linearity, accuracy, precision, sensitivity, solution stability, and robustness. The method showed good linearity with R² ≥ 0.999 and F_Mandel < F_tab(95%) ranging from 0.33 to 8.00 ng/ml. The low limits of detection of N-nitrosamines were in the range of 0.22–0.80 ng/ml (0.0014–0.0050 ppm). The low limits of quantification were in the range of 0.33–1.20 ng/ml (0.0021–0.0075 ppm), which were lower than the acceptable limits in metronidazole benzoate pharmaceuticals and indicated the high sensitivity of the method. The recoveries of N-nitrosamines ranged from 84% to 97%. Thus, this method exhibits good selectivity, sensitivity, and accuracy. Moreover, it is a simple, convenient, and scientific strategy for detecting N-nitrosamine impurities in pharmaceuticals to support the development of the pharmaceutical industry.     

The Synthetic Strategy toward of ACE-Inhibitors

Angiotensin II is an important octapeptide which is responsible for the increase in blood pressure in three major mechanisms. It acts as a hormone to attack the receptor on the blood vessels, which cause strong vasoconstriction. It is also the major stimulus for release another hormone, aldolsterone, which promote the excretion of potassium ion and retention of sodium and waster. Both of the above effects increase the blood pressure. On the other hand, ACE (Angiotensin Converting Enzyme) catalyzes the hydrolysis of bradykinin that is a potent vasodilator. Therefore, the inhibitor of ACE can act as an efficient anti-hypertensive agent through multiple routes.     

Sensitive assay for serum angiotensin-converting enzyme and separation of angiotensin analogues by high-performance liquid chromatography with fluorescence detection

A high-performance liquid chromatographic method is described for the assay of angiotensin-converting enzyme in human serum and for the separation of angiotensins and their analogues after pre-column fluorescence derivatization with benzoin. Angiotensin II, formed enzymatically from angiotensin I, is converted into a fluorescent derivative which is then separated isocratically from the substrate and biological substances in the enzyme reaction mixture on a reversed-phase column (TSK gel ODS-120T). The lower limit of detection for angiotensin II is 0.66 pmol per enzyme assay tube. The method is simple and sensitive, and requires as little as 5 microliter of human serum. Angiotensin analogues can also be separated and quantified by the chromatographic technique, and thus this method permits the use of the analogues of angiotensin I as substrates.     

A synthetic approach to F-analogues of Angiotensin converting enzyme inhibitors

Studies on the synthetic routes to F-analogues of captopril, which is known as an Angiotensin converting enzyme inhibitor, have been undertaken.     

Fragmentation study of peptides using Fourier transform ion cyclotron resonance with infrared multiphoton dissociation: experiment and simulation

In this study, the fragmentation of gas-phase protonated Angiotensin II is investigated using electrospray ionization (ESI), Fourier-transform ion cyclotron resonance (FT-ICR), and mass spectrometry (MS) with a laser cleavage infrared multiphoton dissociation (IRMPD) technique. The experimental results show that the spectra peaks for the photoproducts are y2/b6- and y7-type ions, corresponding to the cleavage of His-Pro and Asp-Arg in the parent amino acid sequence. The fragmentation of the peptide under collision-free vacuum conditions is modeled using molecular dynamics simulations (MD). The binding energy for the peptide bonds (C'-N bond) of Angiotensin II is estimated from ab initio calculations. The calculations are directed at predicting experimental measurements of the product ions from the photodissociation of the peptide. The product distributions simulated by the MD dissociation trajectories include predominantly y7/b1 and y2/b6 pair ions.     

LC and Principal Component Analysis in the Lipophilicity Study of Seven Angiotensin II-AT1 Receptor Antagonists (Sartans)

Seven sartans have been chromatographed with acetonitrile-buffer and methanol–buffer in different proportions as mobile phases. The retention values, log k or R _M were extrapolated to zero organic modifier content to obtain the log k _w or R _MW values. Calibration equations were obtained for standards of known lipophilicity. A simple method employing a gradient procedure of 10–100% acetonitrile or methanol in 60 min and standards of the extreme lipophilicity was also elaborated. Chromatographic log P values were compared to those calculated by use of different software products. Finally, principal component analysis was performed to explore and visualize similarities and differences among the drugs and among the methods.     

LC and Principal Component Analysis in the Lipophilicity Study of Seven Angiotensin II-AT1 Receptor Antagonists (Sartans)

Seven sartans have been chromatographed with acetonitrile-buffer and methanol–buffer in different proportions as mobile phases. The retention values, log k or R _M were extrapolated to zero organic modifier content to obtain the log k _w or R _MW values. Calibration equations were obtained for standards of known lipophilicity. A simple method employing a gradient procedure of 10–100% acetonitrile or methanol in 60 min and standards of the extreme lipophilicity was also elaborated. Chromatographic log P values were compared to those calculated by use of different software products. Finally, principal component analysis was performed to explore and visualize similarities and differences among the drugs and among the methods.

     

Secondary Effects of Hypochlorite Treatment on the Emerging Pollutant Candesartan: The Formation of Degradation Byproducts and Their Toxicological Profiles

In recent years, many studies have reported the frequent detection of antihypertensive agents such as sartans (olmesartan, valsartan, irbesartan and candesartan) in the influents and effluents of wastewater treatment plants (WWTPs) and in the superficial waters of rivers and lakes in both Europe and North America. In this paper, the degradation pathway for candesartan (CAN) was investigated by simulating the chlorination process that is normally used to reduce microbial contamination in a WWTP. Twelve isolated degradation byproducts (DPs), four of which were isolated for the first time, were separated on a C-18 column by employing a gradient HPLC method, and their structures were identified by combining nuclear magnetic resonance and mass spectrometry and comparing the results with commercial standards. On the basis of these results, a mechanism of formation starting from the parent drug is proposed. The ecotoxicity of CAN and its DPs was studied by conducting a battery of ecotoxicity tests; bioassays were performed using Aliivibrio fischeri (bacterium), Daphnia magna (planktonic crustacean) and Raphidocelis subcapitata (alga). The ecotoxicity results shed new light on the increased toxicity of DPs compared with the parent compound.     

Physicochemical Profiling of Sartans: A Detailed Study of Ionization Constants and Distribution Coefficients

A detailed investigation of the ionization and lipophilicity profiles of selected sartans (valsartan, losartan, irbesartan, candesartan, candesartan cilexetil), a class of antihypertensives commonly used in therapy, is presented. The pK_a macroconstants were determined by integrated potentiometry, capillary electrophoresis, and UV spectrophotometry. The measured pK_a macroconstants were connected with the ionizable centers present in each molecule with the aid of model compounds. Potentiometric titrations with the GLpKa apparatus were performed to determine the distribution profile (log D vs. pH) of valsartan, while the shake‐flask procedure was used to characterize the distribution profile of the other compounds. Valsartan showed a lipophilicity profile consistent with the presence of two acidic centers. Losartan and irbesartan, which contain one acidic and one basic center, displayed the classical bell‐shaped profile of ordinary ampholytes. By contrast, a more complex situation emerged in the case of candesartan, due to the large number of ionization equilibria involved. The low solubility of candesartan cilexetil, together with the ease of hydrolysis of the ester moiety, prevented a successful investigation of its ionization and lipophilicity profiles.     

壳聚糖固定化血管紧张素转化酶及其性质

以壳聚糖微球为载体, 戊二醛为交联剂固定化血管紧张素转化酶, 研究了酶固定化的最优条件和固定化酶的性质. 结果表明, 在戊二醛质量分数为2.5%、给酶量为8 mg/mL时, 固定化酶的比活性最大, 为0.085 U/g. 固定化酶在40~50 ℃, pH在7~9之间有最大活性, 其米氏常数Km为2.39 mmol/L. 同时, 固定化酶具有良好的稳定性, 可重复利用.     

Bioconjugates for tunable peptide fragmentation: free radical initiated peptide sequencing (FRIPS)

The free radical initiator Vazo 68 is coupled to a peptide and electrosprayed into an ion trap mass spectrometer. On collisional activation, the Vazo 68-peptide conjugate generates a free radical, which can be collisionally activated to cleave the peptide backbone. Mostly z-type fragments are formed, as in CAD of other radical peptides and ECD fragmentation. We present data for the Angiotensin II-Vazo 68 conjugate and discuss possible sites of H atom abstraction from the peptide. This experimental methodology for generating peptide fragments is a useful step toward the development of a completely gas-phase approach to protein sequencing.     

Role of protein kinase C in homologous desensitization of angiotensin II-induced phosphoinositide hydrolysis in rat renal mesangial cells

Conclusions These results indicate that, in rat mesangial cells, angiotensin II induces a homologous desensitization of phospholipase C stimulation. It is proposed that protein kinase C activation plays an important role in the molecular mechanism of desensitization of angiotensin II-stimulated polyphosphoinositide metabolism.

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Die Rolle der Proteinkinase C bei der homologen Desensitisierung der Angiotensin II stimulierten Hydrolyse von Phosphoinositiden

     

A diversity-oriented-synthesis protocol for scaffold discovery based on a general synthetic route to spirocycles

A diversity-oriented synthesis (DOS) protocol for scaffold discovery is described. A general synthetic route is developed from a single lactam for the access to various multi-functionalized spirocyclic keto-lactams and their derived spirocyclic keto-amines. This work provides the foundation for a sequential DOS strategy from scaffold discovery to drug discovery.     

Simple titrimetric method for the analytical control of macromolecular polypeptides

A simple potentiometric procedure based on the determination of the primary amino groups in macromolecular polypeptides is presented. The method was found suitable for the detection of decomposition processes involving splitting of the peptide chain (liberation of primary amino groups) and deamination. The method has been applied to analysis of corticotropin fragments (ACTH(1-28) and ACTH(1-32)), Angiotensin II, and the basic trypsin inhibitor Kunitz base (Trasylol).