A Novel Series Of Benzofuran Bisindole Hybrids

Published Date: 02 Nov 2017

Hyperlipidemia, a key feature of the metabolic syndrome and is the major cause of heart disease, stroke and death in most industrialized societies [1]. Analysis of epidemiological data reveals that dyslipidemia and coagulation disturbances are among the most significant risk factors to the progression of atherosclerotic condition [2]. Elevated plasma triglycerides (TG), low density lipoprotein cholesterol (LDL-C) and low high density lipoprotein cholesterol (HDL-C) are diagnostic indicators for metabolic syndrome [3]. Current therapies includes the use of the statin class of drugs to lower cholesterol levels by inhibiting the 3-hydroxy-3-methylglutaryl co-enzyme A reductase (HMG-CoA) enzyme [4] and the fibrate class of drugs lowering serum triglycerides (TG) levels and raising HDL-cholesterol levels by activation of peroxisome proliferator activated receptors (PPAR), which are pretty efficient [5]. Statins are the know drug for dyslipidemia in market such as atorvastatin, lovastatin, fluvastatin, simvastatin, and pravastatin, which work via inhibition of HMG-CoA reductase, a key enzyme in cholesterol biosynthetic pathway, it leading to a reduced the cholesterol concentration and a consequent increase in expression of the low-density lipoprotein receptor (LDLR), the main receptor involved in the hepatic clearance of LDL cholesterol. Atorvastatin (Lipitor generic name) is still remains the best selling branded lipid lowering drug worldwide [6]. However, disorders of muscles, severe myopathy (rhabdomyolysis) symptoms with marked creatine kinase elevation, which may precipitate renal failure, are among most discussed adverse side effects associated with statins [7]. Fibrate class of drugs, require high doses to show significant efficacy and are also associated with primary muscle injury, especially when used in combination with a statin. The withdrawal of cerivastatin in 2001 due to serious safety concerns and in light of the recent warning by the US FDA, that statins may increase the risk of diabetes mellitus, clearly underscores the constant need for new class of drug to combat this dreaded metabolic disorder disease without severe side effects.

Increase in oxidative stress implicated in several other metabolic risk factors such as diabetes and coronary heart disease (CAD) [8]. Reactive oxygen metabolites, such as hydrogen peroxide (H2O2), superoxide anions (O2-) or hydroxyl radicals (â‹…OH), as a by-product of oxidative metabolism can damage the cells resulting lipid peroxidation, modification of protein and nucleic acids. Excess of hydroxyl free radicals are the major factor for the peroxidative damage to lipoproteins present in the blood, which are responsible for the initiation and progression of atherosclerosis in the hyperlipidemic conditions [9]. Therefore, it is envisaged that, if a chemical compound has cholesterol lowering, hypolipidemic and antioxidant properties it will be able to protect endothelial and myocardial function as well as endow with as a better anti-atherosclerotic agent.

Several drugs contain indole moiety, either as a basic pharmocophore or as an attached templete to invoke specific properties. Indole and their derivatives are known to exert antihypertension, antitubercular [10], anticancer [11], antiviral [12], antioxidant properties [13], and free radical induced lipid peroxidation [14]. Furthermore, fluvastatin which is a statin class of drug also contain this important scaffold

On the other hand, Benzofuran derivatives are versatile biodynamic agents both from synthetic as well as natural origin [15]. During the recent decades, great attention has been given to studies focused on the synthesis of benzofuran-containing agents and their pharmacological activities. In addition, the natural product tournefolic acids A and B have shown potent anti-lipid-peroxidative properties [16]. Furthermore, a literature survey based on the framework reveals that benzofuran ring containing moiety, exhibit antihyperlipidemic activity (Fig. 1) [17]. From these studies, it was found that compounds containing the benzofuran ring have a promising potential effect as lipid-lowering agents. In continuation of our drug discovery programme on new antidyslipidemic agents [18], and our laboratory experiences on molecular hybridization approach [19], we herein report the synthesis and biological evaluation of benzofuran-bisindole hybrids as antidyslipidemic agents.(our prototype in Fig. 1)

The synthesis of target and intermediate compounds is outlined in the scheme 1. The Duff reaction [20] on ortho-substituted phenols (1a-f) in the presence of hexamethylenetetraamine (HMTA) and TFA at 120 ºC gave aromatic dicarbaldehyde (2a-f). The Rap-Stoermer reaction [21] on compounds (2a-f) with different phenacylbromides in the presence of K2CO3 furnished benzofuran carbaldehyde derivatives (3a-j) in quantitative yields. Furthermore, introduction of indole templete was achieved by the reaction of different indoles in the presence of iodine and acetonitrile as a solvent at room temperature to give the final benzofuran-bisindole hybrids 4a-s. All the synthesized compounds were characterized using 1H NMR, 13C NMR, IR spectroscopy and ESI-MS.

4.1. The lipid lowering activity of benzofuran-bisindole hybrids.

The present study has been undertaken to evaluate the lipid lowering activity of benzofuran-bisindole hybrids (4a-4s) in an acute triton induced hyperlipidemic model. Administration of triton WR–1339 in rats induced markedly increased the plasma level of total cholesterol TC (4.05 fold), phospholipids PL (3.31 fold) and triglyceride TG (2.67 fold) ) and plasma post heparin lipolytic activity (PHLA) (28%) as compared to control Treatment of hyperlipidemic rats with benzofuran-bisindole hybrids (4a-4s) at the dose of 100 mg/kg p.o. reversed the plasma levels of lipid with varying extents. The synthesized derivatives inhibited lipoprotein cholesterol metabolism and activity of lipolytic enzymes to early clearance of lipids from blood circulation in triton induced hyperlipidemia. Compound 4j was found to be the most potent in the series as it showed 28%, 29% and 28%, lowering in TC, PL and TG respectively, while compounds 4a, 4c and 4h showed significantly 23%, 24% and 24% by lowering of TC levels, 23%, 23%, and 23% by lowering of PL levels, 24%, 23% and 23% lowering of TG levels respectively. These data were comparable with standard hypolipidemic drug gemfibrozil which at the dose of 100 mg/kg decreased levels of TC, PL and TG in plasma by 34%, 35% and 34%, respectively. Compounds 4a, 4c, 4h and 4j showed significant reversal of PHLA in plasma of hyperlipidemic rats by 16%, 17%, 16% and 18% respectively, comparable to gemfibrozil, which caused 20% reversal of activity of this enzyme as compared to control group and the results are summarised in Table 1.

4.2. Effect of compounds 4a, 4c, 4h and 4j on lipid lowering at different doses in triton induced hyperlipidemic rat.

After the confirmation of the most active compounds in primary screening we further, evaluate the activity of compounds 4a, 4c, 4h and 4j was studied at different doses in 50 to 150 mg/kg body weight. In these compounds 4a, 4c and 4h lowers the TC by 15% to 25%, 20% to 27% and 17% to 24%, respectively, also lowers PL by 17% to 24%, 20% to 23% and 18% to 26% respectively, and further lowers TG by 16% to 25%, 21% to 24% and 16% to 24% respectively. Similarly most potent compound 4j lowers the TC by 22% to 29%, PL by 20% to 29%, and TG by 20% to 30% respectively. The results are summarised in Fig. 2

4.3. Effect of compounds 4a, 4c, 4h and 4j on lipoprotein cholesterol level and LCAT activity in triton induced hyperlipidemic rat.

The analysis of hyperlipidemic plasma of triton administered rats showed a significant increase in the level of lipoprotein lipids and these effects were pronounced for VLDL and LDL followed by a decrease in HDL as compared to control rats. After treatment with most active compounds 4a, 4c, 4h and 4j significantly reversed VLDL, LDL and HDL levels as shown in Fig. 2. Furthermore, triton administration markedly decreases the level of LCAT in rat, on treatment with compounds 4a, 4c, 4h and 4j LCAT activity were significantly increased followed by standard drug gimfibrozil (Fig. 3). In our study, most active hybrids at most steadfast dose (100mg/kg) decreased the plasma TC, PL and TG in triton induced hyperlipidemic rats, which may be due to inhibition of exogenous absorption and formation. In addition, compounds 4a, 4c, 4h and 4j increased the LCAT activity, which plays a key role in lipoprotein metabolism contributing to an increased level of HDL-C in plasma. [25].

4.4. Effect of compounds 4a-4s on superoxide anions, hydroxyl radicals and lipid-peroxidation

Antioxidant activities of compounds 4a-4s at 200µg/mL were evaluated by generating free radicals [superoxide ions (O2-), hydroxyl radicals (⋅OH), microsomal lipid peroxidation] in vitro in the absence and presence of these compounds. The results of this study are shown in Fig. 4. compounds 4a and 4j significantly suppressed the superoxide ions by 33% and 31%, hydroxyl radical’s by 30% and 27% and microsomal lipid peroxidation by 31% and 32%, respectively. The standard drug Alloperinol, at 200µg/mL, showed 51% inhibition in superoxide ions. Mannitol and α-tocopherol, at the same dose, showed 49% and 52% inhibition of hydroxyl ions and microsomal lipid peroxidation, respectively in in vitro system. The scavenging potential of the other derivatives was modest at best.

Interestingly, in terms of structure activity relationship, among the series methoxy substituted indole and benzofuran compounds (4a, 4c, 4h and 4j) exhibited potent activity. Furthermore, in the absence of methoxy group or its replacement with electron withdrawing groups results in diminished activity. From the above results reveal that hybrids containing methoxy group were elevate the activity where as indole hybrids containing without methoxy group will decrease the activity.

5. Conclusion

In conclusion, inspired by the molecular hybridization approach lipid lowering effect of the newly synthesized hybrids were evaluated in triton WR-1339 induced hyperlipidemic rats the most active compounds 4a, 4c, 4h and 4j decreased total cholesterol (TC), phospholipids (PL) and triglycerides (TG), of hyperlipidemic rats significantly, at 100 mg/kg body weight. In addition, treatment with active hybrids effectively reversed the levels of VLDL, LDL and HDL also increased the LCAT activity, which plays a key role in lipoprotein metabolism contributing to an increased level of HDL-C in plasma. Furthermore, the synthesized compounds 4a and 4j exhibited significantly inhibiting superoxide ions, hydroxyl radicals and microsomal lipid peroxidation, which illustrates potent antioxidant properties of hybrids. Moreover these benzofuran-bisindole hybrids, mitigates dyslipidemia via activation of LCAT.