Design and synthesis of new flavonols as dual ɑ-amylase and ɑ-glucosidase inhibitors: Structure-activity relationship, drug-likeness, in vitro and in silico studies

Highlights

• Seventeen brominated-flavonol derivatives were synthesized and characterized.

• In vitro evaluation of prepared compounds against a-amylase and a-glucosidase enzymes.

• Limited structure-activity relationship was established.

• Molecular modelling studies of most active compounds for both enzymes.

• The drug-likeness and bioactivity scores were calculated and interpreted.

Abstract

In this study, a library of new intriguing flavonol derivatives (1–17) was designed and synthesized through a facile route involving Algar-Flynn-Oyamada reaction in a one-pot synthesis. The molecular structures of all newly synthesized compounds were unequivocally corroborated by different spectroscopic techniques such as FTIR, UV–Vis, ¹H NMR and ¹³C NMR and mass spectrometry (EI-MS). All the synthesized analogs (1-17) were evaluated in vitro for their inhibitory potential against ɑ-amylase and ɑ-glucosidase enzymes. Interestingly, all the synthetic compounds displayed good to moderate inhibition potential with IC₅₀ values ranging from 4.86 ± 1.39 to 265.61 ± 5.85 μM for a-amylase, and 70.57 ± 1.13 to 322.98 ± 4.43 μM for a-glucosidase in comparison to the standard acarbose (IC₅₀ = 5.03 ± 9.44 μM for a-amylase and IC₅₀ = 75.26 ± 0.15 μM for α-glucosidase). It is worth mentioning that amongst the series, the compounds 9 (IC₅₀ = 4.86 ± 1.39 μM for a-amylase and IC₅₀ = 70.57 ± 1.13 μM for α-glucosidase) and 14 (IC₅₀ = 5.02 ± 1.35 for a-amylase and IC₅₀ = 71.69 ± 5.85 μM for α-glucosidase) were found the most potent dual inhibitors, even more active than standard. Furthermore, the target compounds (1-17) exhibited moderate to good antioxidant activities. Molecular simulations studies were conducted to correlate the in vitro results and to identify the possible mode of binding interaction of ligands with the active site of enzymes. Moreover, molecular description was performed with the drug-likeness and bioactivity scores. The results showed that some compounds are in a linear correlation with Lipinski’s rule of five demonstrating good drug-likeness and bioactivity score for drug targets. Structure-activity relationships delivered useful insights towards this class of compounds, and thus paved the way to design novel analogs with improved potency.

Introduction

Diabetes mellitus (DM) has become the most debatable issue concerning public health around the globe. International Diabetes Federation declared that 415 million patients are suffering from diabetes which is multiplying rapidly. This figure may reach to 642 million in 2040 [1]. DM is a multifactorial metabolic disorder, characterized by chronic hyperglycemia and can be largely classified as type 1 (insulin-dependent DM) and type 2 (non-insulin dependent DM) [2]. Type 2 is the most common form of DM. It accounts for more than 90% of all diabetic patients. It emanates from the collaboration among behavioral, environmental, progressive urbanization, overpopulation, high caloric diet, aging, fast food and genetic risk factors [[3], [4], [5]]. The risk of happening type 2 DM (T2DM) is much higher in Asian countries like China, India and Japan due to heavy industry and socio-economic enlargement [6]. A detailed survey in 2010 explored that China has more than 113.9 million diabetes mellitus patients and 493.4 million adults were expected to have pre-diabetes mellitus condition. Another literature survey put the USA at third number having diabetes mellitus patients. In many Asian countries, particularly in India and China, the health care and societal burden of diabetes is alarming. Estimates of diabetes prevalence and impaired glucose tolerance (IGT) are high for all Asian countries and are expected to rise further over the next two decades. The latest/global trend shows that more than 60% of the diabetic population worldwide will be in Asia. It is estimated that in South Asian countries (India, Pakistan, Bangladesh, Sri Lanka, China and Nepal) 300 million people will have the disease by the year 2025 and that it will be able to reach 366 million in the year 2030 [7,8]. Analysis of the latest statistical data reveals that T2DM has become a serious issue in developed countries like the USA, Japan and China particularly being 45-64 years old and this issue is comparatively less harmful in lower middle income countries like Brazil, Pakistan, Bangladesh Russia and Indonesia [9]. An enlargement of weight during the childhood stage has resulted in T2DM becoming more common in teenagers and children, which is a very serious issue and a new public health problem in the future [10]. Diabetic problem becomes more serious if remained untreated for example, vision disorder, heart disease, nephropathy, neuropathy, stroke and peripheral vascular disease, which later converted into ulcer [11].

For long term cure and determent of DM, medical approaches usually involve drugs that can be used together with lifestyle interventions for glycemic control and delay the inchoation of diabetic complications [12]. An efficacious prevention of hyperglycemia in type 2 DM includes retarding, regulation and inhibition of carbohydrate hydrolyzing enzymes [13]. In due course, α-amylase is used in decomposing long chain of starch and α-glucosidase breaks down oligosaccharides and disaccharides [14], and thus are accountable to DM disease. Inhibitors of these enzymes slow down carbohydrate digestion, thus prolong overall digestion time, causing a reduction in glucose absorption and consequently blunting postprandial plasma glucose [15]. One of the effective therapeutic strategies for the treatment of DM is to prevent the reaction of pancreatic α-amylase and intestinal α-glucosidase. For the cure of T2DM, the commercially available drugs are acarbose, miglitol, and voglibose which act as inhibitors of both α-amylase and α-glucosidase enzymes. Nevertheless, these hypoglycemic agents have certain limitations due to their side effects like stress, allergic reaction, infection, abdominal discomfort, flatulence, diarrhea, and meteorism [16,17]. Thus, the exploration of such effective therapeutic methods is indispensable for the prevention of diabetes and related complications.

Flavonoids are a group of more than 4000 polyphenolic compounds that are ubiquitously found throughout the plant kingdom. These compounds possess a common phenylbenzopyrone framework (C₆-C₃-C₆ arrangement), and they are categorized according to the saturation level and opening of the central pyran ring, mainly into Aurones, Anthocyanins, Chalcones, Flavones, Flavanols, Isoflavones and Flavanones as sub-classes [18,19]. Flavonoids occupy a special place in the realm of natural and synthetic organic chemistry owing to their useful biological activities such as antioxidant [20,21], anxiolytic [22], anticancer, analgesic and anti-inflammatory, antimicrobial [23] and enzyme inhibition assays [24]. Since prehistoric times flavonoids have been used for the treatment of diabetes mellitus. Few papers report the inhibition of flavonoids against ɑ-amylase and ɑ-glucosidase [[25], [26], [27]]. In a broader sense, the number of reported flavonoids holds strong antioxidant activity [[28], [29], [30]] by scavenging hydroxyl radicals, lipid per oxyradicals and superoxide anions [31]. Being available for wide spectrum drugs [32] none of the therapy possesses favorable effects and their responses vary among patients might be due to the individual immune status, secondary complications and micro and macro-vascular damages. In this connection, flavonoids abundantly exist in nature and thus have been exhibiting strong anti-diabetic activities in-vitro and in-vivo for a long time [[33], [34], [35]]. However, in spite of many natural flavonoids, in particular flavonols, have the potential to inhibit ɑ-amylase and ɑ-glucosidase enzymes but to best of our knowledge, synthetic flavonols have remained a challenge for such an activity. Although, a number of related heterocyclic structures have been reported as potent ɑ-amylase and ɑ-glucosidase inhibitors [36,37].

Encouraged by the above-mentioned facts, herein we report efficient synthesis, characterization and biological investigation of varyingly substituted brominated-flavonols as potent ɑ-amylase and ɑ-glucosidase inhibitors. Also, the synthetic analogs (1-17) were scrutinized for their antioxidant activities and the experimental results were verified through computational studies as well.