Docking and SAR studies of salacinol derivatives as alpha-glucosidase inhibitors

Bio-Guided Isolation of Alpha-Glucosidase Inhibitory Compounds from Vietnamese Lichen Roccella Montagnei

A bio-guided isolation was applied to the Vietnamese lichen Roccella montagnei based on alpha-glucosidase inhibition. Six compounds were isolated and structurally elucidated, including a new ortho depside, montagneside A (1), together with five known compounds, sekikaic acid (2), lanost-7-en-3β-ol (3), ethyl orsellinate (4), D-montagnetol (5), and D-erythrin (6). Their chemical structures were identified by extensive 1D and 2D NMR analysis, high-resolution mass spectroscopy, and comparisons with those reported in the literature. D-Erythrin (6), a major component, was selected for further modification using Smiles rearrangement. Three erythritol derivatives 6a-6c were synthesized. Compounds 1-3, 6, and 6a-6c were evaluated for alpha-glucosidase inhibition. Compounds 2 and 6a-6c showed significant alpha-glucosidase inhibition with IC50 values ranging from 7.9 to 149 μM, respectively. Molecular docking was applied to the most active compound 6a to clarify the inhibitory mechanism.

Role of the thiosugar ring in the inhibitory activity of salacinol, a potent natural α-glucosidase inhibitor

Herein, ring-cleaved (24) and truncated (25) analogues of an azasugar, 1-deoxynojirimycin (23), exhibited inhibitory activity (Ki = 4-10 μM) equal to that of the parent compound (1, Ki = 14 μM). Based on this structure-activity relationship (SAR), four ring-cleaved (26a-26c and 27c) and three truncated (28a-28c) analogues of salacinol (1), a potent thiosugar-ring-containing α-glucosidase inhibitor, were synthesised. Bioassay results revealed that all the synthetics were inactive, indicating that the 5-membered thiosugar ring of 1 played an essential role in the potent activities of sulfonium-type inhibitors. The present findings are interesting and important in understanding the function of salacinol, considering that the observed inhibitory activity trend was contrary to the SAR observed in aza-compounds (23, 24, and 25) in a previous study, which suggested that the cyclic structure did not contribute to their strong inhibitory activity.

Synthesis and structure-activity relationship studies of benzimidazole-thioquinoline derivatives as α-glucosidase inhibitors

In this article, different s-substituted benzimidazole-thioquinoline derivatives were designed, synthesized, and evaluated for their possible α-glucosidase inhibitory activities. The most active compound in this series, 6j (X = 4-bromobenzyl) exhibited significant potency with an IC₅₀ value of 28.0 ± 0.6 µM compared to acarbose as the positive control with an IC₅₀ value of 750.0 µM. The kinetic study showed a competitive inhibition pattern against α-glucosidase for the 6j derivative. Also, the molecular dynamic simulations were performed to determine key interactions between compounds and the targeted enzyme. The in silico pharmacodynamics and ADMET properties were executed to illustrate the druggability of the novel derivatives. In general, it can be concluded that these derivatives can serve as promising leads to the design of potential α-glucosidase inhibitors.

Design and Synthesis of Sulfonium Derivatives: A Novel Class of α-Glucosidase Inhibitors with Potent In Vivo Antihyperglycemic Activities

We report the first attempt of double-spot structural modification on a side-chain moiety of sulfonium-type α-glucosidase inhibitors isolated from genus Salacia. A series of sulfonium salts with benzylidene acetal linkage at the C3' and C5' positions were designed and synthesized. In vitro enzyme inhibition evaluation showed that compounds with a strong electron-withdrawing group attached at the ortho position on the phenyl ring present stronger inhibitory activities. Notably, the most potent inhibitor 21b (1.0 mpk) can exhibit excellent hypoglycemic effects in mice, which can still compete with those of acarbose (20.0 mpk). Molecular docking of 21b demonstrated that besides conventional interacting patterns, the newly introduced benzylidene acetal moiety plays an important role in anchoring the whole molecule in a concave pocket of the enzyme. The successful identification of 21b as a lead compound for new drug discovery may provide a means for structure modification and diversification of the distinguished sulfonium-type α-glucosidase inhibitors.

Pharmaceutical Food Science: Search for Bio-Functional Molecules Obtained from Natural Resources to Prevent and Ameliorate Lifestyle Diseases

In this review, our resent pharmaceutical food science research for bio-functional molecules obtained from natural resources that contribute to i) suppression of postprandial blood glucose elevation and/or improvement of glucose tolerance and ii) reduction of visceral fat accumulation and improvement of lipid metabolism were summarized. Based on studies using MONOTORI science, salacinol (1), neokotalanol (4), and trans-tiliroside (20) have been approved or notified by the Consumer Affairs Agency in Japan as functional substances in food with health claims, Food for Specified Health Use and Food with Functional Claims.

Synthesis of Novel N-Methylmorpholine-Substituted Benzimidazolium Salts as Potential α-Glucosidase Inhibitors

The α-glucosidase enzyme, located in the brush border of the small intestine, is responsible for overall glycemic control in the body. It hydrolyses the 1,4-linkage in the carbohydrates to form blood-absorbable monosaccharides that ultimately increase the blood glucose level. α-Glucosidase inhibitors (AGIs) can reduce hydrolytic activity and help to control type 2 diabetes. Aiming to achieve this, a novel series of 1-benzyl-3-((2-substitutedphenyl)amino)-2-oxoethyl)-2-(morpholinomethyl)-1H-benzimidazol-3-ium chloride was synthesized and screened for its α-glucosidase inhibitory potential. Compounds 5d, 5f, 5g, 5h and 5k exhibited better α-glucosidase inhibitions compared to the standard drug (acarbose IC50 = 58.8 ± 0.012 µM) with IC50 values of 15 ± 0.030, 19 ± 0.060, 25 ± 0.106, 21 ± 0.07 and 26 ± 0.035 µM, respectively. Furthermore, the molecular docking studies explored the mechanism of enzyme inhibitions by different 1,2,3-trisubstituted benzimidazolium salts via significant ligand–receptor interactions.

Identification of Cyclic Sulfonamides with an N-Arylacetamide Group as α-Glucosidase and α-Amylase Inhibitors: Biological Evaluation and Molecular Modeling

Diabetes mellitus (DM), a complicated metabolic disorder, is due to insensitivity to insulin function or reduction in insulin secretion, which results in postprandial hyperglycemia. α-Glucosidase inhibitors (AGIs) and α-amylase inhibitors (AAIs) block the function of digestive enzymes, which delays the carbohydrate hydrolysis process and ultimately helps to control the postprandial hyperglycemia. Diversified 2-(3-(3-methoxybenzoyl)-4-hydroxy-1,1-dioxido-2H-benzo[e][1,2]thiazin-2-yl)-N-arylacetamides were synthesized and evaluated for their in vitro inhibitory potential against α-glucosidase and α-amylase enzymes. The compounds with chloro, bromo and methyl substituents demonstrated good inhibition of α-glucosidase enzymes having IC50 values in the range of 25.88-46.25 μM, which are less than the standard drug, acarbose (IC50 = 58.8 μM). Similarly, some derivatives having chloro, bromo and nitro substituents were observed potent inhibitors of α-amylase enzyme, with IC50 values of 7.52 to 15.06 μM, lower than acarbose (IC50 = 17.0 μM). In addition, the most potent compound, N-(4-bromophenyl)-2-(4-hydroxy-3-(3-methoxybenzoyl)-1,1-dioxido-2H-benzo[e][1,2]thiazin-2-yl)acetamide (12i), was found to be a non-competitive and competitive inhibitor of α-glucosidase and α-amylase enzymes, respectively, during kinetic studies. The molecular docking studies provided the binding modes of active compounds and the molecular dynamics simulation studies of compound 12i in complex with α-amylase also showed that the compound is binding in a fashion similar to that predicted by molecular docking studies.

Antidiabetic Phytochemicals From Medicinal Plants: Prospective Candidates for New Drug Discovery and Development

Diabetes, a chronic physiological dysfunction affecting people of different age groups and severely impairs the harmony of peoples' normal life worldwide. Despite the availability of insulin preparations and several synthetic oral antidiabetic drugs, there is a crucial need for the discovery and development of novel antidiabetic drugs because of the development of resistance and side effects of those drugs in long-term use. On the contrary, plants or herbal sources are getting popular day by day to the scientists, researchers, and pharmaceutical companies all over the world to search for potential bioactive compound(s) for the discovery and development of targeted novel antidiabetic drugs that may control diabetes with the least unwanted effects of conventional antidiabetic drugs. In this review, we have presented the prospective candidates comprised of either isolated phytochemical(s) and/or extract(s) containing bioactive phytoconstituents which have been reported in several in vitro, in vivo, and clinical studies possessing noteworthy antidiabetic potential. The mode of actions, attributed to antidiabetic activities of the reported phytochemicals and/or plant extracts have also been described to focus on the prospective phytochemicals and phytosources for further studies in the discovery and development of novel antidiabetic therapeutics.

Discovery of Amide-Functionalized Benzimidazolium Salts as Potent α-Glucosidase Inhibitors

α-Glucosidase inhibitors (AGIs) are used as medicines for the treatment of diabetes mellitus. The α-Glucosidase enzyme is present in the small intestine and is responsible for the breakdown of carbohydrates into sugars. The process results in an increase in blood sugar levels. AGIs slow down the digestion of carbohydrates that is helpful in controlling the sugar levels in the blood after meals. Among heterocyclic compounds, benzimidazole moiety is recognized as a potent bioactive scaffold for its wide range of biologically active derivatives. The aim of this study is to explore the α-glucosidase inhibition ability of benzimidazolium salts. In this study, two novel series of benzimidazolium salts, i.e., 1-benzyl-3-{2-(substituted) amino-2-oxoethyl}-1H-benzo[d]imidazol-3-ium bromide 9a-m and 1-benzyl-3-{2-substituted) amino-2-oxoethyl}-2-methyl-1H-benzo[d] imidazol-3-ium bromide 10a-m were screened for their in vitro α-glucosidase inhibitory potential. These compounds were synthesized through a multistep procedure and were characterized by 1H-NMR, 13C-NMR, and EI-MS techniques. Compound 10d was identified as the potent α-glucosidase inhibitor among the series with an IC50 value of 14 ± 0.013 μM, which is 4-fold higher than the standard drug, acarbose. In addition, compounds 10a, 10e, 10h, 10g, 10k, 10l, and 10m also exhibited pronounced potential for α-glucosidase inhibition with IC50 value ranging from 15 ± 0.037 to 32.27 ± 0.050 µM when compared with the reference drug acarbose (IC50 = 58.8 ± 0.12 μM). A molecular docking study was performed to rationalize the binding interactions of potent inhibitors with the active site of the α-glucosidase enzyme.

Synthetic access to thiolane-based therapeutics and biological activity studies

Secondary metabolites isolated from bioactive extracts of natural sources iteratively pioneer the research in drug discovery. Modern medicine is often inspired by bioactive natural products or the bio-functional motifs embedded in them. One of such consequential bio-functional motifs is the thiolane unit. Thiolane-based bioactive organic compounds have manifested a plethora of astonishing biological activities such as anti-viral, anti-cancer, anti-platelet, α-glucosidase inhibition, anti-HIV, immunosuppressive and anti-microbial activities which renders them excellent candidates in drug discovery. Hence, to scale up the accessibility of thiolane-based therapeutics its chemical syntheses is essential and in addition; a sneak peek in its biosynthesis would give a perspective for developing biomimetic syntheses. This review highlights the development of important thiolane-based therapeutics such as (i) Nuphar sesquiterpene thioalkaloids (ii) Thiosugar sulphonium salts from Salacia sp. (iii) Albomycins (iv) Thiolane-based therapeutics from Allium sp. (v) 4'-thionucleosides summarizing various synthetic strategies, biosynthesis and biological activity studies, covering literature till 2021. We anticipate that this review will inspire chemists and biochemists to take up the challenges encountered in the synthesis and development of thiolane-based therapeutics.

A review of antidiabetic active thiosugar sulfoniums, salacinol and neokotalanol, from plants of the genus Salacia

During our studies characterizing functional substances from food resources for the prevention and treatment of lifestyle-related diseases, we isolated the active constituents, salacinol (1) and neokotalanol (4), and related thiosugar sulfoniums, from the roots and stems of the genus Salacia plants [Celastraceae (Hippocrateaceae)] such as Salacia reticulata Wight, S. oblonga Wall., and S. chinensis L., and observed their antidiabetic effects. These plant materials have been used traditionally in Ayurvedic medicine as a specific remedy at the early stage of diabetes, and have been extensively consumed in Japan, the United States, and other countries as a food supplement for the prevention of obesity and diabetes. Here, we review our studies on the antidiabetic effects of plants from the genus Salacia, from basic chemical and pharmacological research to their application and development as new functional food ingredients.

Synthesis and α-Glucosidase Inhibition Activity of 2-[3-(Benzoyl/4-bromobenzoyl)-4-hydroxy-1,1-dioxido-2H-benzo[e][1,2]thiazin-2-yl]-N-arylacetamides: An In Silico and Biochemical Approach

Diabetes mellitus (DM) is a chronic disorder and has affected a large number of people worldwide. Insufficient insulin production causes an increase in blood glucose level that results in DM. To lower the blood glucose level, various drugs are employed that block the activity of the α-glucosidase enzyme, which is considered responsible for the breakdown of polysaccharides into monosaccharides leading to an increase in the intestinal blood glucose level. We have synthesized novel 2-(3-(benzoyl/4-bromobenzoyl)-4-hydroxy-1,1-dioxido-2H-benzo[e][1,2]thiazin-2-yl)-N-arylacetamides and have screened them for their in silico and in vitro α-glucosidase inhibition activity. The derivatives 11c, 12a, 12d, 12e, and 12g emerged as potent inhibitors of the α-glucosidase enzyme. These compounds exhibited good docking scores and excellent binding interactions with the selected residues (Asp203, Asp542, Asp327, His600, Arg526) during in silico screening. Similarly, these compounds also showed good in vitro α-glucosidase inhibitions with IC₅₀ values of 30.65, 18.25, 20.76, 35.14, and 24.24 μM, respectively, which were better than the standard drug, acarbose (IC₅₀ = 58.8 μM). Furthermore, a good agreement was observed between in silico and in vitro modes of study.

Anti-melanogenic activity of salacinol by inhibition of tyrosinase oligosaccharide processing

Hyperpigmentation that manifests through melasma and solar lentigo (age spots), although mostly harmless for health, bothers many people. Controlling the rate-limiting activity of tyrosinase is most effective for suppressing excessive melanin formation and accordingly recent research has focused on the maturation of tyrosinase. Salacia, a medicinal plant, has been used to treat diabetes in India and Sri Lanka. Salacia extract reportedly contains components that inhibit the activity of α-glucosidase. Salacinol, the active ingredient in Salacia extract, has unique thiosugar sulphonium sulphate inner salt structure. Here, we observed that the salacinol component of Salacia extract possesses anti-melanogenic activity in comparison to various existing whitening agents. Although the anti-melanogenic mechanism of salacinol is presumably medicated by inhibition of tyrosinase activity, which is often found in existing whitening agents, salacinol did not inhibit tyrosinase activity in vitro. Analysis of the intracellular state of tyrosinase showed a decrease in the mature tyrosinase form due to inhibition of N-linked oligosaccharide processing. Salacinol inhibited the processing glucosidase I/II, which are involved in the initial stage of N-linked glycosylation. Owing to high activity, low cytotoxicity and high hydrophilicity, salacinol is a promising candidate compound in whitening agents aimed for external application on skin.

Elongation of the side chain by linear alkyl groups increases the potency of salacinol, a potent α-glucosidase inhibitor from the Ayurvedic traditional medicine "Salacia," against human intestinal maltase

Four chain-extended analogs (12a-12d) and two related de-O-sulfonated analogs (13a and 13c) by introducing alkyl groups (a: R = C₃H₇, b R = C₆H₁₃, c: R = C₈H₁₇, d: R = C₁₀H₂₁) to the side chains of salacinol (1), a natural α-glucosidase inhibitor from Ayurvedic traditional medicine "Salacia", were synthesized. The α-glucosidase inhibitory activities of all the synthesized analogs were evaluated in vitro. Against human intestinal maltase, the inhibitory activities of 12a and 13a with seven-carbon side chain were equal to that of 1. In contrast, analogs (12b-12d, and 13c) exhibited higher level of inhibitory activity against the same enzyme than 1 and had equal or higher potency than those of the clinically used anti-diabetics, voglibose, acarbose, and miglitol. Thus, elongation of the side chains of 1 was effective for specifically increasing the inhibitory activity against human intestinal maltase.

Recent Progress in the Construction of Natural De-O-Sulfonated Sulfonium Sugars with Antidiabetic Activities

A group of sulfonium salts equipped with a polyhydroxylated side-chain structure have been isolated and identified as potent α-glycosidase inhibitors. Consequently, they have become an attractive target in diverse research disciplines, including organic synthesis, drug discovery, and chemical biology. To this end, the development of practical and effective synthetic strategies, especially for more bioactive de-O-sulfonated sulfonium salts, is a significant research area in organic synthesis. An ideal synthetic methodology should provide easily accessible intermediates with high chemical stability for the key coupling reaction to diastereoselectively construct the sulfonium cation center. This minireview summarizes recently developed strategies applied in the construction of natural de-O-sulfonated sulfonium sugars: 1) acid-catalyzed de-O-sulfonation of sulfonium sulfate inner salts, 2) a coupling reaction between side-chain fragments containing leaving groups and a thiosugar, 3) a coupling reaction between side-chain fragments containing epoxide structures and a thiosugar, and 4) a two-step sequential S_N 2 nucleophilic substitution between side-chain fragments containing thiol groups and a diiodide derivative.

Practical Route to Neokotalanol and Its Natural Analogues: Sulfonium Sugars with Antidiabetic Activities

An efficient and divergent approach toward the synthesis of all four de-O-sulfonated sulfonium type α-glucosidase inhibitors, originally isolated from plants of genus Salacia, is reported for the first time. The key strategy features a coupling reaction between thiol derivatives and a diiodide counterpart. The newly designed thiol coupling partner presents high chemical stability, while the diiodide partner could be easily obtained with increased overall yields compared with conventional routes. The intermolecular nucleophilic substitution reaction followed by a diastereoselective intramolecular cyclization provided the target five-member sulfonium salt structure, which was connected in an α-orientation to a polyhydroxylated side-chain moiety.

Rosmarinic acid and its ester derivatives for enhancing antibacterial, α-glucosidase inhibitory, and lipid accumulation suppression activities

Rosmarinic acid (RA), commonly found in Nepetoidae subfamily of Lamiaceae family, possesses various biological activities. To expand its application, RA was modified by esterification with methyl (me), propyl (pro), and hexyl (hex) alcohols and then tested antibacterial, α-glucosidase inhibitory, and lipid accumulation suppression activities. Consequently, RA derivatives enhanced antibacterial activity, especially the RA-pro and RA-hex, which effectively inhibited the growth of Bacillus cereus rather than tannic acid, a natural antibacterial agent. RA-hex also inhibited α-glucosidase inhibitory activity greater than luteolin. By computational molecular docking, dihydroxyphenyl group and hexyl group were selected as essential groups for interaction with the active site of α-glucosidase through hydrogen bonding and hydrophobic interaction, contributing to the great inhibitory activity. Furthermore, RA-pro and RA-hex effectively suppressed lipid accumulation of 3T3-L1 cells, superior to EGCG, a well-known anti-obesity phytochemical. These biological effects of RA derivatives commonly attributed to hydrophobicity, hydrogen bonding, and steric bulkiness of the side chain. PRACTICAL APPLICATIONS: Rosmarinic acid (RA), a fundamental compound in the family Lamiaceae, is one of powerful naturally occurring antioxidants as well as other biological activities. Furthermore, its abundance in nature was also high in amount in the plant kingdom. So, natural RA can be one of possible natural resources for creating potent natural drugs and biologically useful substances after chemical modification. Studies on various biological activities may intensively expand usage and application of RA. In this study, RA was derivatized to corresponding ester such as methyl, propyl, and hexyl alcohols with higher hydrophobicity, and found great antibacterial, α-glucosidase inhibitory, and lipid accumulation suppression activities. RA-pro and RA-hex significantly suppressed lipid accumulation and cell differentiation. Therefore, RA derivatives with multiple biological activities have the potential to be applied in the food and pharmaceutical industries as food ingredients and supplements.

Aspects of extraction and biological evaluation of naturally occurring sugar-mimicking sulfonium-ion and their synthetic analogues as potent α-glucosidase inhibitors from Salacia: a review

A review of the selective inhibitory activities of sulfonium compounds ofSalaciaagainst intestinal α-glucosidases, structural features important for effective inhibition and the toggling approach for controlling starch digestion and glucose release.

Hydrophobic substituents increase the potency of salacinol, a potent α-glucosidase inhibitor from Ayurvedic traditional medicine 'Salacia'

Using an in silico method, seven analogs bearing hydrophobic substituents (8a: Me, 8b: Et, 8c: n-Pent, 8d: n-Hept, 8e: n-Tridec, 8f: isoBu and 8g: neoPent) at the 3'-O-position in salacinol (1), a highly potent natural α-glucosidase inhibitor from Ayurvedic traditional medicine 'Salacia', were designed and synthesized. In order to verify the computational SAR assessments, their α-glucosidase inhibitory activities were evaluated in vitro. All analogs (8a-8g) exhibited an equal or considerably higher level of inhibitory activity against rat small intestinal α-glucosidases compared with the original sulfonate (1), and were as potent as or higher in potency than the clinically used anti-diabetics, voglibose, acarbose or miglitol. Their activities against human maltase exhibited good relationships to the results obtained with enzymes of rat origin. Among the designed compounds, the one with a 3'-O-neopentyl moiety (8g) was most potent, with an approximately ten fold increase in activity against human maltase compared to 1.

Improvement in Human Immune Function with Changes in Intestinal Microbiota by Salacia reticulata Extract Ingestion: A Randomized Placebo-Controlled Trial

Plants belonging to the genus Salacia in the Hippocrateaceae family are known to inhibit sugar absorption. In a previous study, administration of Salacia reticulata extract in rats altered the intestinal microbiota and increased expression of immune-relevant genes in small intestinal epithelial cells. This study aimed to investigate the effect of S. reticulata extract in human subjects by examining the gene expression profiles of blood cells, immunological indices, and intestinal microbiota. The results revealed an improvement in T-cell proliferation activity and some other immunological indices. In addition, the intestinal microbiota changed, with an increase in Bifidobacterium and a decrease in Clostridium bacteria. The expression levels of many immune-relevant genes were altered in blood cells. We concluded that S. reticulata extract ingestion in humans improved immune functions and changed the intestinal microbiota.

TRIAL REGISTRATION

UMIN Clinical Trials Registry UMIN000011732.

Isolation, structure identification and SAR studies on thiosugar sulfonium salts, neosalaprinol and neoponkoranol, as potent α-glucosidase inhibitors

Two hitherto missing members of sulfonium salts family in Salacia genus plants as a new class of α-glucosidase inhibitors, neoponkoranol (7) and neosalaprinol (8), were isolated from the water extracts, and their structures were unambiguously identified. For further SAR studies on this series of sulfonium salts, several epimers of 7 and 8 were synthesized, and their inhibitory activities against rat small intestinal α-glucosidases were evaluated. Among them, 3'-epimer of 7 was found most potent in this class of molecules, and revealed as potent as currently used antidiabetics, voglibose and acarbose.