Inhibition of recombinant human maltase glucoamylase by salacinol and derivatives

Exploring the interaction of phytochemicals from Hibiscus rosa-sinensis flowers with glucosidase and acetylcholinesterase: An integrated in vitro and in silico approach

Targeting multiple factors such as oxidative stress, alpha glucosidase and acetylcholinesterase (AChE) are considered advantageous for the treatment of diabetes and diabetes associated-cognitive dysfunction. In the present study, Hibiscus rosa-sinensis flowers anthocyanin-rich extract (HRA) was prepared. Phytochemical analysis of HRA using LC-ESI/MS/MS revealed the presence of various phenolic acids, flavonoids and anthocyanins. HRA showed in vitro antioxidant activity at low concentrations. HRA inhibited all the activities of mammalian glucosidases and AChE activity. The IC50 value of HRA for the inhibition of maltase, sucrase, isomaltase, glucoamylase and AChE was found to be 308.02 ± 34.25 µg/ml, 287.8 ± 19.49 µg/ml, 424.58 ± 34.75 µg/ml, 408.94 ± 64.82 µg/ml and 264.13 ± 30.84 µg/ml, respectively. Kinetic analysis revealed mixed-type inhibition against all the activities except for glucoamylase (competitive) activity. In silico analysis confirmed the interaction of two active constituents cyanidin 3-sophoroside (CS) and quercetin 3-O-sophoroside (QS) with four subunits, n-terminal and c-terminal subunits of human maltase-glucoamylase and sucrase-isomaltase as well as with AChE. Molecular dynamics simulation, binding free energy calculation, DCCM, PCA, PCA-based free energy surface analysis ascertained the stable binding of CS and QS with target proteins studied. HRA could be used as complementary therapy for diabetes and cognitive improvement.

Alpha-amylase as molecular target for treatment of diabetes mellitus: A comprehensive review

The alpha (α)-amylase is a calcium metalloenzyme that aids digestion by breaking down polysaccharide molecules into smaller ones such as glucose and maltose. In addition, the enzyme causes postprandial hyperglycaemia and blood glucose levels to rise. α-Amylase is a well-known therapeutic target for the treatment and maintenance of postprandial blood glucose elevations. Various enzymatic inhibitors, such as acarbose, miglitol and voglibose, have been found to be effective in targeting this enzyme, prompting researchers to express an interest in developing potent alpha-amylase inhibitor molecules. The review mainly focused on designing different derivatives of drug molecules such as benzofuran hydrazone, indole hydrazone, spiroindolone, benzotriazoles, 1,3-diaryl-3-(arylamino) propan-1-one, oxadiazole and flavonoids along with their target-receptor interactions, IC₅₀ values and other biological activities.

Inhibitory Effect of Antidesma bunius Fruit Extract on Carbohydrate Digestive Enzymes Activity and Protein Glycation In Vitro

Antidesma bunius (L.) spreng (Mamao) is widely distributed in Northeastern Thailand. Antidesma bunius has been reported to contain anthocyanins, which possess antioxidant and antihypertensive actions. However, the antidiabetic and antiglycation activity of Antidesma bunius fruit extract has not yet been reported. In this study, we investigated the inhibitory activity of anthocyanin-enriched fraction of Antidesma bunius fruit extract (ABE) against pancreatic α-amylase, intestinal α-glucosidase (maltase and sucrase), protein glycation, as well as antioxidant activity. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) chromatogram revealed that ABE contained phytochemical compounds such as cyanidin-3-glucoside, delphinidin-3-glucoside, ellagic acid, and myricetin-3-galactoside. ABE inhibited intestinal maltase and sucrase activity with the IC₅₀ values of 0.76 ± 0.02 mg/mL and 1.33 ± 0.03 mg/mL, respectively. Furthermore, ABE (0.25 mg/mL) reduced the formation of fluorescent AGEs and the level of N^ε-carboxymethyllysine (N^ε-CML) in fructose and glucose-induced protein glycation during four weeks of incubation. During the glycation process, the protein carbonyl and β-amyloid cross structure were decreased by ABE (0.25 mg/mL). In addition, ABE exhibited antioxidant activity through DPPH radical scavenging activity and Trolox equivalent antioxidant capacity (TEAC) with the IC₅₀ values 15.84 ± 0.06 µg/mL and 166.1 ± 2.40 µg/mL, respectively. Meanwhile, ferric reducing antioxidant power (FRAP) showed an EC₅₀ value of 182.22 ± 0.64 µg/mL. The findings suggest that ABE may be a promising agent for inhibiting carbohydrate digestive enzyme activity, reducing monosaccharide-induced protein glycation, and antioxidant activity.

Proteins with Evolutionarily Hypervariable Domains are Associated with Immune Response and Better Survival of Basal-like Breast Cancer Patients

Maltase-glucoamylase (MGAM) and MGAM2 both belong to the glycoside hydrolase family 31. MGAM, a therapeutic target for type 2 diabetes, is α-1,4-glucosidase and expressed in the intestine to catalyze starch digestion. MGAM2, however, is largely uncharacterized. By investigating The Cancer Genome Atlas data, we found that among breast cancer subtypes, MGAM2 expression is nearly exclusive to basal-like breast cancers (BLBCs), whereas MGAM tends to express in luminal A breast cancers. Moreover, MGAM2 expression is associated with better patient survival and correlated with immune genes/signatures, unlike MGAM. Both genes have emerged in mammals, but diverged after the placental-marsupial split. In placentals, MGAM2 has likely lost its α-1,4-glucosidase activity due to mutations in key catalytic sites, and has acquired a large domain that is extracellular, threonine-rich and evolutionarily hypervariable (EHV). Guided by MGAM2 findings, our genome-wide search identified >1000 human proteins with EHV regions. These proteins are enriched in immune functions and molecules, including major histocompatibility complex proteins. Their genes are expressed higher in BLBCs and are associated with better patient survival, like MGAM2. Their EHV-coding sequences are rich in simple repeats and harbor more cancer passenger mutations. In conclusion, MGAM2 diverges from MGAM structurally and likely functionally in placentals. MGAM2 is among >1000 human proteins with EHV regions and associated with immune response. We propose that these EHV molecules may have significant implication in cancer immunotherapy and BLBC treatment.

Different inhibition properties of catechins on the individual subunits of mucosal α-glucosidases as measured by partially-purified rat intestinal extract

Mucosal α-glucosidases from rat intestinal powder were employed, with a step to remove α-amylase, to measure the possibility of different inhibition of catechins, particularly those found in tea, on the four α-glucosidase enzymes.

Mulberry leaf extract reduces the glycemic indexes of four common dietary carbohydrates

BACKGROUND

1-Deoxynojirimycin (DNJ), a component of mulberry leaf extract (MLE), reduces postprandial hyperglycemia by inhibiting intestinal a-glycosidase. The aim of this exploratory study was to investigate the effects of MLE on the glycemic indexes (GI) of common dietary carbohydrates.

METHODS

This single-center, randomized, open-label, 7-cycle self-controlled crossover study enrolled 15 healthy volunteers at the National Drug Clinical Trial Institution, Second Affiliated Hospital of Tianjin University of Traditional Chinese Medicine (June 2014 to December 2014). The participants were randomized to receive glucose (3 occasions), glucose+MLE, sucrose+MLE, maltose+MLE, and maltodextrin+MLE orally during 7 visits (every 3 days). Blood glucose level was tested at 15 minutes before and at 15, 30, 45, 60, 90, and 120 minutes after carbohydrate intake. The GI of each carbohydrate relative to glucose (GI = 100) was calculated using the incremental area under the curve method. Safety was assessed at each visit.

RESULTS

All participants completed the protocol. After carbohydrate ingestion, blood glucose level peaked at 30 minutes (glucose, glucose+MLE, sucrose+MLE, and maltose+MLE) or 45 minutes (maltodextrin+MLE) before returning to preprandial levels at 120 minutes. At 30 minutes, the change in blood glucose level was lower for sucrose+MLE, maltose+MLE, and maltodextrin+MLE than for glucose or glucose+MLE (P < .05). GI was lowest for sucrose+MLE (43.22 ± 17.47) and maltose+MLE (49.23 ± 22.39), intermediate for maltodextrin+MLE (75.90 ± 26.01), and higher for glucose+MLE (91.88 ± 27.24). MLE reduced the GIs for maltose, sucrose, maltodextrin, and glucose by 53.11%, 33.51%, 31.00%, and 8.12%, respectively. MLE was well tolerated.

CONCLUSIONS

Coconsumption of MLE with sucrose, maltose, or maltodextrin can reduce the GI values of these carbohydrates.

TRIAL REGISTRATION

Chinese Clinical Trial Registry Platform, no. ChiCTR-IPR-15006484. Registered on May 28, 2015.

Identification of novel nt-MGAM inhibitors for potential treatment of type 2 diabetes: Virtual screening, atom based 3D-QSAR model, docking analysis and ADME study

In this study, a virtual screening procedure was applied to identify new potential nt-MGAM inhibitors as a possible medication for type 2 diabetes. To this aim, a series of salacinol analogues were first investigated by docking analysis for their binding to the X-ray structure of the biological target nt-MGAM. Key interactions for ligand binding into the receptor active site were identified which shared common features to those found for other known inhibitors, which strengthen the results of this study. 3D QSAR model was then built and showed to be statistically significant and with a good predictive power for the training (R² = 0.99, SD = 0.17, F = 555.3 and N = 27) and test set (Q² = 0.81, Pearson(r) = 0.92, RMSE = 0.52, N = 08). The model was then used to virtually screen the ZINC database with the aim of identifying novel chemical scaffolds as potential nt-MGAM inhibitors. Further, in silico predicted ADME properties were investigated for the most promising molecules. The outcome of this investigation sheds light on the molecular characteristics of the binding of salacinol analogues to nt-MGAM enzyme and identifies new possible inhibitors which have the potential to be developed into drugs, thus significantly contributing to the design and optimization of therapeutic strategies against type 2 diabetes.

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.

Functional Properties of Novel Epigallocatechin Gallate Glucosides Synthesized by Using Dextransucrase from Leuconostoc mesenteroides B-1299CB4

Epigallocatechin gallate (EGCG) is the most abundant catechin found in the leaves of green tea, Camellia sinensis. In this study, novel epigallocatechin gallate-glucocides (EGCG-Gs) were synthesized by using dextransucrase from Leuconostoc mesenteroides B-1299CB4. Response surface methodology was adopted to optimize the conversion of EGCG to EGCG-Gs, resulting in a 91.43% conversion rate of EGCG. Each EGCG-G was purified using a C₁₈ column. Of nine EGCG-Gs identified by nuclear magnetic resonance analysis, five EGCG-Gs (2 and 4-7) were novel compounds with yields of 2.2-22.6%. The water solubility of the five novel compounds ranged from 229.7 to 1878.5 mM. The 5'-OH group of EGCG-Gs expressed higher antioxidant activities than the 4'-OH group of EGCG-Gs. Furthermore, glucosylation at 7-OH group of EGCG-Gs was found to be responsible for maintaining tyrosinase inhibitory activity and increasing browning-resistant activities.

Tea Polysaccharides and Their Bioactivities

Tea (Camellia sinensis) is a beverage beneficial to health and is also a source for extracting bioactive components such as theanine, tea polyphenols (TPP) and tea polysaccharides (TPS). TPS is a group of heteropolysaccharides bound with proteins. There is evidence showing that TPS not only improves immunity but also has various bioactivities, such as antioxidant, antitumor, antihyperglycemia, and anti-inflammation. However, inconsistent results concerning chemical composition and bioactivity of TPS have been published in recent years. The advances in chemical composition and bioactivities of TPS are reviewed in the present paper. The inconsistent and controversial results regarding composition and bioactivities of TPS are also discussed.

Re-exploring promising α-glucosidase inhibitors for potential development into oral anti-diabetic drugs: Finding needle in the haystack

Treatment of diabetes mellitus by oral α-glucosidase inhibitors is currently confined to acarbose, miglitol and voglibose marred by efficacy problems and unwanted side effects. Since the discovery of the drugs more than three decades ago, no significant progress has been made in the drug development area of anti-diabetic α-glucosidase inhibitors. Despite existence of a wide chemical diversity of α-glucosidase inhibitors identified to date, majority of them are simply piled up in publications and reports thus creating a haystack destined to be forgotten in the scientific literature without given consideration for further development into drugs. This review finds those "needles" in that haystack and lays groundwork for highlighting promising α-glucosidase inhibitors from the literature that may potentially become suitable candidates for pre-clinical or clinical trials while drawing attention of the drug development community to consider and take already-identified promising α-glucosidase inhibitors into the next stage of drug development.

Dietary phenolic compounds selectively inhibit the individual subunits of maltase-glucoamylase and sucrase-isomaltase with the potential of modulating glucose release

In this study, it was hypothesized that dietary phenolic compounds selectively inhibit the individual C- and N-terminal (Ct, Nt) subunits of the two small intestinal α-glucosidases, maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI), for a modulated glycemic carbohydrate digestion. The inhibition by chlorogenic acid, caffeic acid, gallic acid, (+)-catechin, and (-)-epigallocatechin gallate (EGCG) on individual recombinant human Nt-MGAM and Nt-SI and on mouse Ct-MGAM and Ct-SI was assayed using maltose as the substrate. Inhibition constants, inhibition mechanisms, and IC50 values for each combination of phenolic compound and enzymatic subunit were determined. EGCG and chlorogenic acid were found to be more potent inhibitors for selectively inhibiting the two subunits with highest activity, Ct-MGAM and Ct-SI. All compounds displayed noncompetitive type inhibition. Inhibition of fast-digesting Ct-MGAM and Ct-SI by EGCG and chlorogenic acid could lead to a slow, but complete, digestion of starch for improved glycemic response of starchy foods with potential health benefit.

Sulfonium ions as inhibitors of the mycobacterial galactofuranosyltransferase GlfT2

The mycobacterial cell wall possesses a core galactan moiety composed of approximately 30 galactofuranosyl residues attached via alternating β-(1→5) and β-(1→6) linkages.

Inhibition of human intestinal α-glucosidases by calystegines

Calystegines are polyhydroxylated nortropane alkaloids found in Convolvulaceae, Solanaceae, and other plant families. These plants produce common fruits and vegetables. The calystegine structures resemble sugars and suggest interaction with enzymes of carbohydrate metabolism. Maltase and sucrase are α-glucosidases contributing to human carbohydrate degradation in the small intestine. Inhibition of these enzymes by orally administered drugs is one option for treatment of diabetes mellitus type 2. In this study, inhibition of maltase and sucrase by calystegines A3 and B2 purified from potatoes was investigated. In silico docking studies confirmed binding of both calystegines to the active sites of the enzymes. Calystegine A3 showed low in vitro enzyme inhibition; calystegine B2 inhibited mainly sucrose activity. Both compounds were not transported by Caco-2 cells indicating low systemic availability. Vegetables rich in calystegine B2 should be further investigated as possible components of a diet preventing a steep increase in blood glucose after a carbohydrate-rich meal.

Structural enzymology of Cellvibrio japonicus Agd31B protein reveals α-transglucosylase activity in glycoside hydrolase family 31

The metabolism of the storage polysaccharides glycogen and starch is of vital importance to organisms from all domains of life. In bacteria, utilization of these α-glucans requires the concerted action of a variety of enzymes, including glycoside hydrolases, glycoside phosphorylases, and transglycosylases. In particular, transglycosylases from glycoside hydrolase family 13 (GH13) and GH77 play well established roles in α-glucan side chain (de)branching, regulation of oligo- and polysaccharide chain length, and formation of cyclic dextrans. Here, we present the biochemical and tertiary structural characterization of a new type of bacterial 1,4-α-glucan 4-α-glucosyltransferase from GH31. Distinct from 1,4-α-glucan 6-α-glucosyltransferases (EC 2.4.1.24) and 4-α-glucanotransferases (EC 2.4.1.25), this enzyme strictly transferred one glucosyl residue from α(1→4)-glucans in disproportionation reactions. Substrate hydrolysis was undetectable for a series of malto-oligosaccharides except maltose for which transglycosylation nonetheless dominated across a range of substrate concentrations. Crystallographic analysis of the enzyme in free, acarbose-complexed, and trapped 5-fluoro-β-glucosyl-enzyme intermediate forms revealed extended substrate interactions across one negative and up to three positive subsites, thus providing structural rationalization for the unique, single monosaccharide transferase activity of the enzyme.

Inhibitory effects of epigallocatechin gallate and its glucoside on the human intestinal maltase inhibition

Human intestinal maltase (HMA) is an α-glucosidase responsible for the hydrolysis of α-1,4-linkages from the non-reducing end of malto-oligosaccharides. HMA has become an important target in the treatment of type-2 diabetes. In this study, epigallocatechin gallate (EGCG) and EGCG glucoside (EGCG-G1) were identified as inhibitors of HMA by an in vitro assay with IC₅₀ of 20 ± 1.0 and 31.5 ± 1.0 μM, respectively. A Lineweaver-Burk plot confirmed that EGCG and EGCG-G1 were competitive inhibitors of maltose substrate against HMA and inhibition kinetic constants (K_i) calculated from a Dixon plot were 5.93 ± 0.26 and 7.88 ± 0.57 μM, respectively. Both EGCG and EGCG-G1 bound to the active site of HMA with numerous hydrophobic and hydrogen bond interactions.

Modulation of starch digestion for slow glucose release through "toggling" of activities of mucosal α-glucosidases

Starch digestion involves the breakdown by α-amylase to small linear and branched malto-oligosaccharides, which are in turn hydrolyzed to glucose by the mucosal α-glucosidases, maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI). MGAM and SI are anchored to the small intestinal brush-border epithelial cells, and each contains a catalytic N- and C-terminal subunit. All four subunits have α-1,4-exohydrolytic glucosidase activity, and the SI N-terminal subunit has an additional exo-debranching activity on the α-1,6-linkage. Inhibition of α-amylase and/or α-glucosidases is a strategy for treatment of type 2 diabetes. We illustrate here the concept of "toggling": differential inhibition of subunits to examine more refined control of glucogenesis of the α-amylolyzed starch malto-oligosaccharides with the aim of slow glucose delivery. Recombinant MGAM and SI subunits were individually assayed with α-amylolyzed waxy corn starch, consisting mainly of maltose, maltotriose, and branched α-limit dextrins, as substrate in the presence of four different inhibitors: acarbose and three sulfonium ion compounds. The IC(50) values show that the four α-glucosidase subunits could be differentially inhibited. The results support the prospect of controlling starch digestion rates to induce slow glucose release through the toggling of activities of the mucosal α-glucosidases by selective enzyme inhibition. This approach could also be used to probe associated metabolic diseases.

Structural insight into substrate specificity of human intestinal maltase-glucoamylase

Human maltase-glucoamylase (MGAM) hydrolyzes linear alpha-1,4-linked oligosaccharide substrates, playing a crucial role in the production of glucose in the human lumen and acting as an efficient drug target for type 2 diabetes and obesity. The amino- and carboxyl-terminal portions of MGAM (MGAM-N and MGAM-C) carry out the same catalytic reaction but have different substrate specificities. In this study, we report crystal structures of MGAM-C alone at a resolution of 3.1 Å, and in complex with its inhibitor acarbose at a resolution of 2.9 Å. Structural studies, combined with biochemical analysis, revealed that a segment of 21 amino acids in the active site of MGAM-C forms additional sugar subsites (+ 2 and + 3 subsites), accounting for the preference for longer substrates of MAGM-C compared with that of MGAM-N. Moreover, we discovered that a single mutation of Trp1251 to tyrosine in MGAM-C imparts a novel catalytic ability to digest branched alpha-1,6-linked oligosaccharides. These results provide important information for understanding the substrate specificity of alpha-glucosidases during the process of terminal starch digestion, and for designing more efficient drugs to control type 2 diabetes or obesity.

Discovery of novel inhibitors for human intestinal maltase: virtual screening in a WISDOM environment and in vitro evaluation

Human intestinal maltase (HMA) is an α-glucosidase that hydrolyses α-1,4-linkages from the non-reducing end of malto-oligosaccharides. HMA is an important target to discover of new drugs for the treatment of type 2 diabetes. In this study, 308,307 compounds were virtually screened with HMA using Autodock 3.0.5 in a WISDOM production environment to discover novel inhibitors. The 42 top-scoring free binding energy compounds, representing 17 groups containing potential hydrogen bonding with key residues in the active site pocket of HMA, were tested in vitro for their inhibitory activities against recombinant HMA expressed from Pichia pastoris. Compounds 17 and 18 were competitive inhibitors exclusively for HMA without any in vitro inhibition for human pancreatic α-amylase. The K(i) values were 20 μM for both compound 17 and 18.

New glucosidase inhibitors from an ayurvedic herbal treatment for type 2 diabetes: structures and inhibition of human intestinal maltase-glucoamylase with compounds from Salacia reticulata

An approach to controlling blood glucose levels in individuals with type 2 diabetes is to target alpha-amylases and intestinal glucosidases using alpha-glucosidase inhibitors acarbose and miglitol. One of the intestinal glucosidases targeted is the N-terminal catalytic domain of maltase-glucoamylase (ntMGAM), one of the four intestinal glycoside hydrolase 31 enzyme activities responsible for the hydrolysis of terminal starch products into glucose. Here we present the X-ray crystallographic studies of ntMGAM in complex with a new class of alpha-glucosidase inhibitors derived from natural extracts of Salacia reticulata, a plant used traditionally in Ayuverdic medicine for the treatment of type 2 diabetes. Included in these extracts are the active compounds salacinol, kotalanol, and de-O-sulfonated kotalanol. This study reveals that de-O-sulfonated kotalanol is the most potent ntMGAM inhibitor reported to date (K(i) = 0.03 microM), some 2000-fold better than the compounds currently used in the clinic, and highlights the potential of the salacinol class of inhibitors as future drug candidates.

Structural basis for substrate selectivity in human maltase-glucoamylase and sucrase-isomaltase N-terminal domains

Human maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI) are small intestinal enzymes that work concurrently to hydrolyze the mixture of linear alpha-1,4- and branched alpha-1,6-oligosaccharide substrates that typically make up terminal starch digestion products. MGAM and SI are each composed of duplicated catalytic domains, N- and C-terminal, which display overlapping substrate specificities. The N-terminal catalytic domain of human MGAM (ntMGAM) has a preference for short linear alpha-1,4-oligosaccharides, whereas N-terminal SI (ntSI) has a broader specificity for both alpha-1,4- and alpha-1,6-oligosaccharides. Here we present the crystal structure of the human ntSI, in apo form to 3.2 A and in complex with the inhibitor kotalanol to 2.15 A resolution. Structural comparison with the previously solved structure of ntMGAM reveals key active site differences in ntSI, including a narrow hydrophobic +1 subsite, which may account for its additional substrate specificity for alpha-1,6 substrates.

Towards the elusive structure of kotalanol, a naturally occurring glucosidase inhibitor

This Highlight describes the detailed approach used to determine the absolute stereochemistry of the stereogenic centers in the acyclic side chain of kotalanol, a naturally occurring glucosidase inhibitor isolated from the plant Salacia reticulata. The plant extract itself is used in Ayurvedic medicine for the treatment of Type 2 diabetes. We highlight the syntheses of proposed candidates based on structure-activity relationships, the total synthesis of kotalanol, and crystallographic studies of kotalanol and its de-O-sulfonated derivative complexed with recombinant human maltase glucoamylase (MGA), a critical intestinal glucosidase involved in the breakdown of glucose oligomers into glucose.

Human lysosomal alpha-mannosidases exhibit different inhibition and metal binding properties

Two structurally-related members of the lysosomal mannosidase family, the broad substrate specificity enzyme human lysosomal alpha-mannosidase (hLM, MAN2B1) and the human core alpha-1, 6-specific mannosidase (hEpman, MAN2B2) act in a complementary fashion on different glycosidic linkages, to effect glycan degradation in the lysosome. We have successfully expressed these enzymes in Drosophila S2 cells and functionally characterized them. hLM and hEpman were significantly inhibited by the class II alpha-mannosidase inhibitors, swainsonine and mannostatin A. We show that three pyrrolidine-based compounds designed for selective inhibition of Golgi alpha-mannosidase II (GMII) exhibited varying degrees of inhibition for hLM and hEpman. While these compounds inhibited hLM and GMII similarly, they inhibited hEpman to a lesser extent. Further, the two lysosomal alpha-mannosidases also show differential metal dependency properties. This has led us to propose a secondary metal binding site in hEpman. These results set the stage for the development of selective inhibitors to members of the GH38 family, and, henceforth, the further investigation of their physiological roles.

Sulfonium-ion glycosidase inhibitors isolated from Salacia species used in traditional medicine, and related compounds

A novel class of naturally-occurring glycosidase inhibitors, having sulfonium sulfate structures, has been isolated as bioactive components from Indian plants, belonging to the Salacia genus in the family Celastraceae, and used in Ayurvedic medicine for the treatment of type-2 diabetes. Thus far, five such sulfonium salts, namely, salacinol, kotalanol, salaprinol, ponkoranol and de-O-sulfonated kotalanol, have been isolated from this plant species. These structurally unique zwitterionic glycosidase inhibitors have received much attention due to their therapeutic potential in the treatment of type-2 diabetes. We recently reported a review article which focused mainly on salacinol and related analogues. The present review presents an update on the remaining four compounds from this class of glycosidase inhibitors, with respect to their isolation, glucosidase inhibitory activities, and synthesis. In addition, progress towards the stereochemical structure elucidation of kotalanol, through synthesis of analogues, is described. Review with 42 references.

Studies directed toward the stereochemical structure determination of the naturally occurring glucosidase inhibitor, kotalanol: synthesis and inhibitory activities against human maltase glucoamylase of seven-carbon, chain-extended homologues of salacinol

The synthesis of new seven-carbon, chain-extended sulfonium salts of 1,4-anhydro-4-thio- d-arabinitol, analogues of the naturally occurring glycosidase inhibitor salacinol, are described. These compounds were designed on the basis of the structure activity data of chain-extended analogues of salacinol, with the intention of determining the hitherto unknown stereochemical structure of kotalanol, the naturally occurring seven-carbon chain-extended analogue of salacinol. The target zwitterionic compounds were synthesized by means of nucleophilic attack of the PMB-protected 1,4-anhydro-4-thio- d-arabinitols at the least hindered carbon atom of two 1,3-cyclic sulfates differing in stereochemistry at only one stereogenic center. The desired cyclic sulfates were synthesized starting from d-glucose via Wittig olefination and Sharpless asymmetric dihydroxylation. Deprotection of the coupled products by using a two-step sequence afforded two sulfonium sulfates. Optical rotation data for one of our compounds indicated a correspondence with that reported for kotalanol. However, comparison of (1)H and (13)C NMR spectral data of the synthetic compounds with those of kotalanol indicated discrepancies. The collective data from this and published work were used to propose a tentative structure for the naturally occurring compound, kotalanol. Comparison of physical data of previously synthesized analogues with those for the recently isolated six-carbon chain analogue, ponkoranol or reticulanol, also led to elucidation of this structure. Interestingly, both our compounds inhibited recombinant human maltase glucoamylase (MGA), as expected from our previous structure activity studies of lower homologues, with K i values of 0.13 +/- 0.02 and 0.10 +/- 0.02 microM.

Luminal starch substrate "brake" on maltase-glucoamylase activity is located within the glucoamylase subunit

The detailed mechanistic aspects for the final starch digestion process leading to effective alpha-glucogenesis by the 2 mucosal alpha-glucosidases, human sucrase-isomaltase complex (SI) and human maltase-glucoamylase (MGAM), are poorly understood. This is due to the structural complexity and vast variety of starches and their intermediate digestion products, the poorly understood enzyme-substrate interactions occurring during the digestive process, and the limited knowledge of the structure-function properties of SI and MGAM. Here we analyzed the basic catalytic properties of the N-terminal subunit of MGAM (ntMGAM) on the hydrolysis of glucan substrates and compared it with those of human native MGAM isolated by immunochemical methods. In relation to native MGAM, ntMGAM displayed slower activity against maltose to maltopentose (G5) series glucose oligomers, as well as maltodextrins and alpha-limit dextrins, and failed to show the strong substrate inhibitory "brake" effect caused by maltotriose, maltotetrose, and G5 on the native enzyme. In addition, the inhibitory constant for acarbose was 2 orders of magnitude higher for ntMGAM than for native MGAM, suggesting lower affinity and/or fewer binding configurations of the active site in the recombinant enzyme. The results strongly suggested that the C-terminal subunit of MGAM has a greater catalytic efficiency due to a higher affinity for glucan substrates and larger number of binding configurations to its active site. Our results show for the first time, to our knowledge, that the C-terminal subunit of MGAM is responsible for the MGAM peptide's "glucoamylase" activity and is the location of the substrate inhibitory brake. In contrast, the membrane-bound ntMGAM subunit contains the poorly inhibitable "maltase" activity of the internally duplicated enzyme.

Synthesis of aza- and thia-spiroheterocycles and attempted synthesis of spiro sulfonium compounds related to salacinol

The synthesis of aza- and thia-spiroheterocycles and the attempted synthesis of spiro sulfonium compounds related to salacinol are described. The binding of the nanomolar inhibitor swainsonine to Drosophila Golgi alpha-mannosidase II (dGMII) involves a large contribution of interactions between the six-membered ring of the inhibitor and the hydrophobic pocket within the enzyme active site. Salacinol, a naturally occurring sulfonium ion, is one of the active principles in the aqueous extracts of Salacia reticulata that are traditionally used in Sri Lanka and India for the treatment of diabetes. Spiro aza- and thia-heterocycles and a spiro analogue of salacinol were designed with the expectation that the hydrocarbon portions would make hydrophobic contributions to binding. The former sets of compounds were synthesized successfully but the salacinol analogue proved to be elusive. The stereochemistry of the final compounds was determined by means of 1D-NOESY experiments. The aza- and thia-heterocycles were not effective inhibitors of Golgi alpha-mannosidase II or human maltase glucoamylase.