Synthesis and alpha-D-glucosidase inhibitory activity of N-substituted valiolamine derivatives as potential oral antidiabetic agents

Inhibitory potential of ginger extracts against enzymes linked to type 2 diabetes, inflammation and induced oxidative stress

Ginger (Zingiber officinale Roscoe) continues to be used as an important cooking spice and herbal medicine around the world. Gingerols, the major pungent components of ginger, are known to improve diabetes, including the effect of enhancement against insulin sensitivity. In the current study, ginger sequentially extracted with different solvents-namely, hexane, ethyl acetate, methanol, 70% methanol-water and water-were screened to determine the variations in phenolic-linked active constituents. The potential of these extracts to inhibit key enzymes relevant to type 2 diabetes and inflammation was studied. Phenolic compounds-namely, gingerols and shoagols-were quantified using high-performance liquid chromatography. Ethyl acetate extract showed higher activity compared with other extracts. These studies indicate that ginger has very good potential for α-glucosidase and α-amylase inhibition relevant for type 2 diabetes management and cyclooxygenase inhibition for inflammation.

16-[(E)-Benzyl-idene]-13-hy-droxy-4-methyl-2-phenyl-4,14-diaza-penta-cyclo-[12.3.1.0.0.0]octa-deca-7(12),8,10-triene-6,17-dione

In the title compound, C₃₀H₂₆N₂O₃, the two pyrrolidine rings adopt twisted and envelope conformations, whereas the cyclo­pentane ring adopts an envelope conformation. The least-squares planes through the pyrrolidine rings form a dihedral angle of 41.72 (10)°. The mol­ecular structure is stabilized by an intra­molecular O—H⋯N hydrogen bond, which generates an S(5) ring motif. Centrosymmetrically related mol­ecules are linked via two pairs of inter­molecular C—H⋯O inter­actions, forming R₂²(16) ring motifs. In the crystal packing, the mol­ecules are linked into two-dimensional networks parallel to the ab plane via C—H⋯O inter­actions.

(1S)-1,5-anhydro-1-[5-(4-ethoxybenzyl)-2-methoxy-4-methylphenyl]-1-thio-D-glucitol (TS-071) is a potent, selective sodium-dependent glucose cotransporter 2 (SGLT2) inhibitor for type 2 diabetes treatment

Derivatives of a novel scaffold, C-phenyl 1-thio-D-glucitol, were prepared and evaluated for sodium-dependent glucose cotransporter (SGLT) 2 and SGLT1 inhibition activities. Optimization of substituents on the aromatic rings afforded five compounds with potent and selective SGLT2 inhibition activities. The compounds were evaluated for in vitro human metabolic stability, human serum protein binding (SPB), and Caco-2 permeability. Of them, (1S)-1,5-anhydro-1-[5-(4-ethoxybenzyl)-2-methoxy-4-methylphenyl]-1-thio-D-glucitol (3p) exhibited potent SGLT2 inhibition activity (IC(50) = 2.26 nM), with 1650-fold selectivity over SGLT1. Compound 3p showed good metabolic stability toward cryo-preserved human hepatic clearance, lower SPB, and moderate Caco-2 permeability. Since 3p should have acceptable human pharmacokinetics (PK) properties, it could be a clinical candidate for treating type 2 diabetes. We observed that compound 3p exhibits a blood glucose lowering effect, excellent urinary glucose excretion properties, and promising PK profiles in animals. Phase II clinical trials of 3p (TS-071) are currently ongoing.

In vitro potential of Ascophyllum nodosum phenolic antioxidant-mediated alpha-glucosidase and alpha-amylase inhibition

Ascophyllum nodosum is a brown seaweed that grows abundantly in the Northeast coastal region. In this study, the potential of A. nodosum for type 2 diabetes management through antioxidant-mediated alpha-glucosidase and alpha-amylase inhibition was investigated. After the initial screening of 4 locally harvested seaweeds, A. nodosum was chosen for its highest phenolic content and was subjected to water extraction. Among extraction ratios of 50 g to 100 to 1000 mL at room temperature, 50 g/400 mL yielded the highest phenolic content of 4.5 mg/g wet weight. For evaluation of extraction temperature ranging from 20 to 80 degrees C, 50 g/400 mL was chosen as a minimum amount of extractant. Among temperatures studied, extraction at 80 degrees C resulted in the highest total phenolic contents (4.2 mg/g wet weight). All extracts had similar levels of antioxidant activity in the range of 60% to 70% in terms of 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity. The 80 degrees C extract had the highest alpha-glucosidase and alpha-amylase inhibitory activity with IC(50) of 0.24 and 1.34 microg phenolics, respectively, compared to the IC(50) of acarbose, reference inhibitor, being 0.37 and 0.68 microg. The results show that fresh A. nodosum has strong alpha-glucosidase and mild alpha-amylase inhibitory activities that correlated with phenolic contents. This study suggests a nutraceutical potential of A. nodosum based on phytochemical antioxidant and antihyperglycemia activities.

Combination treatment with alogliptin and voglibose increases active GLP-1 circulation, prevents the development of diabetes and preserves pancreatic beta-cells in prediabetic db/db mice

AIM

Alogliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, and voglibose, an alpha-glucosidase inhibitor, have different but complementary mechanisms of action on glucagon-like peptide-1 (GLP-1) regulation and glucose-lowering effects. The present study evaluated the chronic effects of combination treatment with alogliptin and voglibose in prediabetic db/db mice.

METHODS

Alogliptin (0.03%) and voglibose (0.001%) alone or in combination were administered in the diet to prediabetic db/db mice.

RESULTS

After 3 weeks, voglibose treatment increased GLP-1 secretion (voglibose alone, 1.6-fold; alogliptin plus voglibose, 1.5-fold), while it decreased plasma glucose-dependent insulinotropic polypeptide (GIP) (voglibose alone, -30%; alogliptin plus voglibose, -29%). Alogliptin, voglibose and combination treatment decreased plasma DPP-4 activity by 72, 15 and additively by 80%, respectively, and increased plasma active GLP-1 levels by 4.5-, 1.8- and synergistically by 9.1-fold respectively. Combination treatment increased plasma insulin by 3.6-fold (alogliptin alone, 1.3-fold; voglibose alone, 1.8-fold), decreased plasma glucagon by 30% (alogliptin alone, 11%; voglibose alone, 8%), and prevented the development of diabetes, much more effectively than either agent alone. After 4 weeks, alogliptin, voglibose and combination treatment increased pancreatic insulin content by 1.6-, 3.4- and synergistically by 8.5-fold respectively. Furthermore, combination treatment resulted in an increased expression of insulin, pancreatic and duodenal homeobox 1 (PDX1) and glucose transporter 2 (GLUT2), and maintenance of normal beta/alpha-cell distribution in the pancreatic islet.

CONCLUSIONS

Chronic treatment with alogliptin in combination with voglibose concurrently increased active GLP-1 circulation, increased insulin secretion, decreased glucagon secretion, prevented the onset of the disease, and preserved pancreatic beta-cells and islet structure in prediabetic db/db mice.

Chaperone therapy for neuronopathic lysosomal diseases: competitive inhibitors as chemical chaperones for enhancement of mutant enzyme activities

Chaperone therapy is a newly developed molecular approach to lysosomal diseases, a group of human genetic diseases causing severe brain damage. We found two valienamine derivatives, N-octyl-4-epi-β-valienamine (NOEV) and N-octyl-β-valienamine (NOV), as promising therapeutic agents for human β-galactosidase deficiency disorders (mainly G_M1-gangliosidosis) and β-glucosidase deficiency disorders (Gaucher disease), respectively. We briefly reviewed the historical background of research in carbasugar glycosidase inhibitors. Originally NOEV and NOV had been discovered as competitive inhibitors, and then their paradoxical bioactivities as chaperones were confirmed in cultured fibroblasts from patients with these disorders. Subsequently G_M1-gangliosidosis model mice were developed and useful for experimental studies. Orally administered NOEV entered the brain through the blood-brain barrier, enhanced β-galactosidase activity, reduced substrate storage, and improved neurological deterioration clinically. Furthermore, we executed computational analysis for prediction of molecular interactions between β-galactosidase and NOEV. Some preliminary results of computational analysis of molecular interaction mechanism are presented in this article. NOV also showed the chaperone effect toward several β-glucosidase gene mutations in Gaucher disease. We hope chaperone therapy will become available for some patients with G_M1-gangliosidosis, Gaucher disease, and potentially other lysosomal storage diseases with central nervous system involvement.

Chronic administration of voglibose, an alpha-glucosidase inhibitor, increases active glucagon-like peptide-1 levels by increasing its secretion and decreasing dipeptidyl peptidase-4 activity in ob/ob mice

Administration of an alpha-glucosidase inhibitor, voglibose, increases the secretion of glucagon-like peptide (GLP)-1, a key modulator of pancreatic islet hormone secretion and glucose homeostasis. In the present study, novel mechanisms by which voglibose increases active GLP-1 circulation were evaluated. Voglibose (0.001 and 0.005%) was administered in the diet to ob/ob mice for 1 day or 3 to 4 weeks to determine effects on incretin profiles and plasma activity of dipeptidyl peptidase-4 (DPP-4), an enzyme responsible for GLP-1 degradation. Voglibose showed no direct inhibitory effect against DPP-4 in vitro (DPP-4 inhibitor alogliptin, IC(50) < 10 nM). Likewise, 1-day treatment with voglibose did not change plasma DPP-4 activity; however, it increased plasma active GLP-1 by 1.6- to 3.4-fold. After chronic treatment, voglibose stimulated GLP-1 secretion, as evidenced by the 1.3- to 1.5-fold increase in plasma active plus inactive amidated GLP-1 levels. Plasma DPP-4 activity was decreased unexpectedly by 40 to 51%, resulting from reduced plasma DPP-4 concentrations in voglibose-treated mice. Voglibose increased GLP-1 content by 1.5- to 1.6-fold and 1.4- to 1.6-fold in the lower intestine and colon, respectively. The increased GLP-1 content in the colon was associated with elevated expression of gut glucagon gene. Chronic treatment with voglibose resulted in 1.9- to 4.1-fold increase in active GLP-1 circulation, which was higher than 1-day treatment. A similar treatment with pioglitazone (0.03%), an insulin sensitizer, did not affect plasma DPP-4 activity or GLP-1 levels. These results suggest that increased GLP-1 secretion, decreased DPP-4 activity, and increased gut GLP-1 content may have contributed to increased active GLP-1 circulation after chronic treatment with voglibose in a glucose control-independent manner in ob/ob mice.

Protective effects of dietary chamomile tea on diabetic complications

Matricaria chamomilla L., known as "chamomile", has been used as an herbal tea or supplementary food all over the world. We investigated the effects of chamomile hot water extract and its major components on the prevention of hyperglycemia and the protection or improvement of diabetic complications in diabetes mellitus. Hot water extract, esculetin (3) and quercetin (7) have been found to show moderate inhibition of sucrase with IC50 values of 0.9 mg/mL and 72 and 71 microM, respectively. In a sucrose-loading test, the administration of esculetin (50 mg/kg body weight) fully suppressed hyperglycemia after 15 and 30 min, but the extract (500 mg/kg body weight) and quercetin (50 mg/kg body weight) were less effective. On the other hand, a long-term feed test (21 days) using a streptozotocin-induced rat diabetes model revealed that the same doses of extract and quercetin showed significant suppression of blood glucose levels. It was also found that these samples increased the liver glycogen levels. Moreover, chamomile extract showed potent inhibition against aldose reductase (ALR2), with an IC50 value of 16.9 microg/mL, and its components, umbelliferone (1), esculetin (3), luteolin (6), and quercetin (7), could significantly inhibit the accumulation of sorbitol in human erythrocytes. These results clearly suggested that daily consumption of chamomile tea with meals could contribute to the prevention of the progress of hyperglycemia and diabetic complications.

A New Method for Production of Valienamine with Microbial Degradation of Acarbose

A new method for the production of valienamine with the microbial degradation of acarbose is described. The microorganism was screened by our laboratory and identified as Stenotrophomonas maltrophilia. After separation, valienamine was analyzed with UV, IR, and 1H and 13C NMR. The yield was more than 60%.

Intramolecular direct aldol reactions of sugar diketones: syntheses of valiolamine and validoxylamine G

A new and stereoselective intramolecular direct aldol reaction of diketones derived from carbohydrates has been developed to construct carbocycles with D-gluco-, D-galacto-, D-manno-, and L-ido-configurations. The stereochemical outcome of the aldol reaction of the diketone is dependent on the base used. Transformation of D-gluco-aldols readily affords valiolamine which also constitutes a formal synthesis of voglibose. Facile conversion of D-gluco-cyclohexanones into validoxylamine G has been achieved in 12 steps with 15.1% overall yield from D-glucose.

Discovery of antimycobacterial spiro-piperidin-4-ones: an atom economic, stereoselective synthesis, and biological intervention

An atom economic and stereoselective synthesis of several spiro-piperidin-4-ones through 1,3-dipolar cycloaddition of azomethine ylides generated in situ from isatin and alpha-amino acids viz . proline, phenylglycine, and sarcosine to a series of 1-methyl-3,5-bis[(E)-arylmethylidene]tetrahydro-4(1H)-pyridinones is described. These compounds were evaluated for their in vitro and in vivo activity against Mycobacterium tuberculosis H37Rv (MTB), multidrug resistant Mycobacterium tuberculosis (MDR-TB), and Mycobacterium smegmatis (MC(2)). Compound 4-(4-fluorophenyl)-5-phenylpyrrolo(spiro[2.3'']oxindole)spiro[3.3']-1'-methyl-5'-(4-fluorophenylmethylidene)piperidin-4'-one (4e) was found to be the most active in vitro with a MIC value of 0.07 microM against MTB and was 5.1 and 67.2 times more potent than isoniazid and ciprofloxacin, respectively. In vivo, compound 4e decreased the bacterial load in lung and spleen tissues with 1.30 and 3.73-log 10 protections respectively and was considered to be promising in reducing bacterial count in lung and spleen tissues.

Effects of a late evening snack combined with alpha-glucosidase inhibitor on liver cirrhosis

AIM

A late evening snack (LES) is recommended for protein-energy malnutrition in patients with liver cirrhosis. However, many cases of liver cirrhosis have accompanying impaired glucose tolerance and there are concerns that LESs might aggravate glucose intolerance. In this study, we concomitantly used an alpha-glucosidase inhibitor with a LES and examined the effects on glucose tolerance. In addition, we examined whether or not there was an improvement in energy metabolism by slowing glucose absorption with the concomitant use of the alpha-glucosidase inhibitor.

METHODS

The subjects were 11 patients with liver cirrhosis. From before the study, all the patients had been taking a LES supplementation with a branched-chain amino acid (BCAA)-enriched nutrient mixture. The patients were started on the concomitant use of alpha-glucosidase inhibitor (0.2 mg) taken just prior to the LES. The change of glucose tolerance and energy metabolism were examined using a 75-g oral glucose tolerance test and indirect calorimetry.

RESULTS

One week and three months after the start of the concomitant use of the alpha-glucosidase inhibitor, the area under the concentration curve for plasma glucose was significantly decreased. Three months after the concomitant use, the non-protein respiratory quotient was significantly improved. There were no serious side effects during the follow-ups.

CONCLUSION

The concomitant use of the alpha-glucosidase inhibitor use with LES showed the possibility of improving glucose tolerance and energy metabolism. In patients with impaired glucose tolerance, the concomitant use of an alpha-glucosidase inhibitor with LES might be a useful measure for nutritional management.

In vitro inhibition of glycogen-degrading enzymes and glycosidases by six-membered sugar mimics and their evaluation in cell cultures

We investigated in vitro inhibition of mammalian carbohydrate-degrading enzymes by six-membered sugar mimics and their evaluation in cell cultures. 1-Deoxynojirimycin (DNJ) showed no significant inhibition toward glycogen phosphorylase (GP) but was a potent inhibitor of another glycogen-degrading enzyme, amylo-1,6-glucosidase (1,6-GL), with an IC(50) value of 0.16 microM. In primary rat hepatocytes, the inhibition of glycogen breakdown by DNJ reached plateau at 100 microM with 25% inhibition and then remained unchanged. The potent GP inhibitor 1,4-dideoxy-1,4-imino-D-arabinitol (D-AB1) inhibited hepatic glucose production with an IC(50) value of about 9 microM and the inhibition by D-AB1 was further enhanced in the presence of DNJ. DNJ and alpha-homonojirimycin (HNJ) are very potent inhibitors of rat intestinal maltase, with IC(50) values of 0.13 and 0.08 microM, respectively, and also showed a similar strong inhibition toward maltase in Caco-2 cell model system, with IC(50) value of 0.05 and 0.10 microM, respectively. D-Isofagomine (D-IFG) and L-IFG are competitive and noncompetitive inhibitors of human lysosomal beta-glucosidase (beta-GL), respectively, with K(i) values of 8.4 nM and 6.9 microM. D-IFG increased intracellular beta-GL activity by twofold at 10 microM in Gaucher N370S cell line as an 'active-site-specific' chaperone, and surprisingly a noncompetitive inhibitor L-IFG also increased intracellular beta-GL activity by 1.6-fold at 500 microM.

In vitro studies of eggplant (Solanum melongena) phenolics as inhibitors of key enzymes relevant for type 2 diabetes and hypertension

National Diabetes Education Program of NIH, Mayo Clinic and American Diabetes Association recommend eggplant-based diet as a choice for management of type 2 diabetes. The rationale for this suggestion is the high fiber and low soluble carbohydrate content of eggplant. We propose that a more physiologically relevant explanation lies in the phenolic-linked antioxidant activity and alpha-glucosidase inhibitory potential of eggplant which could reduce hyperglycemia-induced pathogenesis. Results from this study indicate that phenolic-enriched extracts of eggplant with moderate free radical scavenging-linked antioxidant activity had high alpha-glucosidase inhibitory activity and in specific cases moderate to high angiotensin I-converting enzyme (ACE) inhibitory activity. Inhibition of these enzymes provide a strong biochemical basis for management of type 2 diabetes by controlling glucose absorption and reducing associated hypertension, respectively. This phenolic antioxidant-enriched dietary strategy also has the potential to reduce hyperglycemia-induced pathogenesis linked to cellular oxidation stress. These results provide strong rationale for further animal and clinical studies.

5''-(4-Chloro-benzyl-idene)-1',1''-dimethyl-3'-phenyl-acenaphthene-1-spiro-2'-pyrrolidine-3'-spiro-3''-pyridine-2,4''-dione

In the title compound, C₃₄H₂₈Cl₂N₂O₂, the five-membered pyrrolidine ring adopts an envelope conformation and the six-membered piperidinone ring is in a distorted half-chair conformation. The mol­ecular structure shows three intra­molecular C—H⋯O inter­actions and the crystal packing is stabilized through inter­molecular C—H⋯O and C—H⋯π inter­actions.

Health benefits of traditional corn, beans, and pumpkin: in vitro studies for hyperglycemia and hypertension management

Levels of obesity-linked non-insulin-dependent diabetes mellitus (NIDDM) and hypertension are highest among indigenous communities in North America. This is linked to changes in dietary pattern towards high calorie foods such as sugar, refined grain flour, and sweetened beverages. Therefore, a return to traditional dietary patterns may help to reduce these disease problems because of better balance of calories and beneficial nutrients. Further protective non-nutrient phenolic phytochemicals against NIDDM and hypertension are potentially high in these foods but less understood. In this study antidiabetic- and antihypertension-relevant potentials of phenolic phytochemicals were confirmed in select important traditional plant foods of indigenous communities such as pumpkin, beans, and maize using in vitro enzyme assays for -glucosidase, alpha-amylase, and angiotensin I-converting enzyme (ACE) inhibitory activities. In vitro inhibitory activities of these enzymes provide a strong biochemical rationale for further in vivo studies and dietary management strategy for NIDDM through the control of glucose absorption and reduction of associated hypertension. These enzyme inhibitory activities were further compared to total soluble phenolic content and antioxidant activity of the above-targeted plant foods. Pumpkin showed the best overall potential. Among the varieties of pumpkin extracts P5 (round orange) and P6 (spotted orange green) had high content of total phenolics and moderate antioxidant activity coupled to moderate to high alpha-glucosidase and ACE inhibitory activities. Therefore this phenolic antioxidant-enriched dietary strategy using specific traditional plant food combinations can generate a whole food profile that has the potential to reduce hyperglycemia-induced pathogenesis and also associated complications linked to cellular oxidation stress and hypertension.

Synthesis and evaluation of ketophosph(on)ates as beta-lactamase inhibitors

A series of amidoketophosph(on)ates of general structure PhCH2OCONHCH(R)COCHR'(CH2)n(O)P(O2-)(O)R'' (R = H, CH3; R' = H, CH3; n = 0, 1; R'' = H, CH3, Et, Ph) have been prepared as a potential source of beta-lactamase inhibitors. The phosphonates (n = 0) were obtained by means of the Arbuzov reaction while most of the phosphates were achieved from reaction of phosph(or/on)ic acids with the appropriate diazoketone PhCH2OCONHCH(R)COCR'N2. The electrophilicity of the carbonyl group in the resulting phosph(on)ates was assessed by the degree of hydration in aqueous solution, determined from NMR spectra. These compounds inhibited typical class C and class D beta-lactamases, particularly the latter group, but showed no activity against class A enzymes. To enhance the carbonyl electrophilicity, an alpha-difluorinated analogue (R = H, CHR' = CF2, n = 0, R'' = Et) was also prepared, but no enhanced inhibitory activity was observed. All evidence suggested that these compounds inhibited in the carbonyl form rather than by formation of tetrahedral adducts at the beta-lactamase active site. They show promise as leads to specific class D beta-lactamase inhibitors.