Dilip D. Dhavale

Synthesis of silver nanoparticles using Dioscorea bulbifera tuber extract and evaluation of its synergistic potential in combination with antimicrobial agents.

Background Development of an environmentally benign process for the synthesis of silver nanomaterials is an important aspect of current nanotechnology research. Among the 600 species of the genus Dioscorea, Dioscorea bulbifera has profound therapeutic applications due to its unique phytochemistry. In this paper, we report on the rapid synthesis of silver nanoparticles by reduction of aqueous Ag+ ions using D. bulbifera tuber extract. Methods and results Phytochemical analysis revealed that D. bulbifera tuber extract is rich in flavonoid, phenolics, reducing sugars, starch, diosgenin, ascorbic acid, and citric acid. The biosynthesis process was quite fast, and silver nanoparticles were formed within 5 hours. Ultraviolet-visible absorption spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, energy dispersive spectroscopy, and x-ray diffraction confirmed reduction of the Ag+ ions. Varied morphology of the bioreduced silver nanoparticles included spheres, triangles, and hexagons. Optimization studies revealed that the maximum rate of synthesis could be achieved with 0.7 mM AgNO3 solution at 50°C in 5 hours. The resulting silver nanoparticles were found to possess potent antibacterial activity against both Gram-negative and Gram-positive bacteria. Beta-lactam (piperacillin) and macrolide (eryth-romycin) antibiotics showed a 3.6-fold and 3-fold increase, respectively, in combination with silver nanoparticles selectively against multidrug-resistant Acinetobacter baumannii. Notable synergy was seen between silver nanoparticles and chloramphenicol or vancomycin against Pseudomonas aeruginosa, and was supported by a 4.9-fold and 4.2-fold increase in zone diameter, respectively. Similarly, we found a maximum 11.8-fold increase in zone diameter of streptomycin when combined with silver nanoparticles against E. coli, providing strong evidence for the synergistic action of a combination of antibiotics and silver nanoparticles. Conclusion This is the first report on the synthesis of silver nanoparticles using D. bulbifera tuber extract followed by an estimation of its synergistic potential for enhancement of the antibacterial activity of broad spectrum antimicrobial agents.

Gnidia glauca flower extract mediated synthesis of gold nanoparticles and evaluation of its chemocatalytic potential.

BackgroundNovel approaches for synthesis of gold nanoparticles (AuNPs) are of utmost importance owing to its immense applications in diverse fields including catalysis, optics, medical diagnostics and therapeutics. We report on synthesis of AuNPs using Gnidia glauca flower extract (GGFE), its detailed characterization and evaluation of its chemocatalytic potential.ResultsSynthesis of AuNPs using GGFE was monitored by UV-Vis spectroscopy and was found to be rapid that completed within 20 min. The concentration of chloroauric acid and temperature was optimized to be 0.7 mM and 50°C respectively. Bioreduced nanoparticles varied in morphology from nanotriangles to nanohexagons majority being spherical. AuNPs were characterized employing transmission electron microscopy, high resolution transmission electron microscopy. Confirmation of elemental gold was carried out by elemental mapping in scanning transmission electron microscopic mode, energy dispersive spectroscopy and X-ray diffraction studies. Spherical particles of size ~10 nm were found in majority. However, particles of larger dimensions were in range between 50-150 nm. The bioreduced AuNPs exhibited remarkable catalytic properties in a reduction reaction of 4-nitrophenol to 4-aminophenol by NaBH4 in aqueous phase.ConclusionThe elaborate experimental evidences support that GGFE can provide an environmentally benign rapid route for synthesis of AuNPs that can be applied for various purposes. Biogenic AuNPs synthesized using GGFE exhibited excellent chemocatalytic potential.

Antidiabetic Activity of Gnidia glauca and Dioscorea bulbifera: Potent Amylase and Glucosidase Inhibitors

Diabetes is a metabolic disorder affecting about 220 million people worldwide. One of the most critical complications of diabetes is post-prandial hyper-glycemia (PPHG). Glucosidase inhibitor and α-amylase inhibitors are class of compounds that help in managing PPHG. Low-cost herbal treatment is recommended due to their lesser side effect for treatment of diabetes. Two plants with significant traditional therapeutic potential, namely, Gnidia glauca and Dioscorea bulbifera, were tested for their efficiency to inhibit α-amylase and α-glucosidase. Stem, leaf, and flower of G. glauca and bulb of D. bulbifera were sequentially extracted with petroleum ether, ethyl acetate, and methanol as well as separately with 70% ethanol. Petroleum ether extract of flower of G. glauca was found to inhibit α-amylase significantly (78.56%). Extracts were further tested against crude murine pancreatic, small intestinal, and liver glucosidase enzyme which revealed excellent inhibitory properties. α-glucosidase inhibition provided a strong in vitro evidence for confirmation of both G. glauca and D. bulbifera as excellent antidiabetic remedy. This is the first report of its kind that provides a strong biochemical basis for management of type II diabetes using G. glauca and D. bulbifera. These results provide intense rationale for further in vivo and clinical study.

1-Aza-sugars from d-glucose. Preparation of 1-deoxy-5-dehydroxymethyl-nojirimycin, its analogues and evaluation of glycosidase inhibitory activity

D-glucose derived pentodialdoses 11a-c on reduction followed by tosylation, azide displacement, hydrogenation and protection with -Cbz group gave N-Cbz protected compounds 14a-c, respectively, which on removal of 1,2-acetonide functionality and hydrogenation afforded corresponding 1-aza-sugars 3, 9 and 10 in good overall yields. The glycosidase inhibition activity of these 1-aza-sugars was tested with sweet almond as a rich source of different glycosidases.

Synthesis of gold nanoanisotrops using dioscorea bulbifera tuber extract

Biosynthesis of metal nanoparticles employing plant extracts and thereby development of an environmentally benign process is an important branch of nanotechnology. Here, the synthesis of gold nanoparticles using Dioscorea bulbifera tuber extract (DBTE) as the reducing agent is reported. Field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDX), X-ray diffraction (XRD), and UV-visible absorption spectroscopy confirmed the reduction of gold ions to AuNPs. The anisotropic nanoparticles consist of a mixture of gold nanotriangles, nanoprisms, nanotrapezoid, and spheres. The kinetics of particle formation was time dependent and was enhanced by the increase of temperature from 6° to 50°, the optimum being 50°. The optimum concentration of chloroauric acid was found to be 1mM. Complete reduction of the metal ions within 5 hours by DBTE highlights the development of a novel ecofriendly route of biological synthesis of gold nanoparticles. This is the first paper on synthesis of gold nanoparticles using DBTE.

Isolation, characterization, and plasmid pUPI126-mediated indole-3-acetic acid production in acinetobacter strains from rhizosphere of wheat.

Thirty-seven strains of Acinetobacter isolated and characterized from rhizosphere of wheat were screened for indole-3-acetic acid (IAA) production. Only eight Acinetobacter strains showed IAA production. The genus Acinetobacter was confirmed by chromosomal DNA transformation assay. Biotyping of eight strains was carried out and they were found to be genospecies of A. junii, A. baumannii, A. genospecies 3, and A. haemolyticus. Five of eight strains produced IAA at the early stationary phase: A. haemolyticus (A19), A. baumannii (A18, A16, A13), and Acinetobacter genospecies 3 (A15). A. junii A6 showed maximum IAA production at log phase and A. genospecies 3 and A. baumannii (A28, A30) at late stationary phase. IAA was extracted by ethyl acetate and purified by preparative thin-layer chromatography. Purified IAA was confirmed by 1H-nuclear magnetic resonance and infrared spectrum analysis. Pot experiments showed a significant increase in plant growth inoculated with eight Acinetobacter genospecies as compared to control plants. IAA production was found to be encoded by plasmid pUPI126. All eight strains of Acinetobacter contain a plasmid pUPI126 with a molecular weight of 40 kb. Plasmid pUPI126 was transformed into Escherichia coli HB101 at a frequency of 5 × 10−5, and E. coli HB101 (pUPI126) transformants also showed IAA activity. PUPI126 also encoded resistance to selenium, tellurium, and lead. This is the first report of plasmid-encoded IAA production in the genus Acinetobacter.

Diosgenin from Dioscorea bulbifera: Novel Hit for Treatment of Type II Diabetes Mellitus with Inhibitory Activity against α-Amylase and α-Glucosidase

Diabetes mellitus is a multifactorial metabolic disease characterized by post-prandial hyperglycemia (PPHG). α-amylase and α-glucosidase inhibitors aim to explore novel therapeutic agents. Herein we report the promises of Dioscorea bulbifera and its bioactive principle, diosgenin as novel α-amylase and α-glucosidase inhibitor. Among petroleum ether, ethyl acetate, methanol and 70% ethanol (v/v) extracts of bulbs of D. bulbifera, ethyl acetate extract showed highest inhibition upto 72.06 ± 0.51% and 82.64 ± 2.32% against α-amylase and α-glucosidase respectively. GC-TOF-MS analysis of ethyl acetate extract indicated presence of high diosgenin content. Diosgenin was isolated and identified by FTIR, 1H NMR and 13C NMR and confirmed by HPLC which showed an α-amylase and α-glucosidase inhibition upto 70.94 ± 1.24% and 81.71 ± 3.39%, respectively. Kinetic studies confirmed the uncompetitive mode of binding of diosgenin to α-amylase indicated by lowering of both Km and Vm. Interaction studies revealed the quenching of intrinsic fluorescence of α-amylase in presence of diosgenin. Similarly, circular dichroism spectrometry showed diminished negative humped peaks at 208 nm and 222 nm. Molecular docking indicated hydrogen bonding between carboxyl group of Asp300, while hydrophobic interactions between Tyr62, Trp58, Trp59, Val163, His305 and Gln63 residues of α-amylase. Diosgenin interacted with two catalytic residues (Asp352 and Glu411) from α-glucosidase. This is the first report of its kind that provides an intense scientific rationale for use of diosgenin as novel drug candidate for type II diabetes mellitus.

Chiron approach to the synthesis of (2S,3R)-3-hydroxypipecolic acid and (2R,3R)-3-hydroxy-2-hydroxymethylpiperidine from D-glucose

The first chiron approach from d-glucose for the total synthesis of (2 S,3 R)-3-hydroxypipecolic acid (-)-1a and (2R,3R)-3-hydroxy-2-hydroxymethylpiperidine (-)-2a is reported. The synthetic pathway involves conversion of d-glucose into 3-azidopentodialdose (5) followed by the Wittig olefination and reduction to give the piperidine ring skeleton (8) with a sugar appendage that on cleavage of an anomeric carbon followed by oxidation gives (-)-1a which on reduction affords (-)-2a.

Stereocontrolled 1,3-addition reaction of silyl ketene acetal to sugar nitrone: synthesis of d-gluco-homo-1-deoxynojirimycin and l-ido-homo-1-deoxynojirimycin

Abstract The 1,3-addition reaction of silyl ketene acetal 6 to d -glucose derived nitrone 7 followed by reductive cleavage of the N–O bond afforded d -gluco- and l -ido-β-amino ester derivatives of 9a and 9b. The diastereoselectivity in addition reaction was improved as well as altered by making use of different Lewis acids. Reduction of the ester group in 9a followed by hydrogenolysis gave amino alcohol 12a. Selective N-Cbz protection, hydrolysis and intramolecular reductive amination afforded d -gluco-homo-1-deoxynojirimycin 1d. Analogously, β-amino ester 9b was converted to l -ido-homo-1-deoxynojirimycin 1c.

Concise and practical synthesis of (2S, 3R, 4R, 5R) and (2S, 3R, 4R, 5S)-1,6-dideoxy-1,6-iminosugars

Abstract The syntheses of (2 S ,3 R ,4 R ,5 R ) and (2 S ,3 R ,4 R ,5 S )-1,6-dideoxy-1,6 iminosugars 1a and 1b , respectively, from d -glucose are described. The key transformations in this reaction sequence include regio-selective epoxide ring opening with N -benzylamine followed by intramolecular reductive amination of amino-aldehyde.