Structural insights into the interaction of antifungal peptides and ergosterol containing fungal membrane.

The treatment of invasive drug-resistant and potentially life-threatening fungal infections is limited to few therapeutic options that are usually associated with severe side effects. The development of new effective antimycotics with a more tolerable side effect profile is therefore of utmost clinical importance. Here, we used a combination of complementary in vitro assays and structural analytical methods to analyze the interaction of the de novo antimicrobial peptide VG16KRKP with the sterol moieties of biological cell membranes. We demonstrate that VG16KRKP disturbs the structural integrity of fungal membranes both invitro and in model membrane system containing ergosterol along with phosphatidylethanolamine lipid and exhibits broad-spectrum antifungal activity. As revealed by systematic structure-function analysis of mutated VG16KRKP analogs, a specific pattern of basic and hydrophobic amino acid side chains in the primary peptide sequence determines the selectivity of VG16KRKP for fungal specific membranes.

Virstatin-Conjugated Gold Nanoparticle with Enhanced Antimicrobial Activity against the Vibrio cholerae El Tor Biotype.

Because of the emergence of multidrug-resistant pathogenic bacteria, there is a growing interest for the development of an efficient alternative to antibiotics. Gold nanoparticles (AuNPs) are promising candidates due to their inherent non-toxicity and can be used as effective carriers of drugs. Cholera caused by Gram-negative Vibrio cholerae is still a potential threat in many developing countries. Virstatin, a small molecule, has been reported to inhibit virulence regulation in V. cholerae. Herein, we report an efficient synthesis of virstatin-conjugated gold nanoparticles (VL-AuNPs) and their antibacterial efficacy against the El Tor biotype of V. cholerae (VcN16961). The spherical-shaped NPs have an average diameter of ∼17 nm. The uniqueness of VL-AuNPs relies in the enhanced antibacterial efficacy compared to virstatin, as evidenced from the inhibitory concentration obtained from growth kinetics, and attributed to the inhibition of ATPase activity and DNA damage. More importantly, the expression of cholera toxin, the most important virulence factor of V. cholera, is reduced to a far greater extent than by any of the component molecules. The effect of VL-AuNPs on VcN16961 was monitored using various assays such as confocal microscopy, FACS, fluorescence spectroscopy, and so on. Overall, VL-AuNPs could be a potential candidate for the use as an effective agent for combating diarrheal diseases caused by V. cholera.

Synthesis of the tetrasaccharide repeating unit of the O-specific polysaccharide of Azospirillum doebereinerae type strain GSF71T using linear and one-pot iterative glycosylations.

A straightforward synthetic strategy was developed for the synthesis of the tetrasaccharide repeating unit corresponding to the O-specific polysaccharide of Azospirillum doebereinerae type strain GSF71T in a very good yield adopting sequential glycosylation followed by removal of the p-methoxybenzyl (PMB) group in the same pot. Further, the synthetic strategy was modified by carrying out three stereoselective iterative glycosylations followed by in situ removal of the PMB group in one pot. The stereochemical outcome of the newly formed glycosidic linkages was excellent using thioglycoside derivatives as glycosyl donors and a combination of N-iodosuccinimide (NIS) and perchloric acid supported on silica (HClO4-SiO2) as the glycosyl activator.

Convenient synthesis of the pentasaccharide repeating unit corresponding to the cell wall O-antigen of Escherichia albertii O4.

A straightforward sequential synthetic strategy has been developed for the synthesis of a pentasaccharide repeating unit corresponding to the cell wall O-antigen of the Escherichia albertii O4 strain in very good yield with the desired configuration at the glycosidic linkages using thioglycosides and trichloroacetimidate derivatives as glycosyl donors and perchloric acid supported over silica (HClO4/SiO2) as a solid supported protic acid glycosyl activator. The expected configuration at the glycosidic linkages was achieved using a reasonable selection of protecting groups in the manosaccharide intermediates.

Influence of remote functional groups towards the formation of 1,2-cis glycosides: special emphasis on ß-mannosylation.

A convenient straightforward method has been developed for 1,2-cis glycosylation and ß-mannosylation in excellent yields using glycosyl donors having a 4,6-O-benzylidene acetal together with a p-methoxybenzyl (PMB) or 2-naphthylmethyl (NAP) group at the C-3 position under standard glycosylation conditions.

Convergent synthesis of the pentasaccharide repeating unit of the biofilms produced by Klebsiella pneumoniae.

A pentasaccharide repeating unit containing α-linked D-glucuronic acid, ß-linked D-mannose, corresponding to the repeating unit of biofilms produced by Klebsiella pneumoniae, has been synthesized using a stereoselective [2 + 3] convergent glycosylation strategy. The ß-D-mannosidic moiety has been synthesized using a D-mannose-derived thioglycoside by a two-step activation process. Late stage TEMPO-mediated oxidation of the pentasaccharide derivative using phase-transfer reaction conditions furnished the target compound in satisfactory yield.

Development of novel anti-filarial agents using carbamo(dithioperoxo)thioate derivatives.

A series of novel carbamo(dithioperoxo)thioate derivatives have been prepared in excellent yield using a significantly fast, one-pot three component reaction and experimented for their potential as anti-filarial agents against model filarial nematode Setaria cervi. Among 23 compounds (4a-w) evaluated for the anti-filarial activities, five compounds (4a, 4b, 4c, 4d and 4h) have shown promising anti-proliferative effects on the juvenile stage microfilariae (mf) as well as in adults in a time and dose dependent manner. Compound 4a was found most active against oocytes, mf and adult nematods as well as non-cytotoxic to the normal cells. It has been established that the anti-filarial activity of the compounds were observed due to the involvement of reactive oxygen species (ROS) and apoptosis. Several biochemical and microscopic experiments have been carried out to establish the fact that both intrinsic and extrinsic pathways of apoptosis contribute to the compound 4a mediated death phenomenon of the filarial nematodes.

Preparation of glycosyl thiourea derivatives from glycosyl azides using sulfamic acid and sodium iodide in one-pot.

Novel one-pot reaction conditions have been developed for the preparation of glycosyl thiourea derivatives directly from glycosyl azides mediated by a combination of sulfamic acid and sodium iodide. The reaction conditions were clean, non-toxic and the products were isolated in good to excellent yield.