Biosynthesis and Molecular Genetics of Clavulanic Acid

The biosynthesis of clavulanic acid and related clavam metabolites is only now being elucidated. Understanding of this pathway has resulted from a combination of both biochemical studies of purified biosynthetic enzymes, and molecular genetic studies of the genes encoding these enzymes. Clavulanic acid biosynthesis has been most thoroughly investigated in Streptomyces clavuligerus where the biosynthetic gene cluster resides immediately adjacent to the cluster of cephamycin biosynthetic genes. A minimum of eight structural genes have been implicated in clavulanic acid biosynthesis, although more are probably involved. While details of the early and late steps of the pathway remain unclear, synthesis proceeds from arginine and pyruvate, as the most likely primary metabolic precursors, through the monocyclic -lactam intermediate, proclavaminic acid, to the bicyclic intermediate, clavaminic acid, which is a branch point leading either to clavulanic acid or the other clavams. Conversion of clavaminic acid to clavulanic acid requires side chain modfication as well as inversion of ring stereochemistry. This stereochemical change occurs coincident with acquisition of the -lactamase inhibitory activity which gives clavulanic acid its therapeutic and commercial importance. In contrast, the other clavam metabolites all arise from clavaminic acid with retention of configuration and lack -lactamase inhibitory activity.     

Effect of potassium chloride and cationic drug on swelling, erosion and release from kappa-carrageenan matrices

The basic objective of this work was to study the effect of model cationic drug metformin HCl on swelling and erosion and, in turn, the release of KCl and drug itself, from the kappa-carrageenan matrices. Water uptake by the matrix up to 2 hours was found to increase with KCl concentration from the plain matrix. Erosion was not affected by concentration of KCl. Incorporation of drug favors water uptake, but in presence of KCl it was found to be reduced. Drug-containing matrices have shown higher release of KCl as compared with plain batches. Drug release was retarded as KCl concentration increased up to 5%, above which the reduced cohesivity of the matrix caused increase in drug release.     

Preparation and evaluation of diltiazem hydrochloride-gelucire 43/01 floating granules prepared by melt granulation

The basic objective of this study was to explore the application of Gelucire 43/01 for the design of multi-unit floating systems of a highly water-soluble drug diltiazem HCl. Diltiazem HCl-Gelucire 43/01 granules were prepared by melt granulation technique. The granules were evaluated for in vitro and in vivo floating ability, surface topography, and in vitro drug release. Aging effect on storage was vvaluated using scanning electron microscopy, hot stage polarizing microscopy (HSPM), differential scanning calorimetry (DSC), and in vitro drug release. Granules were retained in stomach at least for 6 hours. Approximately 65% to 80% drug was released over 6 hours with initial fast release from the surface. Surface topography, HSPM, DSC study of the aged samples showed phase transformation of Gelucire. The phase transformation also caused significant increase in drug release. In conclusion, hydrophobic lipid, Gelucire 43/01, can be considered as an effective carrier for design of a multi-unit floating drug delivery system of highly water-soluble drugs such as diltiazem HCl.     

High-yield production of a human therapeutic protein in tobacco chloroplasts

Transgenic plants have become attractive systems for production of human therapeutic proteins because of the reduced risk of mammalian viral contaminants, the ability to do large scale-up at low cost, and the low maintenance requirements. Here we report a feasibility study for production of a human therapeutic protein through transplastomic transformation technology, which has the additional advantage of increased biological containment by apparent elimination of the transmission of transgenes through pollen. We show that chloroplasts can express a secretory protein, human somatotropin, in a soluble, biologically active, disulfide-bonded form. High concentrations of recombinant protein accumulation are observed (>7% total soluble protein), more than 300-fold higher than a similar gene expressed using a nuclear transgenic approach. The plastid-expressed somatotropin is nearly devoid of complex post-translational modifications, effectively increasing the amount of usable recombinant protein. We also describe approaches to obtain a somatotropin with a non-methionine N terminus, similar to the native human protein. The results indicate that chloroplasts are a highly efficient vehicle for the potential production of pharmaceutical proteins in plants.     

A Role for the Insulin Receptor in the Suppression of Dengue Virus and Zika Virus in Wolbachia-Infected Mosquito Cells

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Pyrazolo[1,5-a]pyrimidines as orally available inhibitors of cyclin-dependent kinase 2

Properly substituted pyrazolo[1,5-a]pyrimidines are potent and selective CDK2 inhibitors. Compound 15j is orally available and showed efficacy in a mouse A2780 xenograft model.     

A novel Streptoverticillium cinnamonium var scleroticum producing a polyene antibiotic

A novel Streptoverticillium sp. G-55 was isolated from a soil sample (collected from Panjim, Goa) which produces sclerotia under specific environmental conditions, both in liquid and solid media. It was further identified by taxonomic studies as Streptoverticillium cinnamoneum var scleroticum. The species produces a pentaene polyene macrolide antibiotic (HA-94) under submerged culture conditions which shows promising antifungal and antibacterial activity in vitro.     

Effect of Oppositely Charged Polymer and Dissolution Media on Rheology of Spray-Dried Ionic Complexes

The purpose of this research was to address the utility of rheological study in understanding the influence of oppositely charged polymers on release of naproxen sodium encapsulated in chitosan particles. The interaction between oppositely charged κ-carrageenan (κ-Ca) and chitosan leads to relatively higher gel strength, which is proportional to the ability to retard the drug release at acidic pH. The oscillatory tests within the linear viscoelastic range where the stress is proportional to the applied strain were performed on the hydrated sample matrices containing chitosan-naproxen sodium spray-dried complexes and k-Ca or hydroxypropyl methylcellulose (HPMC) in various ratios. It was observed that the effect of pH change on the dynamic moduli in spray-dried complexes containing κ-Ca was much stronger than that with HPMC reflecting presence of strong ionic interaction between κ-Ca and chitosan. The combination of oppositely charged polymers in different ratios proved to be useful in modulating the rheological properties of the hydrated formulations and their release-retarding properties. Dynamic moduli can be used to measure gel strength and are significant for the interpretation of oral sustained release spray-dried complexes.     

Preparation and characterization of Pluronic-colloidal silicon dioxide composite particles as liquid crystal precursor

The purpose of this study was to produce spray-dried Pluronic-colloidal silicon dioxide (Aerosil) composite particles as a liquid crystal precursor that would form a liquid crystalline phase upon hydration. A Pluronic-colloidal silicon dioxide dispersion in isopropyl alcohol was spray-dried to obtain composite particles using different concentrations of Aerosil. Polarizing microscopy, gelation, gel melting, and rheological studies were employed to characterize the composite particles. The composite particles obtained were irregular, with concave depression. Gelation was found to decrease with the addition of Aerosil, while gel melting was found to increase with the concentration of Aerosil. Rheological studies showed an increase in elasticity as well as viscosity with an increase in the concentration of Aerosil. Composite particles showed improved gelation and rheological properties. These composite particles and the process by which they were obtained may be useful for designing various drug delivery systems.