Mannopeptimycin esters and carbonates, potent antibiotic agents against drug-resistant bacteria

A series of ester and carbonate derivatives of the glycopeptide mannopeptimycin alpha (1) with potent activity against G+ bacteria, including the methicillin-resistant staphylococci and vancomycin-resistant enterococci, was synthesized. The SAR data obtained from natural and semisynthetic compounds demonstrated the importance of a hydrophobic group in the terminal mannosyl moiety for antibacterial activity.

Distal symmetrical polyneuropathy: Definition for clinical research

The objective of this report was to develop a case definition of "distal symmetrical polyneuropathy" to standardize and facilitate clinical research and epidemiological studies. A formalized consensus process was employed to reach agreement after a systematic review and classification of evidence from the literature. The literature indicates that symptoms alone have relatively poor diagnostic accuracy in predicting the presence of polyneuropathy; signs are better predictors of polyneuropathy than symptoms; and single abnormalities on examination are less sensitive than multiple abnormalities in predicting the presence of polyneuropathy. The combination of neuropathic symptoms, signs, and electrodiagnostic findings provides the most accurate diagnosis of distal symmetrical polyneuropathy. A set of case definitions was rank ordered by likelihood of disease. The highest likelihood of polyneuropathy (useful for clinical trials) occurs with a combination of multiple symptoms, multiple signs, and abnormal electrodiagnostic studies. A modest likelihood of polyneuropathy (useful for field or epidemiological studies) occurs with a combination of multiple symptoms and multiple signs when the results of electrodiagnostic studies are not available. A lower likelihood of polyneuropathy occurs when electrodiagnostic studies and signs are discordant. For research purposes, the best approach for defining distal symmetrical polyneuropathy is a set of case definitions rank ordered by estimated likelihood of disease. The inclusion of this formalized case definition in clinical and epidemiological research studies will ensure greater consistency of case selection.

In VitroPermeability of Poorly Aqueous Soluble Compounds Using Different Solubilizers in the PAMPA Assay with Liquid Chromatography/Mass Spectrometry Detection

PURPOSE

This study compares the use of UV-VIS detection with liquid chromatography/mass spectrometry (LC/MS) detection for the PAMPA (Parallel Artificial Membrane Permeability Assay) permeability determination of compounds in the drug discovery stage. LC/MS detection offers a selective and sensitive method for the determination of the PAMPA permeability for compounds that do not contain a UV chromophore or possess a low UV extinction coefficient. To enhance the reliability of our permeability measurements for compounds with low aqueous solubility, we demonstrated the use of LC/MS detection as a means for facilitating the study of solubilizing agents to enhance aqueous solubility that normally would interfere with UV-VIS detection. In doing so, the PAMPA assay can be expanded to study the in vitro permeability of poorly water soluble compounds and evaluate the effects of solubilizers' on the membrane permeability of different compounds. This might be useful in selecting solubilizers for poorly water soluble compounds to be used for further in vivo studies.

METHODS

A diverse set of 20 drugs using UV-VIS detection were compared with data using LC/MS detection. A PAMPA screening method was designed which used solubilizers (Brij 35, Cremophor EL, ethanol, and Tween 80) for compounds with low aqueous solubility. The stability of the artificial membrane was determined using various solubilizer concentrations (0.1-5% w/v) to ensure the phospholipid membrane was not disrupted. Two compounds, amiodarone and miconazole, with low aqueous solubility yielding an undetected response in the PAMPA assay using UV-VIS detection were subjected to the different solubilizing agents and their PAMPA permeability was measured using LC/MS detection.

RESULTS

Most of the compounds showed similar PAMPA permeability using the two detection systems. However, for compounds lacking a UV chromophore or with a low UV extinction coefficient, LC/MS was the detection method of choice for determination of PAMPA permeability values. LC/MS also gave reliable quantification data for compounds containing impurities, as well as compounds that were not stable during the assay. Although many solubilizers were found to interfere with UV-VIS detection, the LC/MS approach was applicable to determine the permeability values of compounds with normally low aqueous solubility.

CONCLUSIONS

LC/MS detection offered greater sensitivity and selectivity as compared with UV-VIS detection for the PAMPA assay. With this added versatility in detection, PAMPA can be used in both discovery and pre-formulation applications, which has not been described before.

Purification, structure determination, and antimicrobial activity of neutramycins B-G

Neutramycins B-G were purified from a historical sample of neutramycin in our antibiotic collection. The structures of the compounds were solved by 2D NMR spectroscopic analysis. Four of the compounds (2-5) are probable biosynthetic intermediates or shunt metabolites of neutramycin biosynthesis, while two (6, 7) are likely to be degradation products. Only one intermediate (5) showed weak Gram-positive activity.

Cytosporacin, a highly unsaturated polyketide: application of the ACCORD-ADEQUATE experiment to the structural determination of natural products

Cytosporacin (1), a novel antibacterial polyketide containing naphthopyranone and isochromandione moieties, was isolated from the fermentation broth of the fungus Cytospora rhizophorae. A (1)H-detected ACCORD-ADEQUATE pulse sequence that distinguished (2)J(CH) from (3)J(CH) correlations provided critical information for structural determination. NOE studies established the relative configuration and revealed the presence of two rotamers. A biosynthetic (13)C-labeling experiment indicated that cytosporacin was derived from acetate origin.

Novel sulfur-containing rapamycin analogs prepared by precursor-directed biosynthesis

[reaction: see text] Two novel sulfur-containing analogs of the immunosuppressive natural product rapamycin (1) were obtained by feeding cultures of Streptomyces hygroscopicus with l-nipecotic acid (4) and either (S)-1,3-thiazane-4-carboxylic acid (5) or (S)-1,4-thiazane-3-carboxylic acid (6). The structures of the two new compounds, 20-thiarapamycin (2) and 15-deoxo-19-sulfoxylrapamycin (3), were determined by spectroscopic methods.

FTMS structure elucidation of natural products: application to muraymycin antibiotics using ESI multi-CHEF SORI-CID FTMS(n), the top-down/bottom-up approach, and HPLC ESI capillary-skimmer CID FTMS

The molecular formulas for the structures and substructures of muraymycin antibiotics A1 (C52H90N14O19, MW 1214) and B1 (C49H83N11O18, MW 1113) were determined using electrospray ionization (ESI) Fourier transform mass spectrometry (FTMS). The muraymycin A1 and B1 structures were elucidated by utilizing capillary-skimmer fragmentation with up to five stages of mass spectrometry (MS5). Multi-CHEF, a multiple ion isolation method, was used at each stage of MS(n) to isolate a parent ion and up to four reference ions, for exact-mass calibration. The parent ions were fragmented by SORI-CID and the product ions internally calibrated with average absolute mass errors less than 1 ppm at each stage in the fragmentation processes. Using the top-down/bottom-up approach, the molecular formulas for the antibiotics were determined by summing the elemental formulas of the neutral losses, obtained by measuring the mass differences (<500 Da) between the genetically related sequential parent ion masses in the MS(n) spectra, with the unique elemental formula of the lowest parent ion mass (<500 Da). The structures of 12 additional compounds in the muraymycin complex were elucidated using HPLC ESI capillary-skimmer CID FTMS by correlating their fragmentation patterns with those of muraymycins A1 and B1. Sequential neutral losses of an aminosugar, a valine, a uridine, and an ester fatty acid from the muraymycin parent ions provided diagnostic fragments for characterization.

Structure determination of glycinocins A to D, further evidence for the cyclic structure of the amphomycin antibiotics

Four novel cyclolipopeptides, glycinocins A to D, were isolated from the fermentation broth of an unidentified terrestrial Actinomycete species. These compounds were separated and purified from the fermentation broth by 1-butanol extraction, followed by repeated reversed-phase HPLC. Their structures were elucidated by spectroscopic and chemical degradation studies. The absolute configuration of the amino acid residues was determined using Marfey's methodology. The glycinocin antibiotics are structurally related to amphomycin that was originally reported as a linear lipopeptide with C-terminal diketopiperazine moiety. Our degradation study of the glycinocin antibiotics also yielded diketopiperazine-containing fragments, but these have been shown to be hydrolytic by-products generated by condensation of the pipecolinic acid and diamino propionic acid residues.

High throughput artificial membrane permeability assay for blood-brain barrier

The recent advances in high throughput screening for biological activities and combinatorial chemistry have greatly expanded the number of drug candidates. Rapid screening for BBB penetration potential early in drug discovery programs provides important information for compound selection and guidance of synthesis for desirable CNS properties. In this paper, we discuss a modification of the parallel artificial membrane permeation assay (PAMPA) for the prediction of blood-brain barrier penetration (PAMPA-BBB). The assay was developed with 30 structurally diverse commercial drugs and validated with 14 Wyeth Research compounds. The PAMPA-BBB assay has the advantages of: predicting passive blood-brain barrier penetration with high success, high throughput, low cost, and reproducibility.

Acremonidins, New Polyketide-derived Antibiotics Produced by Acremonium sp., LL-Cyan 416

Acremonidins A to approximately E (1 to approximately 5) were produced by fermentation of Acremonium sp., LL-Cyan 416, in heterogeneous phases. The structures of these compounds, containing a bridging keto group, were determined by spectroscopic analysis. Acremonidins A and B showed moderate activity against Gram-positive bacteria, including the methicillin-resistant staphylococci and vancomycin-resistant enterococci. Selective acylations of acremonidin B afforded ester derivatives 6 to approximately 9 that exhibited improved antibacterial activity.

In support of the original medermycin/lactoquinomycin A structure

[structure: see text] Herein we report a significant body of spectroscopic data that supports the originally proposed structure of medermycin/lactoquinomycin A. In addition, we demonstrate that these data are inconsistent with the revised structure reported recently in the literature.

Charcot-Marie-Tooth neuropathy: clinical phenotypes of four novel mutations in the MPZ and Cx 32 genes

Charcot-Marie-Tooth Hereditary Neuropathy is a heterogeneous syndrome associated with mutations in several different genes including peripheral myelin protein 22, myelin P0, connexin 32, and early growth response 2. There is considerable variability in the phenotypic expression of this syndrome and the relationship of this variability to mutation genotypes requires extensive analysis. Here we describe the phenotypes and genotypes of four new mutations underlying the Charcot-Marie-Tooth syndrome and document segregation with disease. Four families with Charcot-Marie-Tooth were ascertained, examined, and evaluated electrophysiologically. Each family had peripheral blood DNA screened for mutations in myelin protein 22, myelin P0, and connexin 32. Two families were found with new mutations in the myelin P0 gene: S140T in the extracellular domain and K236del in the cytoplasmic domain. All families showed segregation of the mutations with the Charcot-Marie-Tooth phenotype as did a new family with the rare G163R mutation in the membrane domain. A 49-year-old man with the S140T mutation demonstrated conduction block on electrophysiological testing. A family with a novel S49P mutation in the connexin 32 gene had a neuropathy with very slow nerve conduction. These new mutations in the myelin P0 and connexin 32 genes help to clarify the pathophysiology of the clinical Charcot-Marie-Tooth syndrome. The S140T mutation in myelin P0 can be associated with conduction block and Charcot-Marie-Tooth should be part of the differential diagnosis of that phenomenon. Mutations in the cytoplasmic domain of myelin P0 can cause clinical neuropathy. The S49P mutation in the connexin 32 gene can produce aspects of a demyelinating type of X-linked hereditary neuropathy.

Structures of the muraymycins, novel peptidoglycan biosynthesis inhibitors

The muraymycins, a family of nucleoside-lipopeptide antibiotics, were purified from the extract of Streptomyces sp. LL-AA896. The antibiotics were purified by chromatographic methods and characterized by NMR spectroscopy, degradation studies, and mass spectrometry. The structures of 19 compounds were established. The muraymycins constitute a new antibiotic family whose core structure contains a glycosylated uronic acid derivative joined by an aminopropane group to a hexahydro-2-imino-4-pyrimidylglycyl residue (epicapreomycidine) containing dipeptide that is further extended by a urea-valine moiety. Members of this family show broad-spectrum in vitro antimicrobial activity against a variety of clinical isolates (MIC 2 to >64 mug/mL). The muraymycins inhibited peptidoglycan biosynthesis. The fatty acid substituent and the presence or absence of the amino sugar play important roles in biological activity. One of the most active compounds, muraymycin A1, demonstrated protection in vivo against Staphylococcus aureus infection in mice (ED50 1.1 mg/kg).

Mannopeptimycins, novel antibacterial glycopeptides from Streptomyces hygroscopicus, LL-AC98

A series of novel antibiotics with activity against methicillin-resistant staphylococci and vancomycin-resistant enterococci has been purified, and their structures have been characterized using spectroscopic analyses and chemical conversions. These antibiotics, designated mannopeptimycins alpha-epsilon (1-5), are glycosylated cyclic hexapeptides containing two stereoisomers of an unprecedented amino acid, alpha-amino-beta-[4'-(2'-iminoimidazolidinyl)]-beta-hydroxypropionic acid (Aiha), as a distinguishing feature. The cyclic peptide core of these antibiotics is attached to a mannosyl monosaccharide moiety in 2 and to mannosyl monosaccharide and disaccharide moieties in 1, 3, 4, and 5. The presence and position of an isovaleryl group in the terminal mannose (Man-B) in 3-5 are critical for retaining antibacterial potency.

Use of a linear gradient flow program for liquid chromatography-mass spectrometry protein-binding studies

A rapid screening method to measure drug-protein binding using an immobilized human serum albumin (HSA) column was developed. This method utilizes a linear gradient flow-rate to accelerate the elution of strong binders to the HSA column. Post-column addition of a pressure relief valve enables mass spectrometric detection at relatively high mobile phase flow-rates (i.e., 2 ml/min).