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Lipopolysaccharide from Escherichiu coli 01 11, its gulE derivative when grown in galactose, E. coli 086, and Sulmonella typhimuvium LT2 all contain antigenic side chains and separate into more than 40 components by electrophoresis in gradients of polyacrylaniide containing sodium dodecylsulfate. These components from E. coli 0111 are not interconvertible and show a heterogeneous size distribution when fractionated with Sephadex (3-200. Isoelectric focusing of this mixture in pH 3.5 -10 ampholines reveals a single component, ruling out extensive charge heterogeneity.The relative antigenic side chain lengths for the components, estimated using ratios of galactose in antigenic side chain to phosphate in the lipid-A-core oligosaccharide region, show that the size heterogeneity is due to differences in the number of antigenic side chain units per molecule and ranges from none to over 40. Preference for molecules of specific chain lengths, especially short ones, was observed.In contrast, the galE mutant grown without galactose does not synthesize antigenic side chains, and more than 90 % of its lipopolysaccharide migrates as a single band at a position corresponding to the lowest-molecular-weight component from the above preparations. Lipopolysaccharide from E. coli PL2, a K12 strain lacking antigenic side chain, separates into two low-molecular-weight components on electrophoresis. These results confirm that the heterogeneity which we observe in lipopolysaccharide containing antigenic side chains, is due to the side chain rather than the lipid-A -core oligosaccharide region.Lipopolysaccharide is found uniquely in the outer membrane of gram-negative bacteria and is important in the structure [ 1,2] and function [3,4] of this membrane. Variations in its composition also influence host responses to invasion by gram-negative organisms [5].Lipopolysaccharide consists of lipid A, core oligosaccharide, and antigenic side chain. The linkage of sugar residues [6] and the chemical structure within the lipid A moiety [7,8] is known for lipopolysaccharide from several organisms. Biosynthesis of lipid A has also been investigated [9].

SUMMARYThere is an urgent need for the discovery and development of new antitubercular agents that target novel biochemical pathways and treat drug-resistant forms of the disease. One approach to addressing this need is through high-throughput screening of drug-like small molecule libraries against the whole bacterium in order to identify a variety of new, active scaffolds that will stimulate additional biological research and drug discovery. Through the Molecular Libraries Screening Center Network, the NIAID Tuberculosis Antimicrobial Acquisition and Coordinating Facility tested a 215,110-compound library against M. tuberculosis strain H37Rv. A medicinal chemistry survey of the results from the screening campaign is reported herein. CONFLICT OF INTEREST STATEMENTCompeting interests: Dr. Goldman is a NIAID staff member who either in the past or currently provides oversight for the project that generated the data used as the basis for this work.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public AccessAuthor Manuscript Tuberculosis (Edinb) The MLSCN was established in 2005 as a pilot program to assemble a large library of biologically relevant small molecules and make them available through a network of HTS laboratories to researchers worldwide through a competitive assay submission process. Acceptance of the TAACF assay into the MLSCN program made available the unique resources of the NIH Small Molecule Repository (SMR), significantly expanding the spectrum of molecules tested for activity against TB. For this screen, a 215,110-compound library from the SMR was examined for anti-TB activity using the assay described previously, 7 with the only change to the screening protocol being the elimination of the polyethylene incubator bags, resulting in the identification of a number of novel chemical scaffolds. Moreover, even for classes of compounds identified earlier during testing of the NIAID ChemBridge library, 7 additional examples emerged that further clarified the structure-activity picture. Since the compounds in the SMR have been examined in scores of diverse assays undertaken by the MLSCN, and the results published on the NIH PubChem website, 8 another motivation for conducting the MLSCN campaign is the ability to correlate antituberculosis activity of the hits with other biological activities that these compounds may possess, potentially providing information about possible mechanisms of action or toxicity. The raw screening results upon which the structural analysis below is based are now publicly available on PubChem (assay AIDs 1332 and 1626). MATERIALS ...