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Development of a general Ag(I)-promoted reaction for the direct conversion of thioamides to amidines is disclosed. This reaction was employed to prepare a key series of vancomycin aglycon residue 4 substituted amidines that were used to clarify their interaction with model ligands of peptidoglycan precursors and explore their resulting impact on antimicrobial properties.

The glycopeptide antibiotics are the most important class of drugs used in the treatment of resistant bacterial infections including those caused by methicillin-resistant Staphylococcus aureus (MRSA). After more than 50 years of clinical use, the emergence of glycopeptide-resistant Gram-positive pathogens such as vancomycin-resistant enterococci (VRE) and vancomycin-resistant Staphylococcus aureus (VRSA) presents a serious global challenge to public health at a time few new antibiotics are being developed. This has led to renewed interest in the search for additional effective treatments including the development of new derivatives of the glycopeptide antibiotics. General approaches have been explored for modifying glycopeptide antibiotics, typically through the derivatization of the natural products themselves or more recently through chemical total synthesis. In this Perspective, we consider recent efforts to redesign glycopeptide antibiotics for the treatment of resistant microbial infections, including VRE and VRSA, and examine their future potential for providing an even more powerful class of antibiotics that are even less prone to bacterial resistance.

The total synthesis of [Ψ[C(═S)NH]Tpg(4)]vancomycin aglycon (8) and its unique AgOAc-promoted single-step conversion to [Ψ[C(═NH)NH]Tpg(4)]vancomycin aglycon (7), conducted on a fully deprotected substrate, are disclosed. The synthetic approach not only permits access to 7, but it also allows late-stage access to related residue 4 derivatives, alternative access to [Ψ[CH(2)NH]Tpg(4)]vancomycin aglycon (6) from a common late-stage intermediate, and provides authentic residue 4 thioamide and amidine derivatives of the vancomycin aglycon that will facilitate ongoing efforts on their semisynthetic preparation. In addition to early stage residue 4 thioamide introduction, allowing differentiation of one of seven amide bonds central to the vancomycin core structure, the approach relied on two aromatic nucleophilic substitution reactions for formation of the 16-membered diaryl ethers in the CD/DE ring systems, an effective macrolactamization for closure of the 12-membered biaryl AB ring system, and the defined order of CD, AB, and DE ring closures. This order of ring closures follows their increasing ease of thermal atropisomer equilibration, permitting the recycling of any newly generated unnatural atropisomer under progressively milder thermal conditions where the atropoisomer stereochemistry already set is not impacted. Full details of the evaluation of 7 and 8 along with several related key synthetic compounds containing the core residue 4 amidine and thioamide modifications are reported. The binding affinity of compounds containing the residue 4 amidine with the model D-Ala-D-Ala ligand 2 was found to be only 2-3 times less than the vancomycin aglycon (5), and this binding affinity is maintained with the model d-Ala-d-Lac ligand 4, representing a nearly 600-fold increase in affinity relative to the vancomycin aglycon. Importantly, the amidines display effective dual, balanced binding affinity for both ligands (K(a)2/4 = 0.9-1.05), and they exhibit potent antimicrobial activity against VanA resistant bacteria ( E. faecalis , VanA VRE) at a level accurately reflecting these binding characteristics (MIC = 0.3-0.6 μg/mL), charting a rational approach forward in the development of antibiotics for the treatment of vancomycin-resistant bacterial infections. In sharp contrast, 8 and related residue 4 thioamides failed to bind either 2 or 4 to any appreciable extent, do not exhibit antimicrobial activity, and serve to further underscore the remarkable behavior of the residue 4 amidines.

The emergence of bacteria resistant to vancomycin, often the antibiotic of last resort, poses a major health problem. Vancomycin-resistant bacteria sense a glycopeptide antibiotic challenge and remodel their cell wall precursor peptidoglycan terminus from d-Ala-d-Ala to d-Ala-d-Lac, reducing the binding of vancomycin to its target 1000-fold and accounting for the loss in antimicrobial activity. Here, we report [Ψ[C(═NH)NH]Tpg(4)]vancomycin aglycon designed to exhibit the dual binding to d-Ala-d-Ala and d-Ala-d-Lac needed to reinstate activity against vancomycin-resistant bacteria. Its binding to a model d-Ala-d-Ala ligand was found to be only 2-fold less than vancomycin aglycon and this affinity was maintained with a model d-Ala-d-Lac ligand, representing a 600-fold increase relative to vancomycin aglycon. Accurately reflecting these binding characteristics, it exhibits potent antimicrobial activity against vancomycin-resistant bacteria (MIC = 0.31 μg/mL, VanA VRE). Thus, a complementary single atom exchange in the vancomycin core structure (O → NH) to counter the single atom exchange in the cell wall precursors of resistant bacteria (NH → O) reinstates potent antimicrobial activity and charts a rational path forward for the development of antibiotics for the treatment of vancomycin-resistant bacterial infections.

© 2015 by The American Society for Biochemistry and Molecular Biology, Inc. The spliceosome is a dynamic complex of five structural RNAs and dozens of proteins, which assemble together to remove introns from nascent eukaryotic gene transcripts in a process called splicing. Small molecules that target different components of the spliceosome represent valuable research tools to investigate this complicated macromolecular machine. However, the current collection of spliceosome inhibitors is very limited. To expand the toolkit we used a high-throughput in vitro splicing assay to screen a collection of pre-fractions of natural compounds derived from marine bacteria for splicing inhibition. Further fractionation of initial hits generated individual peaks of splicing inhibitors that interfere with different stages of spliceosome assembly. With additional characterization of individual peaks, we identified N-palmitoyl-L-leucine as a new splicing inhibitor that blocks a late stage of spliceosome assembly. Structure-activity relationship analysis of the compound revealed that length of carbon chain is important for activity in splicing, as well as for effects on the cytological profile of cells in culture. Together these results demonstrate that our combination of in vitro splicing analysis with complex natural product libraries is a powerful strategy for identifying new small molecule tools with which to probe different aspects of spliceosome assembly and function.

Several soil ingestion studies have indicated that some children ingest substantial amounts of soil on given days. Although the EPA has assumed that 95% of children ingest 200 mg soil/day or less for exposure assessment purposes, some children have been observed to ingest up to 25-60 g soil during a single day. In light of the potential for children to ingest such large amounts of soil, an assessment was made of the possibility for soil pica episodes to result in acute intoxication from contaminant concentrations the EPA regards as representing conservative screening values (i.e., EPA soil screening levels and EPA Region III risk-based concentrations for residential soils). For a set of 13 chemicals included in the analysis, contaminant doses resulting from a one-time soil pica episode (5-50 g of soil ingested) were compared with acute dosages shown to produce toxicity in humans in clinical studies or case reports. For four of these chemicals, a soil pica episode was found to result in a contaminant dose approximating or exceeding the acute human lethal dose. For five of the remaining chemicals, the contaminant dose from a soil pica episode was well within the reported dose range in humans for toxicity other than lethality. Because both the exposure episodes and the toxicological response information are derived from observations in humans, these findings are regarded as particularly relevant for human health risk assessment. They suggest that, for some chemicals, ostensibly conservative soil criteria based on chronic exposure using current EPA methodology may not be protective of children during acute soil pica episodes.

Considers the need for major shifts in strategy resulting from various changes affecting the marketing environment. Examines a case study of NCR, the founding company of the business machine industry. Argues that marketing strategies alone cannot function effectively and must be developed together with other key strategies, which are outlined.

We present CoLe, a model for cooperative agents for mining knowledge from heterogeneous data. CoLe allows for the cooperation of different mining agents and the combination of the mined knowledge into knowledge structures that no individual mining agent can produce alone. CoLe organizes the work in rounds so that knowledge discovered by one mining agent can help others in the next round. We implemented a multi-agent system based on CoLe for mining diabetes data, including an agent using a genetic algorithm for mining event sequences, an agent with improvements to the PART algorithm for our problem and a combination agent with methods to produce hybrid rules containing conjunctive and sequence conditions. In our experiments, the CoLe-based system outperformed the individual mining algorithms, with better rules and more rules of a certain quality. From the medical perspective, our system confirmed hypertension has a tight relation to diabetes, and it also suggested connections new to medical doctors.

Objective. We examined the location of commercial plasma donation centers in the United States over the period 1980 to 1995 relative to the geographic distribution of risk behaviors associated with transfusion-transmissible infections. Methods. The census tract locations of commercial source plasma clinics were described by measures of neighborhood social disadvantage and the prevalence of illicit drug use and active local drug economies. Results. Depending on the measure of social environment used, commercial plasma clinics were 5 to 8 times more likely to be located in census tracts designated high-risk than would be expected by chance. Conclusions. Commercial source plasma clinics were overrepresented in neighborhoods with very active local drug economies. These patterns persisted after the links between human immunodeficiency virus and hepatitis C virus infections and plasma products had been established and may present risks to blood system safety.

Let Φ \Phi be a subset of the unit sphere of l 1 {l_1} and let X be c 0 {c_0} , renormed by using Φ \Phi and letting x = y x = y if | | | x − y | | | = 0 |||x - y||| = 0 . Two conditions are given, which together imply X is “almost isometric” to a subspace of c 0 {c_0} . One condition is satisfied if Φ \Phi is the unit sphere of a linear subset of l 1 {l_1} . Both conditions are satisfied if X is a quotient c 0 / W {c_0}/W and Φ \Phi is the subset of the unit sphere whose members are zero on W.

The natural definition of orthogonality of elements of an abstract Euclidean space is that x ly if and only if the inner product (x, y) is zero. Two definitions have been given [11](2) which are equivalent to this and can be generalized to normed linear spaces, preserving the property that every twodimensional linear subset contain nonzero orthogonal elements. The definition which will be used here (Definition 1.2) has the added advantage of being closely related to the theories of linear functionals and hyperplanes. The theory and applications of this orthogonality have been organized in the following sections, which are briefly outlined: 1. Fundamental definitions. An element x is orthogonal to an element y if and only if j|x+kyjj > ||x|l for all k. This orthogonality is homogeneous, but is neither symmetric nor additive. 2. Existence of orthogonal elements. An element x of a normed linear space is orthogonal to at least one hyperplane through the origin, while for elements x and y there is at least one number a for which ax+y Ix or ||ax+yj| is minimum (Theorems 2.2-2.3). 3. Orthogonality in general normed linear spaces. The limits N?(x; y) =+lim,+.?|lnx+yil jjnxjj =liml0?o [||x+hyjj -lixil ]/hexistandsatisfyweakened linearity conditions. Also, x Iax+y if and only if N_(x; y) < -a||x

It has been conjectured that a closed convex subset C of a Banach space B is weakly compact if and only if each continuous linear functional on B attains a maximum on C [5]. This reduces easily to the case in which C is bounded, and will be answered in the affirmative [Theorem 4] after some preliminary results are established. Following suggestions by Namioka and Peck, the result is then generalized, first to weakly closed subsets of Banach spaces and then to weakly closed subsets of complete locally convex linear spaces. The original motivation for this conjecture was the knowledge that it is true when C is the unit sphere of a separable Banach space [2], which was later extended to arbitrary Banach spaces [3, Theorem 5]. Additional support was given the conjecture when V. L. Klee [5] proved a seemingly related theorem-namely, that if C is a bounded closed non-weakly-compact convex subset of a Banach space, then there is a decreasing sequence {K1} of nonempty closed convex subsets of C such that, for each x E C and each m E [0, 1), the set x + m(C x) meets only finitely many of the sets {Ki}. Iff is a continuous linear functional whose sup on C is M and if there is no x in C for which f(x) = M, then a suitable choice for Klee's sequence {Ki} is to let Kn = C r1 {x:f (x) > M l/n} for each n. It is interesting to note that the conjecture can be verified easily for a bounded closed convex set that is symmetric about an interior point x, since if x is translated to 0, then the convex set as a unit sphere induces a norm for which the new Banach space is isomorphic to the original space. More generally, if 0 is an interior point of a bounded convex set C and K is the closed convex span of Cu ( C), then K is symmetric about 0 and the sup on K of a continuous linear functional is the larger of its sups on C and C. Therefore for convex bodies the conjecture can be established by using the known theorem for unit spheres [3, Theorem 5, p. 215]. The following theorem is a generalization of a characterization of weak compactness of the unit sphere that was useful in [2]. In the proof of this theorem and thereafter, we shall use the convention that a sequence of nonoverlapping

The purpose of this paper is to develop characterizations of weakly compact subsets of a Banach space in terms of separation properties. The sets A and B are said to be separated by a hyperplane H if A is contained in one of the two closed half-spaces determined by H, and B is contained in the other; A and B are strictly separated by H if A is contained in one of the two open half-spaces determined by H, and B is contained in the other. The following are known to be true for locally convex topological linear spaces.

The publication of Banach's book [2] in 1932 might be regarded as marking the beginning of the systematic study of Banach spaces. Research activity in this area has expanded dramatically during the past two decades. Interesting new directions have developed and interplays between Banach space theory and other mathematics have proved to be very valuable. Most well-known classical problems have been solved, but some remain and important new problems have arisen. Our purpose is very limited. It is to discuss some of the most important and fundamental facts about bases in Banach spaces, particularly those that may be interesting and useful for mathematicians in other fields. Often, only sketches of proofs will be given, while others are given in more detail because they are relatively easy and may contribute to developing intuitive feeling for the concepts involved. It will be seen that many very important and beautiful theorems have very easy and natural proofs. A basis (or Schauder basis) for a Banach space X is a sequence (en: n > 1) of members of X which has the property that, for each x in X, there is exactly one sequence of scalars (xi} for which x = xiei in the sense that lim.nX lix - E ixieijj = 0. Some important Banach spaces have very natural bases. If (en} is a complete orthonormal sequence in Hilbert space H and x is any member of H, then there is exactly one sequence (xn} of scalars such that lim x yn- lxieill = 0. For this sequence of scalars, each xi is (x, ei) and n 00 ~~~~~1/2

The theorem on p. 632 is false without an additional hypothesis. The proof becomes correct if the definition of Q-subset is strengthened to include the condition: (C) For some p > 0, (qPI CO / TITP2I eC ( whenever IIP1 P211 < p and both T , and TP2 belong to (F; and if, in lines 7-8 on p. 633, '(P +1 A) is replaced by min{2(An+I An)P and IIXkll is replaced by IIIXklllR. C. James, Renorming the Banach space co, Proc. Amer. Math. Soc 80 (1980), 631-634. DEPARTMENT OF MATHEMATICS, CLAREMoNT GRADUATE SCHOOL, CLAREMONT, CALIFoRNIA 91711

ABsmAcT. Let 4) be a subset of the unit sphere of 11 and let X be c0, renormed by using 4) and letting x = y if ljjx yljl = 0. Two conditions are given, which together imply X is "almost isometric" to a subspace of c0. One condition is satisfied if 4) is the unit sphere of a linear subset of 11. Both conditions are satisfied if X is a quotient c0/ W and 4) is the subset of the unit sphere whose members are zero on W.

Tlhe first section of this paper will be devoted to the study of two particular surfaces. The methods used to treat thiese surfaces will then be extended to develop a classificationof surfaces, each class consisting of combinatorially eauivalent surfaces. Applications will be made to tlhe study of the topological nature of covering surfaces and of Riemann surfaces in particular. It will be assumed that the reader is familiar with the material of Chapter V, pages 235-244 and 256-264, in the book What Is 4lathsrmatics? by Courant and Robbins. Other than for references to this book, no previous knowledge of Topology will be assumed.