David Hendlin

Bio: David Hendlin is an academic researcher from Merck & Co.. The author has contributed to research in topics: Cephamycin & Cefoxitin. The author has an hindex of 23, co-authored 53 publications receiving 2327 citations.

Phosphonomycin, a New Antibiotic Produced by Strains of Streptomyces

Abstract: Phosphonomycin is a newly discovered antibiotic produced by streptomycetes. It is effective, when administered by the oral route, to mice infected with Gram-positive or Gram-negative microorganisms. The antibiotic is bactericidal and inhibits cell-wall synthesis.

Thienamycin, a new beta-lactam antibiotic. I. Discovery, taxonomy, isolation and physical properties.

Abstract: A new β-lactam antibiotic, named thienamycin, was discovered in culture broths of Streptomyces MA4297. The producing organism, subsequently determined to be a hitherto unrecognized species, is designated Streptomyces cattleya (NRRL 8057). The antibiotic was isolated by adsorption on Dowex 50, passage through Dowex 1, further chromatography on Dowex 50 and Bio-Gel P2, and final purification and desalting on XAD-2. Thienamycin is zwitterionic, has the elemental composition C11H16N2O4S (M. W.=272.18) and possesses a distinctive UV absorption (λmax=297 nm, e=7, 900). Its β-lactam is unusually sensitive to hydrolysis above pH 8 and to reaction with nucleophiles such as hydroxylamine, cysteine and, to a lesser degree, the primary amine of the antibiotic itself. The latter reaction results in accelerated inactivation at high antibiotic concentrations.

Cephamycins, a New Family of β-Lactam Antibiotics I. Production by Actinomycetes, Including Streptomyces lactamdurans sp. n

Abstract: A number of actinomycetes isolated from soil were found to produce one or more members of a new family of antibiotics, the cephamycins, which are structurally related to cephalosporin C The cephamycins were produced in submerged fermentation in a wide variety of media by one or more of eight different species of Streptomyces , including a newly described species, S lactamdurans These antibiotics exhibit antibacterial activity against a broad spectrum of bacteria which includes many that are resistant to the cephalosporins and penicillins

Cefoxitin, a Semisynthetic Cephamycin Antibiotic: Resistance to Beta-Lactamase Inactivation

Abstract: Cefoxitin is a new, cephalosporin-like antibiotic which is highly resistant to hydrolysis by beta-lactamase. Ninety-one cultures were selected either for their general resistance to cephalosporin antibiotics or for their ability to produce beta-lactamase. Some of these cultures were resistant to cefoxitin. The capacity of each of the 91 strains to hydrolyze cefoxitin with beta-lactamase was determined. Only seven of the cultures degraded the antibiotic as determined by a general assay for beta-lactamase. Several others were able to hydrolyze cefoxitin after enzyme was induced by low concentrations of the antibiotic. The role of the constitutive and inducible enzyme in bacterial resistance to the antibiotic was investigated. Enzymatic destruction of cefoxitin was found to be an important factor contributing to bacterial resistance. However, the complete and rapid degradation of cefoxitin is not essential to resistance since one strain, Enterobacter cloacae 1316, hydrolyzed the antibiotic very slowly but was able to grow unaffected in the presence of cefoxitin. The presence of the enzyme is not necessarily sufficient to confer resistance since another culture, Klebsiella D535, readily hydrolyzed the antibiotic but was susceptible to it.

Cefoxitin, a Semisynthetic Cephamycin Antibiotic: Susceptibility Studies

Abstract: Cefoxitin, 3-carbamoyloxymethyl-7-α-methoxy-7-[2-(2-thienyl)acetamido]-3-cephem-4- carboxylic acid, is a new semisynthetic cephamycin with broad antibacterial activity. It is highly active against gram-negative microorganisms including indole-positive Proteus and Serratia strains, which are ordinarily reistant to the cephalosporins. Cefoxitin is also highly active against many strains of Escherichia coli and Proteus mirabilis which are resistant to the cephalosporins. Furthermore, E. coli and Klebsiella strains which are susceptible to the cephalosporins are generally more susceptible to the cephamycin analog. The susceptibility of the gram-positive bacteria falls well within the effective range of the antibiotic for gram-negative organisms, but cefoxitin is less active than cephalothin or cephaloridine. As is the case with the cephalosporins, strains of Pseudomonas and group D streptococci are resistant to cefoxitin. Changes in pH, inoculum density, and growth medium have no significant effect on the activity of the antibiotic.

Click Chemistry: Diverse Chemical Function from a Few Good Reactions.

Abstract: Examination of nature's favorite molecules reveals a striking preference for making carbon-heteroatom bonds over carbon-carbon bonds-surely no surprise given that carbon dioxide is nature's starting material and that most reactions are performed in water. Nucleic acids, proteins, and polysaccharides are condensation polymers of small subunits stitched together by carbon-heteroatom bonds. Even the 35 or so building blocks from which these crucial molecules are made each contain, at most, six contiguous C-C bonds, except for the three aromatic amino acids. Taking our cue from nature's approach, we address here the development of a set of powerful, highly reliable, and selective reactions for the rapid synthesis of useful new compounds and combinatorial libraries through heteroatom links (C-X-C), an approach we call "click chemistry". Click chemistry is at once defined, enabled, and constrained by a handful of nearly perfect "spring-loaded" reactions. The stringent criteria for a process to earn click chemistry status are described along with examples of the molecular frameworks that are easily made using this spartan, but powerful, synthetic strategy.

Carbapenemases: the versatile beta-lactamases.

Abstract: Carbapenemases are β-lactamases with versatile hydrolytic capacities. They have the ability to hydrolyze penicillins, cephalosporins, monobactams, and carbapenems. Bacteria producing these β-lactamases may cause serious infections in which the carbapenemase activity renders many β-lactams ineffective. Carbapenemases are members of the molecular class A, B, and D β-lactamases. Class A and D enzymes have a serine-based hydrolytic mechanism, while class B enzymes are metallo-β-lactamases that contain zinc in the active site. The class A carbapenemase group includes members of the SME, IMI, NMC, GES, and KPC families. Of these, the KPC carbapenemases are the most prevalent, found mostly on plasmids in Klebsiella pneumoniae. The class D carbapenemases consist of OXA-type β-lactamases frequently detected in Acinetobacter baumannii. The metallo-β-lactamases belong to the IMP, VIM, SPM, GIM, and SIM families and have been detected primarily in Pseudomonas aeruginosa; however, there are increasing numbers of reports worldwide of this group of β-lactamases in the Enterobacteriaceae. This review updates the characteristics, epidemiology, and detection of the carbapenemases found in pathogenic bacteria.

Click-Chemie: diverse chemische Funktionalität mit einer Handvoll guter Reaktionen

Abstract: Betrachtet man die in der Natur am haufigsten vorkommenden Verbindungen, so fallt auf, dass die Bildung von Kohlenstoff-Heteroatom-Bindungen gegenuber der von Kohlenstoff-Kohlenstoff-Bindungen deutlich bevorzugt ist Da zum einen Kohlendioxid die Basisverbindung der Natur ist und andererseits das Medium naturlicher Reaktionen zumeist Wasser ist, uberrascht dies sicherlich nicht Nucleinsauren, Proteine und Polysaccharide sind polymere Kondensationsprodukte kleiner Untereinheiten, die durch Kohlenstoff-Heteroatom-Bindungen verknupft sind Sogar die etwa 35 Baueinheiten, aus denen diese essentiellen Verbindungen bestehen, enthalten nicht mehr als sechs aufeinander folgende C-C-Bindungen, sieht man einmal von den drei aromatischen Aminosauren ab Mit der Natur als Vorbild richteten wir unser Interesse auf die Entwicklung leistungsfahiger, gut funktionierender und selektiver Reaktionen fur die effiziente Synthese neuartiger nutzlicher Verbindungen sowie kombinatorischer Bibliotheken mittels Heteroatomverknupfungen (C-X-C) Diese Synthesestrategie nennen wir „Click-Chemie“ Click-Chemie ist durch eine Auswahl einiger weniger nahezu idealer Reaktionen charakterisiert, mit all ihren Grenzen und Moglichkeiten In diesem Beitrag werden zum einen die strengen Kriterien, die Reaktionen erfullen mussen, um die Bezeichnung „Click-Chemie“ zu verdienen, definiert, zum anderen werden Beispiele fur molekulare Strukturen gegeben, die mit dieser spartanischen, aber dennoch leistungsfahigen Synthesestrategie leicht hergestellt werden konnen

Challenges of Antibacterial Discovery

Abstract: Summary: The discovery of novel small-molecule antibacterial drugs has been stalled for many years. The purpose of this review is to underscore and illustrate those scientific problems unique to the discovery and optimization of novel antibacterial agents that have adversely affected the output of the effort. The major challenges fall into two areas: (i) proper target selection, particularly the necessity of pursuing molecular targets that are not prone to rapid resistance development, and (ii) improvement of chemical libraries to overcome limitations of diversity, especially that which is necessary to overcome barriers to bacterial entry and proclivity to be effluxed, especially in Gram-negative organisms. Failure to address these problems has led to a great deal of misdirected effort.

Carbapenems: Past, Present, and Future

Abstract: In this review, we summarize the current "state of the art" of carbapenem antibiotics and their role in our antimicrobial armamentarium. Among the β-lactams currently available, carbapenems are unique because they are relatively resistant to hydrolysis by most β-lactamases, in some cases act as "slow substrates" or inhibitors of β-lactamases, and still target penicillin binding proteins. This "value-added feature" of inhibiting β-lactamases serves as a major rationale for expansion of this class of β-lactams. We describe the initial discovery and development of the carbapenem family of β-lactams. Of the early carbapenems evaluated, thienamycin demonstrated the greatest antimicrobial activity and became the parent compound for all subsequent carbapenems. To date, more than 80 compounds with mostly improved antimicrobial properties, compared to those of thienamycin, are described in the literature. We also highlight important features of the carbapenems that are presently in clinical use: imipenem-cilastatin, meropenem, ertapenem, doripenem, panipenem-betamipron, and biapenem. In closing, we emphasize some major challenges and urge the medicinal chemist to continue development of these versatile and potent compounds, as they have served us well for more than 3 decades.