Attaching Metal-Containing Moieties to ß-Lactam Antibiotics: The Case of Penicillin and Cephalosporin.

Procedures for the preparation of transition metal complexes having intact bicyclic cepham or penam systems as ligands have been developed. Starting from readily available 4-azido-2-azetidinones, a synthetic approach has been tuned using a copper-catalyzed azide-alkyne cycloaddition between 3-azido-2-azetinones and alkynes, followed by methylation and transmetalation to Au(I) and Ir(III) complexes from the mesoionic carbene Ag(I) complexes. This methodology was applied to 6-azido penam and 7-azido cepham derivatives to build 6-(1,2,3-triazolyl)penam and 7-(1,2,3-triazolyl)cepham proligands, which upon methylation and metalation with Au(I) and Ir(III) complexes yielded products derived from the coordination of the metal to the penam C6 and cepham C7 positions, preserving intact the bicyclic structure of the penicillin and cephalosporin scaffolds. The crystal structure of complex 28b, which has an Ir atom directly bonded to the intact penicillin bicycle, was determined by X-ray diffraction. This is the first structural report of a penicillin-transition-metal complex having the bicyclic system of these antibiotics intact. The selectivity of the coordination processes was interpreted using DFT calculations.

Design, synthesis and cytotoxic evaluation of peptoid analogs of an anticancer active triazolylpeptidyl penicillin.

Aim: Encouraged by the antitumor activity exhibited by triazolylpeptidyl penicillins, we decided to synthesize and evaluate a library of peptoid analogs. Results: The replacement of the dipeptide unit of the reference compound, TAP7f, was investigated. In addition, the effect of the triazole linking group on the biological activity of these new derivatives was evaluated, exchanging it with a glycine spacer. The cytotoxic effect of the library compounds was determined in the B16-F0 cell line and compared with the effects on normal murine mammary gland cells. Conclusion: Among the tested compounds, peptoid 4e exhibited the highest antiproliferative activity.

[The organization of industrial production of penicillin in the USSR].

The article on the basis of analysis of declassified materials of the State Archive of the Russian Federation covers the history of the organization of industrial production of penicillin in the USSR in second half of the 1940s. The analysis of the documents demonstrated that existed huge gap between health needs of the antibiotic and actual quantity of its production by the end of 1945. This raised the question of organizing its large-scale production. The Soviet Government tried to solve the problem in the least expensive way i.e. through using available industrial areas for the development of penicillin production, refusing to buy ready-made penicillin plants abroad, maximal application of resources of international organizations. The problem of mastering advanced technologies of antibiotic production, as well as development of national equipment for penicillin plants was mainly solved through efforts of intelligence service activities. Due to organizational, technological, foreign policy causes, the development of new penicillin plants was delayed for a long time. The amounts of penicillin production by existing enterprises did not cover the needs of health care in the antibiotic.

6-Arylmethylidene Penicillin-Based Sulfone Inhibitors for Repurposing Antibiotic Efficiency in Priority Pathogens.

The ability of 6-(aryl)methylidene penicillin-based sulfones 1-7 to repurpose ß-lactam antibiotics activity with bacterial species that carry carbapenem-hydrolyzing class D ß-lactamases (OXA-23, OXA-24/40 and OXA-48), as well as with class A (TEM-1, CTX-M-2) and class C (CMY-2, DHA-1) enzymes, is reported. The combinations imipenem/3 and imipenem/4 restored almost completely the antibiotic efficacy in OXA-23 and OXA-24/40 carbapenemase-producing A. baumannii strains (1 µg mL-1) and also provided good results for OXA-48 carbapenemase-producing K. pneumoniae strains (4 µg mL-1). Compounds 2-6 in combinations with ceftazidime and ampicillin were also efficient in restoring antibiotic efficacy in E. coli strains carrying class C (CMY-2 and DHA-1) and class A (TEM-1 and CTX-M-2) ß-lactamase enzymes, respectively. Kinetic and inhibition studies with the OXA-24/40 enzyme, protein mass spectrometry analysis and docking studies allowed us to gain an insight into the inhibition mechanism and the experimentally observed differences between the ligands.

Synthesis of nanostructured Ag@SiO2-Penicillin from high purity Ag NPs prepared by electromagnetic levitation melting process.

Nanostructured Ag@SiO2-Penicillin was synthesized from high-purity Ag0 NPs with a mean particle size of about 10 nm produced by electromagnetic levitation gas condensation (ELGC) method. The silver and penicillin contents of the synthesized nano-antibiotic were about 34 wt% and 2.5 wt% respectively, as determined by ICP-OES and TGA analyses. The antibacterial properties and synergistic effects of nanostructured Ag@SiO2 and Ag@SiO2-Penicillin on killing the Methicillin-susceptible S. aureus (MSSA) and Methicillin-resistant S. aureus (MRSA) bacteria were also examined. The nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Ag@SiO2-Penicillin NPs showed an outstanding antibacterial activity compared to Penicillin and Ag@SiO2 NPs. The Fractional inhibitory concentration (FIC) indexes were 0.54 and 0.52 against MSSA and MRSA bacteria respectively, illustrating the synergistic effects of Ag@SiO2-Penicillin NPs. In addition, Ag@SiO2-Penicillin NPs showed promising dose-dependent cytotoxicity effects indicating the protective effects emanating from anti-inflammatory properties of penicillin.

Recent advances in ß-lactam synthesis.

During the past century, ß-lactams have been identified as the core of penicillin and since then several strategies have been developed for their synthesis. Traditional methods for ß-lactam synthesis usually involved amide bond formation and the Staudinger reaction. In recent years, by the advancement of photo- and transition metal-catalysis, several new methods have been reported for ß-lactam synthesis. For instance: ligand assisted metal catalyzed C-H activation/intermolecular oxidative amidation draws attention for ß-lactam synthesis. In this review we introduce methods for ß-lactam synthesis and present newly developed reactions. We approach the synthesis of ß-lactams according to different retro synthesis strategies.

A brief history of antibiotics and select advances in their synthesis.

The advent of modern antibiotics contributed enormously to the dramatic extension of human lifespan since their discovery by virtue of their lethal and selective action against pathogenic microbes. And yet despite our powerful arsenal of weapons against these pathogens, the war against them has not been won. And it may never be. Drug resistance is still menacing the society with many lives being lost due to deadly infections caused by continuously evolving strains spread beyond our means to eradicate them or prevent their spreading. Herein, the emergence and evolution of antibiotics is briefly reviewed, and a select number of total syntheses of naturally occurring antibiotics from the authors' laboratories are highlighted. The article concludes with a strong endorsement of the current efforts to intensify our fight against these dangerous pathogens with the hope that, this time, these initiatives will be sufficiently focused and serious enough so as to achieve our set goals of, at least, being prepared and ahead of them as part of our drive to improve humanity's healthcare and wellbeing.

Modified Penicillin Molecule with Carbapenem-Like Stereochemistry Specifically Inhibits Class C ß-Lactamases.

Bacterial ß-lactamases readily inactivate most penicillins and cephalosporins by hydrolyzing and "opening" their signature ß-lactam ring. In contrast, carbapenems resist hydrolysis by many serine-based class A, C, and D ß-lactamases due to their unique stereochemical features. To improve the resistance profile of penicillins, we synthesized a modified penicillin molecule, MPC-1, by "grafting" carbapenem-like stereochemistry onto the penicillin core. Chemical modifications include the trans conformation of hydrogen atoms at C-5 and C-6 instead of cis, and a 6-α hydroxyethyl moiety to replace the original 6-ß aminoacyl group. MPC-1 selectively inhibits class C ß-lactamases, such as P99, by forming a nonhydrolyzable acyl adduct, and its inhibitory potency is ∼2 to 5 times higher than that for clinically used ß-lactamase inhibitors clavulanate and sulbactam. The crystal structure of MPC-1 forming the acyl adduct with P99 reveals a novel binding mode for MPC-1 that resembles carbapenem bound in the active site of class A ß-lactamases. Furthermore, in this novel binding mode, the carboxyl group of MPC-1 blocks the deacylation reaction by occluding the critical catalytic water molecule and renders the acyl adduct nonhydrolyzable. Our results suggest that by incorporating carbapenem-like stereochemistry, the current collection of over 100 penicillins and cephalosporins can be modified into candidate compounds for development of novel ß-lactamase inhibitors.

Poly(2-oxazoline)-Antibiotic Conjugates with Penicillins.

The conjugation of antibiotics with polymers is rarely done, but it might be a promising alternative to low-molecular-weight derivatization. The two penicillins penicillin G (PenG) and penicillin V (PenV) were attached to the end groups of different water-soluble poly(2-oxazoline)s (POx) via their carboxylic acid function. This ester group was shown to be more stable against hydrolysis than the ß-lactam ring of the penicillins. The conjugates are still antimicrobially active and up to 20 times more stable against penicillinase catalyzed hydrolysis. The antibiotic activity of the conjugates against Staphylococcus aureus in the presence of penicillinase is up to 350 times higher compared with the free antibiotics. Conjugates with a second antimicrobial function, a dodecyltrimethylammonium group (DDA-X), at the starting end of the PenG and PenV POx conjugates are more antimicrobially active than the conjugates without DDA-X and show high activity in the presence of penicillinase. For example, the conjugates DDA-X-PEtOx-PenG and DDA-X-PEtOx-PenV are 200 to 350 times more active against S. aureus in the presence of penicillinase and almost as effective as the penicillinase stable cloxacollin (Clox) under these conditions. These conjugates show even greater activity compared to cloxacollin without this enzyme present. Further, both conjugates kill Escherichia coli more effectively than PenG and Clox.

Targeted synthesis of novel ß-lactam antibiotics by laccase-catalyzed reaction of aromatic substrates selected by pre-testing for their antimicrobial and cytotoxic activity.

The rapidly increasing problem of antimicrobial-drug resistance requires the development of new antimicrobial agents. The laccase-catalyzed amination of dihydroxy aromatics is a new and promising method to enlarge the range of currently available antibiotics. Thirty-eight potential 1,2- and 1,4-hydroquinoid laccase substrates were screened for their antibacterial and cytotoxic activity to select the best substrates for laccase-catalyzed coupling reaction resulting in potent antibacterial derivatives. As a result, methyl-1,4-hydroquinone and 2,3-dimethyl-1,4-hydroquinone were used as parent compounds and 14 novel cephalosporins, penicillins, and carbacephems were synthesized by amination with amino-ß-lactam structures. All purified products were stable in aqueous buffer and resistant to the action of ß-lactamases, and in agar diffusion and broth micro-dilution assays, they inhibited the growth of several Gram-positive bacterial strains including multidrug-resistant Staphylococcus aureus and Enterococci. Their in vivo activity and cytotoxicity in a Staphylococcus-infected, immune-suppressed mouse model are discussed.

Sulfur Containing Scaffolds in Drugs: Synthesis and Application in Medicinal Chemistry.

The impact of the development of sulfur therapeutics is instrumental to the evolution of the pharmaceutical industry. Sulfur-derived functional groups can be found in a broad range of pharmaceuticals and natural products. For centuries, sulfur continues to maintain its status as the dominating heteroatom integrated into a set of 362 sulfur-containing FDA approved drugs (besides oxygen or nitrogen) through the present. Sulfonamides, thioethers, sulfones and Penicillin are the most common scaffolds in sulfur containing drugs, which are well studied both on synthesis and application during the past decades. In this review, these four moieties in pharmaceuticals and recent advances in the synthesis of the corresponding core scaffolds are presented.

Novel Penicillin Analogues as Potential Antimicrobial Agents; Design, Synthesis and Docking Studies.

A number of penicillin derivatives (4a-h) were synthesized by the condensation of 6-amino penicillinic acid (6-APA) with non-steroidal anti-inflammatory drugs as antimicrobial agents. In silico docking study of these analogues was performed against Penicillin Binding Protein (PDBID 1CEF) using AutoDock Tools 1.5.6 in order to investigate the antimicrobial data on structural basis. Penicillin binding proteins function as either transpeptidases or carboxypeptidases and in few cases demonstrate transglycosylase activity in bacteria. The excellent antibacterial potential was depicted by compounds 4c and 4e against Escherichia coli, Staphylococcus epidermidus and Staphylococcus aureus compared to the standard amoxicillin. The most potent penicillin derivative 4e exhibited same activity as standard amoxicillin against S. aureus. In the enzyme inhibitory assay the compound 4e inhibited E. coli MurC with an IC50 value of 12.5 µM. The docking scores of these compounds 4c and 4e also verified their greater antibacterial potential. The results verified the importance of side chain functionalities along with the presence of central penam nucleus. The binding affinities calculated from docking results expressed in the form of binding energies ranges from -7.8 to -9.2kcal/mol. The carboxylic group of penam nucleus in all these compounds is responsible for strong binding with receptor protein with the bond length ranges from 3.4 to 4.4 Ǻ. The results of present work ratify that derivatives 4c and 4e may serve as a structural template for the design and development of potent antimicrobial agents.

[Enzymatic Synthesis of Acidic ß-Lactams (Review)].

The currently known methods of enzymatic ß-lactam synthesis, as well as the enzymes and heterogeneous biocatalysts used for this purpose, are presented, and the published reports on advances in the field of enzymatic synthesis of selected antibiotics belonging to the groups of acidic penicillins and acidic cephalosporins are summarized in the present review. The key conditions and parameters of biocatalytic processes, such as the biocatalyst form, concentration of the precursor compounds, solvent type, pH, temperature, etc. are analyzed and compared, and guidelines for further optimization of ß-lactam synthesis are given. The present review may be of use for a wide range of readers, as well as to enzymology and biotechnology experts.

Organocatalytic enantioselective α-amination of 5-substituted rhodanines: an efficient approach to chiral N,S-acetals.

We report a highly efficient approach to constructing chiral N,S-acetals using 5-substituted rhodanines as sulfur-bound pronucleophiles catalyzed by natural cinchona alkaloids quinine or quinidine. This α-amination reaction has a broad substrate scope, and the products featuring both rhodanine and N,S-acetal structural motifs were obtained in high yields and excellent enantioselectivities.

How thiostrepton was made in the laboratory.

Thiostrepton, a powerful antibiotic belonging to the thiopeptide class, was synthesized in the laboratory for the first time in 2004 through an arduous campaign involving novel strategies and tactics, scenic detours, and unexpected roadblocks. In this Review the author narrates the long journey to success, not so dissimilar to Odysseus' return voyage to Ithaca, full of adventure, knowledge, and wisdom.

Penicillin inhibitors of purple acid phosphatase.

Purple acid phosphatases (PAPs) are binuclear metallohydrolases that have a multitude of biological functions and are found in fungi, bacteria, plants and animals. In mammals, PAP activity is linked with bone resorption and over-expression can lead to bone disorders such as osteoporosis. PAP is therefore an attractive target for the development of drugs to treat this disease. A series of penicillin conjugates, in which 6-aminopenicillanic acid was acylated with aromatic acid chlorides, has been prepared and assayed against pig PAP. The binding mode of most of these conjugates is purely competitive, and some members of this class have potencies comparable to the best PAP inhibitors yet reported. The structurally related penicillin G was shown to be neither an inhibitor nor a substrate for pig PAP. Molecular modelling has been used to examine the binding modes of these compounds in the active site of the enzyme and to rationalise their activities.

Mercuric mercaptide of penicillenic acid, a novel hapten for relevant immunoassay, synthesized from penicillin.

The synthesis of mercuric mercaptide of penicillenic acid (MMPA) has been the basis for detection of penicillin for nearly 40 years (J. Pharm. Pharmacol., 1972, 24, 790; Chinese Pharmacopoeia Ed. II, 1995). Herein, experiments were performed on: (1) synthesis of MMPA used as a novel mercuric hapten, (2) preparation of mercuric antigen of MMPA-BSA, (3) production of antibodies by rabbits immunized with the antigen, and (4) properties of the antibodies studied by ELISA. The results show that: (1) the antigen is safe for immunized animals; (2) high titer antibodies against MMPA are obtained implying good immunogenicity of the antigen; (3) antisera show slightly higher affinity to OVA-GHS-HgCl than OVA-GSH, indicating weak specific affinity of antisera against mercuric ion. Even the weak specific affinity, the hapten and its antigen have potential uses in immunoassays of mercuric ion in environment and food samples, because of easy chemical selective conversion from mercuric ion to MMPA and complete decomposition of un-reacted penicillin in acidic solution.

Different roads to discovery; Prontosil (hence sulfa drugs) and penicillin (hence beta-lactams).

The important chemotherapeutic agents, Prontosil and pentenylpenicillin (penicillin F), were investigated initially by two men, Domagk and Fleming, who had been influenced by the horrendous wound infections of World War I. The very different pathways leading to their development and to that of the successor antibacterials (sulfa drugs, further penicillins, semi-synthetic penicillins), including the role played by patents, are discussed.

Cyclobutanone mimics of penicillins: effects of substitution on conformation and hemiketal stability.

The tendency for carbocyclic analogues of penicillins to undergo hydrate and hemiketal formation is central to their ability to function as beta-lactamase inhibitors. 2-Thiabicyclo[3.2.0]heptan-6-one-4-carboxylates with alkoxy functionality at C3 have been prepared through two complementary diastereoselective substitution reactions following a highly stereoselective chlorination with sulfuryl chloride. We have found that carbocyclic analogues with 3beta substituents favor an endo envelope conformation in solution, the solid state, and the gas phase, whereas those with 3alpha substituents adopt an exo envelope. Evidence from X-ray crystal structures and ab initio calculations suggests that an anomeric effect contributes to the large conformational preference of the tetrahydrothiophene ring that favors the C3 substituent in an axial orientation. In addition, the envelope conformation of the bicycle, which is determined by the stereochemistry of the C3 substituent, has a dramatic effect on the ability of the cyclobutanone to undergo hemiketal formation in methanol-d4.

Development of the semi-synthetic penicillins and cephalosporins.

Semi-synthetic penicillins and cephalosporins both derive from their respective chemical nuclei, 6-aminopenicillanic acid (6-APA) and 7-aminocephalosporanic acid (7-ACA). Work leading to their isolation was being carried out in parallel, but following very different pathways, during the last half of the 1950s. The development of 6-APA was reviewed recently in this journal, and in the present article I take a closer look at early work on 'penicillin amidase' and revisit the steps that led to 7-ACA.