Mildred Rebstock: Profile of the Medicinal Chemist Who Synthesized Chloramphenicol.

This year marks the 70th anniversary since Parke-Davis and Company announced the synthesis of chloramphenicol, the first naturally occurring antibiotic to be chemically generated in vitro for large-scale production. The effort was led by the chemist Mildred Rebstock, Ph.D., (1919 to 2011), who would turn 100 years old this year. Her accomplishment, at a time when very few chemists in the United States were women, was celebrated internationally. This commentary reviews her important contribution.

Dual effect of chloramphenicol peptides on ribosome inhibition.

Chloramphenicol peptides were recently established as useful tools for probing nascent polypeptide chain interaction with the ribosome, either biochemically, or structurally. Here, we present a new 10mer chloramphenicol peptide, which exerts a dual inhibition effect on the ribosome function affecting two distinct areas of the ribosome, namely the peptidyl transferase center and the polypeptide exit tunnel. According to our data, the chloramphenicol peptide bound on the chloramphenicol binding site inhibits the formation of both acetyl-phenylalanine-puromycin and acetyl-lysine-puromycin, showing, however, a decreased peptidyl transferase inhibition compared to chloramphenicol-mediated inhibition per se. Additionally, we found that the same compound is a strong inhibitor of green fluorescent protein synthesis in a coupled in vitro transcription-translation assay as well as a potent inhibitor of lysine polymerization in a poly(A)-programmed ribosome, showing that an additional inhibitory effect may exist. Since chemical protection data supported the interaction of the antibiotic with bases A2058 and A2059 near the entrance of the tunnel, we concluded that the extra inhibition effect on the synthesis of longer peptides is coming from interactions of the peptide moiety of the drug with residues comprising the ribosomal tunnel, and by filling up the tunnel and blocking nascent chain progression through the restricted tunnel. Therefore, the dual interaction of the chloramphenicol peptide with the ribosome increases its inhibitory effect and opens a new window for improving the antimicrobial potency of classical antibiotics or designing new ones.

Transesterification Synthesis of Chloramphenicol Esters with the Lipase from Bacillus amyloliquefaciens.

This work presents a synthetic route to produce chloramphenicol esters by taking advantage the high enantio- and regio-selectivity of lipases. A series of chloramphenicol esters were synthesized using chloramphenicol, acyl donors of different carbon chain length and lipase LipBA (lipase cloned from Bacillus amyloliquefaciens). Among acyl donors with different carbon chain lengths, vinyl propionate was found to be the best. The influences of different organic solvents, reaction temperature, reaction time, enzyme loading and water content on the synthesis of the chloramphenicol esters were studied. The synthesis of chloramphenicol propionate (0.25 M) with 4.0 g L-1 of LipBA loading gave a conversion of ~98% and a purity of ~99% within 8 h at 50 °C in 1,4-dioxane as solvent. The optimum mole ratio of vinyl propionate to chloramphenicol was increased to 5:1. This is the first report of B. amyloliquefaciens lipase being used in chloramphenicol ester synthesis and a detailed study of the synthesis of chloramphenicol propionate using this reaction. The high enzyme activity and selectivity make lipase LipBA an attractive catalyst for green chemical synthesis of molecules with complex structures.

Enantioselective synthesis of (-)-chloramphenicol via silver-catalysed asymmetric isocyanoacetate aldol reaction.

The highly enantio- and diastereoselective aldol reaction of isocyanoacetates catalysed by Ag2O and cinchona-derived amino phosphines applied to the synthesis of (-)- and (+)-chloramphenicol is described. The concise synthesis showcases the utility of this catalytic asymmetric methodology for the preparation of bioactive compounds possessing α-amino-ß-hydroxy motifs.

Inhibition of Helicobacter pylori aminoacyl-tRNA amidotransferase by chloramphenicol analogs.

Genomic studies revealed the absence of glutaminyl-tRNA synthetase and/or asparaginyl-tRNA synthetase in many bacteria and all known archaea. In these microorganisms, glutaminyl-tRNA(Gln) (Gln-tRNA(Gln)) and/or asparaginyl-tRNA(Asn) (Asn-tRNA(Asn)) are synthesized via an indirect pathway involving side chain amidation of misacylated glutamyl-tRNA(Gln) (Glu-tRNA(Gln)) and/or aspartyl-tRNA(Asn) (Asp-tRNA(Asn)) by an amidotransferase. A series of chloramphenicol analogs have been synthesized and evaluated as inhibitors of Helicobacter pylori GatCAB amidotransferase. Compound 7a was identified as the most active competitive inhibitor of the transamidase activity with respect to Asp-tRNA(Asn) (K(m)=2µM), with a K(i) value of 27µM.

Synthesis, Analytical Characterization and Spectroscopic Investigation of Chloramphenicol Impurity A for the Quality Control of Chloramphenicol and its Formulation as Per International Compendium.

OBJECTIVE: The main aim of the present work is to synthesize chloramphenicol impurity A (CLRMIMP- A) in the purest form and its subsequent characterization by using a panel of sophisticated analytical techniques (LC-MS, DSC, TGA, NMR, FTIR, HPLC, and CHNS) to provide as a reference standard mentioned in most of the international compendiums, including IP, BP, USP, and EP. The present synthetic procedure has not been disclosed anywhere in the prior art. METHODS: A simple, cheaper, and new synthesis method was described for the preparation of CLRM-IMP-A. It was synthesized and characterized by FTIR, DSC, TGA, NMR (1H and 13C), LC-MS, CHNS, and HPLC. RESULTS: CLRM-IMP-A present in drugs and dosage form can alter the therapeutic effects and adverse reaction of a drug considerably, it is mandatory to have a precise method for the estimation of impurities to safeguard the public health. Under these circumstances, the presence of CLRM-IMP-A in chloramphenicol (CLRM) requires strict quality control to satisfy the specified regulatory limit. The synthetic impurity obtained was in the pure form to provide a certified reference standard or working standard to stakeholders with defined potency. CONCLUSION: The present research describes a novel technique for the synthesis of pharmacopoeial impurity, which can help in checking/controlling the quality of the CLRM in the international markets.

Design and synthesis of novel chloramphenicol amine derivatives as potent aminopeptidase N (APN/CD13) inhibitors.

Herein we report a series of novel chloramphenicol amine derivatives as aminopeptidase N (APN)/CD13 inhibitors. All compounds were synthesized starting from commercially available (1S,2S)-2-amino-1-(4-nitrophenyl) propane-1,3-diol. The preliminary biological screening showed that some compounds exhibited potent inhibitory activity against APN. It should be noted that one compound, 13b (IC(50)=7.1 microM), possess similar APN inhibitory activity compared with Bestatin (IC(50)=3.0 microM).

Successful co-encapsulation of benzoyl peroxide and chloramphenicol in liposomes by a novel manufacturing method - dual asymmetric centrifugation.

Encapsulation of more than one active pharmaceutical ingredient into nanocarriers such as liposomes is an attractive approach to achieve a synergic drug effect and less complicated dosing schedules in multi-drug treatment regimes. Liposomal drug delivery in acne treatment may improve drug efficiency by targeted delivery to pilosebaceous units, reduce adverse effects and improve patient compliance. We therefore aimed to co-encapsulate benzoyl peroxide (BPO) and chloramphenicol (CAM) into liposomes using the novel liposome processing method - dual asymmetric centrifugation (DAC). Liposomes were formed from soybean lecithin, propylene glycol and distilled water (2:1:2w/v/v ratio), forming a viscous liposome dispersion. Liposomes containing both drugs (BPO-CAM-Lip), single drug (BPO-Lip and CAM-Lip), and empty liposomes were prepared. Drug entrapment of BPO and CAM was determined by a newly developed HPLC method for simultaneous detection and quantification of both drugs. Encapsulation of around 50% for BPO and 60% for CAM respectively was obtained in both single-drug encapsulated formulations (BPO-Lip and CAM-Lip) and co-encapsulated formulations (BPO-CAM-Lip). Liposome sizes were comparable for all liposome formulations, ranging from 130 to 150nm mean diameter, with a polydispersity index <0.2 for all formulations. CAM exhibited a sustained release from all liposomal formulations, whereas BPO appeared retained within the liposomes. BPO retention could be attributed to its poor solubility. However, HaCaT cell toxicity was found dependent on BPO released from the liposomes. In the higher concentration range (4%v/v), liposomal formulations were less cytotoxic than the corresponding drug solutions used as reference. We have demonstrated that DAC is a fast, easy, suitable method for encapsulation of more than one drug within the same liposomes.

Hybrids of antibiotics inhibiting protein synthesis. Synthesis and biological activity.

Four hybrid antibiotics combining structural features of chloramphenicol (1a), sparsomycin (2b), lincomycin (5c), and puromycin (6d)--lincophenicol (1c), chloramlincomycin (5a), sparsolincomycin (5b), and sparsopuromycin (6b)--were synthesized. They were investigated as inhibitors of several partial reactions of procaryotic and eucaryotic protein synthesis as well as potential antimicrobial agents. Lincophenicol (1c) was active as inhibitor of Escherichia coli ribosomal peptidyltransferase-catalyzed puromycin reaction. Both lincophenicol (1c) and sparsophenicol (1b) inhibited the binding of the iodophenol analogue of sparsomycin to E. coli ribosomes. The results are discussed in terms of a retro-inverso hypothesis advanced earlier for interpretation of biological activity of chloramphenicol (1a) and sparsophenicol (1b). Chloramlincomycin (5a) suppressed the growth of Streptococcus pyogenes with MIC 6.25 micrograms/mL.

An efficient synthesis of (-)-chloramphenicol via asymmetric catalytic aziridination: a comparison of catalysts prepared from triphenylborate and various linear and vaulted biaryls.

[reaction--see text] The antibiotic (-)-choramphenicol has been synthesized in only four steps from p-nitro-benzaldehyde in optically pure form from an asymmetric catalytic aziridination reaction with a chiral catalyst prepared from triphenylborate and the (R)-VAPOL ligand. Catalysts generated from the VAPOL and VANOL ligands give much higher asymmetric induction than do catalysts prepared from 6,6'-diphenylVAPOL, BINOL, and BANOL ligands.

[Synthesis and antibacterial activity of perchlorylchloramphenicol]. / Synthese und antibakterielle Aktivität von Perchlorylchloramphenicol.

Starting from p-perchloryl acetophenone we have synthesized the perchloryl analogue of chloramphenicol. The new compound is the first chloramphenicol analogue possessing a higher antimicrobial activity as chloramphenicol itself. It showed an about twofold activity against 18 different microbes in the hole plate diffusion test, compared with the parent compound.

The identification and characterisation of chloramphenicol-aldehyde, a new human metabolite of chloramphenicol.

The toxic aldehyde derivative of chloramphenicol has previously been reported as a metabolic product only in the rat. Chloramphenicol-aldehyde has been synthesised and characterised and shown to exist in at least two forms, possibly due to rearrangement within the molecule. The authenticated compound has been used to identify chloramphenicol-aldehyde as a metabolic product excreted in the urine of children treated with chloramphenicol.

Pyrrole analogues of chloramphenicol. I. Synthesis and antibacterial activity of DL-threo-1-(1-methyl-4-nitropyrrole-2-yl)-2-dichloroacetamidopropane-1,3-diol.

The seven-stage synthesis of a pyrrole analogue of chloramphenicol [IX] was described. The compound exhibits a significant antibacterial activity, over the 12-50% range of the chloramphenicol activity.

Pyrrole analogues of chloramphenicol. II. Synthesis and antibacterial activity of DL-threo-1-(1-methyl-5-nitro-pyrrole-2-yl)-2-dichloroacetamidopropane-1, 3-diol.

The seven-stage synthesis of a pyrrole analogue of chloramphenicol (VII) was described. The compound exhibits a significant antibacterial activity.

Pyrrole analogues of chloramphenicol. III. Synthesis and antibacterial activity of DL-threo-1-(1-methylsulfonylpyrrole-3-yl)-2-dichloroacetamidopropane-1,3-diol.

A seven-stage synthesis of a pyrrole analogue of chloramphenicol (9) is described. The compound exhibits a significant antibacterial activity, over the 3% to 50% range of the chloramphenicol activity: over the 6% to 100% range of the thiamphenicol activity and florfenicol.

Synthesis and evaluation of hetero- and homodimers of ribosome-targeting antibiotics: antimicrobial activity, in vitro inhibition of translation, and drug resistance.

In this study, we describe the synthesis of a full set of homo- and heterodimers of three intact structures of different ribosome-targeting antibiotics: tobramycin, clindamycin, and chloramphenicol. Several aspects of the biological activity of the dimeric structures were evaluated including antimicrobial activity, inhibition of in vitro bacterial protein translation, and the effect of dimerization on the action of several bacterial resistance mechanisms that deactivate tobramycin and chloramphenicol. This study demonstrates that covalently linking two identical or different ribosome-targeting antibiotics may lead to (i) a broader spectrum of antimicrobial activity, (ii) improved inhibition of bacterial translation properties compared to that of the parent antibiotics, and (iii) reduction in the efficacy of some drug-modifying enzymes that confer high levels of resistance to the parent antibiotics from which the dimers were derived.