Joyce Kohler

Direct interaction of a vancomycin derivative with bacterial enzymes involved in cell wall biosynthesis

BACKGROUND The glycopeptide antibiotic vancomycin complexes DAla-DAla termini of bacterial cell walls and peptidoglycan precursors and interferes with enzymes involved in murein biosynthesis. Semisynthetic vancomycins incorporating hydrophobic sugar substituents exhibit efficacy against DAla-DLac-containing vancomycin-resistant enterococci, albeit by an undetermined mechanism. Contrasting models that invoke either cooperative dimerization and membrane anchoring or direct inhibition of bacterial transglycosylases have been proposed to explain the bioactivity of these glycopeptides. RESULTS Affinity chromatography has revealed direct interactions between a semisynthetic hydrophobic vancomycin (DCB-PV), and select Escherichia coli membrane proteins, including at least six enzymes involved in peptidoglycan assembly. The N(4)-vancosamine substituent is critical for protein binding. DCB-PV inhibits transglycosylation in permeabilized E. coli, consistent with the observed binding of the PBP-1B transglycosylase-transpeptidase. CONCLUSIONS Hydrophobic vancomycins interact directly with a select subset of bacterial membrane proteins, suggesting the existence of discrete protein targets. Transglycosylase inhibition may play a role in the enhanced bioactivity of semisynthetic glycopeptides.

Synthesis and activity of 2-(sulfonamido)methyl-carbapenems: Discovery of a novel, anti-MRSA 1,8-naphthosultam pharmacophore

A series of 1beta-methyl carbapenems substituted at the 2-position with lipophilic, acyclic and cyclic (sulfonamido)methyl groups was prepared and evaluated for activity against resistant gram-positive bacteria. From these studies, the 1,8-naphthosultamyl group emerged as a novel, PBP2a-binding, anti-MRSA pharmacophore worthy of further exploration.

Synthesis and properties of 2-(naphthosultamyl)methyl-carbapenems with potent anti-MRSA activity: discovery of L-786,392.

A series of 1beta-methyl-2-(naphthosultamyl)methyl-carbapenems bearing dicationic groups on the naphthosultamyl moiety was prepared and evaluated for activity against resistant gram-positive bacteria. Based on a combination of excellent in vitro antibacterial activity, acceptable mouse acute toxicity, and a desirable fragmentation pattern on beta-lactam ring opening, the analog 2g (L-786,392) was selected for extended evaluation.

Benzothiazolylthio carbapenems: potent anti-MRSA agents

Abstract A series of sulfur-linked benzothiazolyl carbapenems has been prepared and evaluated against a battery of microorganisms. Many of the compounds displayed good activity against methicillin-resistant Staphylococcus aureus (MRSA). Data is presented which delimits the pharmacophore and provides a preliminary SAR.

Protoplast fusion inStreptomyces avermitilis

SummaryThe power of protoplast fusion as a generally applicable method for obtaining genetic recombination is demonstrated by the recombination of genes involved in avermectin biosynthesis. A backcross ofStreptomyces avermitilis strain MA6202, an improved mutant that had lost the ability to carry out the methylation of the C-5 hydroxyl of the avermectin molecule, with the original soil isolate MA4680 resulted in the recovery of at least one unambiguous recombinant class despite the instability of rifampicin resistance, one of two markers initially used for recombinant selection. Such intrinsic instability is frequently encountered in streptomycete genetics, and this result delineates the utility of protoplast fusion as a genetic tool. Other difficulties addressed include recovery of complementary recombinant classes, differences in recombination frequency due to colony density on regeneration medium, and alteration in plating efficiency on diagnostic media following protoplasting and regeneration. The results of a cross between a nicotinamide auxotroph MRG1003 and a lysine auxotroph MRG 1004 are included to aid in the elucidation of these problems as well as to support the finding of homologous recombination inS. avermitilis.

Antibacterial activity of G6-quaternary ammonium derivatives of a lipophilic vancomycin analogue.

A series of G6-amino derivatives of a lipophilic vancomycin analogue was prepared. Antibacterial activity of the analogues was inversely proportional to the degree of substitution of the G6-nitrogen. The fully substituted (quaternary) analogues were essentially inactive against vanA phenotype VREF strains but retained substantial activity against other bacteria, a profile reminiscent of teicoplanin.