An Advanced Apralog with Increased in†vitro and in†vivo Activity toward Gram-negative Pathogens and Reduced ex vivo Cochleotoxicity.

We describe the convergent synthesis of a 5-O-ß-D-ribofuranosyl-based apramycin derivative (apralog) that displays significantly improved antibacterial activity over the parent apramycin against wild-type ESKAPE pathogens. In addition, the new apralog retains excellent antibacterial activity in the presence of the only aminoglycoside modifying enzyme (AAC(3)-IV) acting on the parent, without incurring susceptibility to the APH(3') mechanism that disables other 5-O-ß-D-ribofuranosyl 2-deoxystreptamine type aminoglycosides by phosphorylation at the ribose 5-position. Consistent with this antibacterial activity, the new apralog has excellent 30 nM activity (IC50 ) for the inhibition of protein synthesis by the bacterial ribosome in a cell-free translation assay, while retaining the excellent across-the-board selectivity of the parent for inhibition of bacterial over eukaryotic ribosomes. Overall, these characteristics translate into excellent in vivo efficacy against E. coli in a mouse thigh infection model and reduced ototoxicity vis à vis the parent in mouse cochlear explants.

Structure-Based Design and Synthesis of Apramycin-Paromomycin Analogues: Importance of the Configuration at the 6'-Position and Differences between the 6'-Amino and Hydroxy Series.

The preparation of a series of four analogues of the aminoglycoside antibiotics neomycin and paromomycin is described in which ring I, involved in critical binding interactions with the ribosomal target, is replaced by an apramycin-like dioxabicyclo[4.4.0]octane system. The effect of this modification is to lock the hydroxymethyl side chain of the neomycin or paromomycin ring I, as part of the dioxabicyclooctane ring, into either the gauche-gauche or the gauche-trans conformation (respectively, axial or equatorial to the bicyclic system). The antiribosomal activity of these compounds is investigated with cell-free translation assays using both bacterial ribosomes and recombinant hybrid ribosomes carrying eukaryotic decoding A site cassettes. Compounds substituted with an equatorial hydroxyl or amino group in the newly formed ring are considerably more active than their axial diastereomers, lending strong support to crystallographically derived models of aminoglycoside-ribosome interactions. One such bicyclic compound carrying an equatorial hydroxyl group has activity equal to that of the parent yet displays better ribosomal selectivity, predictive of an enhanced therapeutic index. A paromomycin analog lacking the hydroxymethyl ring I side chain is considerably less active than the parent. Antibacterial activity against model Gram negative and Gram positive bacteria is reported for selected compounds, as is activity against ESKAPE pathogens and recombinant bacteria carrying specific resistance determinants. Analogues with a bicyclic ring I carrying equatorial amino or hydroxyl groups mimicking the bound side chains of neomycin and paromomycin, respectively, show excellent activity and, by virtue of their novel structure, retain this activity in strains that are insensitive to the parent compounds.

Importance of the 6'-hydroxy group and its configuration for apramycin activity.

A series of apramycin derivatives was prepared and investigated for antibacterial activity and the ability to inhibit protein synthesis in cell-free translation assays. The effect of various modifications at the 6'- and N7'-positions on antiribosomal activity is discussed in terms of their influence on drug binding to specific residues in the decoding A-site. These studies contribute to the development of a structure-activity relationship for the antibacterial activity of the apramycin class of aminoglycosides and to the future design and development of more active and less toxic antibiotics.

Aminoglycoside antibiotics. XIV. Synthesis and activity of 6-O-(3-amino-3-deoxy-alpha-D-glucopyranosyl)-and 5-O-(beta-D-ribofuranosyl)apramycins.

6-O-(3-Amino-3-deoxy-alpha-d-glucopyranosyl)apramycin (17) was prepared by glycosidation of a suitably blocked 5,6-dihydroxy derivative (11) of apramycin with a blocked 3-aminoglucosyl chloride (15). Ribosylation of the 5-hydroxy-6-O-tetrahydropyranyl (THP) derivative (19) of apramycin gave 5-O-(beta-d-ribofuranosyl)apramycin (24) along with the 6 alpha (25) and 6 beta (26) isomers. Similar reaction with the 6-hydroxy-5-O-THP derivative (20) or 11 gave only 25 and 26, but not 24. 17 was at least as active as apramycin against most Gram-positive and Gram-negative bacteria tested and more active than apramycin against most Gram-positive and Gram-negative bacteria tested and more active than apramycin against strains producing aminoglycoside-modifying enzymes. Strains of Pseudomonas aeruginosa were generally less sensitive to 17 than to apramycin. 24 was the most active of the three ribofuranosyl derivatives prepared though it was less active than 17.