Effects of the 1- N-(4-Amino-2 S-hydroxybutyryl) and 6'- N-(2-Hydroxyethyl) Substituents on Ribosomal Selectivity, Cochleotoxicity, and Antibacterial Activity in the Sisomicin Class of Aminoglycoside Antibiotics.

Syntheses of the 6'- N-(2-hydroxyethyl) and 1- N-(4-amino-2 S-hydroxybutyryl) derivatives of the 4,6-aminoglycoside sisomicin and that of the doubly modified 1- N-(4-amino-2 S-hydroxybutyryl)-6'- N-(2-hydroxyethyl) derivative known as plazomicin are reported together with their antibacterial and antiribosomal activities and selectivities. The 6'- N-(2-hydroxyethyl) modification results in a moderate increase in prokaryotic/eukaryotic ribosomal selectivity, whereas the 1- N-(4-amino-2 S-hydroxybutyryl) modification has the opposite effect. When combined in plazomicin, the effects of the two groups on ribosomal selectivity cancel each other out, leading to the prediction that plazomicin will exhibit ototoxicity comparable to those of the parent and the current clinical aminoglycoside antibiotics gentamicin and tobramycin, as borne out by ex vivo studies with mouse cochlear explants. The 6'- N-(2-hydroxyethyl) modification restores antibacterial activity in the presence of the AAC(6') aminoglycoside-modifying enzymes, while the 1- N-(4-amino-2 S-hydroxybutyryl) modification overcomes resistance to the AAC(2') class but is still affected to some extent by the AAC(3) class. Neither modification is able to circumvent the ArmA ribosomal methyltransferase-induced aminoglycoside resistance. The use of phenyltriazenyl protection for the secondary amino group of sisomicin facilitates the synthesis of each derivative and their characterization through the provision of sharp NMR spectra for all intermediates.

Synthesis and spectrum of the neoglycoside ACHN-490.

ACHN-490 is a neoglycoside, or "next-generation" aminoglycoside (AG), that has been identified as a potentially useful agent to combat drug-resistant bacteria emerging in hospitals and health care facilities around the world. A focused medicinal chemistry campaign produced a collection of over 400 sisomicin analogs from which ACHN-490 was selected. We tested ACHN-490 against two panels of Gram-negative and Gram-positive pathogens, many of which harbored AG resistance mechanisms. Unlike legacy AGs, ACHN-490 was active against strains expressing known AG-modifying enzymes, including the three most common such enzymes found in Enterobacteriaceae. ACHN-490 inhibited the growth of AG-resistant Enterobacteriaceae (MIC(90), ≤4 µg/ml), with the exception of Proteus mirabilis and indole-positive Proteae (MIC(90), 8 µg/ml and 16 µg/ml, respectively). ACHN-490 was more active alone in vitro against Pseudomonas aeruginosa and Acinetobacter baumannii isolates with AG-modifying enzymes than against those with altered permeability/efflux. The MIC(90) of ACHN-490 against AG-resistant staphylococci was 2 µg/ml. Due to its promising in vitro and in vivo profiles, ACHN-490 has been advanced into clinical development as a new antibacterial agent.

Semisynthetic aminoglycoside antibacterials. 6. Synthesis of sisomicin, Antibiotic G-52, and novel 6'-substituted analogues of sisomicin from aminoglycoside 66-40C.

The discovery of aminoglycoside 66-40C, a novel dimeric, unsaturated imine produced by Micromonospora inyoensis, afforded a versatile intermediate for the synthesis of a variety of sisomicin analogues modified at the 6' position. The conversion of 66-40C into sisomicin, antibiotic G-52, and a series of novel 6'-substituted analogues of sisomicin is described, and the biological activity of the products is discussed.