Synthesis of Gentamicins C1, C2, and C2a and Antiribosomal and Antibacterial Activity of Gentamicins B1, C1, C1a, C2, C2a, C2b, and X2

Abstract

Complementing our earlier syntheses of the gentamicins B1, C1a, C2b, and X2, we describe the synthesis of gentamicins C1, C2, and C2a characterized by methyl substitution at the 6′-position, and so present an alternative access to previous chromatographic methods for accessing these sought-after compounds. We describe the antiribosomal activity of our full set of synthetic gentamicin congeners against bacterial ribosomes and hybrid ribosomes carrying the decoding A site of the human mitochondrial, A1555G mutant mitochondrial, and cytoplasmic ribosomes and establish structure−activity relationships with the substitution pattern around ring I to antiribosomal activity, antibacterial resistance due to the presence of aminoglycoside acetyl transferases acting on the 6′-position in ring I, and literature cochlear toxicity data.

Experimental Determination of the pKa Values of Clinically Relevant Aminoglycoside Antibiotics: Toward Establishing pKa─Activity Relationships

“…Gentamicin is a 4,6-disubstituted deoxystreptamine derivative containing purpurosamine at the 4-O and garosamine (3-methyl amino-3-deoxy-4- C -methyl-β- l -arabinose) at the 6-O positions (Figure A). Naturally produced gentamicin is a mixture of five major compounds C1, C1a, C2, C2a, and C2b differing by the substituents at the 6′ position of the purpurosamine ring . Gentamicin C1, C2a, and C2b have three primary amine (i.e., monosubstituted ammonia) groups, N-1 and N-3 on the DOS moiety and N-2′ on purpurosamine; as well as two secondary amines, N-6′ on purpurosamine and N-3′′ on garosamine.…”

“…Naturally produced gentamicin is a mixture of five major compounds C1, C1a, C2, C2a, and C2b differing by the substituents at the 6′ position of the purpurosamine ring. 23 Gentamicin C1, C2a, and C2b have three primary amine (i.e., monosubstituted ammonia) groups, N-1 and N-3 on the DOS moiety and N-2′ on purpurosamine; as well as two secondary amines, N-6′ on purpurosamine and N-3′′ on garosamine. In gentamicin C1a and C2, N-6′ is a primary amine bringing the balance to four primary and one secondary amine instead.…”

“…Cell-free in vitro translation inhibition assays were performed as described previously using bacterial S30 extracts and luciferase mRNA . In brief, firefly luciferase mRNA was transcribed in vitro using a T7 RNA polymerase.…”

“…Cell-free in vitro translation inhibition assays were performed as described previously using bacterial S30 extracts and luciferase mRNA. 23 In brief, firefly luciferase mRNA was transcribed in vitro using a T7 RNA polymerase. Each reaction comprised bacterial S30 extract, 0.2 mM amino acid mix, 6 μg of tRNA, 0.4 μg of hFluc mRNA, 0.3 μL of protease inhibitor, 12 U of RNase inhibitor, and 6 μL of S30 premix without amino acids, plus a defined concentration of aminoglycoside antibiotic.…”

In vitro susceptibility of Neisseria gonorrhoeae to netilmicin and etimicin in comparison to gentamicin and other aminoglycosides

“…These findings confirm similar observations previously reported for other Gram-negative pathogens, and is in support of proposals of gentamicin formulations selectively enriched in less toxic but equally potent congeners, for instance by removal of gentamicin C2 from the natural gentamicin complex [ 8 , 9 ]. Apart from chromatographic separation, chemical synthesis of individual gentamicin C congeners may provide an alternative strategy [ 14 ].…”