Synthesis of Bradyrhizose from d-Glucose

Exploring a De Novo Route to Bradyrhizose: Synthesis and Isomeric Equilibrium of Bradyrhizose Diastereomers≠

A de novo asymmetric strategy for the synthesis of d-bradyrhizose diastereomers from an achiral ketoenolester precursor is described. Key transformations used in the stereodivergent approach include two Noyori asymmetric reductions, an Achmatowicz rearrangement, diastereoselective alkene oxidations, and the first example of a palladium(0)-catalyzed glycosylation of a vinylogous pyranone. The isomeric composition of the bicyclic reducing sugars obtained was analyzed and their behaviour was compared to the natural product, revealing key stereocentres that impact the overall distribution.

Synthesis and Antibacterial Activity of Propylamycin Derivatives Functionalized at the 5''- and Other Positions with a View to Overcoming Resistance Due to Aminoglycoside Modifying Enzymes

Propylamycin (4'-deoxy-4'-propylparomomycin) is a next generation aminoglycoside antibiotic that displays increased antibacterial potency over the parent, coupled with reduced susceptibility to resistance determinants and reduced ototoxicity in the guinea pig model. Propylamycin nevertheless is inactivated by APH(3')-Ia, a specific aminoglycoside phosphotransferase isozyme that acts on the primary hydroxy group of the ribofuranosyl moiety (at the 5''-position). To overcome this problem, we have prepared and studied the antibacterial and antiribosomal activity of various propylamycin derivatives carrying amino or substituted amino groups at the 5''-position in place of the vulnerable hydroxy group. We find that the introduction of an additional basic amino group at this position, while overcoming the action of the aminoglycoside phosphoryltransferase isozymes acting at the 5''-position as anticipated, results in a significant drop in selectivity for the bacterial over the eukaryotic ribosomes that is predictive of increased ototoxicity. In contrast, 5''-deoxy-5''-formamidopropylamycin retains the excellent across-the-board levels of antibacterial activity of propylamycin itself, while circumventing the action of the offending aminoglycoside phosphotransferase isozymes and affording even greater selectivity for the bacterial over the eukaryotic ribosomes. Other modifications to address the susceptibility of propylamycin to the APH(3')-Ia isozyme including deoxygenation at the 3'-position and incorporation of a 6',5''-bis(hydroxyethylamino) modification offer no particular advantage.

Stereospecific synthesis of methyl 2-amino-2,4-dideoxy-6S-deuterio-α-D-xylo-hexopyranoside and methyl 2-amino-2,4-dideoxy-6S-deuterio-4-propyl-α-d-glucopyranoside: Side chain conformation of the novel aminoglycoside antibiotic propylamycin

The stereospecific syntheses of methyl 2-amino-2,4-dideoxy-4-C-propyl-α-d-glucopyranoside and of methyl 2-amino-2,4-dideoxy-α-D-xylo-hexopyranoside and of their 6S-deuterioisotopomers are described as models for ring I of the aminoglycoside antibiotics propylamycin and 4'-deoxyparomomycin, respectively. Analysis of the ¹H NMR spectra of these compounds and of methyl 2-amino-2-deoxy-α-d-glucopyranoside, a model for paromomycin itself, reveals that neither deoxygenation at the 4-position, nor substitution of the C-O bond at the 4-postion by a C-C bond significantly changes the distribution of the side chain population between the three possible staggered conformations. From this it is concluded that the beneficial effect on antiribosomal and antibacterial activity of the propyl group in propylamycin does not derive from a change in side chain conformation. Rather, enhanced basicity of the ring oxygen and increased hydrophobicity and/or solvation effects are implicated.