Synthesis of HCV Replicase Inhibitors: Base-Catalyzed Synthesis of Protected α-Hydrazino Esters and Selective Aerobic Oxidation with Catalytic Pt/Bi/C for Synthesis of Imidazole-4,5-dicarbaldehyde

A robust convergent synthesis of the prodrugs of HCV replicase inhibitors 1-5 is described. The central 5H-imidazo[4,S-d]pyridazine core was formed from acid-catalyzed cyclocondensation of an imidazole-4,5-dicarbaldehyde (20) and a alpha-hydrazino ester, generated in situ from the bis-BOC-protected precursors 25 and 33. The acidic conditions not only released the otherwise unstable alpha-hydrazino esters but also were the key to avoid facile decarboxylation to the parent drugs from the carboxylic ester prodrugs 1-5. The bis-BOC alpha-hydrazino esters 25 and 33 were prepared by addition of ester enolates (from 23 and 32) to di-tert-butyl azodicarboxylate via catalysis with mild inorganic bases, such as Li2CO3. A selective aerobic oxidation with catalytic 5% Pt-Bi/C in aqueous KOH was developed to provide the dicarbaldehyde 20 from the diol 27

Biofilm formation on stainless steel and gold wires for bonded retainers in vitro and in vivo and their susceptibility to oral antimicrobials

<p>Bonded retainers are used in orthodontics to maintain treatment result. Retention wires are prone to biofilm formation and cause gingival recession, bleeding on probing and increased pocket depths near bonded retainers. In this study, we compare in vitro and in vivo biofilm formation on different wires used for bonded retainers and the susceptibility of in vitro biofilms to oral antimicrobials.</p><p>Orthodontic wires were exposed to saliva, and in vitro biofilm formation was evaluated using plate counting and live/dead staining, together with effects of exposure to toothpaste slurry alone or followed by antimicrobial mouthrinse application. Wires were also placed intra-orally for 72 h in human volunteers and undisturbed biofilm formation was compared by plate counting and live/dead staining, as well as by denaturing gradient gel electrophoresis for compositional differences in biofilms.</p><p>Single-strand wires attracted only slightly less biofilm in vitro than multi-strand wires. Biofilms on stainless steel single-strand wires however, were much more susceptible to antimicrobials from toothpaste slurries and mouthrinses than on single-strand gold wires and biofilms on multi-strand wires. Also, in vivo significantly less biofilm was found on single-strand than on multi-strand wires. Microbial composition of biofilms was more dependent on the volunteer involved than on wire type.</p><p>Biofilms on single-strand stainless steel wires attract less biofilm in vitro and are more susceptible to antimicrobials than on multi-strand wires. Also in vivo, single-strand wires attract less biofilm than multi-strand ones.</p><p>Use of single-strand wires is preferred over multi-strand wires, not because they attract less biofilm, but because biofilms on single-strand wires are not protected against antimicrobials as in crevices and niches as on multi-strand wires.</p>