Synthesis of α-(S)- acylamino-n-(hydroxydioxocyclobutenyl)- γ-lactams

Monocyclic γ - lactams 2, activated by a hydroxycyclobutenedione moiety have been prepared from (L)-N^tBoc-glutamine, as potential antibacterial agents.     

Synthesis of methyl O-(3-deoxy-3-fluoro-β- -galactopyranosyl)-(1→6)-O-β- -galactopyranosyl-(1→6)-3-deoxy-3-fluoro -β- -galactopyranoside and related n.m.r. studies

Sequential tritylation, benzoylation, and detritylation of methyl 3-deoxy-3-fluoro-β- -galactopyranoside gave crystalline methyl 2,4-di-O-benzoyl-3-deoxy-3-fluoro-β- -galactopyranoside (9), which was used as the initial nucleophile in the synthesis of the target oligosaccharide (16). Treatment of 9 with 2,3,4-tri-O-benzoyl-6-O-bromoacetyl-α- -galactopyranosyl bromide gave the corresponding disaccharide derivative 13, having a selectively removable blocking group at O-6′. Debromoacetylation of 13 afforded the disaccharide nucleophile 14 which, when treated with 2,4,6-tri-O-benzoyl-3-deoxy-3-fluoro-α- -galactopyranosyl bromide, gave the fully protected trisaccharide 15. Debenzoylation of 15 gave the title glycoside 16. Condensation reactions were performed with silver trifluoromethane-sulfonate as a promoter in the presence of sym-collidine under base-deficient conditions, and gave excellent yields of the desired β-(trans)-products. Analyses of the ¹H- and ¹³C-n.m.r. spectra, as well as determination of the J_CF and J_HF coupling constants, were made by using various one- and two-dimensional n.m.r. techniques.