Synthesis, and carbon-13 n.m.r. study, of O-α- -rhamnopyranosyl-(1→3)-O-α- -rhamnopyranosyl-(1→2)- -rhamnopyranose and O-α- -rhamnopyranosyl-(1→3)-O-α- -rhamnopyranosyl (1→3)- -rhamnopyranose, constituents of bacterial, cell-wall polysaccharides

O-α- -Rhamnopyranosyl-(1→3)- -rhamnopyranose (19) and O-α- -rhamnopyranosyl-(1→2)- -rhamnopyranose were obtained by reaction of benzyl 2,4- (7) and 3,4-di-O-benzyl-α- -rhamnopyranoside (8) with 2,3,4-tri-O-acetyl-α- -rhamnopyranosyl bromide, followed by deprotection. The per-O-acetyl α-bromide (18) of 19 yielded, by reaction with 8 and 7, the protected derivatives of the title trisaccharides (25 and 23, respectively), from which 25 and 23 were obtained by Zemplén deacetylation and catalytic hydrogenolysis, With benzyl 2,3,4-tri-O-benzyl-β- -galactopyranoside, compound 18 gave an ≈3:2 mixture of benzyl 2,3,4-tri-O-benzyl-6-O-[2,4-di-O-acetyl-3-O-(2,3,4-tri-O-acetyl-α- -rhamnopyranosyl)-α- -rhamnopyranosyl]-β- -galactopyranoside and 4-O-acetyl-3-O-(2,3,4-tri-O-acetyl-α- -rhamnopyranosyl)-β- -rhamnopyranose 1,2-(1,2,3,4-tetra-O-benzyl-β- -galactopyranose-6-yl (orthoacetate). The downfield shift at the α-carbon atom induced by α- -rhamnopyranosylation at HO-2 or -3 of a free α- -rhamnopyranose is 7.4-8.2 p.p.m., ≈1 p.p.m. higher than when the (reducing-end) rhamnose residue is benzyl-protected (6.6-6.9 p.p.m.). α- -Rhamnopyranosylation of HO-6 of gb- -galactopyranose deshields the C-6 atom by 5.7 p.p.m. The 1 2-orthoester ring structure [O₂,C(me)OR] gives characteristic resonances at 24.5 ±0.2 p.p.m. for the methyl, and at 124.0 ±0.5 p.p.m. for the quaternary, carbon atom.     

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.     

BtrI, a novel restriction endonuclease, recognises the non-palindromic sequence 5′-CACGTC(-3/-3)-3′

The recognition sequence and cleavage positions of a new restriction endonuclease BtrI isolated from Bacillus stearothermophilus SE-U62 have been determined. BtrI belongs to a rare type IIQ of restriction endonucleases, which recognise non-palindromic nucleotide sequences and cleave DNA symmetrically within them.     

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.