Selective cleavage of welan gum (S-130) by oxidative decarboxylation with lead tetraacetate

A strategy for the synthesis of low-molecular-weight welan gum by eliminating capsule form of Sphingomonas strains

Welan gum is widely used in food, concrete additives, and oil recovery. Here we changed the capsule form of Sphingomonas strains by knocked out the sortase gene (srtW). The obtained welan gum was mainly composed of mannose, glucose, rhamnose, and glucuronic acid at a molar ratio of 4.0:5.8:1.6:1, respectively. Meanwhile, the molecular weight of welan gum decreased sharply (about 68 kDa). Moreover, the low molecular weight (LMW) welan gum was characterized by FT-IR and NMR spectroscopy. The rheological results revealed that the LMW welan gum solution is a pseudoplastic fluid with a lower apparent viscosity. Furthermore, the oscillation test illustrated stable dynamic viscoelasticity within the temperature range of 5-68 °C and frequency range of 0.01-15 rad/s. To the best of our knowledge, this is the first report of LMW welan gum production and characterization. These results provide references for LMW welan gum applications, and likely applicable for other biopolymers production.

Peptide-Cleavable Self-immolative Maytansinoid Antibody-Drug Conjugates Designed To Provide Improved Bystander Killing

A new type of antibody–drug conjugate (ADC) has been prepared that contains a sulfur-bearing maytansinoid attached to an antibody via a highly stable tripeptide linker. Once internalized by cells, proteases in catabolic vesicles cleave the peptide of the ADC’s linker causing self-immolation that releases a thiol-bearing metabolite, which is then S-methylated. Conjugates were prepared with peptide linkers containing only alanyl residues, which were all l isomers or had a single d residue in one of the three positions. A d-alanyl residue in the linker did not significantly impair a conjugate’s cytotoxicity or bystander killing unless it was directly attached to the immolative moiety. Increasing the number of methylene units in the maytansinoid side chain of a conjugate did not typically affect an ADC’s cytotoxicity to targeted cells but did increase bystander killing activity. ADCs with the highest in vitro bystander killing were then evaluated in vivo in mice, where they displayed improved efficacy compared to previously described types of maytansinoid conjugates.

Transition-Metal-Free Synthesis of C-Glycosylated Phenanthridines via K2S2O8-Mediated Oxidative Radical Decarboxylation of Uronic Acids

We have developed an efficient protocol for the synthesis of C-glycosylated phenanthridines. Tetrafuranos-4-yl and pentapyranos-5-yl radicals, generated from K₂S₂O₈-mediated oxidative decarboxylation of furan- and pyranuronic acids, undergo attack to 2-isocyanodiphenyls and ensuing homolytic aromatic substitution to provide diverse C-glycosylated phenanthridines in satisfactory yields without resort to transition metals. This reaction tolerates various functional groups, and enables ready synthesis of complex oligosaccharide-based phenanthridines. The C-glycosylated phenanthridine derived from β-cyclodextrin has been prepared, which might be potential in medicinal and biological chemistry due to its flexible conformation.

Genome sequence of the welan gum-producing strain Sphingomonas sp. ATCC 31555

Sphingomonas sp. strain ATCC 31555 can produce an anionic heteropolysaccharide, welan gum, which shows excellent stability and viscosity retention even at high temperatures. Here we present a 4.0-Mb assembly of its genome sequence. We have annotated 10 coding sequences (CDSs) responsible for the welan gum biosynthesis and 55 CDSs related to monosaccharide metabolism.

Structural studies of the O-antigenic polysaccharide from Plesiomonas shigelloides strain AM36565

The structure of the repeating unit of the O-antigenic polysaccharide from Plesiomonas shigelloides strain AM36565 has been determined. Component analysis and (1)H and (13)C NMR spectroscopy experiments were employed to elucidate the structure. Inter-residue correlations were determined by (1)H,(13)C heteronuclear multiple-bond correlation, (1)H,(1)H-NOESY, and (1)H,(13)C-HSQC-(1)H,(1)H-NOESY experiments. The O-antigen polysaccharide is composed of repeating units with the following structure: →3)-α-L-Rhap-(1→2)-α-L-Rhap-(1→4)[β-D-GalpNAc-(1→3)]-α-D-GlcpNAc-(1→, in which the monosaccharide side-chain substitutes the backbone in half of the repeating units. A matrix-assisted laser desorption/ionization mass spectrometry experiment suggested that the polysaccharide consists of two regions, one with tetrasaccharide repeating units and one with trisaccharide repeating units.

The Ruff degradation: a review of previously proposed mechanisms with evidence that the reaction proceeds by a Hofer-Moest-type reaction

The Ruff degradation reaction is critically reviewed. Based on available information, the Hofer-Moest decarboxylation mechanism is presented as the mechanism for it. Cu(III) is proposed as the active species of the copper variant of the Ruff degradation, which is the most efficient form of the reaction.