Chemical and Chemoenzymatic Syntheses of Bacillithiol: A Unique Low-Molecular-Weight Thiol amongst Low G + C Gram-Positive Bacteria

P(v) intermediate-mediated E1cB elimination for the synthesis of glycals

Glycals are highly versatile and useful building blocks in the chemistry of carbohydrate and natural products. However, the practical synthesis of glycals remains a long-standing and mostly unsolved problem in synthetic chemistry. Herein, we present an unprecedented approach to make a variety of glycals using phosphonium hydrolysis-induced, P(v) intermediate-mediated E1cB elimination. The method provides a highly efficient, practical and scalable strategy for the synthesis of glycals with good generality and excellent yields. Furthermore, the strategy was successfully applied to late-stage modification of complex drug-like molecules. Additionally, the corresponding 1-deuterium-glycals were produced easily by simple ^tBuONa/D₂O-hydrolysis–elimination. Mechanistic investigations indicated that the oxaphosphorane intermediate-mediated E1cB mechanism is responsible for the elimination reaction.

A novel glucosylphosphonium-hydrolysis induced E1cB-elimination provides a highly efficient, practical and scalable method for the synthesis of glycals with good compatibility and excellent yields.

Total Synthesis of Tri-, Hexa- and Heptasaccharidic Substructures of the O-Polysaccharide of Providencia rustigianii O34

A general and efficient strategy for synthesis of tri-, hexa- and heptasaccharidic substructures of the lipopolysaccharide of Providencia rustigianii O34 is described. For the heptasaccharide seven different building blocks were employed. Special features of the structures are an α-linked galactosamine and the two embedded α-fucose units, which are either branched at positions-3 and -4 or further linked at their 2-position. Convergent strategies focused on [4+3], [3+4], and [4+2+1] couplings. Whereas the [4+3] and [3+4] coupling strategies failed the [4+2+1] strategy was successful. As monosaccharidic building blocks trichloroacetimidates and phosphates were employed. Global deprotection of the fully protected structures was achieved by Birch reaction.

Biophysical features of bacillithiol, the glutathione surrogate of Bacillus subtilis and other firmicutes

Bacillithiol (BSH) is the major low-molecular-weight (LMW) thiol in many low-G+C Gram-positive bacteria (Firmicutes). Evidence now emerging suggests that BSH functions as an important LMW thiol in redox regulation and xenobiotic detoxification, analogous to what is already known for glutathione and mycothiol in other microorganisms. The biophysical properties and cellular concentrations of such LMW thiols are important determinants of their biochemical efficiency both as biochemical nucleophiles and as redox buffers. Here, BSH has been characterised and compared with other LMW thiols in terms of its thiol pKa , redox potential and thiol-disulfide exchange reactivity. Both the thiol pKa and the standard thiol redox potential of BSH are shown to be significantly lower than those of glutathione whereas the reactivities of the two compounds in thiol-disulfide reactions are comparable. The cellular concentration of BSH in Bacillus subtilis varied over different growth phases and reached up to 5 mM, which is significantly greater than previously observed from single measurements taken during mid-exponential growth. These results demonstrate that the biophysical characteristics of BSH are distinctively different from those of GSH and that its cellular concentrations can reach levels much higher than previously reported.

A tandem chemoenzymatic methylation by S-adenosyl-L-methionine

Keep 'em methylated: The in situ preparation of the cofactor AdoMet was achieved by allowing the biosynthetic enzyme SalL to operate in the reverse direction by presentation of 5'-chloro-5'-deoxyadenosine at low salt concentrations. This reaction was readily coupled with DNA and small molecule methyltransferases to afford a regioselective method for chemo-enzymatic methylation and isotope incorporation.

Analysis of mutants disrupted in bacillithiol metabolism in Staphylococcus aureus

Bacillithiol (BSH), an α-anomeric glycoside of l-cysteinyl-d-glucosaminyl-l-malate, is a major low molecular weight thiol found in low GC Gram-positive bacteria, such as Staphylococcus aureus. Like other low molecular weight thiols, BSH is likely involved in protection against a number of stresses. We examined S. aureus transposon mutants disrupted in each of the three genes associated with BSH biosynthesis. These mutants are sensitive to alkylating stress, oxidative stress, and metal stress indicating that BSH and BSH-dependent enzymes are involved in protection of S. aureus. We further demonstrate that BshB, a deacetylase involved in the second step of BSH biosynthesis, also acts as a BSH conjugate amidase and identify S. aureus USA 300 LAC 2626 as a BSH-S-transferase, which is able to conjugate chlorodinitrobenzene, cerulenin, and rifamycin to BSH.