Complex biohopanoids synthesis: efficient anchoring of ribosyl subunits onto a C(30) hopane

Synthesis and Preliminary Immunological Evaluation of a Pseudotetrasaccharide Related to a Repeating Unit of the Streptococcus pneumoniae Serotype 6A Capsular Polysaccharide

2-Aminoethyl glycoside of the pseudotetrasaccharide α-d-Glcp-(1→3)-α-l-Rhap-(1→3)-d-Rib-ol-(5-P-2)-α-d-Galp corresponding to a repeating unit of the Streptococcus pneumoniae type 6A capsular polysaccharide has been synthesized. A suitably protected pseudotrisaccharide α-d-Glcp-(1→3)-α-l-Rhap-(1→3)-d-Rib-ol with a free 5-OH group in the ribitol moiety and a 2-OH derivative of 2-trifluoroacetamidoethyl α-d-galactopyranoside have been efficiently prepared and then connected via a phosphate bridge using the hydrogen phosphonate procedure. Preliminary immunological evaluation of this pseudotetrasaccharide and the previously synthesized pseudotetrasaccharide corresponding to a repeating unit of the capsular polysaccharide of S. pneumoniae serotype 6B has shown that they contain epitopes specifically recognized by anti-serogroup 6 antibodies and are able to model well the corresponding capsular polysaccharides. Conjugates of the synthetic pseudotetrasaccharides with bovine serum albumin were shown to be immunogenic in mice.

Quantitative hopanoid analysis enables robust pattern detection and comparison between laboratories

Hopanoids are steroid-like lipids from the isoprenoid family that are produced primarily by bacteria. Hopanes, molecular fossils of hopanoids, offer the potential to provide insight into environmental transitions on the early Earth, if their sources and biological functions can be constrained. Semiquantitative methods for mass spectrometric analysis of hopanoids from cultures and environmental samples have been developed in the last two decades. However, the structural diversity of hopanoids, and possible variability in their ionization efficiencies on different instruments, have thus far precluded robust quantification and hindered comparison of results between laboratories. These ionization inconsistencies give rise to the need to calibrate individual instruments with purified hopanoids to reliably quantify hopanoids. Here, we present new approaches to obtain both purified and synthetic quantification standards. We optimized 2-methylhopanoid production in Rhodopseudomonas palustris TIE-1 and purified 2Me-diplopterol, 2Me-bacteriohopanetetrol (2Me-BHT), and their unmethylated species (diplopterol and BHT). We found that 2-methylation decreases the signal intensity of diplopterol between 2 and 34% depending on the instrument used to detect it, but decreases the BHT signal less than 5%. In addition, 2Me-diplopterol produces 10× higher ion counts than equivalent quantities of 2Me-BHT. Similar deviations were also observed using a flame ionization detector for signal quantification in GC. In LC-MS, however, 2Me-BHT produces 11× higher ion counts than 2Me-diplopterol but only 1.2× higher ion counts than the sterol standard pregnane acetate. To further improve quantification, we synthesized tetradeuterated (D4) diplopterol, a precursor for a variety of hopanoids. LC-MS analysis on a mixture of (D4)-diplopterol and phospholipids showed that under the influence of co-eluted phospholipids, the D4-diplopterol internal standard quantifies diplopterol more accurately than external diplopterol standards. These new quantitative approaches permit meaningful comparisons between studies, allowing more accurate hopanoid pattern detection in both laboratory and environmental samples.

Hemisynthesis of deuteriated adenosylhopane and conversion into bacteriohopanetetrol by a cell-free system from Methylobacterium organophilum

(²H₂)Adenosylhopane was synthesised via a reaction sequence including a cross metathesis followed by N₂²H₂ reduction of the resulting olefin.

Ribosylhopane, a novel bacterial hopanoid, as precursor of C35 bacteriohopanepolyols in Streptomyces coelicolor A3(2)

Wild-type Streptomyces coelicolor A3(2) produces aminobacteriohopanetriol as the only elongated C35 hopanoid. The hopanoid phenotype of two mutants bearing a deletion of genes from a previously identified hopanoid biosynthesis gene cluster provides clues to the formation of C35 bacteriohopanepolyols. orf14 encodes a putative nucleosidase; its deletion induces the accumulation of adenosylhopane as it cannot be converted into ribosylhopane. orf18 encodes a putative transaminase; its deletion results in the accumulation of adenosylhopane, ribosylhopane, and bacteriohopanetetrol. Ribosylhopane was postulated twenty years ago as a precursor for bacterial hopanoids but was never identified in a bacterium. Absence of the transaminase encoded by orf18 prevents the reductive amination of ribosylhopane into aminobacteriohopanetriol and induces its accumulation. Its reduction by an aldose-reductase-like enzyme produces bacteriohopanetetrol, which is normally not present in S. coelicolor.

Diastereoselective Synthesis of Aminobacteriohopanetetrol, a Biomarker for Methanotrophic Bacteria: Confirmation of the Absolute Configuration

A short and convenient strategy was developed for the first stereoselective chemical synthesis of aminobacteriohopanetetrol (= (1R,2R,3S,4S)-5-amino-1-[(22R)-hopan-30-yl]pentane-1,2,3,4-tetrol; 1), a typical biomarker for methanotrophic bacteria. Comparison of the NMR spectra of the synthetic and natural (peracetylated) product enabled us to unambiguously corroborate the absolute configuration of the functionalized pentyl side chain of 1.