Structure Revision of a Widespread Marine Sulfonolipid Class Based on Isolation and Total Synthesis.

The cosmopolitan marine Roseobacter clade is of global biogeochemical importance. Members of this clade produce sulfur-containing amino lipids (SALs) involved in biofilm formation and marine surface colonization processes. Despite their physiological relevance and abundance, SALs have only been explored through genomic mining approaches and lipidomic studies based on mass spectrometry, which left the relative and absolute structures of SALs unresolved, hindering progress in biochemical and functional investigations. Herein, we report the structural revision of a new group of SALs, which we named cysteinolides, using a combination of analytical techniques, isolation and degradation experiments and total synthetic efforts. Contrary to the previously proposed homotaurine-based structures, cysteinolides are composed of an N,O-acylated cysteinolic acid-containing head group carrying various different (α-hydroxy)carboxylic acids. We also performed the first validated targeted-network based analysis, which allowed us to map the distribution and structural diversity of cysteinolides across bacterial lineages. Beyond offering structural insight, our research provides SAL standards and validated analytical data. This information holds significance for forthcoming investigations into bacterial sulfonolipid metabolism and biogeochemical nutrient cycling within marine environments.

Structure-Solubility Relationship of 1,4-Dioxane Complexes of Di(hydrocarbyl)magnesium.

Systematic variation of the 1,4-dioxane (dx) concentration during the precipitation of sparingly soluble [MgBr2 (dx)2 ] from ethereal Grignard solutions of RMgBr has allowed the structural investigation of crystallized [R2 Mg(dx)n ] (n=1, 1.5, 2, and 3), which form during this dioxane method, depending on the bulkiness of R. The numbering of the complexes explored in this study is based on the number n of dioxane molecules per magnesium atom, followed by the substituent R; an apostrophe denotes coordination polymers. The following derivatives were studied by X-ray crystal-structure determination and NMR spectroscopy: n=1: [Me2 Mg(µ-dx)]∞ (1'-Me) and [nPr2 Mg(µ-dx)]∞ (1'-nPr); n=1.5: [{iPr2 Mg(dx)}2 (µ-dx)] (1.5-iPr), [{oTol2 Mg(dx)}2 (µ-dx)] (1.5-oTol), and [(Me3 Si-C≡C)2 Mg(dx)1.5 ]∞ (1.5'-C2 SiMe3 ); n=2: [tBu2 Mg(dx)2 ] (2-tBu) and [oTol2 Mg(dx)2 ] (2-oTol); n=3: [Ph2 Mg(dx)3 ] (3-Ph). In the structure types 1', 1.5, and 2, the magnesium atom exhibits the coordination number 4, whereas pentacoordinate metal atoms are observed in types 3 and 1.5'. The structure type 2' is realized for [(Ph-C≡C)2 Mg(dx)2 ]∞ (2'-C2 Ph), [MgCl2 (dx)2 ]∞ (2'-Cl), and [MgBr2 (dx)2 ]∞ (2'-Br) with hexacoordinate metal atoms. The solubility of the dioxane adducts in common organic solvents strongly depends on the degree of aggregation with the solubility decreasing from molecular to strand to layer structures.