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Chemical Synthesis of a Glycolipid Library by a Solid‐Phase Strategy Allows Elucidation of the Structural Specificity of Immunostimulation by Rhamnolipids
Author(s) -
Bauer Jörg,
Brandenburg Klaus,
Zähringer Ulrich,
Rademann Jörg
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200600482
Subject(s) - glycolipid , chemistry , rhamnolipid , fatty acid , enzyme , molecule , biochemistry , stereochemistry , organic chemistry , combinatorial chemistry , bacteria , biology , pseudomonas aeruginosa , genetics
Abstract The first synthesis of a glycolipid library by hydrophobically assisted switching phase (HASP) synthesis is described. HASP synthesis enables flexible switching between solution‐phase steps and solid‐supported reactions conducted with molecules attached to a hydrophobic silica support. A library of glycolipids derived from the lead compound 1 —a strongly immunostimulatory rhamnolipid—with variations in the carbohydrate part, the lipid components, and the stereochemistry of the 3‐hydroxy fatty acids was designed and synthesized. The enantioselective synthesis of the 3‐hydroxy fatty acid building blocks was achieved by employing asymmetric hydrogenation of 3‐oxo fatty acids. Glycolipids were prepared by this approach without any intermediary isolation steps, mostly in excellent yields. Final deprotection to the carboxylic acids was accomplished by enzymatic ester cleavage. All prepared rhamnolipids were tested for their immunostimulatory properties against human monocyte cells by assaying the secretion of the cytokine tumor necrosis factor α (TNFα) into the medium. The observed structure–activity relationships of rhamnolipids indicate a specific, recognition‐based mode of action, with small structural variations in the rhamnolipids resulting in strong effects on the immunostimulatory activities of the rhamnolipids at low micromolar concentrations.