Synthesis and Structural Characterization of Phosphoglycolipids Unique to Helicobacter pylori.

摘要

Phosphoglycolipids, lipid A (LPA) and &agr;-cholesteryl phosphatidyl glucoside (&agr;CPG), isolated from H. pylori are amphiphilic molecules that are challenging to isolate and characterize. A major contributor to the complexity of characterizing LPA and &agr;CPG have been due to harsh isolation and purification conditions resulting in degraded and possibly misinterpreted structures of these samples. For example, the isolation and characterization of H. pylori LPA from two different research groups, utilizing different isolation conditions, reported two different structures (3 and 4 acyl chains) of the major LPA component isolated from H. pylori. Similar to H. pylori LPA, isolated &agr;CPG samples that have been reported also contains multiple possible chemical structures as the natural &agr;CPG analogs. Furthermore due to the amphiphilic nature of LPA and &agr;CPG along with difficulty in isolating pure samples from natural sources, characterization of phosphoglycolipids reported have been preferential towards using thin-layer chromatography (TLC) and mass spectrometry. Discussed in this dissertation will be the chemical synthesis of LPA mimetics and &agr;CPG analogs for the structural characterization of these molecules via NMR 1D and 2D experiments.;Total synthesis of &agr;CPG analogs and LPA mimetics provided pure samples for complete characterization and biological activity studies to be conducted. Structural components of H. pylori LPA, like the number of acyl chains (4 chains), were mimicked onto a simplified monosaccharide, glucosamine, backbone. Phosphorylation of LPA mimetics was successful with two phosphorylating reagents: pyrophosphate and phosphoramidite. The successful phosphorylation method with phosphoramidites for the LPA mimetics was carried over to synthesize &agr;CPG analogs. After regioselective deprotection of per-O-TMS-&agr;-D-cholesterylglucoside at the C6, three different diacylglycerol phosphoramidites were utilized to phosphorylate the free hydroxyl to afford the cyano ethyl phosphodiester. Oxidation with oxygen and then deprotection of cyano ethyl afforded three &agr;CPG analogs in 16-21% overall yield starting from D-glucose.