Formation of a phospholipid-linked pyrrolecarbaldehyde from model reactions of d-glucose and 3-deoxyglucosone with phosphatidyl ethanolamine

Abstract

Phospholipid-linked ‘advanced glycation end products’ (AGEs) are supposed to play an important role for lipid oxidation in vivo. The identification of the pyrrolecarbaldehyde 1-[2-formyl-5-(hydroxymethyl)-1H-pyrrol-1-yl]-4,10-dioxo-7-(tetradecanoyloxy)-3,5,9-trioxa-4λ5-phosphatricosan-4-olate (7) from model reactions of d-glucose or 3-deoxyglucosone (4, 3-DG) with phosphatidyl ethanolamine (PE) is described. A preparation method is given for 1-(2-hydroxyethyl)-5-(hydroxymethyl)-1H-pyrrole-2-carbaldehyde (8). Independent syntheses as well as unequivocal structural characterization are reported for the substitution products of 8 1-(2-hydroxyethyl)-5-(methoxymethyl)-1H-pyrrole-2-carbaldehyde (9a) and 5-(ethoxymethyl)-1-(2-hydroxyethyl)-1H-pyrrole-2-carbaldehyde (9b). For all these compounds, chromatographic and spectroscopic data were established by GLC–MS and HPLC with diode array detection (DAD). PE and d-glucose or 3-DG 4 were either incubated at pH 7.4, 100°C for 3h or at pH 7.4, 37°C for 5 weeks in neat buffer or ethanol–buffer mixtures. The phospholipid fraction was purified on a C18 solid-phase extraction column and cleaved with ethanolic potassium hydroxide. The carbaldehyde 8, released in this process, was identified by GLC–MS and quantified by HPLC–DAD. Formation of 7 is favored in the ethanol–buffer reactions relative to those in buffer solution only although the amounts determined from the 37°C incubations generally are very low. It seems likely, therefore, that phospholipid-linked pyrrolecarbaldehydes, such as 7, are biomarkers rather than effectors of membrane damage in vivo.