Phospholipids chiral at phosphorus. Absolute configuration of chiral thiophospholipids and stereospecificity of phospholipase D

Abstract

Separate diastereomers of 1,2-dipalmitoyl-sn-glycero-3-thiophosphoethanolamine (DPPsE) were prepared in 97% diastereomeric purity and characterized by 31P, 13C and 1H NMR. The isomers hybrolyzed by phospholipases A2 and C specifically were designated as isomer B (31P NMR .delta. 59.13 in CDCl3 + Et3N) and isomer A (59.29 ppm), respectively, analogous to the isomers B and A of 1,2-dipalmitoyl-sn-glycero-3-thiophosphocholine (DPPsC). Phospholipase D from cabbage was specific to isomer A of DPPsC in transphosphatidylation. The product DPPsE was isomer A. The absolute configuration of chiral DPPsE at phosphorus was elucidated by bromine-mediated desulfurization in H218O to give chiral 1,2-dipalmitoyl-sn-glycero-3-[18O]phosphoethanolamine ([18O]DPPE) followed by 31P NMR analysis. The absolute configuration of chiral DPPsC was elucidated by desulfurization in H218O mediated by bromine or cyanogen bromide to give chiral 1,2-dipalmitoyl-sn-glycero-3-[18O]phosphocholine ([18O]DPPC), which was then converted to [18O]DPPE by phospholipase D with retention of configuration. Isomer A of both DPPsE and DPPsC is SP whereas isomer B is RP.