Design, synthesis and properties of conformationally-restricted lipid mimetics.

Abstract

Polyunsaturated fatty acids (PUFAs) and arachidonic acid in particular, play an important role in membrane biogenesis, metabolic processes and signalling pathways [ 1,2]. At the molecular level, little is known concerning the mechanism by which fatty acids exert their effects despite the fact that specific conformations usually correspond to specific biological activities. It should be possible therefore to select a particular activity by structural modifications of the PUFAs, leading to restricted conformational mobility. Computer simulation studies of arachidonic acid [3,4] enabled the design of conformationally-restricted PUFAs analogues. In particular, peptido-PUFAs where the C=C bonds were replaced by peptide isosters have proved to be successfully constrained analogues, when molecular dynamics simulations have been applied to them [4]. Here we report, for the fmt time, the structural properties, studied by high field NMR, of a series of lipid mimetics detailed in Figure I . Peptido and retro ieptido-arachidonate analogues (M, = 372g/mol), peptido and retro peptido:icosapentaenoate analogues (M, = 387g/mol), peptido and retro peptidodocosahexenoate analogue (M, = 430 g/mol), based on a glycine backbone will be referred respectively thereafter as the Gly3, RetroGly3, Gly4, RetroGly4, Gly5, RetroGlyS analogues. The equivalent analogues with a methyl group at each C, positions will be named after the alanine motif they contain ie : Ala3, RetroAla3 (M, = 414g/mol), Ala4, RetroAld (M, = 443g/mol), Alas, RetroAla5 (M, = 500g/mol). The entire series of analogues except Ala3, Ala4, Alas was synthesized by solid phase synthesis, purified by HPLC and the molecular weight confirmed by electrospray mass spectrometry. ID and 2D high field NMR experiments were performed on a Bruker AM 600 spectrometer. All the analogues were studied in TFE-d2, but RetroAla3, RetroAla4 and RetroAla5 were also studied in D,O plus TSP. Chemical shifts were then referenced to the residual signals for TFE-d2 at 3.9 ppm or TSP at 0 ppm. 2D