Discrimination of Stereoisomers by Their Enantioselective Interactions with Chiral Cholesterol-Containing Membranes

Abstract

Discrimination between enantiomers is an important subject in medicinal and biological chemistry because they exhibit markedly different bioactivity and toxicity. Although stereoisomers should vary in the mechanistic interactions with chiral targets, their discrimination associated with the mode of action on membrane lipids is scarce. The aim of this study is to reveal whether enantiomers selectively act on chiral lipid membranes. Different classes of stereoisomers were subjected at 5–200 μM to reactions with biomimetic phospholipid membranes containing ~40 mol % cholesterol to endow the lipid bilayers with chirality and their membrane interactions were comparatively evaluated by measuring fluorescence polarization. All of the tested compounds interacted with cholesterol-containing membranes to modify their physicochemical property with different potencies between enantiomers, correlating to those of their experimental and clinical effects. The rank order of membrane interactivity was reversed by changing cholesterol to C3-epimeric α-cholesterol. The same selectivity was also obtained from membranes prepared with 5α-cholestan-3β-ol and 5β-cholestan-3α-ol diastereomers. The opposite configuration allows molecules to interact with chiral sterol-containing membranes enantioselectively, and the specific β configuration of cholesterol’s 3-hydroxyl group is responsible for such selectivity. The enantioselective membrane interaction has medicinal implications for the characterization of the stereostructures with higher bioactivity and lower toxicity.

Probing the Role of Chirality in Phospholipid Membranes

“…Cholesterol (nat-chol) is the lipid which drives the enantioselectivity of most membranes, discussed in later sections. [9,10,36,37] Therefore, it is worth exploring what role cholesterol's chirality may play within lipid membranes. The enantiomer of cholesterol (ent-chol) and an epimer of cholesterol (epi-chol), which is different from cholesterol only by the absolute configuration of the 3-hydroxyl group, have been used to probe the role of cholesterol's chirality in intermolecular interactions within the membrane (Figure 2d).…”

“…[67] Phospholipids favored interactions with D-menthol more than L-menthol, and in DOPC membranes with 30 % cholesterol, D-menthol promotes lipid raft formation, while L-menthol suppressed phase separation. [36,67] L-menthol is known to cause a cooling sensation, while D-menthol is a skin irritant. Their different effects on lipid raft formation may help to explain these opposed properties.…”

“…In this case, bupivacaine enantiomers are shown to incorporate into a membrane more or less strongly, represented by the size of each arrow. [36] R-molecules are shown in green, racemic in tan, and S-molecules in red. C) Select graphs demonstrating relative membrane interactions of the different enantiomers of bupivacaine (25 μM) and ropivacaine (50 μM).…”

“…[36] Negative polarization change represents incorporation of the molecule into the membrane and an increase in membrane fluidity. [36] Colors correspond to the colored structures in part B, where green is R-, tan is racemic and red is Schirality. Reproduced with permission from Ref.…”

Dynamic lipid aptamers: non-polymeric chemical path to early life

“…Since a focus of this Viewpoint is on the relevance of ''lipid aptamers'' to prebiotic processes prior to the advent of macromolecules, it is essential to seek evidence for cases in which lipids can selectively recognize and bind small molecules, as reviewed. 24 In one study, 26 the authors question whether membranes composed of chiral lipids, such as glycerophospholipids and cholesterols, could portray enantioselective binding of small molecules. The results show that despite the membrane's fluid disposition, enantiomers of target drug-like compounds bind differentially to the tested membranes, suggesting enantiospecific interactions.…”