Acylglycerols of Myristic Acid as New Candidates for Effective Stigmasterol Delivery—Design, Synthesis, and the Influence on Physicochemical Properties of Liposomes

Abstract

New carriers of phytosterols; acylglycerols containing natural myristic acid at sn-1 and sn-3 positions and stigmasterol residue linked to sn-2 position by carbonate and succinate linker have been designed and synthesized in three-step synthesis from dihydroxyacetone (DHA). The synthetic pathway involved Steglich esterification of DHA with myristic acid; reduction of carbonyl group of 1,3-dimyristoylpropanone and esterification of 1,3-dimyristoylglicerol with stigmasterol chloroformate or stigmasterol hemisuccinate. The structure of the obtained hybrids was established by the spectroscopic methods (NMR; IR; HRMS). Obtained hybrid molecules were used to form new liposomes in the mixture with model phospholipid and their effect on their physicochemical properties was determined, including the polarity, fluidity, and main phase transition of liposomes using differential scanning calorimetry and fluorimetric methods. The results confirm the significant effect of both stigmasterol-containing acylglycerols on the hydrophilic and hydrophobic region of liposome membranes. They significantly increase the order in the polar heads of the lipid bilayer and increase the rigidity in the hydrophobic region. Moreover, the presence of both acylglycerols in the membranes shifts the temperature of the main phase transition towards higher temperatures. Our results indicate stabilization of the bilayer over a wide temperature range (above and below the phase transition temperature), which in addition to the beneficial effects of phytosterols on human health makes them more attractive components of novel lipid nanocarriers compared to cholesterol.

Conjugates of 1,3‐ and 1,2‐Acylglycerols with Stigmasterol: Synthesis, NMR Characterization, and Impact on Lipid Bilayers

“…The opposite effect, i. e., a shift toward lower frequencies in both phases, was caused by the addition of acylglycerols with palmitic acid, especially acylglycerols 4 and 18 . These changes may indicate an increase in the rigidity of the lipid bilayer and are consistent with the results obtained by the fluorimetric method on changes in the anisotropy of the DPH probe and are in agreement with the results of other authors for acylglycerols containing myristic acid at external positions and stigmasterol residue at internal position [41] …”

“…As observed by us in our earlier studies, [41] the regiosomers of diacylgycerols can be differentiated by careful analysis of their NMR spectra. On 1 H NMR spectrum the most informative signals come from diastereotopic protons of CH 2 ‐1 and CH 2 ‐3 of the glycerol skeleton (Figure 2).…”

“…Acyl migration during the reduction of dimirystoyloxypropanone by sodium borohydride was observed earlier by Cockman et al [42] as well as in our studies. [41] As this phenomenon occurs commonly during the preparation of structured acylglycerols by biotechnological and chemical methods, in this work for the first time 1,3-dioleoylglycerol (8) and its 1,2-isomer 8 a were characterized in details by NMR spectroscopy to facilitate their identification and differentiation for future researchers.…”

“…These changes may indicate an increase in the rigidity of the lipid bilayer and are consistent with the results obtained by the fluorimetric method on changes in the anisotropy of the DPH probe and are in agreement with the results of other authors for acylglycerols containing myristic acid at external positions and stigmasterol residue at internal position. [41] An important functional group from the interphase of the lipid bilayer is the carbonyl group (C=O). Its stretching vibration is in the range of 1750-1700 cm À 1 , and the position of the band maximum depends on the conformation of the ester groups and the degree of hydration of the carbonyl region in the DPPC layer.…”